AV Rhythms Flashcard 1

A. Rationale: Atrioventricular blocks delay conduction or completely block impulses from the atria to the ventricles. They are brought about by an increase in vagal tone, which is elicited during sleep, athletic training, pain, or stimulation of the carotid sinus. Vomiting and dizziness are not known to elicit AV blocks. Severe hypokalemia may trigger ventricular arrhythmias.

A. Rationale: AVNRT is paroxysmal, meaning it occurs suddenly and spontaneously resolves. In the common form of AVNRT, the slow pathway traverses the antegrade direction, while the fast pathway traverses the retrograde direction. This causes the atria (the receiving end of the retrograde impulse) and the ventricles (the receiving end of the antegrade impulse) to be activated at approximately the same time.

C. Rationale: A junctional rhythm that exceeds the rate of 100 bpm is known as junctional tachycardia. A junctional rhythm with a rate of 60–100 bpm is known as an accelerated junctional rhythm. A junctional escape rhythm has an inherent rate of 40–60 bpm.

A. Rationale: AVNRT can be influenced by premature atrial beats with first-degree atrioventricular block. AVNRT has two pathways that can be used as a re-entry circuit. One is conducted in an antegrade direction, while the other is conducted in a retrograde direction. Each pathway may have a slow component or a fast component.

Answer choice B – A premature ventricular beat is an early contraction caused by an irritated electrical focus within the ventricles, not the atria.
Answer choice C – A right bundle branch block manifests as a prolonged QRS complex due to a delay in electrical conduction within the right bundle branch.
Answer choice D – A left bundle branch block manifests as a prolonged QRS complex due to a delay in electrical conduction within the left bundle branch.

B. Rationale: The AV node anatomy has a “dual pathway” in patients with AVNRT. A reentry circuit confined to the AV node and the atrial tissue around it has caused a regular supraventricular tachycardia. The QRS complex in AVNRT is narrow (< 0.12 seconds), indicating normal ventricular activation via the His-Purkinje system. This is the common AVNRT variant. Sometimes aberrant conduction occurs, which can result in a wide QRS complex. This aberrant conduction can be a bundle branch block.

A. Rationale: Once the sinoatrial node fails to produce an impulse, the heart switches to the next fastest inherent rate. An atrial focus has the next fastest inherent rate, followed by the AV node, then the bundle of His, and lastly, the bundle branches and Purkinje fibers.

C. Rationale: In atypical AVNRT, the fast conduction is directed in the antegrade direction, while the slow component travels in the retrograde direction. The activation of the atria will occur last. There will be negative P waves in the inferior leads III and aVF. This is seen late, after the QRS complex. The “RP interval” is longer than the PR interval.

Answer choice A – Second-degree AV block, Mobitz Type I will appear as a PR interval that prolongs before a QRS complex is dropped after a non-conducted P wave.
Answer choice B – Second-degree A block, Mobitz Type II will appear as a constant PR interval with regularly non conducted P waves.
Answer choice D – In typical AVNRT, the fast conduction is directed in the retrograde direction, while the slow component travels in the antegrade direction.

A. Rationale: The normal QRS duration is 0.09 seconds or less, which is equivalent to 2 small squares on an ECG. A QRS > 0.12 seconds is considered prolonged. Prolonged QRS duration has an unusual QRS pattern, such as a bundle branch block. The impulse may originate from the ventricles with atrioventricular dissociation. If the ventricular rate is low, it is known as a ventricular escape rhythm.

Answer choice B – Idioventricular rhythm is characterized by a heart rate < 50 bpm, the absence of P waves, and a wide QRS complex.
Answer choice C – An idioventricular rhythm exhibits a slow heart rate.
Answer choice D – A ventricular escape rhythm exhibits a slow heart rate.

B. Rationale: 40% of AV blocks are brought about by ischemic heart disease. Other causes include congenital heart disease, cardiomyopathies, myocarditis, and familial diseases.

D. Rationale: Vagal maneuvers, intravenous adenosine, and intravenous calcium channel blockers or beta-blockers are treatment options for AVNRT. When necessary, during periods of hemodynamic instability, synchronized electrical cardioversion almost always terminates AVNRT in conjunction with the other treatments mentioned above. If there are occasions where sinus rhythm is not achieved after the initial shock, it may be necessary to perform subsequent electrical cardioversion.