Left Bundle Branch Area Pacing Corrected the Functional Block Line Caused by Right Ventricular Apex Pacing

INTRODUCTION: Right ventricular apex (RVA) pacing has been reported to induce pacing-induced cardiomyopathy (PICM), with biventricular pacing being the standard cardiac resynchronization therapy (CRT) for RVA-PICM. However, recent studies suggest that left bundle branch area pacing (LBBAP) may provide even better outcomes as a CRT. In this case, we observed a dynamic alteration in the left ventricular (LV) activation pattern when transitioning from RVA-PICM to LBBAP, including changes in the functional block line. CASE: A female patient with dilated-phase hypertrophic cardiomyopathy (d-HCM), septal, and apical myocardial damage caused by cardiomyopathy, and prior ventricular tachycardia ablations experienced worsening heart failure due to dyssynchronous LV activation from RVA pacing (paced QRS duration of 250 ms). She underwent an upgrade to LBBAP (paced QRS duration of 160 ms) as CRT. Six months later, three-dimensional LV activation mapping was performed during both RVA pacing and LBBAP. During RVA pacing, a functional conduction block was observed in the anterior wall, resulting in unidirectional excitation propagation in a counterclockwise direction from the septum and a significant delay in the basal-mid anterior wall. In contrast, with LBBAP, the functional conduction block shifted to the septal-apical region, enabling bidirectional excitation propagation to the basal-mid lateral wall and facilitating synchronized excitation in vertically opposing LV segments. CONCLUSION: The change in LV activation is specific to this d-HCM case with damaged septum and apex; however, it provides one of the insights into the mechanisms by which LBBAP exerts its beneficial effects when upgrading from RVA-PICM.