PMC9845555_01
Electrocardiograms during sinus rhythm and His lead pacing. A: Sinus rhythm without left bundle branch block (LBBB), QRS 84 ms. B: Sinus rhythm with LBBB starting at a heart rate of 75 beats/min, QRS 153 ms. C: His lead pacing resulting in selective His capture with correction of bundle branch block at a unipolar threshold of 2 V / 1 ms, QRS 92 ms. D: His lead pacing resulting in selective His capture without correction of bundle branch block at a unipolar threshold of 0.9 V / 1 ms, QRS 149 ms.
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Holter monitoring, however, revealed rate-dependent LBBB coinciding with the patient's symptoms starting at a heart rate of 75 bpm (Figure 1). Device interrogation revealed 24% of ventricular pacing over time with a unipolar threshold of 2 V / 1 ms for selective His capture with LBBB correction and a unipolar threshold of 0.9 V / 1 ms for selective His capture without LBBB correction (Figure 1). Similarly, 3D simulation of left ventricular strain map during systole visualized improved ventricular deformation (Figure 3B, Supplemental Videos 1,2,3,4).
Exercise test before and after His bundle pacemaker (HBP) implantation. A: Electrocardiograms (ECGs) during exercise test before HBP implantation. B: ECGs during exercise test after HBP implantation. C: Exercise test before HBP implantation. D: Exercise test after HBP implantation. % refers to age- and sex-adjusted mean.
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Exercise stress testing demonstrated reduced exercise capacity (76 W = 60% of age- and sex-adjusted mean, VO2 max 14.4 mL/min/kg = 52% of age- and sex-adjusted mean) with a decreased maximal O2 pulse of 7 mL/beat (= 64% of age- and sex-adjusted mean), with the LBBB being present throughout the examination (Figure 2).
A: Left ventricular longitudinal strain without (left panel, pacemaker programmed to AAI 100/min) and with (right panel, pacemaker programmed to DDD 100/min with left bundle branch block [LBBB] correction) His pacing demonstrating improved global and segmental strain and mechanical dispersion. LV GLS = left ventricular global longitudinal strain; Mech. Disp. = mechanical dispersion. B: Three-dimensional simulation of left ventricular strain map during systole showing improved regional strain as observed from the apical view. A2C = 2-chamber view; A3C = 3-chamber view; A4C = 4-chamber view; Post = with His bundle pacing, pacemaker programmed to DDD 100/min with LBBB correction; Pre = without His bundle pacing, pacemaker programmed to AAI 100/min.
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Echocardiographic analysis during LBBB vs His bundle-pacing demonstrated improvement in segmental and global longitudinal strain (-13.2% vs -19.3%, respectively; Figure 3A), as well as improved mechanical dispersion (84 ms vs 51 ms, respectively; Figure 3), indicating increased ventricular deformation and synchronicity of contraction. Similarly, 3D simulation of left ventricular strain map during systole visualized improved ventricular deformation (Figure 3B, Supplemental Videos 1,2,3,4).