An electrocardiogram, or EKG, is one of those exceedingly common medical tests that most everyone has heard of. But what does an EKG actually measure? When is it appropriate or even urgent to get one done, and what does an abnormal EKG mean for your health?
EKG: The Language of the Heart
An EKG "measures the directions of electrical signals through the heart in various directions," explains Travis Murphy, MD, an emergency medicine attending physician and fellow in surgical critical care at the University of Florida at Gainesville.
According to the American Heart Association (AHA), these signals are generated with every heartbeat as the heart muscle squeezes and pumps blood out to all parts of the body. EKGs register the activity as a series of electrical "waves." The first wave reflects activity in the heart's upper chamber, the second wave in the bottom chamber, and the third represents the resting/recovery phase between the other two.
Reading the ups and downs of all three waves is like reading a language, Dr. Murphy notes. That requires training because EKGs use a dynamic vocabulary that can be open to interpretation, given that "each person's heart is slightly different in size and shape," he says.
What Does an Abnormal EKG Mean?
For an EKG, according to the U.S. National Heart, Lung, and Blood Institute, up to 12 electrodes are placed on the body of the person having the test. EKGs are non-invasive, totally painless and safe. People undergoing an EKG are not exposed to any externally-generated electricity.
EKG readouts can confirm that a person's heart rhythm and heart rate are normal, states the Mayo Clinic. For adults, a normal resting heart rate is 60 to 100 beats a minute, Mayo says. Or the EKG can spot evidence that there's a problem with heart activity, that it's too slow, too fast or irregular, the AHA notes.
Electrical activity at the bottom of the heart that's too slow will show up as a particular pattern on an EKG known as a "bundle branch block." When such patterns show up for the right side of the heart, it's usually not a cause for concern. But when the left side generates this pattern, it signals that serious heart trouble could be underway, according to Harvard Health. Problems may include a narrowing and hardening of arterial pathways, chronic high blood pressure or coronary heart disease. All can prove fatal if left unspotted and untreated.
EKGs are also good at gauging the amount of electrical activity moving through the heart, alerting cardiologists when some parts of the heart muscle have become dangerously enlarged or over-stressed, states the AHA.
Who Benefits From EKGs?
Outside of an emergency situation, Dr. Murphy points out that the U.S. Preventative Services Task Force (USPSTF) does not advocate routine EKGs for people who face a generally low risk for heart disease, regardless of their age. The concern is that erratic or misinterpreted EKGs might subject otherwise healthy people to unwarranted follow-up screenings and unneeded treatment.
On the other hand, people at high risk for heart disease "should be monitored a little more closely," he says. Essentially that means people of any age who have diabetes and those with high cholesterol or high blood pressure. Other people who should also consider incorporating an EKG into their routine visits to their general practitioners are smokers, people who are obese and those with a family history of heart attack at a young age
Everyone is a candidate for an EKG when a health crisis arises, Murphy notes. The Mayo Clinic cites heart palpitations, a rapid pulse, chest pain, shortness of breath, dizziness, lightheadedness, weakness and fatigue as trouble signs that could indicate that an EKG is in order.
"I personally have a very low threshold for ordering them in the ER," Dr. Murphy says, "since they can provide information about the many conditions that mimic heart attack symptoms or when people present with nausea, upper abdominal pain, shortness of breath or chest discomfort." EKGs, he adds, can also help explain a loss of consciousness.
For many people, an EKG can be a lifesaver, such as when signs of heart trouble are seen in a reading and the EKG triggers further testing, such as an echocardiogram, that may ultimately lead to a lifesaving diagnosis and treatment.