If you have one (or no) risk factors for a heart attack and have no symptoms of coronary heart disease (for example, chest pain), an ECG will probably not be done. But if you have two or more risk factors, have symptoms of coronary heart disease, or have already had a heart attack, you should have an ECG once a year.
An ECG is a painless test that takes five to 10 minutes. While you are lying on your back on an examining table, small metal sensors (electrodes) are attached to the skin on your chest and limbs. The electrodes detect and record the pattern of electrical signals from your heart as it contracts and relaxes during each heartbeat. This pattern can be abnormal when the heart is not receiving enough blood and oxygen through the coronary arteries.
An ECG can also determine whether you are having a heart attack or have had one in the past. It’s also used to identify abnormal heart rhythms and to detect thickening of the wall of the left ventricle (a condition called left ventricular hypertrophy).
A normal resting ECG does not necessarily mean your coronary arteries are healthy, because it’s still possible that inadequate blood flow to the heart (myocardial ischemia) occurs and causes chest pain only during physical activity. To determine this, you may need to undergo an exercise stress test.
Your physician may order an additional ECG test to detect silent coronary heart disease (impaired blood flow to the heart that causes no symptoms). This condition can be identified using a Holter monitor (also called an ambulatory ECG), which continuously records the heart’s electrical activity over a 24-hour period. Holter monitoring is also useful in evaluating people with unexplained lightheadedness, fainting, or heart palpitations and for determining the effectiveness of drug therapy for abnormal heart rhythms.