Abstract:

Heart failure (HF) refers to a condition in which the heart’s capacity to pump blood is reduced, making it unable to meet the body’s demands. It is a syndrome affecting 1 to 2 % of the adult population in the developed world, with its prevalence rising due to the aging of the population. Cardiac resynchronization therapy (CRT) has been identified as an effective treatment for patients with HF and a left ventricular ejection fraction (LVEF) ≤ 35 %. However, approx. 30 % of patients receiving the current standard CRT treatment do not benefit from it in the long run. Alternative pacing strategies targeting the cardiac conduction system emerged in recent years and show the potential to outperform the present standard methods. Nevertheless, the main challenges of predicting the long-term outcome of CRT and choosing the optimal pacing strategy remain since the underlying mechanisms are not well understood.This work uses an electromechanical heart model with an integrated His-Purkinje system (HPS) to simulate different CRT strategies. The basis for the study setup consists of simula- tions for both a healthy heart and one with left bundle branch block (LBBB), varying this scenario in implementing a scar in the septum of the heart. The heart suffering from LBBB with and without scar tissue was then treated with six different pacing strategies. All simula- tions were analyzed and compared using appropriate metrics regarding electrophysiology, mechanics and hemodynamics.Comparing the results from the base simulations, mechanical imbalances appear to be the potential root cause for the pathological decrease in LVEF typical for HF patients. The electrical dyssynchrony induced by LBBB leads to mechanical dyssynchrony without causing a significant reduction in LVEF. In line with clinical data, this work concludes that major reductions in LVEF are a consequence of remodeling due to an unbalanced ventricular load. Analyzing the different pacing methods, selective left bundle branch area pacing (sLBBAP) proves to be the most effective in terms of mechanical resynchronization and reduction of load imbalances for the scenario without scar tissue, closely followed by non-selective left bundle branch area pacing (nLBBAP). Considering both scenarios with and without scar tissue, biventricular pacing (BVP) (with and without interventricular delay) shows a more reliable performance than LBBAP. One disadvantage of BVP is an unphysiological strain peak at the side of the pacing lead. Both right ventricular apex pacing (RVAP) and left ventricular septum pacing (LVSP) provoke only minor improvements compared to the untreated scenario and were thus considered unsuitable for our case. Our work on modeling LBBB and different CRT methods provides valuable insights into the underlying effects following electrical dyssynchrony and resynchronization. Our find- ings indicate that changes in electrical activation immediately affect mechanics more than hemodynamics. For our model, LBBAP showed the best performance in electrically and mechanically resynchronizing the ventricles.