Implantable cardioverter-defibrillators (ICDs) have been used to prolong life in patients with certain types of serious heart disease. An ICD is an electronic device that works by monitoring a patient’s heart rhythm. If the surgically implanted device detects a dangerous rhythm change, it delivers an electric pulse through a lead that rests against the heart tissue. If a patient experiences tachycardia, or a heartbeat that is too fast, for example, the ICD can send an electric signal to stabilize the rhythm before it has an opportunity to harm the patient. Clinical studies have shown that ICDs are very useful in preventing sudden cardiac death in certain patient populations, such as those with a history of sustained tachycardia or heart failure.

Since ICD therapy seems to be so effective in these patients, researchers have been studying their effect in other patient populations, to determine who else might benefit from an ICD device. One such population of interest is recent heart attack victims.

After a heart attack , or myocharidal infarction (MI), patients are at greater risk of developing arrhythmia —an abnormal, sometimes fatal, heart rhythm—for the next 6-12 months. Other than a type of medication called a beta-blocker, no drug therapy that has been consistently shown to reduce this risk. A study published in the December 9th edition of The New England Journal of Medicine evaluated whether the preventive use of an ICD device had an impact on the risk of mortality in patients who had had a recent MI.

About the Study

This was a randomized study that compared 332 patients that received an ICD device with 342 patients who did not (control group). The study included patients aged 18-80 who had all experienced a recent MI. Patients were also required to have some degree of heart failure and evidence of diminished neurologic control over their heart. None, however, showed signs of a dangerous heart rhythm at the time they were enrolled in the study. The patients in the ICD group underwent surgery for implantation of the ICD, and the control group received personalized conventional medical care.

The primary endpoint for the study was mortality from any cause, cardiac or other. The secondary endpoint was death from an arrhythmia.

The Findings

The researchers followed the study participants for an average of 30 months, and during that time, there was no statistical difference between the two groups in terms of mortality. In the ICD treatment group, 62 patients died and in the control group, a total of 58 patients died.

The authors concluded that ICD devices used preventively do not reduce overall mortality in high risk patients who have recently had a heart attack.

Interestingly, the ICD treatment group did in fact experience a reduced risk of death due to arrhythmia. The deaths in the ICD group due to arrhythmia were significantly lower (12 deaths) than the arrhythmia deaths in the control group (29 deaths). However, the ICD group experienced more deaths due to non-cardiac causes, which offset this finding.

How Does This Affect You?

The findings of this study revealed that overall survival in heart attack patients was not improved by the prophylactic use of an ICD device. Previous studies of ICD devices have shown that for other patient types, it is effective at preventing death.

Unfortunately, while the ICD devices in this study appear to have prevented death from arrhythmia, there were enough deaths due to other causes in the ICD group to negate this apparent benefit. The reason for the increased deaths is a bit of mystery since there was no evidence that the increased deaths were in any way associated with the surgical procedure or complications due to the device.

A number of studies have shown ICDs to be effective at preventing death in certain patient populations. Patients with sustained heart failure appear to have the most benefit from ICD devices. However, the positive findings of studies in these patients have led to an increased use of ICDs worldwide, often for patients with many different cardiac problems. What can be learned from this study is that the benefits of ICDs may not necessarily be generalized to all cardiac patients. Another recent study of patients recovering from coronary-artery-bypass-graft surgery (CABG) showed no benefit from ICD implantation either.

Implantation of an ICD device is a complicated procedure that is not appropriate for all patients suffering from a cardiac condition. If you feel you may benefit from an ICD device, or have more questions about its risks and benefits, do not hesitate to discuss it with your cardiologist.