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The chronotropic and dromotropic effects of the intra-atrial administration of 0.97, 1.93 and 2.90 microM/kg Striadyne, the pharmaceutical form of adenosine triphosphate (ATP) for clinical use, ATP, and adenosine, were compared in 13 anesthetized dogs. Striadyne, ATP and adenosine exerted transient dose-dependent negative chronotropic and dromotropic effects. There was no significant difference between the electrophysiologic effects of Striadyne and ATP which were significantly more pronounced than those of adenosine. Atropine (0.2 mg/kg) significantly attenuated the electrophysiologic effects of 2.90 microM/kg Stridyne and ATP but not those of adenosine. It is concluded that Striadyne and ATP have similar electrophysiologic effects which are more pronounced than those of adenosine mainly due to vagal involvement in their mechanism of action.

In a patient with the Wolff-Parkinson-White syndrome, the existence of dual accessory pathways, both right-sided, was suspected during ajmaline test and confirmed during electrophysiologic study. The first accessory pathway was manifest in sinus rhythm while the second was obscured and revealed during low right atrial pacing. Ajmaline abolished conduction over the first pathway which most probably had a long refractory period allowing manifestation of the second pathway which had a very short refractory period. A longer conduction time over the second accessory pathway was suggested to explain its concealment during sinus rhythm.

A 49-year-old man with a silent remote postero-inferior wall myocardial infarction exhibited recurrent episodes of sustained ventricular tachycardia which was hemodynamically well tolerated. Ventricular tachycardia was neither terminated nor prevented by therapy with multiple class I and class III antiarrhythmic drugs. In contrast, ventricular tachycardia was repeatedly terminated within a few minutes following intravenous administration of 10 mg verapamil and did not recur during oral therapy with verapamil (360 mg daily). Electrophysiologic study suggested that ventricular tachycardia was due to a reentrant mechanism rather than to triggered or abnormal automaticity. Thus, in contrast to previous reports, findings in this patient indicate that verapamil may be very effective and safe in certain types of ventricular tachycardia occurring late after a myocardial infarction.

Transcatheter electrical shock ablation of a concealed posteroseptal accessory pathway was performed on a 57-year-old man with drug-refractory paroxysmal supraventricular tachycardia. A single 300-joules shock delivered at the ostium of the coronary sinus abolished conduction in the accessory pathway and resulted in long-term cure of the arrhythmia. No complications were observed during the procedure.

We describe a newborn infant with concealed ventricular preexcitation in sinus rhythm on the early ECGs, and who developed recurrent episodes of preexcited reciprocating tachycardia. Manifestation of the ventricular preexcitation and initiation of the tachycardias were dependent on the presence of severe conduction disturbances in the normal atrioventricular pathway, probably in the atrioventricular node.

The effects of verapamil and bepridil on occlusion and reperfusion ventricular arrhythmias including ventricular fibrillation (VF) were studied in a canine model. The control group consisted of 27 dogs. 30 dogs received intravenous verapamil (0.2 mg/kg/3 min followed by a continuous infusion of 0.01 mg/kg/min for 15 min). 18 dogs received bepridil (0.5 mg/kg/min for 10 min). The left anterior descending coronary artery was occluded in one step 8 min after the commencement of verapamil administration and 5 min after the termination of bepridil infusion. The incidence of ventricular arrhythmias during the occlusion period was 14 (VF, 5/14), 13 (VF, 0/13) and 14 (VF, 9/14) in the control, verapamil and bepridil groups, respectively. The frequencies of reperfusion VF were 8/24 (33%), 4/30 (13.3%) and 0/13 (0%), respectively. It was concluded that (a) verapamil effectively prevents occlusion but not reperfusion VF and (b) bepridil has an arrhythmogenic effect in the ischemic canine heart but reduces the incidence of reperfusion VF.