Pseudo-preexcitation in tricuspid atresia.

Because we have observed a relatively large number of tricuspid atresia patients with a short P-R interval and slurring of the initial QRS pattern suggesting preexcitation, we conducted a retrospective study to determine the frequency of this electrocardiographic pattern and whether or not this represented the presence of a true atrioventricular bypass tract. Three pediatric cardiologists reviewed the surface electrocardiograms of 183 consecutive tricuspid atresia patients who had been evaluated at the Mayo Clinic between 1980 and 1986. The patients' ages ranged from 4 months to 21 years; the male-to-female ratio was 5:4. The criteria for preexcitation included 1) a P-R segment <0.10 sec, 2) a QRS complex >0.10 sec, and 3) slurring of the upstroke of the QRS complex ("delta wave"). Of the 183 patients, 22 (12%) had P-R segments <0.10 sec, 9 of whom fulfilled the criteria for preexcitation. Five of these had a history of supraventricular tachycardia, and 4 of the 5 had undergone invasive electrophysiologic studies: 2 had enhanced atrioventricular-nodal conduction and 1 had normal atrioventricular-nodal conduction; only 1 had an accessory pathway. Our results indicate that, although many patients with tricuspid atresia meet the surface electrocardiographic criteria for preexcitation, many of these patients may not have an atrioventricular bypass tract; this state might be termed "pseudo-preexcitation." In these instances, invasive studies probably would not be necessary; regrettably, it may be difficult to distinguish between the presence and the absence of preexcitation in such patients without invasive electrophysiologic studies.