Understanding the ECG: Reading the waves

The electrocardiogram (ECG) is one of the most common, enduring, and important tests in all of medicine. It's easy to perform, noninvasive, produces results right away, and is useful in diagnosing dozens of heart conditions. The ECG has taken on even more importance lately because a particular ECG pattern, called ST elevation, is a strong indication that a serious heart attack has occurred, and there's more emphasis than ever on treating heart attacks as soon as possible. An ECG isn't necessarily going to be part of a routine physical, but if you need medical attention because you have chest pain, sudden unexplained shortness of breath, or other symptoms that suggest a possible heart attack, you will almost certainly get an ECG.

The ECG is a reading of the electrical impulses in the heart that activate the heart muscle and its blood-pumping action. Twelve electrodes affixed to the skin on the chest, arms, and legs sense those impulses from various vantage points. Part of the reason the ECG has had such staying power is that the output is visual: a line graph with peaks and valleys, not a stream of numbers. As a result, reading an ECG is a matter of pattern recognition, not computation. There are many permutations, but someone can be trained to recognize the most common patterns relatively quickly.

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