Definitions and determinants of success in left bundle branch area pacing: a systematic review.

Background: Left bundle branch area pacing (LBBAP) achieves more physiological ventricular activation by advancing the lead deep into the interventricular septum and recruiting the left conduction system. Although alternative pacing is usually available when LBBAP is unsuccessful, difficult cases may undergo repeated nonproductive septal deployments before crossover, with longer procedure and fluoroscopy times and greater myocardial injury. Preprocedural prediction may therefore improve implantation and backup planning and reduce unnecessary procedural burden. Methods: PubMed and Embase were searched from inception through July 16, 2026. Two reviewers independently screened the literature. Ninety analytic full-text reports were included; preprocedural determinants formed the primary review question, while later-stage evidence was retained to contextualize endpoint definitions and clinical translation. Results: Among 90 analytic full-text reports, evidence was concentrated on capture verification, whereas only 10 evaluated preprocedural determinants. Recurrent candidate signals included left ventricular enlargement, nonclassical conduction phenotypes, and septal scar; no clinically validated threshold was identified. Septal scar was the most anatomically direct preprocedural marker of mechanical deployment difficulty, with scar location and burden linked to the intended lead path in two observational CMR cohorts. Only one multivariable prediction model was identified and it lacked external validation. Acute procedural outcomes varied by endpoint definition and clinical indication and were not directly comparable. Conclusion: Left ventricular enlargement, nonclassical conduction phenotypes, and septal scar may serve as candidate risk indicators for LBBAP procedural difficulty, although no clinically validated thresholds are currently available. When CMR is already available or clinically indicated, septal scar distribution may add information to substrate assessment and estimation of mechanical difficulty; whether dedicated CMR acquisition and CMR-informed planning improve implantation efficiency or outcomes remains untested. Routine CMR screening is unsupported. For preprocedural studies specifically targeting successful left conduction-system recruitment, confirmed capture may serve as a preferred mechanistic anchor endpoint. Mechanical deployment, indication-specific electrical correction, procedural complexity, crossover, and long-term benefit should be reported separately. Future models should incorporate operator and implant-system factors and demonstrate calibration, external validation, and clinical impact. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420261452030, PROSPERO CRD420261452030.