Exercise Training Following Cardiac Resynchronization Therapy in Patients With Chronic Heart Failure

Cardiac resynchronization therapy(CRT) is recommended to reduce mortality and morbidity in chronic heart failure(CHF) patients New York Heart Association(NYHA) class III-IV who are symptomatic despite optimal medical therapy, with a reduced left ventricular(LV) ejection fraction(LVEF) and prolonged complex QRS. CRT improves the prognosis however, despite the improvement, all major trials have demonstrated that one third of the patients are non-responders to CRT. Three months after the CRT implant, the responders have a significant increase in endothelial function(EntF), a decrease in the LV end-systolic volume, and increase in LVEF, 6 minute walk test(6MWT), improvements in NYHA class and quality of life. It is currently unknown if adding an exercise training(ExT) program following CRT provides better clinical outcomes than CRT alone. Prior studies on CRT and ExT have been preliminary in nature, but suggest small improvements in functional capacity(FC). The correction of endothelial dysfunction is associated with a significant improvement in exercise capacity evidenced by a 26%increase in peak oxygen uptake. These findings are important because CHF patients with the greatest sympathetic activation and the most reduced EntF have the poorest prognosis. Our experience with coronary artery disease patients, and most recently data in patients with CHF show that an ExT program that combines aerobic exercise(AE) and resistance exercise training are more effective than an AE program alone, and the aerobic interval training showed better improvements than continuous endurance training. It is unknown how CHF with more severe functional limitations responds to ExT and, more important, the explanation of the physiological mechanism that can explain the improvements as a consequence of ExT. This lack of scientific information is urgent since this is the group of patients that normally is targeted for CRT. The investigators propose to use a stratified randomized longitudinal study to determine the additional effects of a 6 month ExT in addition to CRT in NYHA stage III-IV HF patients. The aims of the study are:1-to determine whether a long-term ExT program follow the CRT provides better clinical outcomes than CRT alone and 2-To identify the mechanisms of the hypothesize improvement. The results of this project will represent an important contribution by understanding the role of ExT after CRT NYHA stage III-IV heart failure(HF) patients, an understudied population with poor clinical outcome. Understanding the potential mechanisms associated with clinical improvement and outcome is essential for the rehabilitative process to develop new innovative therapies in this high risk population. The investigators will use state-of-art methods including an integrated assessment autonomic nervous system(ANS) and arterial function using 123I-MIBG scintigraphy.