Preventing Sudden Death After a Heart Attack

If you've already had a heart attack, you're at high risk of having a sudden cardiac arrest. Dying from sudden cardiac arrest after a heart attack is, unfortunately, all too common. When a person goes into sudden cardiac arrest, he or she needs electric shocks to the heart with a defibrillator immediately because of the chances of survival decrease with every minute, eventually leading to sudden cardiac death, which claims the lives of around 325,000 adults in the United States each year.

Most victims of sudden cardiac death have had a prior myocardial infarction (heart attack) weeks, months, or even years earlier. Heart attacks, the most severe form of the acute coronary syndrome, are produced when a coronary artery becomes suddenly blocked, usually due to the rupture of coronary artery plaque, thus causing the death of a portion of the heart muscle.

The damaged heart muscle eventually heals following a heart attack, but always produces a permanent scar. The scarred portion of the heart can become electrically unstable and the electrical instability can produce a life-threatening heart arrhythmia called ventricular tachycardia (fast heartbeat), which can lead to ventricular fibrillation. Unfortunately, these arrhythmias can occur quite suddenly, without any warning whatsoever, and people can experience them even if everything seems to be going well from a medical standpoint. The arrhythmia can then lead to a sudden cardiac arrest, which often results in death.

The risk of sudden cardiac arrest after you've had a heart attack is highest within the six months following your heart attack. Seventy-five percent of people who have sudden cardiac arrest had a previous heart attack.

The highest risk occurs in people who have already survived a cardiac arrest and have been successfully resuscitated. These individuals have a 20 percent yearly chance of another cardiac arrest. The risk is also relatively high in people whose heart attacks are considered large, that is, whose heart attacks produce a lot of heart muscle scarring.

One good measure that reflects the amount of scarring is the ejection fraction, a measurement to determine how well your heart is pumping blood. The more scarring you have, the lower the ejection fraction. After a heart attack, those with an ejection fraction above 40 percent (a normal ejection fraction is 50 percent or higher) seem to have a relatively low risk of sudden death. The risk of sudden death increases with lower ejection fractions and becomes substantially higher with values of 30 percent or below. For this reason, anyone who has had a heart attack should have their ejection fractions measured.

The risk of sudden death after a heart attack can be greatly reduced by two general kinds of measures:

• Standard medical treatments including beta-blockers, ACE inhibitors, and statin therapy.
• Identifying people who are still at high risk despite medical treatment, and considering an implantable cardioverter-defibrillator (ICD) in these individuals.

Beta-blockers, ACE inhibitors, and statins have all been shown to reduce the risk of dying after a heart attack. While much of this mortality reduction is related to reducing the chances of developing heart failure or further heart attacks, these drugs also modestly reduce the risk of cardiac arrest and sudden death. All survivors of heart attacks should be placed on these drugs unless there's a very good reason not to.

Despite the use of aggressive medical therapy, in some people, the risk of sudden death due to cardiac arrest remains high. You may be a good candidate for an ICD if any of the following is true:

• You've had a prior sudden cardiac arrest, heart attack, or a ventricular arrhythmia
• You have Long Q-T syndrome
• You have congenital heart disease or other conditions that could lead to sudden cardiac arrest

Clinical studies have shown that in any of these circumstances, having an ICD can help prevent sudden cardiac arrest.