Preventing Sudden Death After a Heart Attack

If you've 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, they need electric shocks to the heart with a defibrillator immediately because 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.

Sudden Cardiac Death

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 acute coronary syndrome, occur when a coronary artery is 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 without any warning, 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 a Heart Attack

The risk of sudden cardiac arrest after you've had a heart attack is highest within the six months following your heart attack. In fact, 75% 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. 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.

Ejection Fraction

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% (a normal ejection fraction is 55% 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 35% or below. For this reason, anyone who has had a heart attack should have their ejection fractions measured.

Reducing the Risk of Sudden Cardiac Arrest After a Heart Attack

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

• Standard medical treatments include beta-blockers, ACE inhibitors, statin therapy, and SGLT2 inhibitors.
• Identifying people who are still at high risk despite medical treatment, and considering an implantable cardioverter-defibrillator (ICD) in these individuals.

Medications to Reduce the Risk of Sudden Cardiac Arrest

Beta-blockers, ACE inhibitors, statins, and SGLT2 inhibitors 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.

Implantable Cardioverter Defibrillator (ICD) to Reduce the Risk of Sudden Cardiac Arrest

Despite the use of aggressive medical therapy, in some people the risk of sudden death remains high. After a heart attack, serious consideration should be given to implanting an ICD, in addition to medical treatment, when:

• There has been a prior cardiac arrest, or an episode of prolonged ventricular tachycardia
• The ejection fraction is lower than 30%
• The ejection fraction is between 30% and 35% and symptoms of heart failure have occurred

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