Chapter 37

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Chapter 37

Electrocardiography


Anatomy of the Heart

• Four chambers– Atria: two upper chambers– Ventricles: two lower chambers

• Deoxygenated and oxygenated blood– Cycle begins with each heartbeat

• Coronary arteries


Electrical Conduction System of the Heart

• Sinoatrial (SA) node: body’s natural pacemaker

• Atrioventricular (AV) node: responds to signals from SA node

• Bundle of His and Purkinje fibers: disperses electrical impulses


Electrical Conduction System of the Heart

• Systole: contraction

• Diastole: relaxation

• ECG cycle– Graphic representation of cardiac cycle– Electrical impulses recorded on ECG paper or

displayed on oscilloscope


The Cardiac Cycle and the ECG Cycle

• Baseline or isoelectric line

• Positive and negative deflection

• P, QRS, T waves: depolarization and repolarization of myocardial cells

• Each cardiac cycle takes about 0.8 second


The Cardiac Cycle and the ECG Cycle

• Electrical impulses in cardiac cycle


Calculation of Heart Rate

• On ECG graph paper:– Every fifth line darker than other lines (squares 5 X

5 mm)– Time measured on horizontal line– Voltage measured on vertical line


Types of Electrocardiographs

• Multichannel ECG

• Automatic ECG machines

• Single-channel ECG >>


Types of Electrocardiographs

• ECG telephone transmissions

• Facsimile electrocardiograph

• Interpretive electrocardiograph


ECG Equipment

• Electrocardiograph paper– Black or dark blue– Wax or plastic coated– Heat and pressure sensitive– Heat of stylus can be adjusted to obtain sharp

tracing


ECG Equipment

• Electrolyte– Applied with each electrode to pick up electrical

current – In form of gel, lotion, paste, or pre-saturated pads,

contained within adhesive sensors


ECG Equipment

• Sensors or electrodes– Detect electrical impulses on body surface; relay

them through cables, or lead, wires to ECG machine

– Disposable sensors (electrodes) contain layer of electrolyte gel on adhesive surface; used on limbs and chest


ECG Equipment

• Lead wires– Once self-adhesive

sensors are placed, lead wires from ECG machine are connected to them


ECG Equipment

• Electrocardiograph machine– Electrical activity from body small; made larger by

amplifier of ECG machine

• Care of equipment– Remove lead wires from sensors– Remove sensors from patient– Dispose of sensors– Change paper when necessary


Lead Coding

• 12 leads recorded using 10 lead wires

• Necessary for identification and mounting purposes

• Newer ECGs automatically mark (code) each lead


The Electrocardiograph and Sensor Placement

• 10 sensors that record 12 leads of heart’s electrical activity

• Allows for 3D interpretation of activity

• Electrodes placed on patient’s four limbs and chest


The Electrocardiographand Sensor Placement

• Types of leads– Standard limb or

bipolar leads– Augmented leads– Chest leads or

precordial leads


Standardization and Adjustment of the Electrocardiograph

• Value of recording depends on accuracy

• Universal measurements

• One millivolt (mV) of cardiac electrical activity will deflect stylus exactly 10 mm high


Standard Resting Electrocardiography

• Patient preparation

• Placement of limb and chest leads

• Attachment of lead wires

• Elimination of artifacts vary little from one electrocardiograph to another


Mounting the ECG Tracing

• Commercially prepared mounting forms

• Mount completed tracing after provider has reviewed entire recording

• Patient’s name, date, address, age, sex, blood pressure, height and weight, cardiac medications


Interference or Artifacts

• Somatic tremor artifacts: muscle tremor

• Alternating current (AC) interference: electrical interference

• Wandering baseline artifacts: stylus moves from center of ECG paper


Interference or Artifacts

• Interrupted baseline artifacts: break seen between waves

• Patients with unique problems


Myocardial Infarctions (Heart Attacks)

• Number one cause of death in United States

• Behaviors to adopt for healthy heart


Cardiac Arrhythmias

• Atrial arrhythmias– Premature atrial contractions (PAC)– Paroxysmal atrial tachycardia (PAT)– Atrial fibrillation


Cardiac Arrhythmias

• Ventricular arrhythmias– Premature ventricular contractions (PVCs)– Ventricular tachycardia– Ventricular fibrillation


Defibrillation

• Electrical device that applies countershocks to heart through electrodes or pads placed on chest wall

• Can convert cardiac arrhythmia to normal sinus rhythm

• Automated external defibrillators (AED)


Other Cardiac Diagnostic Tests

• Holter monitor (portable ambulatory electrocardiograph)– Portable continuous recording of cardiac activity

for 24-hour period – Noninvasive test helps to diagnose cardiac

arrhythmias– Digital, three-channel ECG; Windows-based

software– Electrode placement not the same as for standard

12-lead resting ECG



• Holter monitor– Prepare patient– Instruct patient– Check and replace

battery– Apply and remove

monitor



• Holter monitor– Patient activity diary

• Record all activities, emotional states, time of their occurrence

• Record chest pain and other symptoms and time of occurrence

– Removal• Patient returns to office• Tape analyzed by scanner or computer



• Loop ECG– Uses only two electrodes– Records few minutes of ECG at a time on

computer chip– Recorded event transmitted by telephone to

provider



• Treadmill stress test or exercise tolerance ECG– Diagnose heart disorders– Probable cause of patient’s chest pain– Assess patient’s cardiac ability following cardiac

surgery– Noninvasive test– Patient exercises on treadmill at prescribed rates

of speed



• Treadmill stress test or exercise tolerance ECG– Complications ( myocardial infarction or serious

arrhythmia) can occur during testing – Further diagnostic tests such as cardiac

catheterization (angiogram) may be necessary



• Thallium stress test– Similar to treadmill stress– Patient given injection of radioactive (thallium)– Test shows how well blood flows to heart muscle



• Echocardiography/ultrasonography– Noninvasive, diagnostic test– Ultrasound to image internal structures of heart

• CT and MRI coronary imaging– Identify location and thickness of cardiac muscle

scars due to damage


Cardiac Procedures

• Percutaneous transluminal coronary angioplasty (PTCA)– Widens narrowed or blocked coronary artery– Balloon angioplasty – Stents: small mesh tubes compressed around

balloon; permanent intervention


Cardiac Procedures

• Atherectomy and laser angioplast

• Coronary artery bypass

• Heart valve: repaired or replaced

• Procedures for arrhythmias

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Chapter 37