Cardiac resynchronization therapy randomized clinical trials

Cardiac resynchronization therapy (CRT) for systolic congestive heart failure (CHF) represents a new paradigm in cardiology the use of an electrical therapy (cardiac pacing) to treat a mechanical problem. Multiple randomized clinical trials have proven that resynchronization therapy improves symptoms and functional status, increases quality of life, reduces hospitalizations, and prolongs survival in appropriately selected patients. As a result, this therapy has been quickly established as a standard treatment for patients with severe left ventricular dysfunction, moderate-to-severely symptomatic CHF despite optimal medical therapy, and prolonged QRS duration (1,2). 

Table 5.1 Randomized multicenter clinical trials of cardiac resynchronization therapy... 

CRT reduces symptoms of CHF and improves cardiac performance in patients with moderate-to-severely symptomatic heart failure, severe left ventricular systolic dysfunction, normal sinus rhythm and a wide QRS complex. Resynchronization therapy significantly reduces hospitalizations in these patients and is highly cost-effective. Perhaps most important, resynchronization therapy for heart failure improves survival for these patients, particularly when employed in conjunction with an implantable defibrillator. However, randomized clinical trials show that a substantial minority of patients are clinical nonresponders. Therefore, critical questions remain with respect to identifying appropriate candidates for CRT, optimal device programming, and left ventricular lead placement. 

Table 11.1 Randomized clinical trials of Cardiac Resynchronization Therapy. 

The Multicenter InSync ICD Randomized Clinical Evaluation II (MIRACLE ICD II) was a follow-up randomized, double-blind, parallel-conlrolled clinical trial of CRT in New York Heart Association Functional Class II heart failure patients on optimal medical therapy with a left ventricular ejection fraction < 0.35, a QRS > 130ms and a Class I indication for an ICD. Patients were randomized to control group (ICD activated, CRT off) and to CRT group (ICD activated, cardiac-resynchronization therapy on). No significant differences were noted in 6-min walk distance or quality of life scores or peak V02. There were significant improvements in left ventricular diastolic and systolic volumes and in left ventricular ejection fraction (198). 

Pires, L.A., et al.. Clinical predictors and timing of New York Heart Association class improvement with cardiac resynchronization therapy in patients with advanced chronic heart failure results from the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) and Multicenter InSync ICD Randomized Clinical Evaluation (MIRACLE-ICD) trials. Am Heart J, 2006. 151(4) p. 837-13. 

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