case_images: PMC10808645_01
case_images: Holter monitoring of the patient. Holter monitoring in December 2020 (A) revealed an intermittent sinus pause and AVB. Holter monitoring after the first syncope episode in April 2022 (B,C) indicated an intermittent third-degree AVB with (B) and without (C) ventricular escapes. ECG without third-degree AVB (D) showed first-degree AVB, and the morphology of the QRS complex showed an RBBB pattern.
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case_images: F1
case_images: Holter monitoring revealed an intermittent sinus pause and AVB, suggesting SND and conduction disease (Figure 1A). Holter monitoring revealed an intermittent third-degree AVB with and without ventricular escapes (Figures 1B,C). During complete AVB, the heart rate was 38 bpm, and the morphology of ventricular escape exhibited a left bundle branch block (LBBB) pattern (QRS duration: 132 ms), indicating right bundle branch origination (Figure 1B). However, during atrioventricular 1:1 conduction, the PR interval was 220 ms, and the morphology of the QRS complex exhibited a right bundle branch block (RBBB) pattern, indicating conduction through the left bundle branch (Figure 1D).
case_images: Permanent dual-chamber pacemaker implantation. Before the implantation procedure, the intrinsic ECG (A) showed first-degree AVB, RBBB, and LAFB (a sweep speed of 25 mm/s). Paced QRS morphology in the right ventricular septum (B) showed a "w" pattern with a notch at the nadir of the QRS in lead V1 (a sweep speed of 100 mm/s). With the lead screwed into the interventricular septum, the terminal R-wave of the paced QRS appeared in lead V1 (marked with a black arrow) (C) (a sweep speed of 100 mm/s). The left bundle branch potential (marked with a black arrow) was recorded from a Model 3830 lead tip (D) (unipolar, a sweep speed of 100 mm/s), and the left bundle branch potential to V6RWPT in the intrinsic rhythm was 58.33 ms. (E) Pacing at high voltage (5 V @ 0.4 ms) with the stimulus to V6RWPT of 78.28 ms (a sweep speed of 100 mm/s). (F) Pacing at low voltage (0.5 V @ 0.4 ms) with the stimulus to V6RWPT of 78.28 ms and a V6-V1 inter-peak interval of 41.67 ms (a sweep speed of 100 mm/s). (G,H) Positions of the pacing leads.
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case_images: F2
case_images: Because the PR interval was 250 ms and the frontal plane axis showed a left deviation of -43 , consistent with a left anterior fascicular block (LAFB), a diagnosis of first-degree AVB and LAFB was confirmed, and supraventricular excitation was presumed to be conducted through the left posterior fascicle (Figure 2A). The QRS morphology in the pacing site showed a "w" pattern with a notch at the nadir of the QRS in lead V1 (Figure 2B). Then, the lead was screwed into the interventricular septum until a paced QRS (voltage output at 5 V @ 0.4 ms in the unipolar mode) of RBBB morphology with a terminal R-wave in lead V1 was obtained (Figure 2C). The left bundle branch potential could be recorded when the lead was deeply screwed into the subendocardial area on the left side of the interventricular septum (Figure 2D). When pacing at high and low output voltages, consistent values of the stimulus to V6 R-wave peak time (V6RWPT) were recorded, as shown in Figures 2E,F. The V6-V1 inter-peak interval was 41.67 ms (Figure 2F), and the stimulus to V6RWPT was 78.28 ms (Figure 2F). Because the left bundle branch potential to V6RWPT in intrinsic rhythm was 58.33 ms (Figure 2D), the difference between the potential to V6RWPT and the stimulus to V6RWPT was 19.95 ms. The positions of the leads are shown in Figures 2G,H.
case_images: One-year follow-up visit. The intrinsic rhythm (A) was a sinus rhythm with first-degree AVB. The stimulus to V6RWPT (78 ms) was stable at high (5.0 V @ 0.4 ms) (B) and low (1.0 V @ 0.4 ms) (C) output voltages when the left bundle branch was captured.
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case_images: F3
case_images: At the 1-year follow-up visit, the patient's intrinsic rhythm was a sinus rhythm with first-degree AVB (Figure 3A); therefore, the left bundle branch capture threshold was measured by mandatory ventricular pacing, and the value was 0.75 V @ 0.4 ms. The stimulus to V6RWPT (78 ms) was stable at high (5.0 V @ 0.4 ms) and low (1.0 V @ 0.4 ms) output voltages when the left bundle branch was captured (Figures 3B,C).
case_images: Trends in the RA lead (A,C,E) and LBBP lead (B,D,F) threshold, sensing, and impedance. RA, right atrium; LBB, left bundle branch.
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case_images: F4
case_images: The trends in the right atrial lead and LBBP lead threshold, sensing, and impedance are shown in Figure 4.