Sudden death after a heart attack is all too common. Here's a story every cardiologist has heard many times:
John, 56 years old, sits in the living room watching a sitcom with his wife. John has not led a medically exemplary life, but the heart attack he had a month ago has given him an important wake-up call. "You were lucky this time, John," his doctor told him. "You've had substantial heart damage, but the old pump is still working well enough. If you straighten up your act you've got a good chance of seeing that new grandbaby get married some day."
So John has begun a strict diet, has begun exercising under the watchful eye of a local cardiac rehabilitation program, is taking all the medication his doctor has prescribed to help his heart heal and to help prevent another heart attack, and most importantly, has quit smoking. After only a month, he has already lost 5 pounds and is walking nearly a mile a day. He feels better - more fit and more energetic - than he has in years. He leans back in his easy chair and smiles. "You know," he says to his wife, "that heart attack may turn out to be one of the best things that ever happened to me."
She replies, "You are no doubt referring to the fact that you haven't had to do a lick of housework in over a month."
She expects a return chuckle from John - but doesn't get one. She glances at her husband and is is stunned to see that he has slumped over in his chair, unconscious. Her attempts at arousing him are unsuccessful. She quickly calls 911, but despite the efforts of the paramedics who arrive less than 10 minutes later, John dies.
John has suffered a cardiac arrest, and because attempts to resusitate him were ineffective, the episode ended with his death. This tragic scenario is played out in the United States alone nearly 1000 times each and every day.
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, are produced when a coronary artery becomes suddenly blocked (usually due to rupture of a 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 - ventricular tachycardia and ventricular fibrillation. Unfortunately, these arrhythmias can occur quite suddenly, without any warning whatsoever, and people can experience cardiac arrest even if everything seems to be going well from a medical standpoint - just as in John's example.
How High Is The Risk of Sudden Death After A Heart Attack?On average, the long-term risk of sudden death after a heart attack (once a person has been medically stabilized for a month or so), is between 1 - 2% per year thereafter.
However, for some people the risk is substantially higher. The highest risk occurs in people who have already survived a cardiac arrest and have been successfully resuscitated. These individuals have around a 20% yearly chance of another cardiac arrest.
The risk is also relatively high in people whose heart attacks are "large," that is, whose heart attacks produce a lot of heart muscle scarring. One good measure that reflects the amount of scar is the ejection fraction - the more scar, the lower the ejection fraction. After a heart attack, those with an ejection fraction above 40% (a normal ejection fraction is 50% 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% or below. For this reason, anyone who has had a heart attack should have their ejection fractions measured - and should know what their ejection fraction is.
How To Reduce Your Risk of Sudden Death After a Heart AttackThe risk of sudden death after a heart attack can be greatly reduced by two general kinds of measures:
- Standard medical treatments including beta blockers and ACE inhibitors, and also statins
- Identification of people who are still at high risk despite medical treatment, and considering an implantable cardioverter defibrillator (ICD) in these individuals
Despite the use of aggressive medical therapy, however, in some people the risk of sudden death remains high. Serious consideration should be given to an implanting an ICD when:
- there has been a prior cardiac arrest, or an episode of prolonged ventricular tachycardia
- the ejection fraction is lower than 30%
- heart failure has occurred and the ejection fraction is lower than 35%
Bailey, JJ, Berson, AS, Handelsman, H, Hodges, M. Utility of current risk stratification tests for predicting major arrhythmic events after myocardial infarction. J Am Coll Cardiol 2001; 38:1902.
Zipes, DP, Camm, AJ, Borggrefe, M, et al. ACC/AHA/ESC 2006 guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol 2006; 48:e247.