An unwanted left bundle branch block: The proteus-unveiling of his bundle pacing

Figures

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  Figure 1. Pre-implantation ECG shows sinus rhythm with second-degree type I AV block (A). Decremental test shows the transition from NS to S-HB pacing for output lower than 0.9 mV at 0.75 ms (B). After the implantation, the pacemaker is programmed with DDD mode with HB lead programmed at 2 mV at 0.75 ms, obtaining NS-HB pacing (C).

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  Figure 2. A: Fluoroscopic and B: chest radiograph view of the HB lead after implantation. C: The intracardiac electrogram from the HB lead before fixation shows prolonged AH interval (170 msec) with normal infranodal conduction (HV, 42 msec).

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  Figure 3. A: ECG showing sinus rhythm with S-HB pacing and LBBB QRS morphology. B: Pacemaker inhibition revealing total AV block with ventricular escape rhythm at RBBB morphology. C: Decremental threshold test demonstrating partial loss of capture of left bundle fibers at 2.5 mV at 0.75 ms (red arrow) followed by loss of capture of the left bundle branch at 2.1 mV at 0.75 ms (blue arrow). D: Loss of right bundle fibers capture at 1.3 V at 0.75 ms.