Coronary sinus and cardiac venous anatomy for cardiac resynchronization therapy: A Clinician's view

The coronary sinus and its tributaries constitute the anatomical foundation for successful cardiac resynchronization therapy. Despite the emergence of conduction system pacing as a physiological alternative, conventional transvenous CRT retains its important role-not all clinical scenarios can be addressed by left bundle branch area or His bundle pacing alone. Understanding coronary venous anatomy therefore remains essential for every implanting physician. This review provides a clinically oriented analysis of coronary venous anatomy as it pertains to left ventricular lead implantation. We examine the embryological origins of the coronary sinus, explaining why variants such as persistent left superior vena cava and obstructive Thebesian and Vieussens valves occur. The gross anatomy section details coronary sinus dimensions, ostial localization, and tributary classification using attitudinally correct nomenclature. Microanatomical considerations include wall thickness gradients, subepicardial adipose tissue thickness, and myocardial sleeve distribution. We review imaging modalities-fluoroscopy, computed tomography, and magnetic resonance imaging-emphasizing their complementary roles in preprocedural planning and real-time guidance. Catheter and wire handling techniques are discussed, from cannulation strategies to lead delivery. Electrophysiological parameters including Q-LV and S-QRS intervals are examined in the context of anatomical lead positioning. Finally, we analyze how anatomy influences outcomes, complications, and non-response. Understanding the coronary venous system transforms cardiac resynchronization therapy from a technical procedure into an anatomically informed intervention where success depends on matching therapeutic goals with individual patient anatomy.