Canadian Journal of Cardiology

Phase 4 Atrioventricular Block After Transcatheter Aortic Valve Replacement

Published:October 27, 2022DOI:
      A 77-year-old man with aortic stenosis and preserved left ventricular ejection fraction underwent transcatheter aortic valve replacement (TAVR) for symptomatic severe aortic stenosis. After the procedure, he had a transient left bundle branch block that resolved. Two months later, he presented to the emergency department with syncope. Electrocardiography showed normal intervals (Fig. 1A). Subsequent telemetry revealed paroxysmal complete atrioventricular block (PAVB). At first glance, it appears that PAVB is induced consistently by a conducted junctional extrasystole (Figure 1B, single asterisk) that delays the subsequent sinus P wave. However, on a closer inspection, it is evident that the subsequent sinus P wave occurs on time, buried within the ST segment of the junctional premature extrasystole; however, not conducted to the ventricle which could be due to the retrograde conduction of premature junctional extrasystole (Fig. 1B, single asterisk) into the AV node (concealed conduction) (Fig. 1B, caret) and blocking the sinus P wave. The sinus P wave that follows now conducted via the atrioventricular (AV) node to the His bundle and gets blocked because of the relatively prolonged H-H interval, ie, a pause-dependent block. Pause-dependent, or phase 4, atrioventricular block (AVB) occurs in the diseased His-Purkinje system (HPS) because of spontaneous depolarisation of the diseased conduction system rendering it refractory to subsequent impulses (Fig. 1B). An appropriately timed ventricular extrasystole resets the membrane potential of the HPS to baseline and allows conduction to resume (Fig. 1B, double asterisks). The patient underwent uncomplicated dual-chamber pacemaker implantation.
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      Figure 1Phase 4 atrioventricular block after transcatheter aortic valve replacement and mechanism. (A) Telemetry tracing showing normal intervals. (B) Telemetry tracing showing phase 4 atrioventricular block after transcatheter aortic valve replacement and its mechanism. Single asterisk (): conducted junctional premature extrasystole; caret (ˆ): on-time P wave, buried within the ST segment of the junctional premature extrasystole; double asterisks (∗∗): appropriately timed ventricular extrasystole that resets the membrane potential of the His-Purkinje system (HPS) to baseline. PVC, premature ventricular contraction; SAN, sinoatrial node.
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        • Lee S.
        • Wellens H.J.J.
        • Josephson M.E.
        Paroxysmal atrioventricular block.
        Heart Rhythm. 2009; 6 (1229-3)