Electrophysiologic assessment of the atrioventricular conduction system after surgical correction of ventricular preexcitation.

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Abstract
Patients (19) Wolff-Parkinson-White syndrome underwent electrophysiologic study for 7-39 days (mean 11 days) after operative division of accessory pathways. All patients had a poor response to medical management before surgery. The results from 16 adult patients were compared with control data. No difference occurred between control and postoperative groups in the effective refractory period (ERP) and functional refractory period (FRP) of the atria. The ERP of the atrioventricular (AV) node was significantly shorter in the postoperative group than in the control group with pacing cycle lengths 450-549 ms (275 .+-. 46 ms vs. 336 .+-. 41.7, P < 0.01) and 350-449 ms (244 .+-. 32 ms vs. 333 .+-. 30.3 P < 0.01). At all cycle lengths the FRP of the AV node was significantly shorter in the postoperative group than in the control group. Conduction time over the AV node during fixed-rate atrial pacing was at least 100 ms shorter in the postoperative patients than in controls. Retrograde conduction occurred in 11 of 18 patients and the A-H [atrial His] interval in sinus rhythm was shorter in these patients than in those without conduction in the retrograde direction (52 .+-. 16.5 ms vs. 70 .+-. 8.6 ms, P < 0.01). Retrograde conduction was assessed by by measuring the ventriculoatrial conduction time during fixed-rate pacing of the right ventricle at progressively shorter cycle lengths. Of 11 patients 7, showed < 20 ms increases in ventriculoartrial conduction time at cycle lengths down to 300 ms and 2 patients showed no increase in ventriculoatrial conduction time down to cycle length 240 ms. These findings may represent rapid conduction in the retrograde direction over the specific conduction system rather than a residual accessory pathway. In 8 of 11 patients the sequence of atrial activation during ventricular pacing was determined by endocardial mapping and was consistent with atrial activation over the AV node. Accessory pathways may be divided without damaging the normal conduction system in selected patients. The refractory periods of the AV node may be shorter and conduction faster in some patients with the Wolff-Parkinson-White syndrome than in normal people. Abnormal electrophysiologic parameters may account for the rapid rate of tachycardia in these selected patients whose tachyarrhythmias were refractory to medical therapy.