A short RP tachycardia with alternating ventriculoatrial interval, but identical atrial activation sequence: What is the mechanism?

Figures

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  Figure 1. A: Right ventricular pacing (600 ms). Ventriculoatrial (VA) conduction showed second-degree VA block. B: Spontaneous initiation of tachycardia immediately after sinus rhythm (∗). CS = coronary sinus; CSp = paroxysmal coronary sinus; HBE = His bundle electrogram; HRA = high right atrium; RV = right ventricular. Asterisk (∗) = sinus beat.

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  Figure 2. His bundle refractory ventricular premature depolarization (VPD) from the base of left ventricular advanced tachycardia. Details are described in text. Abbreviations as in Figure 1.

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  Figure 3. A: The local atrial potential at successful ablation site preceded coronary sinus (CS) distal by 24 ms. B: Successful ablation site. The location of the ablation catheter was confirmed by contrast through irrigation lumen. The red line shows the outline of the left atrial appendage. C: Tachycardia was terminated by the ablation in 2 seconds. Paper speed at 50 mm/s. D: Intracardiac electrogram (paper speed at 100 mm/s) at termination of tachycardia. Ventriculoatrial (VA) interval of distal CS in beat ① was 69 ms, which indicated fast retrograde conduction. VA interval of distal CS in beat ③ was 161 ms, which indicated slow retrograde conduction. Tachycardia was terminated with VA block after beats ② and ④. ABL = ablation catheter; AP = anterior posterior position; RAO = right anterior oblique position. Other abbreviations as in Figure 1.