These data suggest the presence of rate-dependent transversal conduction block at the crista terminalis in patients with typical AFL. Block is usually observed at longer pacing cycle lengths with PW pacing than with LW pacing. This difference may be a critical determinant of the counterclockwise rotation of typical AFL.

The initial experience from electrophysiological studies showed that pacing induced termination of ventricular tachycardias is usually possible but requires a critical pacing sequence. Studies on the resetting phenomenon showed, in most instances of failure of termination, that the "limiting factor" to produce ventricular tachycardia termination is usually failure to produce block within the circuit rather than failure to access or interact with the ventricular tachycardia origin. The resetting response is related to tachycardia termination in a number of ways. Of note is that a steeply increasing resetting pattern usually predicts tachycardia termination. Between 50% and 90% of induced ventricular tachycardias will be terminated by trains of rapid ventricular pacing. The analysis of the pacing rate necessary for termination shows that it varies widely. Paced cycle lengths of < 80% of tachycardia cycle length are necessary in at least 20% of tachycardias. In contrast, the incidence of acceleration is closely related to the paced cycle length: it is negligible with paced cycle lengths over 80% of tachycardia cycle length and increases to 36% with paced cycle lengths below 76% of tachycardia cycle length. Present information about efficacy of antitachycardia pacing in spontaneous tachycardias suggests that it is extremely effective, with over 90% success. However, it is likely that these data correspond to a selected group of tachycardias.

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