Sudden Cardiac Arrest: Know Your Ejection Fraction

By Michael D Eifling MD

Every three minutes someone dies from sudden cardiac arrest (SCA) in the United States. In fact, it claims about 300,000 lives in the US each year – more fatalities than from stroke, breast cancer, and HIV/AIDS combined.

Sudden Cardiac Arrest

WHAT IS SUDDEN CARDIAC ARREST?

Every three minutes someone dies from sudden cardiac arrest (SCA) in the United States. In fact, it claims about 300,000 lives in the US each year – more fatalities than from stroke, breast cancer, and HIV/AIDS combined. Although cardiac arrest may occur in people who appear healthy, most of the time SCA happens in patients with coronary artery disease, previous heart attacks, or congestive heart failure.

Sudden Cardiac Arrest is different than a heart attack. A heart attack is a plumbing problem, whereas SCA is an electrical problem. In a heart attack, a clot forms in a narrowed artery supplying blood to the heart and causes chest pain and shortness of breath, often leading to heart muscle damage. In SCA, the electrical rhythm that controls the lower chambers of the heart becomes chaotic, and the heart begins to quiver instead of pumping blood. Patients may experience a racing heart, dizziness, or fainting. Without blood reaching the brain, the patient loses consciousness within seconds; and death may occur if a life-saving shock is not delivered quickly to restore a normal rhythm. The majority of SCA victims die before reaching the hospital.

WHO IS AT RISK FOR SUDDEN CARDIAC ARREST?

People at higher risk for SCA include those who have had:

  • previous heart attack (myocardial infarction)
  • heart failure (poor pumping ability of the heart)
  • previous sudden cardiac arrest
  • family history of sudden cardiac arrest
  • low ejection fraction (EF)

Although 80 percent of people who have a cardiac arrest have evidence of coronary heart disease or previous heart attack, many victims are unaware of their underlying heart disease. There are a number of tests that may be performed to determine if someone is at high risk for SCA. An electrocardiogram (ECG) is a simple test that records the electrical impulses in the heart. It may reveal a previous heart attack or abnormal rhythm. The single most important risk factor for overall mortality and risk of cardiac arrest is reduced ejection fraction (EF).

WHAT IS YOUR EJECTION FRACTION?

During each heartbeat your heart contracts and pushes blood out of the main pumping chamber of your heart called the left ventricle. The term EF refers to the percentage of blood that is pumped out of your left ventricle with each heartbeat. If your heart muscle has been damaged by a heart attack, heart failure, or heart valve problem, your EF may be low.

A normal EF is 50-65 percent. If your EF is below 35 percent, your risk for SCA increases dramatically. The easiest way to determine your EF is a painless ultrasound called an echocardiogram that uses sound waves to produce images of your heart. An individual’s EF may also be determined with a nuclear stress test, MRI or cardiac catheterization.

SUDDEN CARDIAC ARREST PREVENTION AND TREATMENT

There are numerous things people can do to prevent the risk of SCA including exercising regularly, eating a healthy diet, maintaining an ideal weight, and avoiding smoking. It is important to treat conditions such as high blood pressure, high cholesterol, and diabetes. Medications such as aspirin, beta-blockers, ACE-inhibitors, and antiarrhythmic drugs may p heart attacks and improve conditions such as heart failure.

However, these medications have never been proven to reduce the risk of SCA. The most common rhythm that leads to SCA is ventricle fibrillation and it can only be reversed with a shock called defibrillation. Among people who develop ventricle fibrillation, only five percent will survive.

A device called an implantable cardioverter defibrillator (ICD) can increase the odds of surviving SCA to greater than 90 percent. ICD’s are similar to pacemakers and automatically monitor for ventricular fibrillation. These devices can deliver a life-saving shock within 15 seconds, and have been shown to prevent SCA in certain high-risk patients – such as those with an EF less than 35 percent.

Although ICD’s are widely available in the US, only 20 percent of patients who meet the recommended guidelines actually receive one. Patients eligible for an ICD include those who have:

  • history of SCA or life-threatening rhythms
  • EF less than 35 percent

The conditions below require EF less than .35 and congestive heart failure:

  • heart failure
  • more than 40 days after a heart attack
  • heart enlargements and deformities called nonischemic cardiomyopathies

QUESTIONS TO ASK YOUR DOCTOR

  • Should I be concerned with my EF number?
  • Do I need to have my EF rechecked?
  • Do I need additional test to determine my risk of SCA?
  • Do I need to see a doctor who specializes in heart rhythm?

If you are concerned about your risk of sudden cardiac arrest, ask your primary care provider or cardiologist. He or she will know when it is appropriate to administer an echocardiogram or perform any other exams of tests.