ECG, Dysrhythmias and Conduction Problems (Chapter 22)

Key vocabulary terms from ECG/Dysrhythmia/conduction content, with concise definitions to support exam prep.

Electrocardiogram (ECG)

Graphic recording of the heart's electrical activity obtained from skin electrodes; shows waves, segments, and intervals.

Dysrhythmia

Disorder of formation or conduction of electrical impulses in the heart; can affect rate, rhythm, or both and may alter blood flow.

Cardiac conduction system

Network including SA node, AV node, Bundle of His, right and left bundle branches, and Purkinje fibers that coordinates heartbeats.

Automaticity

Ability of cardiac cells to generate their own electrical impulses.

Conductivity

Ability of cardiac cells to transmit an impulse to neighboring cells.

Excitability

Ability of cardiac muscle to shorten and contract in response to stimulation.

Depolarization

Ion exchange (Na+ in, K+ out) that initiates contraction of cardiac cells.

Repolarization

Return of cardiac cells to resting state (K+ in, Na+ out) preparing for next stimulus.

Coronary perfusion

Blood flow to the myocardium via coronary arteries that originate from the aorta; provides oxygen and nutrients.

Left anterior descending (LAD) artery

Supplies anterior left ventricle, anterior septum, and inferior surface of the left ventricle.

Circumflex artery

Supplies the left atrium and lateral/posterior surfaces of the left ventricle.

Right coronary artery (RCA)

Supplies the right atrium, right ventricle, inferior left ventricle surface, SA node, AV node.

Sinoatrial node (SA node)

Primary pacemaker of the heart; inherent rate 60–100/min; initiates sinus rhythms.

Atrioventricular node (AV node)

Backup pacemaker; inherent rate 40–60/min; delays impulse to allow ventricular filling.

Bundle of His

Conduction pathway from AV node to ventricles; part of the AV junction.

Purkinje fibers

Network delivering impulse into ventricular muscle; intrinsic rate 20–40/min; wide QRS if pacing from here.

P wave

Atrial depolarization; corresponds to atrial contraction.

PR interval

From start of P wave to start of QRS; normal 0.12–0.20 s; prolonged suggests first-degree AV block; very short may indicate junctional rhythm.

QRS complex

Ventricular depolarization; normal duration 0.06–0.12 s; wide (>0.12 s) indicates ventricular origin or conduction delay.

ST segment

Interval between QRS and T waves; used to assess ischemia or injury; J point marks its start.

QT interval

From start of Q wave to end of T wave; represents total ventricular depolarization and repolarization.

Isoelectric line

Baseline with no electrical activity; the neutral line on an ECG.

P wave morphology

Shape of the P wave; upright/rounded/smooth; wandering atrial pacemaker has multiple P-wave morphologies.

Lead system

Arrangement of electrode placements and the relationship of heart activity to each lead.

Five-lead monitoring placement

ECG setup using five leads (e.g., white RA, black LA, green RL ground) with specific intercostal placements; leads changed daily.

Twelve-lead ECG

ECG from 12 leads providing multiple views of electrical activity; requires good skin prep for adhesion.

Pacemaker

Electronic device that provides electrical stimuli to the heart when the intrinsic pace is inadequate.

Permanent pacemaker

Chronic implanted device with transvenous leads and a generator under the skin to provide ongoing pacing.

Temporary pacemaker

External pacing system used short-term (often via external pads or transvenous wires).

Transvenous (endocardial) pacemaker

Leads inserted through veins into the heart chambers to deliver pacing.

Transcutaneous pacemaker

External pacing using pads placed on the chest for temporary pacing.

Indications for permanent pacing

Sick sinus syndrome, AV blocks, tachy-brady syndrome, carotid sinus syndrome, neurocardiogenic syncope, prolonged QT.

Pacemaker malfunction: failure to pace

Pacer spikes occur without a resulting heartbeat; device is not firing.

Pacemaker malfunction: failure to capture

Pacer spikes with no myocardial depolarization or capture.

Pacemaker malfunction: failure to sense

Pacer fires despite intrinsic heart activity; device cannot detect the heart’s own rhythm.

Cardioversion

Delivery of synchronized electrical current to depolarize enough cells to restore normal rhythm.

Defibrillation

Delivery of unsynchronized electrical current to terminate life-threatening arrhythmias.

Implantable cardioverter defibrillator (ICD)

Device implanted to detect and terminate tachyarrhythmias and fibrillation; may include antitachycardia pacing.

Life Vest

Wearable external defibrillator with garment, electrode belt, and monitor for temporary protection.

First-degree AV block

PR interval > 0.20 s with all P waves followed by a QRS; slowed conduction but intact rhythm.

Mobitz I (Wenckebach)

Second-degree AV block with progressive PR lengthening until a beat is dropped.

Mobitz II

Second-degree AV block with intermittent dropped beats without prior PR lengthening.

Third-degree AV block

Complete heart block; no atrial-to-ventricular conduction; may require pacing.

Premature atrial contraction (PAC)

Early atrial beat causing irregular rhythm; usually benign but may indicate atrial irritability.

Atrial fibrillation

Irregularly irregular rhythm with absent P waves and variable R-R intervals.

Atrial flutter

Rapid, regular atrial rhythm with sawtooth flutter waves.

Premature ventricular contraction (PVC)

Early ventricular beat; typically wide QRS complex.

Ventricular tachycardia (VT)

Rapid ventricular rhythm that may be stable or unstable; may require treatment.

Ventricular fibrillation (VF)

Chaotic ventricular activity with no effective cardiac output.

Ventricular asystole

Absence of ventricular electrical activity; no cardiac output.