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Figure 1 Subthreshold stimulation (STS) during atrioventricular nodal re-entrant tachycardia at a posteroseptal mapping position. After induction of sustained atrioventricular nodal re-entrant tachycardia (cycle length: 395 ms), STS is applied for 5 s (see arrows). The tachycardia is interrupted due to selective block within the slow anterograde pathway after 1.5 s, and normal sinus rhythm is established. Please note that no apparent capture is visible at surface electrocardiogram or intracardiac recordings. The termination of the tachycardia is preceded by discrete prolongation of the cycle length from 395 to 430 ms. This is suggestive of the slowing of conduction within the slow pathway because the A-to-H interval, but not the H-to-A interval, is prolonged. CSdis = coronary sinus, distal; CSprox = coronary sinus, proximal; HBE = His bundle electrocardiogram; HRA = high right atrium; MAP = mapping catheter; RVA = right ventricular apex.
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