Combined CRT and ICD can improve symptoms and decrease arrhythmias. However, Dr. Stevenson said, the evidence is less convincing regarding the effect of this combination on disease progression in all patients.

It is clear that CRT alone offers tremendous functional improvement in patients with Class III or IV heart failure. Joint guidelines of the American Heart Association, American College of Cardiology and the North American Society of Pacing and Electrophysiology for 2002 reflect this. These guidelines recommend biventricular pacing for Class III or IV heart failure patients who have medically refractory symptoms. These patients should have a QRS duration of at least 130 milliseconds and a left ventricular ejection fraction of less than or equal to 35%.

However, not all of these patients should receive both CRT and an ICD. The proportion of patients who would benefit from the addition of the ICD is small. Patients with ischemic heart failure may benefit, but studies do not show a primary benefit of the ICD in the population of patients with nonischemic cardiomyopathy. Furthermore, not all patients with ischemic cardiomyopathy would be eligible for biventricular pacing. Of those patients, not every one will have a successful implantation.

The benefits of resynchronization therapy are clear. Dr. Abraham and colleagues illustrated this in the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) trial. This study showed an impressive 63% improvement in clinical status of CRT versus medical therapy. Dr. Abraham believes that adding an ICD would be logical in this group of patients with stable biventricular pacing and symptomatic improvement. This may translate into a mortality benefit.

However, it is debatable whether ICDs are beneficial for all patients with left ventricular dysfunction or heart failure. The Multicenter Automatic Defibrillator Implantation Trial-II (MADIT II) looked at the use of prophylactic ICDs in patients with left ventricular dysfunction or heart failure. Investigators reported a 31% reduction in all cause mortality. However, the absolute mortality rate in this trial was low, suggesting that many trial participants did not benefit from receiving an ICD.

Another problem is that published ICD trials include mostly patients with Class I or II heart failure, and often have additional risk factors that increase their risk of ischemia. Perhaps 10% of study participants have had Class III or IV disease. Therefore, there data supporting the use of ICDs in patients with Class III or IV disease are not plentiful. For example, the MADIT II trial excluded Class IV patients, and a large number of patients had Class I heart failure.

Patients with heart failure due to coronary disease may feel good and live longer when they receive CRT plus an ICD. However, this is a small proportion of patients. On the other hand, researchers do not know much about the benefit of CRT plus an ICD in the nonischemic population. In the Asymptomatic Non-sustained Ventricular Tachycardia (AMIOVIRT) trial comparing amiodarone and ICD, total mortality was the same at 4 years. Likewise, the Cardiomyopathy Trial (CAT) provided no evidence that implanting an ICD benefited patients with idiopathic dilated cardiomyopathy and left ventricular dysfunction.

While AMIOVIRT and CAT are not very large studies, there is a very large randomized trial underway. The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) compares medical therapy, medical therapy plus amiodarone and medical therapy plus an ICD. Enrollment criteria include symptomatic heart failure due to ischemic or nonischemic cardiomyopathy. To date, investigators have reported no results from this 2,500 patient trial.

To date, there are no data showing that nonischemic patients receiving CRT should also receive an ICD. A relatively small group of patients with ischemic cardiomyopathy will benefit from the addition of ICD. However, current data do not support the proposition that an ICD will provide a benefit for all patients receiving CRT.