Catecholamine facilitated reentrant ventricular tachycardia: uncoupling of adenosine's antiadrenergic effects

Adenosine has no direct electrophysiologic function in ventricular tissue, but in the presence of cyclic adenosine monophosphate (cAMP), stimulation exerts a potent antiadrenergic effect. This effect has been exploited in the recognition and treatment of ventricular tachycardia (VT) due to cAMP-mediated triggered activity and automaticity, which are respectively terminated and suppressed by adenosine. However, the effects of adenosine on catecholamine-facilitated reentrant VT are unknown. A pivotal issue is whether termination of VT with adenosine is mechanism specific, or whether it represents a nonspecific antiadrenergic effect. The purpose of this study, therefore, was to define the effects of adenosine in a well-characterized group of patients with catecholamine-facilitated reentrant VT.

Fourteen patients with catecholamine-facilitated reentry were studied. In the 12 patients with structural heart disease (including two with arrhythmogenic right ventricular dysplasia), adenosine (260 to 550 microg/kg) failed to slow or terminate VT. Two patients without structural heart disease had intrafascicular tachycardia confined to the left posterior fascicle, a calcium-dependent, verapamil-sensitive arrhythmia. In the absence of isoproterenol, verapamil terminated VT but adenosine did not. However, when isoproterenol was subsequently required for facilitation of tachycardia, adenosine terminated VT in both patients.

Adenosine has no antiadrenergic (antiarrhythmic) effect in patients with catecholamine-facilitated VT due to structural heart disease. Patients with verapamil-sensitive, left posterior intrafascicular reentry have an unusual dual response to adenosine. In the unstimulated state, adenosine has no effect on basal inward calcium current and, therefore, no effect on VT. However, when induction of VT requires amplification of the inward calcium current through stimulation of cAMP, adenosine sensitivity of VT becomes manifest. These results indicate that with few exceptions, termination of VT with adenosine is strongly suggestive of a cAMP-mediated triggered mechanism rather than reentry.