CRAT Ventricular Arrhythmia Identification 2 — Questions and Answers

Question 1: A premature ventricular complex (PVC) is recognized on ECG by which characteristic?

Wide QRS greater than 120 ms appearing earlier than expected with a compensatory pause and no preceding P wave (Correct answer)
Narrow QRS appearing early with a preceding P wave
Wide QRS with a normal preceding P wave and normal PR interval
Regular wide complex at exactly 60 bpm

Correct answer: Wide QRS greater than 120 ms appearing earlier than expected with a compensatory pause and no preceding P wave

PVCs arise from an ectopic ventricular focus, producing a wide (> 120 ms), abnormal QRS complex that occurs early in the cycle, not preceded by a P wave, and typically followed by a full compensatory pause.

PVCs originate below the bundle of His, activating the ventricles via slow myocardial conduction rather than the Purkinje system. Features: premature QRS (early), width > 120 ms, abnormal morphology (slurred, notched, bizarre), no preceding P wave, followed by a full compensatory pause (because the SA node is not reset). T wave deflection is opposite to the main QRS deflection (discordant T wave).

Question 2: PVCs occurring in pairs (two consecutive PVCs) are referred to as which term?

Couplets (Correct answer)
Bigeminy
Trigeminy
Salvos

Correct answer: Couplets

Two consecutive PVCs are called a couplet. Three or more consecutive PVCs constitute a run of ventricular tachycardia.

PVC pattern terminology: isolated PVC (single), couplet (2 consecutive), triplet (3 consecutive — technically a 3-beat run of VT), salvos (short bursts), bigeminy (every other beat is a PVC), trigeminy (every third beat is a PVC). Three or more consecutive PVCs at 100 bpm or greater constitutes ventricular tachycardia. Couplets increase the risk of sustained VT, particularly in patients with structural heart disease.

Question 3: Monomorphic ventricular tachycardia is distinguished from polymorphic VT by which feature?

Monomorphic VT has QRS complexes of uniform appearance; polymorphic VT has QRS complexes that change in morphology and axis (Correct answer)
Monomorphic VT is always slower than polymorphic VT
Monomorphic VT always requires defibrillation
Polymorphic VT is associated with a narrow QRS

Correct answer: Monomorphic VT has QRS complexes of uniform appearance; polymorphic VT has QRS complexes that change in morphology and axis

In monomorphic VT, all QRS complexes originate from the same ventricular focus and appear identical, while polymorphic VT (such as torsades de pointes) has varying QRS morphology because multiple foci are involved.

Monomorphic VT: all QRS complexes have identical morphology because the re-entrant circuit or ectopic focus is stable and in one location — commonly seen in post-MI scar-related reentry. Polymorphic VT: QRS morphology changes beat to beat, reflecting multiple changing activation wavefronts — associated with ischemia, long QT syndrome, and Brugada syndrome. Torsades de pointes is a specific form of polymorphic VT with the characteristic twisting pattern around the baseline.

Question 4: What is the minimum number of consecutive ventricular beats at 100 bpm or greater required to define ventricular tachycardia?

Three or more consecutive beats (Correct answer)
Two consecutive beats
Five or more consecutive beats
Ten or more consecutive beats

Correct answer: Three or more consecutive beats

Ventricular tachycardia is defined as three or more consecutive ventricular complexes (wide QRS) at a rate of 100 bpm or greater, originating from a ventricular focus.

Three consecutive PVCs at 100 bpm or faster is the threshold for VT. Non-sustained VT (NSVT) terminates spontaneously within 30 seconds. Sustained VT persists beyond 30 seconds or requires intervention. The rate threshold of 100 bpm distinguishes VT from accelerated idioventricular rhythm (AIVR), which is 60-100 bpm. Duration and hemodynamic stability guide treatment decisions.

Question 5: PVCs occurring in a pattern of one PVC for every normal beat are called what?

Ventricular bigeminy (Correct answer)
Ventricular trigeminy
Couplets
Ventricular quadrigeminy

Correct answer: Ventricular bigeminy

Ventricular bigeminy describes a pattern where every other beat is a PVC, creating an alternating normal-PVC-normal-PVC rhythm.

Bigeminy: normal beat, PVC, normal beat, PVC — creates a regular-appearing bigeminal rhythm. Trigeminy: two normal beats followed by one PVC. The regularity of bigeminy can give a false sense of stability, but the effective heart rate is halved because PVCs often produce no effective cardiac output. In patients with poor left ventricular function, bigeminy can cause significant hemodynamic compromise.

Question 6: The R-on-T phenomenon in PVCs is dangerous because it does which of the following?

A PVC occurring during the vulnerable period of ventricular repolarization (T wave peak) can initiate ventricular fibrillation (Correct answer)
It causes sinus node suppression
It produces AV block
It prolongs the PR interval

Correct answer: A PVC occurring during the vulnerable period of ventricular repolarization (T wave peak) can initiate ventricular fibrillation

The peak of the T wave represents the vulnerable period of ventricular repolarization — when cells are partially recovered, making them susceptible to fibrillation if an electrical stimulus (PVC) falls during this window.

During the apex of the T wave (relative refractory period), ventricular cells are in varying states of recovery. Some cells are fully recovered, others partially, creating a heterogeneous electrical state that predisposes to re-entrant arrhythmias. A PVC with its QRS falling on the T wave (R-on-T) can trigger VT or VF, particularly in ischemic myocardium or prolonged QT states. This phenomenon was first described by Wiggers and Wegria in 1940.

CRAT Ventricular Arrhythmia Identification 2

A premature ventricular complex (PVC) is recognized on ECG by which characteristic?