Right bundle branch activation during left bundle branch pacing: Marginal gains in left bundle branch pacing–optimized cardiac resynchronization therapy and the effects of atrioventricular delay dynamic optimization

Figures

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  Figure 1. Bipolar and unipolar threshold testing post implantation. A: The first transition occurred at an output of 1.5 V @ 0.4 ms, corresponding with nonselective left bundle branch pacing (ns-LBBP) and anodal loss of capture (note a change in lead V1 from a Qr to a QR pattern). B: As output is further decreased, there is a second transition from a QR pattern to a qR pattern in lead V1, with an isoelectric interval, at an output of 0.25 V @ 0.4 ms corresponding with transition from ns-LBBP to selective (s)-LBBP, followed by the last 3 beats with a Qr pattern (safety pacing at nominal output 3.0 V @ 0.4 ms, ns-LBBP and anodal capture). C: Only 1 transition occurred at low output (anodal capture is not possible). In lead V1, transition from a QR pattern to a qR pattern with an isoelectric interval was noted at an output of 0.25 V @ 0.4 ms, corresponding with transition from ns-LBBP to s-LBBP, followed by the last 3 beats with a similar QR pattern (safety pacing at nominal output 3.0 V @ 0.4 ms, ns-LBBP without anodal capture). D: Left bundle branch potential (Po LBB) was demonstrated at implant. A similar interval was noted between Po LBB to QRS and stim-QRS with s-LBBP.

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  Figure 2. Unipolar and bipolar noninvasive programmed electrical stimulation (NIPS) using the implanted device. A drive train of 8 pulses was delivered at a cycle length (CL) of 450 ms (sinus CL was 550 ms), followed by S2 at 20 ms decrements. A,B: Unipolar NIPS output of 2.5 V @ 0.4 ms (nonselective left bundle branch pacing [ns-LBBP] without anodal capture). NIPS at 450/280 ms resulted in a change in morphology and an isoelectric line between the stimulation spike and QRS. The right bundle branch (RBB) and left ventricular (LV) septum in this instance have a similar effective refractory period (ERP). As a result, the extrastimuli S2 resulted in selective (s)-LBBP and RBB block (RBBB), with a clear isoelectric interval between stim to QRS (green arrowhead). (This is represented schematically in panel F). C: Unipolar NIPS output of 0.75 V @ 0.1 ms (consistent s-LBBP without anodal capture). An isoelectric interval was noted between the stimulus spike and the QRS with a qR pattern in V1 during the drive train. NIPS at 450/280 ms resulted in a change in morphology (similar RBBB morphology as in panel B; s-LBBP and RBBB). The qR pattern during s-LBBP is narrower (incomplete RBBB pattern), as…

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  Figure 3. Baseline, postimplant left bundle branch pacing–optimized cardiac resynchronization therapy (LOT-CRT) and postimplant SyncAV LOT-CRT electrocardiogram (ECG). A: Baseline ECG for patient 2 showing normal sinus rhythm at a rate of 74 beats/min and left bundle branch (LBB) block. QRS duration of 170 ms, notching in leads I and aVL, QS pattern in leads V1 and aVR, and V6 R-wave peak time of 80 ms. B: Postimplant LOT-CRT ECG. Pacing in DDD mode with a short 80 ms atrioventricular (AV) delay. Left bundle branch pacing (LBBP) at an output of 2.5 V @ 0.4 ms (nonselective LBBP [ns-LBBP] and anodal capture) with an offset of +15 ms is followed by epicardial anterior lateral left ventricular (LV) pacing via the coronary sinus (CS) lead (M3-RV coil vector) demonstrated the narrowest fused QRS duration of 120 ms. C: Postimplant LOT-CRT final ECG. LBBP at an output of 2.5 V @ 0.4 ms (ns-LBBP and anodal capture) with an offset of +15 ms is followed by epicardial anterior-lateral LV pacing via the CS lead (vector: M3-RV coil). Sensed AV delay at baseline was measured at 250 ms. SyncAV delta of -80 ms resulted in further narrowing of the QRS to 100 ms. D: Schematic representation of likely…

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  Supplemental Figure 1. A) Post implant bipolar LBBP at an output of 2.5v@0.4ms demonstrating ns-LBBP with anodal capture. QS in V1, QRS duration 140ms, and V6RWPT 80ms. B) Post implant bipolar LBBP at an output of 1.0v@0.4ms demonstrating ns-LBBP without anodal capture. QR in V1, minimal change QRS duration, and V6RWPT remains at 80ms. C) Bipolar LBBP at an output of 2.5v@0.4ms demonstrating a V6RWPT of 80ms, and a V6-V1 interpeak of 40ms.