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

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 less than or equal to 35%, a QRS greater than or equal to 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 (V) over dot O-2, (V) over dot E/(V) over dot CO2, 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 V. O2, 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 (V) over dot E/(V) over dot CO2 ( 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.