By Katie E. Golden, MD

An electrocardiogram (abbreviated as both ECG and EKG) is a simple test that is frequently performed on patients in the emergency room. It is easy, fast, and gives us a lot of important information about your heart. It helps doctors immediately rule out one of the most critical life-threatening emergencies that bring people to the emergency department — a heart attack. But it tells us so much more than that. So let’s take some time to explain this test.

What is an ECG? 

Every heartbeat is controlled by an electrical circuit in the heart – one that fires over and over and over again. The ECG measures those electrical signals, as well as how the heart muscle responds to each of those electrical impulses. It then translates that electrical and muscular activity into a tracing on a page, which gives us a lot of information at once:

  • Heart rate. A normal heart rate is between 60 to 100 beats per minute, so it tells us if your heart is beating too fast or slow.
  • Heart rhythm. A normal heart beats in ‘sinus rhythm’, which means each heart beat is generated by the sinus node, as it should be. Sometimes, the heart beats abnormally and takes its marching orders from other parts of the heart that are not the sinus node. This is called an arrhythmia. There are many different types of arrhythmias, depending on which part of the heart is currently in charge.
  • Heart muscle function. The ECG not only gives us information about the electrical circuit of the heart, but also how the heart muscle is responding to that circuit. That means we can use an ECG to tell us if there is a large part of the muscle that is not getting enough oxygen to pump properly (as in a heart attack). The heart muscle also functions differently in many different other circumstances – like if there are electrolyte changes in the blood (like potassium, calcium, or magnesium), if there is fluid or inflammation around the heart, or if the actual structure of the heart is abnormal.
  • Heart shape and size. Similar to the way an ECG tells us if the heart muscle is not responding properly, it can also tell us if the heart muscle is bigger or thicker than it should be. This occurs, for example, in some types of heart failure.

How is the test performed?

The ECG is a quick, easy, and painless test to perform. A series of electrodes, or ‘leads’, are placed on the patient’s chest. They are specifically positioned to capture the heart’s activity from multiple different angles. Those electrodes then transmit their signal to an ECG machine, which then creates a tracing for each electrode. The result is a paper print out of 12 different squiggly lines, each corresponding to a specific electrode. This essentially gives us a 360 degree view of the heartbeat.

Why do I need one? What does it test for?

For many people coming to the emergency room, an ECG is part of their initial triage assessment. This is certainly true for people with chest pain, but problems with the heart can cause a lot of different symptoms. It can help us evaluate people with dizziness, fatigue, weakness, trouble breathing, palpitations, nausea, etc. In short, it is an easy, fast, and inexpensive screening tool that quickly tells us if someone is having a medical emergency.

Here are just a few of the things that an ECG can help diagnose:

  • A heart attack
  • Fast heart rate, slow heart rate, or abnormal heartbeats
  • An enlarged heart, or heart failure
  • Problems with the heart valves
  • Electrolyte disturbances (particularly abnormal levels of potassium, calcium, or magnesium)
  • Fluid around the heart (‘pericardial effusion’), or inflammation of the lining of the heart (‘pericarditis)
  • Overdoses or abnormally high levels of certain drugs and medications
  • Lung problems (that’s right! The heart sometimes beats differently when there is a problem in the lungs)
  • If you are lying (okay, that one’s a joke)

What does it NOT test for?

 While the ECG can be a treasure chest of information, it does not give us the full picture of heart health. It can often pick up on the complications from heart disease, but cannot diagnose heart disease itself. For example, it will tell us if you are having  a heart attack, but it cannot diagnose coronary artery disease (blockages in the arteries that lead to heart attacks). It also can show changes that suggest the heart is enlarged, but cannot definitively diagnose congestive heart failure, cardiomyopathy (when the heart is not shaped right), or problems with the heart valves. Additional tests are needed to look for these problems, which often include:

  • An ultrasound of the heart, to actually look at its size, shape, and structure
  • A stress test or catheterization, to look for blockages in the coronary arteries
  • A CT scan or MRI can also be used to look at the shape of the heart and the coronary arteries, but this is less common

What does it mean if my EKG is abnormal?

Most people who come to the emergency department with chest pain are not having a heart attack. Thank goodness. That being said, most people don’t have a normal EKG either. It is common for an EKG to be abnormal, but that doesn’t necessarily mean it is abnormal for you. Every person’s heart and heartbeat are slightly different.

It is important to understand that the ECG machine is designed to generate a ‘read’ on every ECG. This interpretation iswhat gets imported into your patient chart and medical record. And while this computer-generated read is helpful, it is not the whole story. It is frequently inaccurate, and doesn’t replace the importance and value in your doctor interpreting your ECG to determine if an abnormality is real or has significance. So don’t panic when you see scary or confusing words like ‘old infarct’, ‘left ventricular hypertrophy’, ‘atrial enlargement’, or ‘ischemia’ (to name just a few). These computer-generated findings are often inaccurate, or normal for your heart.

Should I be worried if my EKG is abnormal?

In the emergency department, we take your ECG very seriously. Every single ECG is reviewed by a physician right after it is performed (even if you end up waiting much longer to see a physician). This is so we can immediately identify and treat any people with worrisome ECG findings.

If you have ECG results that require medical attention or further testing, your emergency physician will tell you. Depending on the abnormality, they may also:

  • Recommend you be hospitalized for further testing
  • Consult with an on-call cardiologist to discuss the results and the next steps
  • Run more tests in the emergency room
  • Recommend outpatient follow up with your doctor or a cardiologist in clinic

In other words, we will do the worrying and heavy lifting for you. If your physician doesn’t mention it, it probably means there is nothing serious or significantly abnormal. But you should never hesitate to bring up any questions or concerns you may have about your ECG. Doctors spend years learning expert ECG interpretation, and we certainly don’t expect you to know or find the answers on your own. In our technologically advanced world, there are still times when a human brain is better than a computer’s analysis, and an in-person answer is better than a search on the internet.