Complete Left Bundle Branch Block Resolution After Cardiac Resynchronization Therapy With Serial Phonocardiographic Changes

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  Visual Summary. Progressive Structural and Electrical Reverse Remodeling After CRT After pulsed field ablation for atrial fibrillation, CLBBB persisted with severe left ventricular mechanical dyssynchrony. CRT pacemaker implantation using the AdaptivCRT algorithm initially applied LV pre-excitation pacing. Serial electrocardiographic and echocardiographic assessments demonstrated progressive QRS narrowing, reduction in left ventricular mechanical dispersion, and improvement in left ventricular ejection fraction. During follow-up, the optimal VV delay shifted from LV pre-excitation to RV pre-excitation, suggesting dynamic changes in ventricular synchrony associated with reverse remodeling. Phonocardiographic findings showed increased S1 amplitude and disappearance of the pansystolic murmur and third/fourth heart sounds, reflecting improved mechanical synchrony and hemodynamic status. Progressive intrinsic conduction recovery ultimately resulted in resolution of CLBBB at 3 months. CLBBB = complete left bundle branch block; CRT = cardiac resynchronization therapy; LV = left ventricular; LVEF = left ventricular ejection fraction; LVMD = left ventricular mechanical dispersion; RV = right ventricular;…

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  Figure 1. Baseline Clinical Findings (A) Electrocardiogram showing atrial fibrillation with rapid ventricular response and CLBBB. (B) Chest radiograph showing mild cardiomegaly (cardiothoracic ratio: 53%) and pulmonary congestion. (C) Transthoracic echocardiography showing severe nonischemic functional mitral regurgitation. CLBBB = complete left bundle branch block.

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  Figure 2. Electrocardiographic Changes and Device Position After CRT Implantation (A to C) Electrocardiograms (A) before CRT pacemaker implantation (QRS duration 152 ms), (B) 5 days after implantation (QRS duration 116 ms), and (C) 1 month after implantation (QRS duration 105 ms). (D) Anterior and right-to-left lateral chest radiography views after CRT pacemaker implantation. CRT = cardiac resynchronization therapy.

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  Figure 3. Speckle-Tracking Analysis Demonstrating Improvement in Mechanical Dyssynchrony After CRT Speckle-tracking analysis from the apical 4-chamber view at (A) pre-CRT pacemaker implantation, (B) 5 days after implantation, and (C) 1 month after implantation. In (A), septal rebound stretch (asterisks), a marker of intraventricular dyssynchrony, and the typical pattern of a left bundle branch block (arrowheads) are shown. Segmental mechanical dispersion derived from 3-view longitudinal strain was 128.2 ms (A), 58.7 ms (B), and 33.6 ms (C). CRT = cardiac resynchronization therapy.

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  Figure 4. Serial Phonocardiographic Changes After CRT Implantation Heart sounds recorded at the fourth left sternal border. Phonocardiograms at (A) pre-CRT pacemaker implantation, (B) 5 days after implantation, and (C) 1 month after implantation, using 2 frequency analysis methods (short-time Fourier transform [STFT] and continuous wavelet transform [CWT]). After CRT device implantation, the amplitude of the first heart sound (S1) increased, with a shift toward higher frequency components. In addition, the third and fourth heart sounds (S3 and S4, respectively) became less prominent over time. The high-frequency pansystolic murmur, consistent with mitral regurgitation, also decreased in intensity. CRT = cardiac resynchronization therapy.

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  Figure 5. Resolution of CLBBB With Recovery of Intrinsic Conduction Electrocardiogram at 3 months after CRT pacemaker implantation (A) during AdaptivCRT algorithm (A pacing, LV pacing), (B) during intrinsic conduction (A pacing, V sensing). A = atrial; CLBBB = complete left bundle branch block; CRT = cardiac resynchronization therapy; LV = left ventricular; V = ventricular.