Cardiac resynchronization therapy with special focus on patency of coronary sinus and its branches: conceptual viewpoint and semi-theoretical considerations on lead-induced obstruction.

Cardiac resynchronization therapy appears to be useful for patients with severe chronic congestive heart failure. However, many questions still arise concerning the effectiveness of this kind of therapy since hemodynamic improvement is not observed in all patients. Heterogeneity of conclusions reported by several multicenter clinical trials and prominent experts demonstrates that many uncertainties related to cardiac resynchronization therapy still exist. We tried to reveal some inadequacies in clinical results by focusing on cardiac venous blood return which is likely complicated by the presence of lead inside the coronary sinus and its branches. Downstream traversing lead may occlude (partially or completely) the ostia of minor tributaries and target vein of lead final positioning. Thrombosis may also be incited within the coronary sinus itself. Remaining lumen predetermined by the lead body and subsequent thrombosis may be insufficient to provide adequate blood flow. Resulting detrimental venous return presumably may slightly depress myocardial contractility which may be significant in very sensitive group of patients assigned to the New York Heart Association class III or IV. Cardiac venous blood pumping conditions (or venous drainage) are likely also complicated by abnormal activation of left ventricle. The contributory role of these two subtle causes unfavorably influencing venous drainage is still unknown. It may be treated as a hypothetical attempt to find the clue and needs future studies for verification.