Troubleshooting right-sided His bundle pacing in isolated persistent left superior vena cava

Figures

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  Figure 1. Baseline pacing dependency and preupgrade findings. A: Transthoracic echocardiography showing preserved cardiac structure and systolic function. B: Chest radiograph showing an abdominal pacemaker generator with epicardial atrial and ventricular leads. C: 12-lead electrocardiogram demonstrating right ventricular pacing morphology with a paced QRS duration of ∼140 ms. D: Wenckebach atrioventricular block during atrial-only pacing at rates of ≥80 beats/min.

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  Figure 2. Venous anatomy and electrophysiological mapping. A: Left axillary venography showing an isolated persistent left superior vena cava. B: Intracardiac electrograms recorded via the device programmer demonstrating distinct atrial (A), His (H), and ventricular (V) potentials, confirming accurate His bundle localization using a lead-as-mapper technique.

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  Figure 3. Physiological confirmation and postupgrade outcome. A: Output decrement testing demonstrating transition from nonselective-to-selective His bundle capture. Pacing output was decremented in 0.1-V steps at a fixed pulse width of 1.0 ms (labels shown above each complex). The upper tracing represents surface lead II, the middle tracing the atrial channel, and the lower tracing surface lead V6. At 2.5 V, a slurred initial upstroke consistent with local myocardial capture (nonselective His bundle pacing) is seen in lead V6. At 2.4 V, the slurred upstroke disappears and an isoelectric interval between the pacing stimulus and QRS onset becomes evident, consistent with selective His bundle capture. B: Chest radiograph obtained after system upgrade. C: Postimplant 12-lead electrocardiogram demonstrating nonselective His bundle capture at programmed output. 12-lead electrocardiogram recorded after implantation during ventricular pacing at 2.5 V at 1.0 ms. The paced QRS demonstrates an initial slurred upstroke (“delta-like” appearance), most evident in the precordial leads, consistent with nonselective His bundle capture (simultaneous local myocardial capture with His–Purkinje recruitment).…