Crossing of strength–duration curves with His bundle pacing and impact of pacing mode on thresholds

Figures

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  Figure 1. Chest radiograph of the patient after implantation of a cardiac resynchronization therapy pacemaker with the His bundle lead (H) connected to the left ventricular port, and the atrial (A) and backup septal right ventricular (RV) lead connected to their respective ports.

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  Figure 2. Upper panel: When pacing the His bundle at a pulse width of 0.4 ms, a QRS transition from nonselective His bundle pacing (NS-HBP) to myocardial capture only is observed with decreasing voltage output (red circles). Lower panel: When pacing the His bundle at a pulse width of 0.2 ms, the QRS transitions from NS-HBP to selective HBP without correction of the underlying right bundle branch block (RBBB) with decreasing voltage output (blue circles). Note QRS narrowing with NS-HBP owing to fusion pacing (capture of the right ventricular myocardium serves to “resynchronize” the conduction delay of RBBB).

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  Figure 3. Strength–duration curves for local right ventricular (RV) myocardium and His bundle in VVI (solid lines) and DDD (dotted lines) pacing mode at 80 beats per minute. Pacing at and above a pulse width of 0.3 ms results in a His threshold (blue lines) that is higher than the local RV threshold (red lines). When pacing with a pulse width less than 0.3 ms, the RV threshold is higher than the His threshold, resulting in a crossover of the curves (green circles), in both a VVI and DDD pacing mode. In the DDD pacing mode, the voltage thresholds are higher for the whole range of pulse durations. At 0.1 ms, only His capture was possible at a threshold of 8 V in the VVI mode (not shown); there was no capture in the DDD mode.