Cardiac Dysrhythmias and Conduction System Flashcards

Vocabulary flashcards generated from lecture notes covering the cardiac conduction system, action potential phases, ECG waveforms and intervals, dysrhythmias, and heart blocks.

Sinoatrial (SA) Node

The primary pacemaker of the heart located in the right atrium that fires electrical impulses to initiate sinus rhythm and atrial depolarization.

Atrioventricular (AV) Node

A specialized cardiac structure that receives electrical impulses from the SA node via internodal pathways and delays the signal before transmitting it to the ventricles.

Bundle of His

The tract of cardiac conduction tissue through which electrical impulses leave the AV node to enter the right and left bundle branches.

Purkinje Fibers

Terminal conductive fibers that extend electrical impulses directly into the ventricular myocardium to trigger ventricular contraction.

Cardiac Conduction System

The pathway of specialized cardiac cells—comprising the SA node, AV node, bundle of His, right and left bundle branches, and Purkinje fibers—that coordinates electrical impulses and muscle contractions.

Phase 0 (Depolarization)

The rapid initial phase of the cardiac action potential caused by the sudden opening of fast $\text{Na}^+$ channels and sodium influx into the cell.

Phase 2 (Plateau State)

The sustained plateau phase of the cardiac action potential maintained by the balanced influx of $\text{Ca}^{++}$ and outflow of $\text{K}^+$.

Ventricular Action Potential Phases

The 5 distinct electrical phases of cardiac ventricular muscle cells: Phase 0 (Depolarization), Phase 1 (Initial Repolarization), Phase 2 (Plateau State), Phase 3 (Repolarization), and Phase 4 (Resting Potential).

P Wave

The first wave on an electrocardiogram (ECG) tracing, representing atrial depolarization.

PR Interval

The ECG interval measuring the time from the beginning of atrial depolarization to the start of ventricular depolarization, with a normal duration of $0.12$ to $0.20\text{ seconds}$.

QRS Complex

The primary ECG waveform representing ventricular depolarization and simultaneous atrial repolarization.

QRS Interval

The ECG interval measuring the duration of ventricular depolarization, normally lasting less than $0.12\text{ seconds}$.

T Wave

The ECG waveform following the QRS complex that represents ventricular repolarization.

QT Interval

The ECG measurement spanning from the beginning of the QRS complex to the end of the T wave, representing total ventricular depolarization and repolarization, normally lasting $0.45$ to $0.48\text{ seconds}$.

U Wave

An extra, small deflection occasionally seen following the T wave on an ECG tracing.

Sinus Bradycardia

A regular sinus rhythm originating from the SA node with a heart rate of less than $60\text{ bpm}$.

Atropine

The first-line anticholinergic medication used to treat symptomatic or unstable sinus bradycardia by blocking vagal stimulation to increase heart rate.

Sinus Tachycardia

A cardiac rhythm originating from the SA node with a heart rate exceeding $100\text{ bpm}$.

Premature Atrial Contractions (PACs)

Early atrial depolarization caused by an ectopic pacemaker close to the SA node firing earlier than expected.

Atrial Fibrillation (AF)

A cardiac dysrhythmia caused by multiple chaotic electrical impulses in the atria, resulting in an irregular, often rapid heart rate, loss of effective cardiac output, and risk of atrial clot formation.

Atrial Flutter

An ectopic atrial dysrhythmia produced outside the SA node, characterized by a regular atrial rhythm with distinct saw-tooth flutter (F) waves.

Supraventricular Tachycardia (SVT)

A fast, regular tachycardia with narrow QRS complexes that originates above the ventricles.

Junctional Rhythm

A cardiac rhythm originating within the AV node at an intrinsic rate of $40$ to $60\text{ bpm}$, typically presenting with retrograde inverted, buried, or absent P waves.

Premature Ventricular Contractions (PVCs)

Ectopic electrical impulses that originate directly in the ventricular myocardium rather than above the ventricles.

Ventricular Tachycardia (VT)

A cardiac dysrhythmia defined by three or more consecutive premature ventricular contractions (PVCs) in a row.

Ventricular Fibrillation (VF)

A lethal dysrhythmia characterized by rapid, disorganized ventricular electrical activity that prevents effective pumping, requiring immediate CPR and defibrillation.

Idioventricular Rhythm (IVR)

A slow escape rhythm originating in the ventricles that occurs when both the SA node and AV node fail.

Asystole

A cardiac arrest rhythm characterized by a complete absence of electrical activity from the heart.

First-Degree AV Block

A conduction delay through the AV node resulting in a consistently prolonged PR interval greater than $0.20\text{ seconds}$ without any dropped QRS complexes.

Second-Degree AV Block Type I (Wenckebach)

An AV conduction block characterized by progressive lengthening of the PR interval with each successive beat until a QRS complex is dropped.

Second-Degree AV Block Type II (Mobitz II)

An AV block characterized by intermittent dropped QRS complexes without prior prolongation of the PR interval.

Third-Degree AV Block (Complete Heart Block)

A total block of impulse transmission through the AV node, resulting in complete dissociation between P waves and QRS complexes.

Heart Block Poem

A mnemonic device for identifying AV blocks: 'If the R is far from P, then you have a FIRST DEGREE. Longer, longer, longer, drop! Then you have a WENCKEBACH. If some Ps don't get through, then you have MOBITZ II. If Ps and Qs don't agree, then you have THIRD DEGREE.'

Transcutaneous Pacing (TCP)

An emergency intervention using external electrode pads on the chest and back to deliver electrical pulses to pace a heart beating too slowly.