Padanilam BJ, Ahmed AS, Clark BA, et al. - Given a lack of sensitivity and specificity of current maneuvers for differentiation of atrioventricular node reentry tachycardia (AVNRT) and atrioventricular reentry tachycardia (AVRT) for AVRT circuits located away from the site of pacing. Researchers hypothesized that a premature His complex (PHC) will always perturb AVRT as the His bundle is obligatory to the circuit. Further, due to the retrograde His conduction time, AVNRT could not be perturbed by a late PHC (≤ 20 ms ahead of the His). The AVNRT circuit may advance with earlier PHCs but only by a quantity less than the prematurity of the PHC. At the distal His location, high-output pacing delivered PHCs. The test led to accurate prediction of AVRT (n = 29) and AVNRT (n = 44) in all cases among the 73 supraventricular tachycardias. This suggests that with 100% specificity and sensitivity, the responses to PHCs distinguished AVRT and AVNRT. As per observations, the mean prematurity of the PHC needed was 48 ms (range, 28–70 ms) to perturb AVNRT, and the advancement less than the prematurity of the PHC (mean, 32 ms; range, 18–54 ms).