Impairment of the antegrade fast pathway in patients with atrioventricular nodal reentrant tachycardia can be functional and treated by slow pathway ablation: a case report study

BACKGROUND: Slow pathway (SP) ablation is considered to be the standard treatment for symptomatic atrioventricular nodal reentrant tachycardia (AVNRT). This may be challenging in patients with documented PR interval prolongation due to the potential increased risk of atrioventricular (AV) block in some patients. CASE SUMMARY: We report two cases of symptomatic recurrent AVNRT refractory to medical treatment with significant baseline PR interval prolongation (304 ms and 336 ms). In both of these cases, the baseline electrophysiological study demonstrated dual AV nodal physiology with a functional antegrade fast pathway and evidence for transient normalization of the PR interval. Slow/fast AVNRT was confirmed in both cases. Slow pathway ablation was successfully performed resulting in normalization of the PR interval to 144 ms and 168 ms with no evidence of AV block. After a mean follow-up of 30 months, the patients remained asymptomatic with normal PR interval, no recurrence of AVNRT, and no documentation of high degree AV block. DISCUSSION: Our cases illustrate a common dilemma when dealing with patients with AVNRT and prolonged baseline interval. We show that SP ablation is feasible and safe as long as a preserved antegrade FP is present.