Electrophysiologic Assessment of the Atrioventricular Conduction System after Surgical Correction of Ventricular Preexcitation

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Nineteen consecutive patients with the Wolff-Parkinson-White syndrome underwent electrophysiologic study 7-39 days (mean 11 days) after operative division of their accessory pathways. All patients had a poor response to medical management before surgery. The results from 16 adult patients were compared with published control data. There was no difference 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 msec (275 ± 46 msec vs 336 ± 41.7, p>0.01) and 350-449 msec (244 ± 32 msec vs 333 i 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. In addition, conduction time over the AV node during fixed-rate atrial pacing was at least 100 msec shorter in the postoperative patients than in controls.

Retrograde conduction was present in 11 of 18 patients and the A-H interval in sinus rhythm was shorter in these patients than in those without conduction in the retrograde direction (52 ± 16.5 msec vs 70 + 8.6 msec, p>0.01). We assessed retrograde conduction by measuring the ventriculoatrial conduction time during fixedrate pacing of the right ventricle at progressively shorter cycle lengths. Seven of 11 patients showed > 20-msec increases in ventriculoatrial conduction time at cycle lengths down to 300 msec. Two patients showed no increase in ventriculoatrial conduction time down to cycle length 240 msec. We think these findings represent rapid conduction in the retrograde direction over the specific conduction system rather than the presence of a residual accessory pathway. In eight 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.

We conclude that accessory pathways may be divided without damaging the normal conduction system in selected patients. Moreover, 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. These abnormal electrophysiologic parameters may account for the rapid rate of tachycardia observed in these selected patients whose tachyarrhythmias were refractory to medical therapy.

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