Atrioventricular (AV) Reciprocating Tachycardia Utilizing Left Lateral AV Bypass Pathway with a Long Retrograde Conduction Time.

A 52-year-old man had suffered from attacks of palpitation for 10 years. The frequency of the attacks had been increasing since June 1991. The electrocardiogram (ECG) at the time of attack showed a heart rate of 175 bpm and RP'/P'R > 1, indicating long RP' tachycardia. Electrophysiological examination of the heart revealed an accessory pathway in the left lateral position. During the tachycardia, PVCs from the right ventricular apex (RVA) captured the atria. On the basis of these findings the patient was diagnosed as having had atrioventricular (AV) reciprocating tachycardia (AVRT). Ventriculoatrial (VA) conduction indicated a decremental conduction curve by single premature stimulation from the RVA, and the atrial cycle length following PVC during tachycardia was prolonged (paradoxical delay). When verapamil was administered intravenously, tachycardia induced by the premature stimulation showed prolongation of the VA interval, associated with an increased tachycardia cycle length. Tachycardia in this patient was completely controlled by administration of verapamil.