Yale-New Haven was recognized this year by U.S. News & World Report for its heart and heart surgery services.

ICDs reduce risk of sudden death

There are currently about five million patients with congestive heart failure in the U.S. This is the largest single population of patients who could potentially benefit from primary prevention of sudden cardiac arrest.

One’s ejection fraction (EF) is currently the most accurate predictor of risk for sudden cardiac death. Not everyone with congestive heart failure has a low EF, but because the number of CHF patients is increasing and because it is the leading reason people are admitted to hospitals, it makes sense to see if the mortality rate of these patients could be reduced with implantable cardiac defibrillators (ICDs).

Ejection fraction basics
What is EF? The two lower chambers (ventricles) of your heart pump blood into your lungs (right ventricle) and to your arteries (left ventricle). When the left ventricle contracts to force blood out, it doesn't pump out all the blood inside it, however. The amount your left ventricle does pump out per beat is called the “ejection fraction.” It's the percentage of the total amount of blood in the ventricle that is pumped out with each heart beat.

If your heart pumps out 55 percent or more of the blood in your left ventricle with each beat, you have good heart function. When your EF goes down, it indicates your heart muscle is weakening and it's not pumping as much blood out with each contraction as it should. Not everyone who has a low EF has symptoms of congestive heart failure, but the lower the EF, the greater your risk of sudden cardiac death.

Study participants
The study mentioned here, SCD-HeFT, used two criteria for selecting study participants: ejection fraction and the New York Heart Association (NYHA) classification system for congestive heart failure. The NYHA system provides a common language for health care professionals to use when describing the severity of congestive heart failure symptoms. Class I patients have no symptoms related to heart failure; Class II patients have symptoms such as shortness of breath with significant exertion; Class III have symptoms with mild exertion; and the Class IV group is symptomatic at rest. SCD-HeFT patients were in the II and III categories, considered mild to moderate.

Various medications such as beta blockers, ACE inhibitors and dioxin have been shown to be effective in reducing symptoms and improving the survival and quality of life of people with congestive heart failure. All of the patients in the SCD-HeFT were already on optimal medical therapy for their condition, which strengthens the results of the study. If some patients had not been receiving “best practice” treatment, the results would be difficult to assess.

How ICDs work
The study demonstrated a significant benefit with ICDs, particularly for Class II patients. ICDs are very effective in restoring the abnormal heart rhythms that can lead to sudden cardiac death. When the ICD senses a dangerous abnormal heart rhythm, it delivers an internal electric shock to the heart, the equivalent of being shocked with paddles outside the body. There is no way to predict if and when an abnormal rhythm will occur, so ICDs are the best way we have to treat them when they occur.

The devices used in the study were basic ICDs. We also have very technically advanced ICDs that can be programmed for specific conditions. Some can actually help treat heart failure, but those used in this study were the most basic, least expensive models. Costs are a very large factor in using ICDs for primary prevention.

Results are far reaching
Given the enormous numbers of people with congestive heart failure, the implications for Medicare are significant. This study has added fuel to the movement to provide “preventive” ICD protection for these patients, and it has led to revised medical guidelines and Medicare reimbursement.

One of the most significant results of the SCD-HeFT is that the findings apply equally to people with and without coronary artery disease (CAD). Several trials have shown benefits of “preventive” ICD treatment, but this is one of the first to show benefits among both categories of congestive heart failure patients—both CAD and non-CAD patients.

One finding of this trial that differed from some other trials was the variable benefit obtained by mild and moderately ill patients. In contrast to SCD-HefT, other studies have indicated more severely ill people benefit most from ICDs, so we need to continue to study this topic.

There are a small number of patients who should not have ICDs. Some congestive heart failure patients have normal ventricular function, and there is no evidence to show that they would benefit from ICDs. Some patients have such advanced disease that ICD implantation is not going to be helpful because they will likely die in a short time.

Patients who have been diagnosed with heart failure should talk with their doctors about whether they might be candidates for an ICD.