Introduction To Electrophysiology

Introduction to ELECTROPHYSIOLOGY

What Are They DOING Over There?!

Basic Principles

Electrophysiology: the study of electrical activity in the body

Three main activities in the EP lab:◦EP Studies◦Device Implants◦Catheter Ablation

Basic Principles

Anatomy of the Cardiac Electrical System

◦SA Node◦AV Node◦His Bundle◦Bundle Branches◦Purkinje Fibers

*Remember: The heart has several levels of backup pacing in place.

Basic Principles

Basic Principles

Normal path of conduction

SA Node AV Node His Bundle Bundle Branches Purkinje Fibers

Start the Heart Animation.url

Basic Principles

Cardiac Action Potential

Basic Principles

Cardiac Action Potential

Basic Principles

Abnormal Heart Rhythms

◦Bradycardia Failure to generate impulse Failure to propagate impulse

◦Tachycardia Automatic- seen in acutely ill patients Reentry Circuits- most common (SVTs, VT) Triggered

Basic Principles

Treatment of Arrhythmias

Drug Therapy

◦Class I through 5 Antiarrhythmics◦Watch out for proarrhythmia!◦Drug toxicity

***Only use antiarrhythmic drugs for patients with significant symptoms or life threatening arrhythmias.

Basic Principles

Non-pharmacologic Therapies

◦Reverse underlying cause Example: hypokalemia

◦Surgery PCI/CAB for ischemia

◦Devices Pacemaker for bradycardia

◦Ablation Can cure certain tachycardias

EP Studies

INTRODUCTION TO EP STUDIES

An EP study is performed by doing two things:

◦Recording

◦Pacing

That’s it! Diagnosis depends on speed of conduction through the system, direction of impulses, and any

arrhythmias induced.

EP Studies

Indications for EP Study

◦Syncope◦Palpitations◦Documented tachycardia◦Suspected SA or AV node disease◦Risk assessment for Sudden Cardiac Death

(SCD)

EP Studies

Electrode Catheters

◦Can use femoral, subclavian, or IJ access

◦Typically use 5.5 and 6 French sheaths for diagnostic studies

◦Similar to temporary pacing catheters, but with more electrodes near the tip

◦Different shapes for different areas of the heart

EP Studies

EP Studies

Electrode Catheters

◦A basic study will use two.

◦More complex studies (SVT studies) will use more.

***Multiple catheters in multiple locations can track the speed and direction of electrical impulses across the heart.

EP Studies

ECG versus EGM◦Surface ECG is a total of all the electrical

activity across the heart

◦EGM = Intracardiac Electrogram Records only the activity of a localized area, i.e.

between electrodes on the catheters

Faster sweep speed used (typically 100mm/sec)

EP Studies

Intracardiac Electrograms (EGMs)

EP Studies

Intracardiac Electrograms

These deflections represent rapid myocardial depolarization only.

Therefore, we do not see the slower conduction through the SA and AV nodes. Remember the different action potentials of

muscles cells versus nodal cells.

EP Studies

By manipulating the electrode catheters, pacing can be performed from virtually any area of the heart.

◦Premature impulses are delivered by the EP MD with precise timing and patterns.

This is called Programmed Stimulation. A stimulator computer program is used to create

the patterns for pacing.

EP Studies

Programmed stimulation can be used to:

◦Measure SA node and AV node function

◦Measure refractory periods of nodes and myocardium

◦Induce and terminate Ventricular Tachycardia

This can determine which patients receive an ICD implant.

Evaluation of SA Node

Sa Node = Pacemaker of the Heart

◦Comma- shaped

◦Located near SVC

◦Has sympathetic (“fight”) and parasympathetic (“flight”) innervation

*SA Node disease is the most common cause of bradycardia.


Types of SA Node Disease:

◦Intermittent or sustained bradycardia

◦Sudden SA Node arrest

◦Periods of bradycardia with tachycardia Brady-Tachy Syndrome

*If significant symptoms are present, these conditions are termed Sick Sinus Syndrome.


Symptoms of SA Node Disease

◦Lightheadedness

◦Dizziness

◦Presyncope

◦Syncope


Causes of SA Node Disease:

◦Fibrosis

◦SA Nodal artery disease

◦Cardiac Trauma

◦Cardiac inflammatory/infiltrative disease

◦Thyroid disorders


Measurement of SA Node Function in EP Lab

◦Sinus node recovery time (SNRT) Based on overdrive suppression

◦Sino-atrial conduction time (SACT) Exit block

Evaluation of AV Node

AV Node = Rate Regulator of the Heart

◦Located on interatrial septum, near TV

◦Has mostly parasympathetic innervation

*AV Node disease is the second major cause of bradycardia.


The major question with AV Node disease is: “Does the patient need a pacemaker?”

◦This depends on:

Symptoms

Site of conduction block

Degree of conduction block


Symptoms are the same as SA Node disease:

◦Lightheadedness

◦Dizziness

◦Presyncope

◦Syncope


Site of AV Block:

General Rule:

Block located in AV Node = no PPM

Block located below AV Node = PPM


Degree of AV Block

General Rule:

If 1st Degree = no PPM

If 2nd Degree = maybe PPM

If 3rd Degree = PPM

HIS Bundle

His Bundle = Conductor to Ventricles

◦Compact bundle of Purkinje fibers arising after AV node

◦Rapid conduction through the fibrous AV skeleton

◦Divides into Right and Left Bundle branches

◦If patient has disease in His Bundle, a PPM may be indicated.

Bundle Branches

Bundle Branches = Coordinators of Ventricular Contraction

◦Left Bundle Branch divides into two: anterior and posterior

All end as Purkinje fibers, which rapidly spread the impulse to all ventricular muscle◦Order of contraction: septum apex lateral

walls base

Bundle Branches

Any delay in impulse conduction in or below the bundle branches = Interventricular Conduction Delay (ICVD)◦Can disrupt normal ventricular contraction

ICVD leads to wide QRS on surface ECG

If delay is significant and leads to heart failure, Cardiac Resynchronization Therapy (CRT) may be indicated.

Bundle Branches

Take Note:

◦If performing a right heart cath on a patient, be prepared if they have existing LBBB:

Swan catheters may hit the Right Bundle Branch, causing Right Bundle Branch Block.

Patient would then have complete heart block and need a temporary pacing wire.

Device Therapy

Three kinds of implants in the EP Lab:

◦Permanent pacemakers (PPM)

◦Implantable Cardioverter-Defibrillators (ICDs)

◦Cardiac Resynchronization Therapy (CRT) devices

Device Therapy

Implanted Devices

◦Most are implanted in the pectoral region

◦Can have one, two, or three leads

◦Can be programmed in a variety of ways, to suit each individual patient

Device Therapy

Permanent Pacemakers

◦Indications for use include:

Symptomatic Sinus Bradycardia AV Conduction Disease Cardioneurogenic Syncope Bradycardia-induced VT Significant Ventricular Dysfunction with wide QRS

Device Therapy

Parts of a Pacemaker

◦Generator- contains the circuitry, computer memory, and battery Typical PPM weighs about an ounce (10cc)

◦Leads- usually inserted through venous system to heart Can be active (screwed into heart muscle) or

passive (distal tines catch onto heart tissue)

Temporary Pacers◦Settings:

Rate

mA (current flow)

Sensitivity: more sensitivity = less pacing less sensitivity = more pacing

asynchronous = pacing regardless of what heart is doing

Device Therapy

Implantable Cardioverter-Defibrillators

◦Indications for use include:

Sustained VT/VF EF < or equal to 35%, Class II/III HF Prior MI with EF < or equal to 30%, Class I HF EF < 40, NSVT, inducible VT

Every 3 minutes someone dies from SCA in the USA.

Device Therapy

Parts of an ICD

◦Generator weighs more that PPM, due to addition of a capacitor Weighs about 3 ounces (36cc) Capacitor stores energy needed for shocks

◦RV lead is designed to deliver shocks to convert VT/VF- looks different from a PPM lead under fluoro

Device Therapy

Cardiac Resynchronization Therapy

◦Indications for use include: Class III/IV heart failure Dilated or ischemic cardiomyopathy QRS interval > or equal to 120ms EF < or equal to 35%

Vast majority of patients fitting this criteria also qualify for ICD therapy.

CRT can improve EF up to 10-15%.

Device Therapy

Parts of a CRT device

◦Generator weighs about

◦Requires placement of an LV lead in coronary sinus Successful transvenous placement in ~95% of

patients Other 5% would need surgical placement

Cardiac Ablation

Ablation: destruction of arrhythmia- causing heart tissue

◦Can be curative, eliminating need for antiarrhytmic drugs or surgery

◦Success rates vary according to arrhythmia, with some over 90%.

◦Major complications occur in about 3% of patients.

Cardiac Ablation

How it works:◦Ablation catheter is inserted (usually through

femoral vein) to heart, along with electrode catheters for recording.

◦Electrical activity is recorded, and abnormal rhythms are tracked.

◦Ablation catheter is placed at area of arrhythmia, and energy is applied to destroy tissue.

◦Pt is monitored for any further signs of arrhythmia before leaving EP lab.

Cardiac Ablation

Indications for Catheter Ablation:

◦Symptomatic SVT due to AVNRT, WPW, unifocal atrial tachycardia, and atrial flutter.

◦Atrial fib with lifestyle-limiting symptoms, after inefficacy/intolerance of at least one antiarrhythmic drug.

◦Symptomatic VT.

Cardiac Ablation

Energy Sources:◦Direct current: in the early days, the ablation

catheter was connected to an external defibrillator Greater than 250J could be delivered inside the

heart, heating catheter tip to thousands of degrees Celsius

Blood was instantly vaporized, causing rise in pressure and flash of light

Created lesions up to 4cm2, with ragged edges Only used to ablate His bundle, with 85% success

rate (complications were suprisingly low).

Cardiac Ablation

Radiofrequency (RF) energy:

◦Most commonly used ◦Same as bovie machines in OR◦Much lower voltage than direct current- no

explosions◦Creates smaller, discrete lesions◦No muscle or nerve stimulation- no general

anesthesia needed

Cardiac Ablation

Complications of Ablation:

◦Complete heart block◦Cardiac perforation and tamponade◦Creating MR/TR◦Embolism/stroke◦Pulmonary vein stenosis◦Coronary artery lesions

Current challenges in EP:

◦Atrial Fib ablation- making it safer and more effective, with less procedure time

◦Optimizing CRT therapy◦Getting ICD therapy to more patients who

qualify

References

R. Fogoros. Electrophysiologic Testing, 4th ed.

Medtronic.comStiffler, J. The Diagnostic EP Study.

Healthworks www.skillstat.comEllenbogen and Wood. Cardiac Pacing &

ICDs, 5th ed.Eprewards.com

http://www.skillstat.com/

Documents

Introduction To Electrophysiology