Sudden Cardiac Death

• One of the most frightening aspects of coronary artery disease (CAD) is that many people die suddenly, out of the hospital, and with little or no warning. Sudden cardiac death refers to death that occurs unexpectedly and presumably due to a heart condition and is generally defined as death within 1 hour of the first symptoms or an unwitnessed event occurring overnight.

• Between 70% and 89% of sudden cardiac deaths occur in men, and the annual incidence is 3 to 4 times higher in men than in women; however, this disparity decreases with advancing age. People who have had a heart attack have a sudden death rate 4 to 6 times that of the general population.

• Approximately 70% of deaths from heart disease is sudden and occurs outside of the hospital and is particularly common among people with heart failure.  This figure is 90% in Sweden. Fifty percent of men and 64% of women who die suddenly of CAD have no previous symptoms of this disease.

• While sudden cardiac death is unexpected, it is potentially survivable and preventable. It is not enough to merely call 911 and wait for paramedics to arrive. A victim has the best chances for good survival if witnesses act quickly. It is imperative for bystanders to start CPR (cardiopulmonary resuscitation), which involves compressing the chest and to apply an AED (automatic external defibrillator) to shock the heart to improve the chances for survival for the victim.

• In sudden cardiac death the heart may have: a) an electrically chaotic rhythm, called ventricular fibrillation, b) no electrical beat at all, called asystole, or c) be so weak that it is unable to mechanically pump any blood.

• There are many causes for sudden cardiac death, which include severe heart failure, heart attack, and certain inherited heart conditions. Sudden cardiac death can also occur in the absence of a heart attack.

• It may occur in people who have diminished heart function – a weakness in the heart muscle from whatever cause. Most diminished heart function develops as a result of CAD and heart attacks, but some people have diminished heart function despite having normal coronary arteries.

• The “ejection fraction” is a number that is used to describe how much blood is pumped out by the heart with every heart beat; normally the heart can eject at least 50% of its contents with every heart beat. Heart function is considered severely diminished if the ejection fraction is less than 35%, and under these circumstances patients can also be at increased risk for sudden cardiac death.

• Victims that do survive sudden cardiac death require testing to determine if the cause for sudden death can be reversed. If it is determined that the risk for another cardiac arrest is high, then an implantable cardioverter defibrillator (ICD) is needed. This is a device, similar to a pacemaker that can shock the heart within seconds if a dangerous heart rhythm is detected.

• In carefully selected patients, an ICD can reduce the risk of sudden deaths by 20-35% at a cost exceeding $100,000.  More than 400,000 ICDs have been implanted in the last 3 years in the US, with a current implantation rate of 10,000 to 12,500 per month (see Heart Disease in the US).

• Many patients are implanted with ICDs before a cardiac arrest has ever occurred if they are identified as having high risk characteristics, such as severe heart dysfunction.

• Substantial progress has been made in modifying cardiovascular disease risk after heart attack and cardiac arrest in the last several decades.^{1, 2} From 1950 to 1999, non-sudden CAD death decreased by 64%, and sudden cardiac death fell by 49%. 

• Most of the sudden deaths occurring at home are unwitnessed and therefore do not benefit from a home defibrillator.

Sources

1. Palmieri L, Bennett K, Giampaoli S, Capewell S. Explaining the decrease in coronary heart disease mortality in Italy between 1980 and 2000. Am J Public Health. Apr 2010;100(4):684-692.

2. Ford ES, Ajani UA, Croft JB, et al. Explaining the decrease in U.S. deaths from coronary disease, 1980-2000. N Engl J Med. Jun 7 2007;356(23):2388-2398.