FIGURE 3.

Patient 2. Intracardiac electrograms of (A,B) fast–slow AVNRT with a bystander cNVP connected to the slow pathway (SP) and (C,D) slow–fast AVNRT. (A) The premature ventricular contraction (PVC) delivered during His‐refractoriness delays the tachycardia 1 cycle later with a delay of the atrium preceding the His delay. This observation is considered diagnostic of fast–slow AVNRT with a bystander cNVP because it indicates presence of a cNVP and excludes ORT (Steps 1 and 2). (B) Right ventricular overdrive pacing results in VA block during the transition zone, which also supports the diagnosis. However, (C) the His‐refractory PVC and (D) right ventricular overdrive pacing fails to detect presence of an AP during the slow–fast AVNRT, possibly due to the SP ERP. Abbreviations are as in Figure 2.