Effects of Cardiac Resynchronization on Disease Progression in Patients With Left Ventricular Systolic Dysfunction, an Indication for an Implantable Cardioverter-Defibrillator, and Mildly Symptomatic Chronic Heart Failure

Abstract

Background— The effects of cardiac resynchronization therapy (CRT) in patients with mildly symptomatic heart failure have not been fully elucidated. Methods and Results— The Multicenter InSync ICD Randomized Clinical Evaluation II (MIRACLE ICD II) was a randomized, double-blind, parallel-controlled clinical trial of CRT in NYHA class II heart failure patients on optimal medical therapy with a left ventricular (LV) ejection fraction ≤35%, a QRS ≥130 ms, and a class I indication for an ICD. One hundred eighty-six patients were randomized: 101 to the control group (ICD activated, CRT off) and 85 to the CRT group (ICD activated, CRT on). End points included peak V̇ o ₂ , V̇ e /V̇ co ₂ , NYHA class, quality of life, 6-minute walk distance, LV volumes and ejection fraction, and composite clinical response. Compared with the control group at 6 months, no significant improvement was noted in peak V̇ o ₂ , yet there were significant improvements in ventricular remodeling indexes, specifically LV diastolic and systolic volumes ( P =0.04 and P =0.01, respectively), and LV ejection fraction ( P =0.02). CRT patients showed statistically significant improvement in V̇ e /V̇ co ₂ ( P =0.01), NYHA class ( P =0.05), and clinical composite response ( P =0.01). No significant differences were noted in 6-minute walk distance or quality of life scores. Conclusions— In patients with mild heart failure symptoms on optimal medical therapy with a wide QRS complex and an ICD indication, CRT did not alter exercise capacity but did result in significant improvement in cardiac structure and function and composite clinical response over 6 months.