A person relaxes on a bed, with wires attached to their arms, legs, and chest, to measure the natural electricity flowing through the heart with each beat. The wires just receive electricity; no current is delivered in. The EKG is completely painless. The “K” in the abbreviation is from the German word; some people do say “ECG,” but most of us prefer “EKG,” since we speak fast & don’t want the same vowel sounds to blur over.
The EKG is excellent at determining the heart’s rate and rhythm. We may order one for patients who have Palpitations (see the topic). EKGs are key if we suspect irregular heart rhythms (Arrhythmias), for people with episodes of Passing Out (see topic), or someone with a Stroke, to see if the cause was Atrial Fibrillation.
Since the person may have a normal rhythm at the time they see us in the office, we may order an “Ambulatory EKG” — a portable patch for 1-2 days, or another kind for 2-4 weeks (showering is possible). If this doesn’t detect anything, we consider an indefinite monitor implanted under the skin, usually only for patients who faint frequently, or infrequent but disabling symptoms like shortness of breath or chest pain.
We can also tell from an EKG if the heart isn’t getting enough blood, if a Heart Attack is in progress, or if one may have happened in the past. But unfortunately, for everything in the previous sentence, its accuracy is only fair. EKG results may often be false-positive (suggesting something’s wrong when it’s really not). On the other hand, the EKG can be normal right in the middle of a heart attack (false-negative).
To avoid this, we should only order EKGs if we think there’s a reason for someone to have heart disease. We can tell this by a patient’s medical history, and a little by physical exam (see our topic Chest Pain). However, it’s not unusual for patients to seek care for chest pain that we know for sure has nothing to do with the heart (for example, they’re young, and the pain hurts with chest movement). Most can be reassured, but for the very anxious, some clinicians do a “therapeutic EKG” (snide medical humor, meaning the test is really a treatment), to tell them “it’s normal” so they feel better (& hoping it doesn’t have false-positives). See “Why Not To Order Tests ‘Just In Case’ in People with Low Likelihood of the Disease“.