Rhythm Analysis: Ventricular/Blocks Flashcards

A patient's ECG strip shows a regular rhythm with a rate of 45 bpm. The QRS complexes are wide (0.14 seconds), and there are no discernible P waves associated with the QRS complexes. Which of the following rhythms is most likely represented?

Answer: Idioventricular rhythm

Idioventricular rhythm is characterized by a regular, slow ventricular rate (typically 20-40 bpm, but sometimes up to 50), wide QRS complexes (≥0.12s), and the absence of associated P waves. It acts as a safety mechanism when higher pacemakers fail.

Which of the following ECG findings is the hallmark characteristic of Third-Degree Atrioventricular (AV) Block?

Answer: Complete AV dissociation with atrial rate faster than ventricular rate

Third-degree, or complete, AV block is defined by the complete absence of conduction between the atria and ventricles. This results in AV dissociation, where the P waves (atrial activity) and QRS complexes (ventricular activity) are independent of each other, with the atrial rate typically being faster than the ventricular escape rate.

A CCT observes a rhythm strip where the PR interval progressively lengthens for three consecutive beats, followed by a P wave that is not followed by a QRS complex. This pattern then repeats. How should this rhythm be identified?

Answer: Mobitz I Second-Degree AV Block (Wenckebach)

The classic finding for Mobitz I Second-Degree AV Block, also known as Wenckebach phenomenon, is a progressive prolongation of the PR interval until a P wave is blocked and a QRS complex is 'dropped'. The cycle then typically resets.

A patient's monitor displays a regular, wide-complex tachycardia at a rate of 180 bpm. Which of the following features, if present, would most definitively confirm the rhythm is Ventricular Tachycardia (VT) rather than Supraventricular Tachycardia (SVT) with aberrancy?

Answer: Presence of fusion and capture beats

While several criteria can suggest VT, the presence of AV dissociation, demonstrated by capture or fusion beats, is a pathognomonic sign of Ventricular Tachycardia. Capture beats are normal-looking QRS complexes that occur when a sinus beat is conducted to the ventricles during the tachycardia, and fusion beats are a hybrid of a sinus and ventricular beat.

When analyzing an ECG for Premature Ventricular Contractions (PVCs), which characteristic is typically observed?

Answer: A wide, bizarre QRS complex followed by a full compensatory pause

PVCs originate from an ectopic focus in the ventricles. This results in a premature, wide (≥0.12s), and abnormally shaped QRS complex because the impulse spreads through the myocardium instead of the rapid conduction pathway. It is typically followed by a compensatory pause, as the sinoatrial node's rhythm is not interrupted.

A patient's ECG shows a regular rhythm with a constant PR interval on all conducted beats. Suddenly, a P wave appears that is not followed by a QRS complex. This occurs unpredictably. This finding is most consistent with:

Answer: Mobitz II Second-Degree AV Block

Mobitz II Second-Degree AV Block is characterized by a constant PR interval in the conducted beats and intermittent, unpredictable non-conducted P waves (dropped QRS complexes). This type of block is considered more dangerous than Mobitz I because it can suddenly progress to complete heart block.