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208 POSTOPERATIVE JUNCTIONAL TACHYCARDIA IN PEDIATRIC PATIENTS

We determined the incidence of cardiac arrhythmias in children post cardiac surgery, the cardiac malformations associated with specific arrhythmias and the ECG characteristics of the arrhythmias. Continuous 2-lead ECG's were recorded in 26 consecutive patients (ages 2 mos-13 yrs) during the first 24 hours after open heart surgery. The most frequent non-sinus arrhythmia was atrioventricular junctional tachycardia (JT) which occurred in 9 patients (39%). Ventricular, junctional and atrial premature depolarizations were infrequent (<5 beats/hr in 16 patients) and atrial tachycardia occurred in 1 patient. JT occurred mainly in patients with tetralogy of Fallot (4 of 5) and endocardial cushion defects (3 of 3). Two types of onset of JT were seen, often in the same patient: the first occurred following sinus pauses > the duration of the basic cardiac cycle (i.e., occurring as accelerated junctional escape); the second occurred when sinus tachycardia supplanted normal sinus rhythm and then was overdriven by an accelerated junctional focus. The second type of onset is consistent with reentry or triggered activity; the first, with an automatic focus. Both JT had similar QRS morphologies and axes and appeared unrelated to perioperative medication and acid-base and electrolyte status. The high incidence of JT after open heart surgery is of interest because of its infrequency in the general pediatric population. It may result from surgical manipulation of the AV junction and it appears that more than one mechanism is responsible for its initiation.