Delayed termination of re-entrant AVN tachycardia by programmed stimulation is not an indicator of the underlying mechanism but may reveal concealed penetration of the tachycardia circuit.
Delayed termination after extrastimuli should not guide mechanism inference in AVNRT; leaves open the role of concealed circuit penetration.
Termination of atrioventricular nodal (AVN) re-entrant tachycardia by one or two induced premature beats generally occurs within one tachycardia cycle from the last premature beat. Two cases are described in which programmed stimulation during sustained re-entrant AVN tachycardia caused delayed termination in the second or third tachycardia cycle following the extrastimuli. The site of block was the antegrade pathway in one case and the retrograde pathway in the other. The most likely mechanism was induced second degree block in one limb of the tachycardia circuit. Delayed termination provided evidence for concealed penetration of the tachycardia circuit in one case. We conclude that delayed termination of tachycardia is not an indicator of the underlying mechanism of tachycardia. Delayed termination may reveal concealed penetration of the tachycardia circuit. Lastly, in unusual cases programmed stimulation may fail to cause immediate termination of re-entrant tachycardia but may perturb the tachycardia circuit enough to cause termination in subsequent tachycardia cycles.
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Ross et al. (1983) studied this question.
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