THE ENRHYTHM CARDIAC PACEMAKER:

GENESIS, CURRENT MODEL, AND DESIGN

RECOMMENDATION

THE BRADY BUNCH

Gabrielle Fantich

Andrew Long

Nidhi Thite

Erik Thomas

John Wuthrich

Submitted December 11th, 2013

for

Engineering 100.100.101

Dr. George T. Wynarsky

Dr. Elizabeth S. Hildinger

Engineering 100.100 Professors

TABLE OF CONTENTS

Foreword………………………………………………………………………………. 1

Summary………………………………………………………………………………. 1

Introduction……………………………………………………………………………. 2

Anatomy of the Heart………………………………………………………………….. 3

Blood Flow through the Heart…………………………………………………. 3

Electrical System of the Heart………………………………………………….. 3

Electrocardiogram (ECG)……………………………………………………… 3

Medical Problem: Arrhythmia………………………………………………………….. 4

Bradycardia…………………………………………………………………….. 4

Atrial Tachycardia……………………………………………………………… 4

The History of Artificial Cardiac Pacemakers…………………………………………. 4

Hopps Pacemaker-Defibrillator………………………………………………... 4

Implantable Pacemaker………………………………………………………… 5

On-Demand Pacemaker………………………………………………………… 5

Improved Battery Life…………………………………………………………... 5

Dynamic Pacemaker……………………………………………………………. 5

Dual Chamber Pacemaker……………………………………………………… 5

Microprocessor-Controlled Pacemaker………………………………………... 6

Managed Ventricular Pacing (MVP)…………………………………………... 6

Components of the EnRhythm Pacemaker……………………………………………... 6

Implantable Pulse Generator (IPG)……………………………………………. 6

Pacing Leads…………………………………………………………………… 6

Implantation of the EnRhythm Pacemaker……………………………………... 7

Function of the EnRhythm Pacemaker…………………………………………………. 7

Sensing………………………………………………………………………….. 7

Pacing…………………………………………………………………………... 8

Dual Chamber Pacing………………………………………………………….. 8

Managed Ventricular Pacing (MVP)…………………………………………... 8

Rate-Responsive Pacing………………………………………………………... 8

Reactive Atrial Antitachycardia Pacing (ATP)………………………………… 9

Cardiac Compass………………………………………………………………. 9

Materials of the EnRhythm Pacemaker………………………………………………… 9

Wire Insulation & Connector Block: Polyurethane……………………………. 9

Electrodes: Platinum Iridium Alloy……………………………………………. 10

Electrode Separation: Silicone Rubber………………………………………… 10

Implantable Pulse Generator: Grade 5 Titanium Alloy………………………... 10

Alternative Treatments for Arrhythmia………………………………………………… 11

Catheter Ablation……………………………………………………………….. 11

Electrical Cardioversion……………………………………………………….. 11

Limitations of the EnRhythm Pacemaker………………………………………………. 12

Current Pacemaker Research…………………………………………………………… 12

Leadless Pacemakers…………………………………………………………… 12

Piezoelectric-Powered Pacemakers……………………………………………. 13

Optogenetic Pacemakers……………………………………………………….. 13

Laser-Based Pacemakers………………………………………………………. 13

Design Recommendation……………………………………………………………….. 13

Components of the Proposed Design…………………………………………… 14

Function of the Proposed Design………………………………………………. 14

Benefits of the Proposed Design……………………………………………….. 14

References……………………………………………………………………………… 15

Appendix A: Pacing Modes……………………………………………………………. 20

Appendix B: Piezoelectricity…………………………………………………………… 21

Appendix C: Ultrasound………………………………………………………………... 22

Brady Bunch 1

FOREWORD

You asked our team to research a biomedical device and provide a design recommendation to

improve the device. We chose to research the Medtronic EnRhythm cardiac pacemaker. This

device treats arrhythmia, a serious heart condition causing an irregular heart rhythm. We

researched the anatomy of the heart, the medical problem of arrhythmia, and the history of

cardiac pacemakers. We also researched the components, function, and materials of the

Medtronic EnRhythm cardiac pacemaker. We then examined alternative treatments for

arrhythmia, the limitations of the EnRhythm pacemaker, and current research of pacemakers. The

purpose of this document is to present our findings and provide our design recommendation for

the Medtronic EnRhythm cardiac pacemaker.

SUMMARY

Arrhythmia is a potentially fatal heart condition resulting in an irregular heart rhythm. Cardiac

pacemakers treat arrhythmia by stimulating the heart with an electrical current. The Medtronic

EnRhythm pacemaker provides relief for patients suffering from arrhythmia.

The heart is separated into four chambers by muscular walls called septa. The top chambers are

the right and left atria, and the bottom chambers are the right and left ventricles. These chambers

contract to pump blood throughout the body. The contractions are controlled by specialized

tissues known as the sinoatrial (SA) node and the atrioventricular (AV) node, which generate

electrical signals that pass through the heart muscle. An electrocardiogram (ECG) is a test used to

monitor the heart’s electrical activity.

Arrhythmia is an abnormal beating of the heart caused by a delay or blockage of the heart’s

electrical signals. A delay or blockage occurs when the SA or AV nodes are not working properly

or when the electrical signals do not progress normally through the heart. Two types of

arrhythmia are bradycardia and atrial tachycardia. Bradycardia causes slow beating of the heart.

Atrial tachycardia causes an abnormally fast heart rhythm in the atria.

The first artificial cardiac pacemaker was introduced in 1950. It was an external device driven by

vacuum tubes. In 1958, implantable pacemakers were developed, which were more convenient

but surgically risky. In 1965, the first on-demand pacemaker was introduced, which stimulates the

heart only when necessary. Lithium-iodine batteries were introduced in 1971, making pacemakers

more reliable. Dual chamber pacemakers, introduced in 1982, have two leads: one in the right

atrium and one in the right ventricle. Dual chamber pacemakers produce more natural heartbeats

but increase the risk of congestive heart failure. The Medtronic EnRhythm pacemaker solved this

problem in 2005 through a program called Managed Ventricular Pacing (MVP).

The EnRhythm pacemaker is composed of an implantable pulse generator (IPG) and two pacing

leads. The IPG is located in the chest cavity near the heart and contains a lithium battery, internal

circuitry, and connector block. The two pacing leads are placed within the right atrium and right

ventricle and attach to the IPG through the connector block. The EnRhythm pacemaker uses

bipolar leads, which have two electrodes.

The EnRhythm pacemaker treats bradycardia and atrial tachycardia by performing two functions:

sensing and pacing. In sensing, the electrodes at the end of each lead detect the electrical signals

produced by the heart. The pacemaker circuitry analyzes these signals to determine if pacing is

necessary to correct an irregular heartbeat. In pacing, the energy from the battery is converted

into an electrical impulse, which travels through the leads to the heart tissue, causing the heart to

beat.

Brady Bunch 2

The EnRhythm pacemaker can stimulate a contraction of the atria followed closely by a

contraction of the ventricles. Managed Ventricular Pacing allows the EnRhythm pacemaker to

switch from only pacing the atria to stimulating both the atria and ventricles. The EnRhythm

pacemaker uses rate-responsive pacing to adjust a patient’s heart rate based on the patient’s

activity level. It also uses Reactive Atrial Antitachycardia Pacing (ATP), which delivers a set of

rapid impulses to the atria to treat atrial tachycardia. Cardiac Compass is a Medtronic program

that allows the EnRhythm pacemaker to store patient information that can be used by physicians

to monitor a patient’s progress and adjust their treatment plan.

The wire insulation and connector block of the IPG are made of polyurethane. Polyurethane’s

high electrical resistivity protects the body from the electrical current that passes through the

wire. The electrodes are made of a platinum iridium alloy with a high electrical conductivity that

allows the electrical current to be transmitted to the heart. Silicone rubber is used to separate the

electrodes because the rubber’s high electrical resistivity prevents current from flowing

simultaneously through the electrodes. The IPG is made out of grade 5 titanium alloy. This alloy

has a high yield strength, which makes the IPG resistant to permanent deformation, protecting its

internal components.

Two alternative treatments for arrhythmia are catheter ablation and electrical cardioversion.

Catheter ablation is a procedure in which ablation catheters (flexible tubes) are used to destroy

diseased sections of the heart that cause arrhythmia. Electrical cardioversion sends timed

electrical shocks through a patient’s chest to correct atrial tachycardia.

Limitations of the EnRhythm pacemaker include implantation risks, postoperative infections, and

allergic reactions. The electrodes of the pacemaker can cause damage to the heart tissue, the leads

can become tangled or dislodged, and the battery life is limited. Patients with pacemakers cannot

participate in full contact sports and cannot be exposed to large magnetic fields.

Medtronic is developing a miniaturized leadless pacemaker that will be implanted into the heart

using a catheter. Researchers are developing a piezoelectric material that would use energy

created by the heart’s beating to power the pacemaker. Scientists have successfully used lasers

instead of leads to pace the heart of a quail embryo. Opsins are light-sensitive proteins that can be

inserted into the heart tissue. When exposed to light, opsins cause the heart to contract.

Our design recommendation is an ultrasonic rechargeable pacemaker that converts ultrasound

waves into electrical energy. An external ultrasound transducer emits ultrasound waves to the

internal system, which converts these waves into a voltage. The internal system consists of four

components: the acoustic lens, matching layer, piezoelectric material, and backing layer. The

acoustic lens focuses the waves onto the matching layer, which then maximizes the transmission

of ultrasound waves and prevents wave reflection. The piezoelectric material, located between the

matching and backing layers, converts the mechanical energy from the ultrasound into a voltage,

which is then used to recharge the battery. The backing layer, located below the piezoelectric

material, decreases reflection by absorbing excess ultrasound waves. Our design does not alter the

implantation procedure, and the ultrasound does not interfere with the pacemaker’s internal

circuitry. Our design increases the pacemaker battery life, reduces the number of replacement

surgeries, and is safe and convenient for patients.

INTRODUCTION Arrhythmias are problems with the rate or rhythm of the heartbeat that cause nearly 500,000

deaths in the United States each year. However, early and appropriate diagnosis and treatment of

arrhythmia decreases arrhythmia-related deaths by 15% to 25% annually [1]. Cardiac pacemakers

Brady Bunch 3

are devices used to treat arrhythmias by stimulating the heart with an electrical current [2]. The

Medtronic EnRhythm pacemaker utilizes unique programs to provide relief for patients suffering

from arrhythmias. This document will discuss the anatomy of the heart, the medical problem of

arrhythmia, the history of cardiac pacemakers, and the function and materials of the Medtronic

EnRhythm cardiac pacemaker. It will then present alternative treatments for arrhythmia, the

limitations of the EnRhythm pacemaker, and current research of pacemakers. Finally, it will

provide our design recommendation for the Medtronic EnRhythm cardiac pacemaker.

ANATOMY OF THE HEART The heart is responsible for circulating blood throughout the human body. Blood carries nutrients

such as oxygen to the cells of the body and is responsible for removing waste products like

carbon dioxide. Without the heart to circulate nutrient-rich blood to the cells, cells would quickly

die. Therefore, a functioning heart is essential for life [2].

The human heart is a hollow specialized muscle about the size of a fist. The heart is divided into

four chambers by muscular walls called septa. As shown in Figure 1, the top chambers are the left

and right atria, and the bottom chambers are the left and right ventricles [2].

Blood Flow through the Heart

The heart’s four chambers use coordinated

contractions to pump blood throughout the

body. Deoxygenated blood enters the heart

in the right atrium. A contraction in the right

atrium pushes the blood into the right

ventricle. A ventricular contraction then

pumps the blood through the pulmonary

artery to the lungs. In the lungs, the blood is

oxygenated and carbon dioxide is removed.

The oxygenated blood then flows into the

left atrium. A second atrial contraction

forces the blood into the left ventricle,

where a final ventricular contraction pumps

the blood throughout the body. This process

repeats when the deoxygenated blood from

the body re-enters the right atrium [3].

Electrical System of the Heart

The heart’s contractions are caused by electrical impulses that travel through the heart, as shown

in Figure 1. The sinoatrial (SA) node is a specialized tissue within the right atrium that serves as

the body’s natural pacemaker. The SA node generates electrical impulses that cause the atria to

contract. These electrical signals travel along special conduction pathways to the atrioventricular

(AV) node located in the center of the heart. The AV node then creates its own electrical signal,

which results in the contraction of the ventricles. These

coordinated signals from the SA and AV nodes cause a

natural heart rhythm, with an atrial contraction followed by

a ventricular contraction [2].

Electrocardiogram (ECG)

An electrocardiogram (ECG) is a test used to monitor the

heart’s electrical activity. The electrical activity is translated

into line tracings on graph paper, as shown in Figure 2. The

Fig. 1: Structure of the heart

Adapted from: [4]

Fig. 2: ECG of the heart

Adapted from: [5]

Brady Bunch 4

first peak represents a contraction of the atria. The second peak represents a contraction of the

ventricles, and the final peak shows the ventricles returning to a resting state [5].

MEDICAL PROBLEM: ARRHYTHMIA Arrhythmia is a problem with the rhythm or rate of the beating of the heart. The heart may beat

too slowly, too quickly, or with an abnormal rhythm. Some arrhythmias can be harmless, while

others may be life-threatening. During an arrhythmia, the heart may be incapable of pumping

enough blood to the body, causing damage to the brain, heart, and other organs [6].

Arrhythmia is caused by a delay or blockage of the electrical signals that control the heartbeat [7].

A delay or blockage occurs when the specialized nerve cells producing the electrical signals in

the SA or AV nodes are not working properly or when the electrical signals do not progress

normally through the heart [6].

Symptoms of potentially dangerous arrhythmias may include anxiety, light-headedness, fainting,

sweating, shortness of breath, or chest pain [6]. In addition, a person with arrhythmia may

experience palpitations, which are sensations in the chest or neck. Palpitations feel as if the heart

is “pounding” or has a skipped or extra beat [8].

Bradycardia

Bradycardia is a type of arrhythmia that results in

slow beating of the heart, defined as less than 60

beats per minute (bpm) [7]. Figure 3 compares the

ECGs of hearts with arrhythmias to the ECG of a

normal heart. The ECG of bradycardia shows that

a heartbeat occurs much less frequently in patients

with bradycardia than in healthy individuals.

Bradycardia can be a serious problem if the heart is

unable to pump enough oxygen-rich blood to the

organs of the body. However, people who are

physically fit can have a heart rate under 60 bpm

and be healthy. Bradycardia is caused by a failure

of the SA node to send enough electrical signals or

by a blockage or delay of electrical signals by the

AV node [9].

Atrial Tachycardia

Atrial tachycardia is a type of arrhythmia that causes fast beating of the atria [8]. A heart rate of

over 100 bpm is considered tachycardia. The ECG of atrial tachycardia in Figure 3 shows that

atrial contractions occur much more frequently in patients with atrial tachycardia than in healthy

individuals. Atrial tachycardia can be caused by AV nodal reentry. AV nodal reentry occurs when

the electrical signals pass in and around the AV node, causing the atria to keep contracting [9].

THE HISTORY OF ARTIFICIAL CARDIAC PACEMAKERS

Pacemakers have been used since the middle of the 20th century. The first pacemakers were

external units that were bulky and unreliable. Over time, improvements made pacemakers

smaller, implantable, more reliable, and longer-lasting.

Hopps Pacemaker-Defibrillator

The first pacemaker was built by John Hopps in 1950. His pacemaker was an external device

driven by vacuum tubes [13]. The vacuum tubes generated electrical impulses that traveled

Fig. 3: Comparison of ECGs

Adapted from: [10, 11, 12]

Brady Bunch 5

through wires to the atria to correct the heart’s rhythm [14].

The pacemaker was powered by a large battery known as a

mains-powered unit. As seen in Figure 4, early pacemakers

were bulky and had to be carried around in a cart.

Additionally, patients frequently experienced painful shocks

and were prone to infections [13].

Implantable Pacemaker

In 1958, pacemakers were improved when Rune Elmqvist

and Ake Sennings introduced the first fully implantable

cardiac pacemaker. This device was more convenient for

patients, but the surgeries were risky, and the battery life was

shorter than that of the external units. Additionally, the

pacemaker stimulated a heartbeat even when it was

unnecessary [15].

On-Demand Pacemaker

In 1965, the first on-demand pacemaker was introduced. On-

demand pacemakers monitor the electrical signals of the

heart. If a normal signal is detected, the pacemaker does not

stimulate the heart. Not only does this reduce patient risk, but

the decreased stimulation results in less battery usage [16].

Improved Battery Life

Researchers began focusing on improving the battery life of implantable pacemakers. In 1970, the

first nuclear-powered pacemaker was introduced, but this was quickly abandoned due to harmful

radiation. In 1971, lithium-iodine batteries were invented. These batteries made the pacemaker

significantly smaller, longer-lasting, and more reliable [17].

Dynamic Pacemaker

In 1980, the first dynamic pacemakers were introduced. These pacemakers set the heart rate

according to factors such as oxygen level, carbon dioxide level, and blood pressure. Dynamic

pacemakers are able to produce a more natural heart rhythm by adjusting heart stimulation in

response to these factors [13].

Dual Chamber Pacemaker

Dual chamber pacemakers were invented in

1982. These pacemakers use two leads

(wires) to produce a more natural heartbeat.

As shown in Figure 5, one lead is located in

the right atrium, and another lead is located

in the right ventricle. This design allows the

pacemaker to stimulate a contraction in the

atria followed closely by a contraction of the

ventricles, mimicking the natural sequence

of a healthy beating heart. However, dual

chamber pacemakers also greatly increased

the risk of congestive heart failure due to

unnecessary stimulation of the right

ventricle [18].

Fig. 5: Dual chamber pacemaker

Adapted from: [15]

Fig. 4: Early cardiac pacemaker

Image from: [13]

Brady Bunch 6

Microprocessor-Controlled Pacemaker

In 1992, pacemakers utilizing microprocessors were introduced. The microprocessor stores

patient data, including blood pressure, pacing history, and oxygen levels. This data can then be

analyzed by doctors to program the pacemakers to meet the specific needs of each patient [13].

Managed Ventricular Pacing (MVP)

In 2005, Medtronic released a program called Managed Ventricular Pacing (MVP) in its

EnRhythm pacemaker. This program allows dual chamber pacemakers to switch from stimulating

both chambers of the heart to only stimulating the atria, thus reducing unnecessary stimulation of

the right ventricle [19].

COMPONENTS OF THE ENRHYTHM PACEMAKER The EnRhythm Pacemaker is composed of an implantable pulse generator and two pacing leads.

The implantable pulse generator produces an electrical impulse, and the two leads direct the

impulse to the heart.

Implantable Pulse Generator (IPG)

The implantable pulse generator (IPG) is the device that

controls the pacemaker. It is approximately two inches

in diameter [15]. As shown in Figure 6, it is composed

of three parts: the battery, the internal circuitry, and the

connector block. The battery is a 2.8-volt lithium

battery located on the bottom of the implantable pulse

generator [20]. It has an average battery life of 8.5 to

10.5 years [15]. The second component of the

implantable pulse generator, the internal circuitry, is

located in the middle of the device. The internal

circuitry coordinates the pacemaker’s function and

allows electricity to flow from the battery to the

connector block. The final part of the implantable pulse

generator is the connector block. The connector block is

located above the internal circuitry and has two

attachment points for the pacing leads [20].

Pacing Leads

Pacing leads are thin insulated wires that direct the

artificial pulse from the implantable pulse generator to the

walls of the heart. The Medtronic EnRhythm pacemaker

has one lead in the right atrium and another lead in the

right ventricle [20]. The insulation covering the leads

protects the body from the electricity generated from the

pacemaker. The outer insulation is made of polyurethane,

shown in light blue in Figure 7. The insulation separating

the anode and cathode is made of silicone rubber, shown

in dark blue in Figure 7 [22].

The EnRhythm pacemaker uses bipolar pacing leads. Bipolar pacing leads are composed of two

electrodes: a negatively-charged anode and a positively-charged cathode. These electrodes are

made of a platinum iridium alloy [22]. As shown in Figure 7, the cathode is located at the tip of

the lead, while the anode is located just behind the cathode [20].

Fig. 6: Components of the implantable

pulse generator

Adapted from: [20]

Fig. 7: Bipolar pacing lead

Adapted from: [20]

Brady Bunch 7

Implantation of the EnRhythm Pacemaker

The Medtronic EnRhythm pacemaker can be implanted with two different types of bipolar leads:

transvenous leads or epicardial leads.

As shown in Figure 8, transvenous

leads are implanted through the

veins leading to the heart. A 2.5

inch incision is made just

underneath the left clavicle

(collarbone). The leads are then

pulled through the subclavian vein

and superior vena cava into the

right chambers of the heart [23].

One of the leads is attached to the

inner wall of the right atrium, and

the other lead is attached to the

inner wall of the right ventricle.

The leads are then attached to the

connector block, and the doctor

programs the implantable pulse

generator [24]. The implantable

pulse generator is placed under the

skin at the point of the incision.

The doctor closes the incision,

completing the implantation [23].

Epicardial leads are not implanted within the heart. Instead, the leads are attached directly to the

epicardial tissue on the outer walls of the right atrium and right ventricle. This type of

implantation is less common and is used for sensitive patients, such as pediatric patients and

patients who have recently undergone heart surgery [20].

FUNCTION OF THE ENRHYTHM PACEMAKER

The EnRhythm cardiac pacemaker treats arrhythmias by delivering small electrical impulses to

the heart to correct irregular heart rhythms. The pacemaker is programmed differently to meet the

unique needs of each patient. Its primary purpose is to treat bradycardia, but it can also be

programmed to treat atrial tachycardia [15]. The

EnRhythm pacemaker treats arrhythmia by

performing two functions: sensing and pacing [2].

Sensing

The EnRhythm pacemaker senses (monitors) the

heart’s natural electrical activity in both the right

atrium and right ventricle by means of the

electrodes at the end of each lead. As shown in

Figure 9, the electrode detects the electrical

impulses that cause a natural heartbeat [18]. These

electrical signals are transmitted through the anode

in the lead to the circuitry within the pulse

generator [20]. If these signals are greater than 0.9

millivolts in the right ventricle or 0.3 millivolts in

the right atrium, then the device is able to detect the

Fig. 8: Transvenous implantation of the pacemaker

Adapted from: [25]

Fig. 9: Magnified view of electrode

sensing the heart’s electrical signals

Adapted from: [20]

Brady Bunch 8

signals. If normal signals are detected, the pacemaker is said to be “inhibited”, meaning it will not

deliver a pacing pulse. If no signals are detected or the signals are too slow, the pacemaker

responds by pacing the appropriate chamber of the heart to correct the variation in the heart’s

natural rhythm [18].

Pacing

The EnRhythm pacemaker corrects

the heart’s rhythm by delivering an

electrical impulse to the heart tissue;

this process is called pacing. If an

abnormal heartbeat is detected, the

pulse generator converts the energy

from the battery into an electrical

impulse. This impulse flows through

the lead to the cathode. As shown in

Figure 10, the cathode then transmits

the impulse to the surrounding heart

tissue. This impulse replicates the

normal electrical signals of the heart,

causing the heart to beat [20]. The

electronic circuitry within the pulse

generator controls the timing and

intensity of these generated impulses

to stimulate more natural heart

rhythms [18].

Dual Chamber Pacing

The EnRhythm pacemaker is a dual chamber pacemaker, meaning it has leads in both the right

atrium and right ventricle. This allows the pacemaker to stimulate a contraction in the atria

followed closely by a contraction in the ventricles, thus mimicking the natural sequence of a

healthy beating heart [18].

Most dual chamber pacing systems run in DDD pacing mode. DDD simply means that the

pacemaker senses and paces in both the right atrium and right ventricle [26]. For more

information on pacing modes and the significance of DDD, see Appendix A. DDD pacing can

lead to severe complications because right ventricular pacing has been linked to congestive heart

failure [19]. To prevent unnecessary pacing in the right ventricle, the EnRhythm pacemaker uses

a Medtronic program called Managed Ventricular Pacing [18].

Managed Ventricular Pacing (MVP)

The EnRhythm pacemaker was the first pacemaker to use Managed Ventricular Pacing (MVP).

This program allows the pacemaker to switch from only pacing the atria to stimulating both the

atria and ventricles when ventricular pacing is necessary. Periodic tests are performed by the leads

to check that the atrioventricular (AV) node is working properly. If the AV node is not sending

electrical signals, then the ventricles also require pacing. The EnRhythm pacemaker responds to a

failed test by switching to DDD pacing mode, allowing pacing in both the atria and ventricles. If

the AV node properly sends electrical signals, the pacemaker only paces the atria [27].

Rate-Responsive Pacing

The EnRhythm pacemaker uses rate-responsive pacing, which adjusts a patient’s heart rate based

on the patient’s level of activity [2]. The accelerometer, a sensor located within the pulse

Fig. 10: Magnified view of pacing the heart

Adapted from: [20, 21]

Brady Bunch 9

generator, detects the patient’s body

motion and converts this motion into

an electrical signal. As patient

activity increases, more frequent and

larger amplitude electrical signals are

created. These signals are sent to the

pacemaker circuitry, and an

algorithm encoded in the

EnRhythm’s programming processes

the signals to determine the proper

pacing rate [28]. As shown in Figure

11, heart rhythms controlled by rate-

responsive pacing almost exactly

mimic a normal heartbeat during

various daily activities.

Reactive Atrial Antitachycardia Pacing (ATP)

The EnRhythm pacemaker can also be programmed to treat atrial tachycardia by using a

Medtronic program called Reactive Atrial Antitachycardia Pacing (ATP). If an atrial tachycardia

episode is detected, the pacemaker responds by delivering a set of rapid impulses to the atria [15].

This coordinated stimulation is designed to terminate the trapped impulse that causes atrial

tachycardia [29].

Cardiac Compass

Cardiac Compass is a Medtronic program that allows the EnRhythm pacemaker to store

information that it collects about a patient within its internal circuitry. This information is

collected for 14 months and provides clinically significant data, including the percentage of daily

pacing needed, frequency and duration of arrhythmia episodes, and physical activity of the

patient. This data can be used by physicians to monitor a patient’s progress and adjust their

treatment plan if necessary [18].

MATERIALS OF THE ENRHYTHM PACEMAKER

Each material used in the EnRhythm pacemaker has specific properties that allow the pacemaker

to function properly within the body’s environment. The materials of the EnRhythm pacemaker

that come into contact with the body are polyurethane, platinum iridium alloy, silicone rubber,

and grade 5 titanium alloy [15].

Wire Insulation & Connector Block: Polyurethane

The lead wire insulation and the casing of the

connector block of the IPG are made of

polyurethane [22]. The properties that make

polyurethane an ideal material for these

components can be seen in Table 1. The tensile

strength for polyurethane is 47 MPa, which is high

enough to prevent the wire insulation and

connector block from breaking. Polyurethane has a

low modulus of elasticity of 0.014 GPa. This

property makes the polyurethane components

flexible [30]. Polyurethane’s high electrical

resistivity value of 109 Ω-m ensures that the wire

insulation and connector block protect the body

Fig. 11: Rate-responsive pacing compared to a normal heart

rate during various daily activities

Adapted from: [2]

Table 1: Material properties of polyurethane

Material Property Value

Tensile Strength 47 MPa

Modulus of Elasticity 0.014 GPa

Electrical Resistivity 109 Ω-m

Degradation Resistance Excellent

Biocompatibility Excellent

Density 1.20 g/cm3

Table values from: [22, 30, 31, 32, 33]

Brady Bunch 10

from electrical current [31]. Polyurethane has excellent degradation resistance and excellent

biocompatibility, allowing it to withstand the body’s environment [32]. Polyurethane has a low

density of 1.20 g/cm3, which means that both components are lightweight [33].

Electrodes: Platinum Iridium Alloy

The electrodes are made of a platinum

iridium alloy. This alloy is used because of

its specific properties listed in Table 2.

Platinum iridium alloy has a high electrical

conductivity value of 4,000,000 (Ω-m)-1.

This high value allows the electrodes to

efficiently transfer electrical impulses to the

heart. Platinum iridium alloy also has

excellent corrosion resistance and

biocompatibility, which allow the electrodes

to function properly within the body [34].

Electrode Separation: Silicone Rubber

Silicone rubber is used to separate the anode and

cathode at the end of each lead. The material

properties that make silicone rubber suitable for

separating the electrodes are shown in Table

3. Silicone rubber has high electrical resistivity of

1012 Ω-m, which prevents current from flowing

simultaneously through both electrodes [35]. The

tensile strength for silicone rubber is 6.5 MPa, which

is sufficient to keep it from breaking. The modulus

of elasticity for silicone rubber is 0.025 GPa, which

allows the leads to be flexible for easy implantation

[36]. Silicone rubber has excellent biocompatibility,

so the lead separation is inert within the heart [37].

Implantable Pulse Generator: Grade 5 Titanium Alloy

The casing of the implantable pulse generator is made

out of grade 5 titanium alloy. Grade 5 titanium alloy

is composed primarily of titanium, aluminum, and

vanadium [38]. The properties that make grade 5

titanium alloy an ideal material for the IPG can be

seen in Table 4. Grade 5 titanium alloy has a high

yield strength value of 795 MPa, which makes the

implantable pulse generator resistant to plastic

(permanent) deformation. This property prevents any

damage to the internal components of the IPG. It has

excellent corrosion resistance and excellent

biocompatibility, allowing it to withstand the body’s

corrosive environment [39]. It has a density of 4.42

g/cm3. This density is low in comparison to other

metals and makes the IPG relatively lightweight [40].

Table 2: Material properties of platinum iridium

alloy

Table values from: [35, 36, 37]

Table values from: [38, 39, 40]

Material Property Value

Electrical Conductivity 4,000,000 (Ω-m)-1

Corrosion Resistance Excellent

Biocompatibility Excellent

Material Property Value

Tensile Strength 6.5 MPa

Modulus of Elasticity 0.025 GPa

Electrical Resistivity 1012 Ω-m

Biocompatibility Excellent

Material Property Value

Yield Strength 795 MPa

Corrosion Resistance Excellent

Biocompatibility Excellent

Density 4.4 g/cm3

Table values from: [34]

Table 3: Material properties of silicone

rubber

Table 4: Material properties of grade 5

titanium alloy

Brady Bunch 11

ALTERNATVE TREATMENTS FOR ARRHYTHMIA

Arrhythmia can be treated using several techniques. Doctors determine the appropriate treatment

based on the type and severity of the patient’s arrhythmia. Cardiac catheter ablation and electrical

cardioversion are two alternatives to cardiac pacemakers [41, 42].

Catheter Ablation

Catheter ablation is an invasive procedure that treats

arrhythmias by destroying diseased tissues [41]. A

visible dye is first inserted into the blood vessels to

provide a visual guide for the doctor. Thin flexible

tubes called ablation catheters are then inserted into

the heart through blood vessels in the arm, groin, or

neck. These catheters have electrode tips that record

the heart’s electrical activity and allow the doctor to

recognize the areas that produce irregular heart

rhythms [43]. The tips of ablation catheters are used

to transmit high-energy waves to destroy tissue cells.

Diseased tissue areas are called hot spots, seen in

Figure 12. The doctor directs the tip of the ablation

catheter to burn the area around a hot spot, creating a

scar called the ablation line [41, 43]. These scars create a barrier between the healthy heart tissue

and the diseased tissue, preventing irregular electrical signals from traveling through the heart.

The surgical procedure lasts three to six hours with a recovery time of about six hours [44].

All types of arrhythmia can be treated with catheter ablation. Unlike pacemakers, which need

periodic care and attention, catheter ablation provides a permanent cure [45]. Consequently, many

cardiologists recommend this technique. However, this procedure can be uncomfortable and

painful for patients [46].

Electrical Cardioversion

Electrical cardioversion is a procedure in which timed electrical shocks are delivered externally to

the chest to permanently correct atrial tachycardia. This process is not recommended for other

types of arrhythmias. As seen in Figure 13,

two electrode cardioversion pads are attached

to the patient’s chest. These pads contain

metallic plates surrounded by a conductive

gel. The electrode cardioversion pads are

analogous to the leads used in pacemakers.

The pads are attached via wires to a

cardioversion machine as seen in Figure

13. The electrode pads detect the electrical

signals within the heart. These signals are

sent to the cardioversion machine, which

records the heart rhythm and determines the

appropriate treatment. A doctor reviews this

information and uses the pads to manually

apply the required stimulation to correct the

irregular heart rhythm. Patients typically only

need one cardioversion procedure to correct

atrial tachycardia [42].

Fig. 12: Catheter ablation procedure

Adapted from: [44]

Fig. 13: Electrical cardioversion procedure

Adapted from: [47]

Brady Bunch 12

LIMITATIONS OF THE ENRHYTHM PACEMAKER The limitations of the EnRhythm pacemaker include risks associated with pacemaker

implantation, restrictions on certain activities, and problems with the performance of the

pacemaker.

Complications can arise from the implantation of a pacemaker. Pacemaker implantation can result

in an infection at the surgical cut. Blood vessels or nerves can be damaged, and the lung may be

punctured, causing a collapsed lung. In addition, the patient can have an allergic reaction to the

medicine used during the surgery [48].

Patients with pacemakers should not perform certain activities. Patients should not play full-

contact sports because intense physical contact can damage the pacemaker or dislodge wires.

Additionally, patients with pacemakers should not be exposed to large magnetic fields, such as

those generated by magnetic resonance imaging (MRI) [49].

Even when patients follow all guidelines, the pacemaker does not always function properly. For

example, the electrodes can damage heart tissue, and the leads of the pacemaker can get

dislodged, tangled, or broken [50, 49].

The EnRhythm cardiac pacemaker has an average battery life of only 8.5 to 10.5 years [15].

When the battery is low, the entire implantable pulse generator must be replaced. This requires

open heart surgery, which can be dangerous for patients, especially the elderly. Additionally, the

limited battery life requires younger patients with pacemakers to have several replacement

procedures throughout their lifetime [51].

The pacemaker’s internal circuitry determines when electrical signals should be sent to the heart,

but the circuitry can malfunction. When this occurs, the pacemaker can fail to deliver enough

electrical signals or can deliver electrical signals when they are not needed. Improperly-timed or

unnecessary pacing can result in damaged heart tissue or death [49].

CURRENT PACEMAKER RESEARCH Researchers are continually suggesting improvements for the current pacemaker design. Three of

the current research projects involving pacemakers are creating leadless pacemakers, replacing

the current lithium batteries with longer-lasting options, and using new pacing techniques that are

safer and more precise than leads.

Leadless Pacemakers

Pacemakers are being developed that do not require leads

to stimulate the heart. In 2010, Medtronic released its plans

for a leadless pacemaker that will be roughly the size of a

grain of rice, making it 1/20th the size of the current

EnRhythm pacemaker. All of the internal components of

current pacemakers will be condensed into a small pill-like

capsule, as shown in Figure 14. Due to its small size, the

entire pacemaker can be implanted directly into the heart

and can stimulate a heartbeat by using attached electrodes

rather than leads, shown in Figure 14. The small design

also enables surgeons to use a much safer implantation

procedure. Rather than performing an open heart surgery,

doctors would be able to insert the pacemaker through the

femoral vein in the leg via a catheter in a five to ten minute

Fig. 14: Proposed Medtronic

leadless pacemaker

Adapted from: [53]

Brady Bunch 13

procedure [52, 53]. The new pacemaker will require less battery power to operate because of its

placement within the heart. The battery will only last for seven years, and once the pacemaker

runs out of power, a new device would be inserted. The inactive pacemaker would remain within

the heart [52]. Medtronic plans to make the pacemaker available to patients as early as 2014 [53].

Piezoelectric-Powered Pacemakers

Scientists could soon harness the energy from a beating heart to power pacemakers. Researchers

at the University of Michigan’s aerospace engineering department are developing a piezoelectric

material that could replace lithium batteries as a power source for pacemakers. Piezoelectric

materials generate a voltage when they are deformed due to an external force. See Appendix B

for a detailed description of piezoelectricity. The new piezoelectric material is a ceramic that

captures the vibrations caused by the heart’s beating to produce electrical energy. The material’s

shape is designed to capture heartbeat vibrations across a wide range of frequencies, and magnets

are used to amplify the electrical signals produced by the piezoelectric material [54]. These two

properties allow the device to always generate more energy than required to power the

pacemaker; less than 1/100th of an inch of the new material has the capability to power 18

pacemakers [55]. Researchers plan to attach the material to the diaphragm, which is a muscle

located just beneath the heart in the chest cavity. The material is still in the development stage,

but if it can be successfully applied to pacemakers, the piezoelectric material will remove the

need for pacemaker replacements throughout a patient’s lifetime [56].

Optogenetic Pacemakers

Researchers at Johns Hopkins University are attempting to stimulate the heart with light through a

new technique called optogenetics. In optogenetics, researchers insert light-sensitive proteins

called opsins within the heart cells. When the opsins are exposed to light, they change the ion

balance in and outside of heart cells, causing the heart tissue to contract. The researchers suggest

that pacemaker leads could be equipped with fiber-optic cables, which would transmit light to the

heart tissue. This technique would enable more precise stimulation of the heart because only cells

injected with opsins would respond to the light, and the light would not damage the heart tissue

[57].

Laser-Based Pacemakers

Researchers have proposed using lasers instead of leads to stimulate the heart. Scientists from

Case Western Reserve University and Vanderbilt University have successfully paced the heart of

a quail embryo using a laser. The laser heats the heart tissue, opening an ion channel that causes

the heart to contract. The technique does not appear to damage heart tissue, and it requires less

energy than the current lead-based approach. Lasers also provide much more precise stimulation

than leads; a laser can stimulate a single heart cell [50].

DESIGN RECOMMENDATION One of the biggest drawbacks of pacemakers is

their limited battery lives that require patients to

undergo frequent replacement surgeries. Our

design recommendation replaces the current

EnRhythm battery with a rechargeable lithium

battery. This new battery will be recharged using

ultrasound waves from an external ultrasound

transducer, shown in Figure 15. The new system

would significantly extend the battery life of the

EnRhythm pacemaker, reducing the number of

invasive heart surgeries for patients.

Fig. 15: Proposed ultrasound recharging

design

Adapted from: [25, 58]

Brady Bunch 14

Components of the Proposed Design

Our design recommendation consists of two parts: an external ultrasound transducer and an

internal system within the connector block of the pacemaker. The ultrasound transducer is a

device that produces ultrasound waves. Ultrasound is a type of sound wave that can pass through

body tissue [59]. For a detailed description of ultrasound, see Appendix C. The internal system

converts the applied force from the ultrasound into electrical energy. The internal system, shown

in Figure 16, has four components:

the acoustic lens, matching layer,

piezoelectric material, and backing

layer. The acoustic lens is a convex

lens placed within the polyurethane

casing of the connector block [60].

The matching layer consists of

several layers of polymers and is

located above the piezoelectric

material [59]. The piezoelectric

material is a ceramic that converts

mechanical energy into electrical

energy [61]. The backing layer is

located beneath the piezoelectric

material and is made of a set of

ceramic materials called lead

zirconate titanate (PZT) [62].

Function of the Proposed Design

The proposed design would convert the ultrasound waves into electrical energy to recharge the

pacemaker’s battery. In theory, a doctor would use the external ultrasound transducer to apply

ultrasound waves to the patient’s chest. The ultrasound waves would pass through the body tissue

and connector block to the internal system. As seen in Figure 16, the acoustic lens would focus

the waves onto the matching layer [59]. The matching layer would maximize the transmission of

the waves to the piezoelectric material by minimizing wave reflection [63]. When the waves

strike the piezoelectric material, the material would vibrate and undergo the piezoelectric effect.

The piezoelectric effect is caused by the ceramic’s ionic structure. When a force is applied, all of

the positive charges of the material collect on one side, and the negative charges collect on the

opposite side, thus producing a voltage [61]. This voltage would be sent through the wires to

recharge the pacemaker battery. The last section is the backing layer, which would absorb most of

the ultrasound that passes through the other layers [63].

Benefits of the Proposed Design

Our improvement is designed to minimize risk for patients without causing them any additional

inconvenience. Currently, the battery of the EnRhythm pacemaker only lasts 8.5 to 10.5 years.

When the battery dies, a patient must have the entire IPG replaced through an invasive surgery.

These surgeries can be dangerous and expensive, especially for the elderly. The rechargeable

batteries would extend the battery life and thus require fewer surgeries. Ultrasound waves are

used in the design because they do not damage body tissue, and the titanium casing of the IPG

blocks the ultrasound from interfering with the internal circuitry. The recharging process would

be convenient for patients. Since patients with pacemakers already regularly visit their doctor,

their pacemaker batteries could be recharged at these appointments. Our design only modifies the

internal portion of the pacemaker. Since the pacemaker retains its compact size, there would be

no additional surgical risk associated with the implantation procedure.

Fig. 16: Schematic diagram of proposed ultrasound

recharging system

Image created by Erik Thomas

Brady Bunch 15

REFERENCES

1. Arrhythmia: A patient guide. (n.d.). Health Central. Retrieved October 19, 2013, from

http://www.healthcentral.com/heart-disease/patient-guide-44628-6.html

2. Medtronic patient manual: EnRhythm pacemaker. (2009). Minneapolis, MN: Medtronic, Inc.

Retrieved October 11, 2013, from

http://manuals.medtronic.com/wcm/groups/mdtcom_sg/@emanuals

3. Cardiac anatomy & physiology. (2012). Medtronic Connect: CorePace. Minneapolis, MN:

Medtronic, Inc. Retrieved October 12, 2013, from

https://wwwp.medtronic.com/mdtConnectPortal/microsite/1581802196969/15818021969

73/1581802196978

4. Electrical conduction system of the heart. (n.d.). Phartoonz. Retrieved October 26, 2013, from

http://www.phartoonz.com/2010/09/02/electrical-conduction-system-of-the-heart/

5. The ECG made even easier. (2011). studentnursediaries. Retrieved October 16, 2013, from

http://studentnursediaries.wordpress.com/2011/06/08/the-ecg-made-even-easier/

6. What is an arrhythmia?. (2011). National Heart, Lung, and Blood Institute. Retrieved October

12, 2013, from http://www.nhlbi.nih.gov/health/health-topics/topics/arr/

7. About arrhythmia. (2012). American Heart Association. Retrieved October 13, 2013, from

http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/About-

Arrhythmia_UCM_002010_Article.jsp

8. Types of arrhythmias. (n.d.). Cleveland Clinic. Retrieved October 13, 2013, from

http://my.clevelandclinic.org/heart/disorders/electric/types.aspx

9. Supraventricular tachycardia. (n.d.). Stanford Hospital & Clinics. Retrieved October 12,

2013, from

http://stanfordhospital.org/cardiovascularhealth/arrhythmia/conditions/supraventricular-

tachycardia.html

10. Circulation. (n.d.). RRAPID homepage. Retrieved October 15, 2013, from

http://rrapid.leeds.ac.uk/ebook/05-circulation-06.html

11. Journal of pediatrics: Accuracy of interpretation of preparticipation screening

electrocardiograms. (2011). Oakwood Sports Medicine. Retrieved October 12, 2013, from

http://oakwoodsportsmedicine.com/2011/07/

12. Page, S.L. (2012). Atrial fibrillation, ventricular tachycardia, ventricular fibrilation, atrial

flutter rhythm strips EKG interpretation. Registered Nurse RN. Retrieved October 14,

2013, from http://www.registerednursern.com/wp-content/uploads/2008/11/a-fib.gif

13. Aquilina, O. (2006). A brief history of cardiac pacing. NCBI. Retrieved October 12, 2013,

from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3232561/

14. The vacuum tube. (1999). Detroit Public TV. Retrieved October 14, 2013, from

http://www.pbs.org/transistor/science/events/vacuumt.html

Brady Bunch 16

15. EnRhythm pacing system. (2010). Medtronic for Healthcare Professionals. Medtronic, Inc.

Retrieved October 12, 2013, from http://www.medtronic.com/for-healthcare-

professionals/products-therapies/cardiac-rhythm/pacemakers/enrhythm-pacing-system/

16. Castellanos, A., Lemberg, L., Jude, J., Mobin-Uddin, K., & Berkovits, B. (1968). Implantable

demand pacemaker. British Heart Journal, 30(1), 29-33. Retrieved October 13, 2013,

from the US National Library of Medicine database.

17. ARCHIVED – The pacemaker: Keeping the beat for 60 years. (2011). National Research

Council Canada. Retrieved October 13, 2013, from http://www.nrc-

cnrc.gc.ca/eng/dimensions/issue7/pacemaker.html

18. Medtronic reference manual: EnRhythm P1501DR. (2013). Minneapolis, MN: Medtronic,

Inc. Retrieved October 11, 2013, from

http://manuals.medtronic.com/wcm/groups/mdtcom_sg/@emanuals/@era/@crdm/docum

ents/documents/contrib_172163.pdf

19. Gillis AM, Pürerfellner H, Israel CW, et al. Reduction of unnecessary right ventricular

pacing due to the managed ventricular pacing (MVP) mode in patients with symptomatic

bradycardia: benefit for both sinus node disease and AV block indications. Heart Rhythm.

2005;Abstract AB21-1.

20. Basic pacing concepts. (2012). Medtronic Connect: CorePace. Minneapolis, MN: Medtronic,

Inc. Retrieved October 12, 2013, from

https://wwwp.medtronic.com/mdtConnectPortal/microsite/1581802196969/15818021969

74/1581802196988

21. How does a pacemaker work?. (2012). National Heart, Lung, and Blood Institute. Retrieved

October 14, 2013, from http://www.nhlbi.nih.gov/health/health-

topics/topics/pace/howdoes.html

22. Pacing leads. (2010). Medtronic for Healthcare Professionals. Retrieved October 12, 2013,

from http://www.medtronic.com/for-healthcare-professionals/products-therapies/cardiac-

rhythm/pacemakers/pacing-leads/index.htm#tab2

23. Surgery: What to expect – Implanting a pacemaker. (2010). Medtronic for Patients.

Retrieved October 14, 2013, from

http://www.medtronic.com/patients/bradycardia/getting-a-device/surgery/index.htm

24. Chinitz, M.D., L. A., Bernstein, M.D., N. E., Aizer, M.D., A., Holmes, M.D., D. S., &

Wilbur, M.D., S. (n.d.). Pacemaker implantation. NYU Langone Medical Center Cardiac

and Vascular Institute. Retrieved October 11, 2013, from

http://cvi.med.nyu.edu/patients/treatment-technologies-surgeries/pacemaker-

implantation#C

25. Diagram of Implantation of Pacemaker. (n.d.). Retrieved October 15, 2013, from

http://www.uofmhealth.org/sites/default/files/healthwise/media/medical/hw/h9991486_0

01.jpg

Brady Bunch 17

26. Pacemaker module. (2002). University of California San Francisco School of Medicine.

Retrieved October 13, 2013, from

http://missinglink.ucsf.edu/lm/pacemaker_module/index.htm

27. Managed Ventricular Pacing (MVP). (2013). Medtronic: Device Features. Medtronic, Inc.

Retrieved October 12, 2013, from http://www.medtronicfeatures.com/browse-

features/all/CDF_DF_M-VENTRICULAR-PACING

28. Pacemaker features. (2012). Medtronic Connect: CorePace. Minneapolis, MN: Medtronic,

Inc. Retrieved October 13, 2013, from

https://wwwp.medtronic.com/mdtConnectPortal/microsite/1581802196969/15818021969

74/1581802196988

29. Atrial tachyarrhythmias: A hybrid treatment approach. (2002). Medtronic Connect:

CorePace. Minneapolis, MN: Medtronic, Inc. Retrieved October 12, 2013, from

https://wwwp.medtronic.com/mdtConnectPortal/presentationtools/109/170/10836106199

54

30. Black, J., & Hastings, G. (Eds.). (1998). Handbook of Biomaterial Properties. N.p.: Springer.

31. RTP company RTP 1201-55D polyurethane thermoplastic elastomer (TPU) glass fiber 10%-

55 Shore D. (n.d.). MatWeb MATERIAL PROPERTY DATA. Retrieved November 15,

2013, from

http://www.matweb.com/search/datasheettext.aspx?matguid=70243df6826841b7b53f1fc

01f2facff

32. Di Fiore, A. (n.d.). Polyurethanes in vascular access: Clinical perspectives. Association for

Vascular Access. Retrieved November 15, 2013, from

http://www.avainfo.org/website/download.asp?id=164430

33. AdvanSource biomaterials ChronoFlex C 55D biodurable medical grade polyurethane. (n.d.).

MatWeb MATERIAL PROPERTY DATA. Retrieved November 14, 2013, from

http://www.matweb.com/search/datasheet.aspx?matguid=5d6a5b18d6484708881387e2de

0ca84b

34. 90/10 & 80/20 platinum/iridium products. (2013). H. Cross Company. Retrieved December

1, 2013, from http://hcrosscompany.com/precious/platirid.htm

35. Silicone rubber. (n.d.). MATBASE. Retrieved November 14, 2013, from

http://www.matbase.com/material-categories/natural-and-synthetic-

polymers/elastomers/material-properties-of-silicone-rubber.html#properties

36. Properties: Silicone rubber. (n.d.). Azom.com: The A to Z of Materials. Retrieved November

14, 2013, from http://www.azom.com/properties.aspx?ArticleID=920

37. Extruded material comparison chart. (n.d.). Kent Elastomer Products, Inc.. Retrieved

November 15, 2013, from http://www.kentelastomer.com/uploads/extruded-material-

comparison-chart.pdf

Brady Bunch 18

38. eFunda: Glossary: Materials: Alloys: Titanium Alloy: Wrought: Ti-6Al-4V. (n.d.). eFunda.

Retrieved November 14, 2013, from

http://www.efunda.com/glossary/materials/alloys/materials--alloys--titanium_alloy--

wrought--ti-6al-4v.cfm

39. Biomedical applications of titanium and its alloys. (2008). Biological Materials Science.

Retrieved November 15, 2013, from

http://www.meyersgroup.ucsd.edu/papers/journals/meyers%20316.pdf

40. Titanium alloys - Ti6Al4V grade 5. (2013). Azom.com: The A to Z of Materials. Retrieved

November 15, 2013, from http://www.azom.com/article.aspx?ArticleID=1547

41. Heart arrhythmias. (n.d.). University of Michigan Health System: Frankel Cardiovascular

Center. Retrieved November 14, 2013, from http://www.umcvc.org/medical-

services/abnormal-heart-rhythms

42. What is cardioversion?. (2012). National Heart, Lung, and Blood Institute. Retrieved

November 15, 2013, from http://www.nhlbi.nih.gov/health/health-topics/topics/crv/

43. What to expect during catheter ablation. (2012). National Heart, Lung, and Blood Institute.

Retrieved November 15, 2013, from http://www.nhlbi.nih.gov/health/health-

topics/topics/ablation/during.html

44. Cardiac ablation. (2010). Cardiologist. Retrieved November 15, 2013, from

http://www.cardiologist.org/cardiac-ablation/

45. Cardiac ablation procedures. (2013). University of Maryland Medical Center. Retrieved

December 6, 2013, from http://umm.edu/health/medical/ency/articles/cardiac-ablation-

procedures

46. Procedures. (n.d.). The Arrhythmia Institute. Retrieved November 16, 2013, from

http://www.arrhythmiainstitute.com/procedures/

47. Cardioversion: Electrical cardioversion. (2010). WebMD. Retrieved November 15, 2013,

from http://www.webmd.com/heart/cardioversion-low-voltage-electrical-cardioversion

48. Pacemaker risks. (2011). Medtronic: Join the Pacemakers. Retrieved November 23, 2013,

from http://www.jointhepacemakers.com/what-is-a-pacemaker/benefits-risks/index.htm

49. How will a pacemaker affect my lifestyle?. (2012). National Heart, Lung, and Blood

Institute. Retrieved November 21, 2013, from http://www.nhlbi.nih.gov/health/health-

topics/topics/pace/lifestyle.html

50. 'Laser pacemaker' controls heartbeat. (2013). Discovery News. Retrieved November 14,

2013, from http://news.discovery.com/tech/laser-heart-pacemaker.htm

51. St. Jude Medical Pediatric Pacemaker Pamphlet: Living with a pacemaker. (2011).

Minnesota, MN; St. Jude Medical. Inc. Item No. N-01052. Retrieved November 15,

2013.

Brady Bunch 19

52. Moylan, M. (2010). Medtronic developing new mini pacemaker. MPR News. Retrieved

November 14, 2013, from

http://minnesota.publicradio.org/display/web/2010/11/01/medtronic-pacemaker

53. That's mint! Pacemaker the size of a Tic Tac set to revolutionise heart treatment. (2012).

Mirror News. Retrieved November 12, 2013, from

http://www.mirror.co.uk/news/technology-science/science/heart-pacemaker-the-size-of-

a-tic-tac-758476

54. Moore, N. (2012). Heart-powered pacemaker could one day eliminate battery-replacement

surgery. ScienceDaily. Retrieved November 15, 2013, from

http://www.sciencedaily.com/releases/2012/03/120302193756.htm

55. Recinto, R. (2013). New-generation pacemaker could be powered by the heart. Yahoo! News.

Retrieved November 14, 2013, from http://news.yahoo.com/researchers-made-strides-in-

developing-heart-powered-pacemaker-173035419.html

56. D. Inman, personal communication, November 18-19, 2013.

57. Boyle, P. M., Williams, J. C., Ambrosi, C. M., Entcheva, E., & Trayanova, N. A. (2013). A

comprehensive multiscale framework for simulating optogenetics in the heart. Nature

Communications. Retrieved November 15, 2013, from

http://www.nature.com/ncomms/2013/130828/ncomms3370/full/ncomms3370.html

58. Ultrasound. (n.d.). BBC News. Retrieved November 24, 2013, from

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/radiation/ultrasound

rev3.shtml

59. Basic principle of medical ultrasonic probes (transducer). (n.d.). Nihon Dempa Kogyo Co.,

LTD. Retrieved November 28, 2013, from

http://www.ndk.com/en/sensor/ultrasonic/basic02.html

60. Zhou, Q., Hyui Cha, J., & Kirk Shung, K. (2009). Alumina/epoxy nanocomposite matching

layers for high-frequency ultrasound transducer application. National Heart, Lung, and

Blood Institute. Retrieved November 29, 2013, from

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2729565/

61. Woodford, C. (2009). Piezoelectricity. Explainthatstuff.com. Retrieved November 15, 2013,

from http://www.explainthatstuff.com/piezoelectricity.html

62. Raina, A., & Qasim. A. Transducer basics. (n.d.). http://echocardiographer.org. Retrieved

November 29, 2013, from

http://echocardiographer.org/Echo%20Physics/BasicTransducers.html

63. Characteristics of piezoelectric transducers. (n.d.). NDT Resource Center. Retrieved

November 29, 2013, from http://www.ndt-

ed.org/EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/characterist

icspt.htm

ACKNOWLEDGEMENT

The Brady Bunch would like to thank Dr. Daniel Inman for providing us with additional

information about his current research on piezoelectric-powered pacemakers.

Brady Bunch 20

APPENDIX A

Pacing Modes

Pacemakers run in different pacing modes, which are represented by the NBG code. The NBG

code is a three to five letter sequence. As Table A-1 shows, the first and second letters represent

the heart chambers that are paced and sensed, respectively. The third letter indicates how the

pacemaker responds to the sensed impulse. “I” means that the pacemaker paces the heart unless a

normal heartbeat is detected; if a normal signal is detected, the pacemaker is said to be

“inhibited” because it does not send a pacing impulse. “T” represents a triggered response and is

common for dual chamber pacemakers. A triggered response means that the pacemaker can

stimulate a contraction in the ventricles following an atrial contraction. “D” means that the

pacemaker has the capability to both inhibit and trigger an impulse. The last two letters are less

commonly used. The fourth letter indicates additional pacing features; this letter is usually “R”,

which identifies a pacemaker that uses rate-responsive pacing. The fifth letter indicates if the

device has antitachycardia features. Because very few pacemakers treat tachycardia, the fifth

letter is rarely used [1].

The NBG code can be used to determine how a pacemaker functions. For example, a pacemaker

operating in DDD pacing mode senses and paces in both chambers of the heart, and it has the

capability to inhibit and trigger an electrical impulse [1].

REFERENCES

1. Pacemaker module. (2002). University of California San Francisco School of Medicine.

Retrieved October 13, 2013, from

http://missinglink.ucsf.edu/lm/pacemaker_module/index.htm

2. Pacemaker EP 2073891 A2. (2007). Google Patents. Retrieved October 26, 2013, from

http://www.google.com/patents/EP2073891A2

Table A-1: NBG Code

Table from: [2]

Brady Bunch 21

APPENDIX B

Piezoelectricity

Piezoelectric materials are electrically neutral under normal conditions. As seen in Figure A-1,

the material’s electrical charges are perfectly balanced and cancel out. If stress is applied and the

piezoelectric material is stretched or squeezed, some of the atoms are pushed closer together or

further apart, disrupting the balance of positive and negative charge. As shown in Figure A-2, this

causes a net electrical charge to appear throughout the whole structure; one face becomes positive

while the other becomes negative. This characteristic allows piezoelectric materials to produce

voltages when an external force is applied. Conversely, a piezoelectric material will experience

deformation when a voltage is applied [1].

REFERENCE

1. Woodford, C. (2009). Piezoelectricity. Explainthatstuff.com. Retrieved November 15, 2013,

from http://www.explainthatstuff.com/piezoelectricity.html

Fig. A-1: Piezoelectric material in neutral state

Adapted from: [1]

Fig. A-2: Piezoelectric material when force is

applied

Adapted from: [1]

Brady Bunch 22

APPENDIX C Ultrasound

Ultrasound waves have a frequency higher than what is considered audible [1]. Wave frequency

is a measure of the amount of wavelengths that pass a given point in a fixed amount of time.

Frequency is measured in waves per second, which is known as Hertz (Hz). Medical ultrasound

waves can have a frequency from 1,000,000 to 5,000,000 Hz [1]. An ultrasound transducer uses

piezoelectric materials to send and receive ultrasound waves. When a voltage is applied through

the transducer, piezoelectric materials vibrate within the transducer. This vibration produces

sound waves that are then transmitted through the transducer. The frequency of these vibrations

determines the frequency of the sound waves that are sent into the body [2].

REFERENCES

1. Freudenrich, C. (2001). How ultrasound works. HowStuffWorks. Retrieved November 29,

2013, from http://science.howstuffworks.com/ultrasound2.htm

2. Ursu, D. (n.d.). How do ultrasound transducers work?. eHow Health. Retrieved November 29,

2013, from http://www.ehow.com/how-does_5213125_do-ultrasound-transducers-work_.html

HONOR PLEDGE

We have neither given nor received any unauthorized help on this assignment, nor have we

concealed any violation of the Honor Code.