Site of reentry in paroxysmal supraventricular tachycardia in man.

a portion of the relative refractory period of the A-V node consistently produced atrial reentry-echoes or sustained SVT. In two patients, APDs falling within the A-V effective refractory period failed to excite the His bundle but still reentered within the A-V node and began SVT. It was noted that the various relationships between atrial and ventricular depolarizations on the surface ECG did not reflect different mechanisms for SVT, but only variations in A-V nodal conduction time.