Case Report: A collateral-supplying major septal artery occlusion: electromechanical consequences leading to low left ventricular ejection fraction and late-onset complete atrioventricular block

This case highlights that occlusion of a collateral-supplying major SA may result not only in conduction disturbances but also in significant left ventricular systolic dysfunction, producing an uncommon combined electromechanical presentation. Recognition of this high-risk anatomy during PCI planning-including an understanding that even anatomically appropriate protection strategies may not fully prevent septal branch loss-underscores the need for individualized, anatomy-guided side-branch protection, vigilant rhythm monitoring, and timely CRT-D implantation in selected patients.