Abstract
The mechanism of 2:1 atrioventricular block in infants with the congenital long QT syndrome has been postulated to result from a long ventricular effective refractory period interrupting conduction of successive sinus impulses. Three infants age 1-2 days exhibited bradycardia demonstrated to be 2:1 atrioventricular block by the surface electrocardiogram. Mean sinus cycle length (SCL) was 0.56 sec where as mean QT interval was 0.65 sec (QTc 0.63); this .07 sec difference between the SCL and mean QTc was sufficient to block successful capture of the ventricles by successive sinus impulses. Programmed ventricular extrastimulation in one patient demonstrated a markedly prolonged ventricular effective period (480 sec) at ventricular basic cycle length (BCL) 1000 msec shortening to 280 msec with a ventricular BCL of 400 msec. Permanent ventricular pacing shortened the ventricular effective refractory period in each infant and effectively suppressed polymorphic ventricular arrhythmias in the affected two. We conclude that the mechanism of 2:1 atrioventricular block in infants with the congenital long QT syndrome is a function of the age related SCL relative to the QT interval as well as the markedly prolonged but rate dependent ventricular effective refractory period. Ventricular pacemaker implant is effective in increasing ventricular rate, shortening ventricular effective refractory period, and suppressing complex ventricular arrhythmias.
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Scott, W., Bromberg, B. & Dick, M. MECHANISM OF 2:1 ATRIOVENTRICULAR BLOCK IN INFANTS WITH CONGENITAL LONG QT SYNDROME. Pediatr Res 21 (Suppl 4), 194 (1987). https://doi.org/10.1203/00006450-198704010-00168
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DOI: https://doi.org/10.1203/00006450-198704010-00168
