An electrocardiogram, called an ECG or EKG, records the electrical signals that make your heart beat. Small sticky electrodes on your chest, arms and legs pick up those signals, and the machine prints them as a set of waves. The recording itself takes about ten seconds, and the whole test, from placing the electrodes to removing them, takes only a few minutes. It is painless, uses no radiation, and sends no electricity into your body.
At NYMD Center we perform ECGs in the office, often at the same visit where a question about the heart first comes up. That means a patient with palpitations, chest discomfort or dizziness, or someone who needs clearance before surgery, can usually have the tracing done and reviewed with the physician before leaving.
An ECG is one of the most useful first steps in heart care, but it is a snapshot. Knowing what it can and cannot show helps explain why your physician may order it, and why a normal result sometimes leads to further testing.
What an ECG shows and who needs one
A resting ECG shows your heart rate and rhythm, including irregular rhythms such as atrial fibrillation or atrial flutter, extra beats, and very fast or very slow rates. It shows how the electrical signal travels through the heart, so it can reveal conduction delays and heart block. It can show signs of a heart attack happening now or one in the past, and it can give clues to thickening or strain of the heart muscle, often related to long-standing high blood pressure or valve disease. The Mayo Clinic describes these same uses.
It also has clear limits. An ECG taken at rest usually cannot show whether coronary arteries are narrowed, because narrowing often causes changes only when the heart is working hard. It also cannot catch a rhythm problem that comes and goes and happens not to be present during those few seconds. For symptoms that appear with exertion, an exercise or stress test is more informative. For palpitations or dizzy spells that come and go, an ambulatory ECG monitor worn for days or longer is the better tool. And as MedlinePlus notes, ECG results do not diagnose a condition on their own; they are interpreted together with your history, exam and other tests.
We commonly order an ECG for:
- Symptoms such as palpitations, chest pain, dizziness, fainting or shortness of breath.
- Pre-operative clearance, when your age, health or the planned surgery calls for it.
- Starting or adjusting medications that can affect heart rhythm, including drugs that prolong the QT interval.
- Follow-up of known heart conditions, high blood pressure or the effect of heart treatment.
- A baseline tracing during an annual exam when your risk profile makes it useful.
An ECG is not a routine screening test for everyone. The U.S. Preventive Services Task Force recommends against screening with resting or exercise ECG in adults who have no symptoms and are at low risk of cardiovascular disease, because an abnormal-looking tracing in a low-risk person more often leads to further testing than to a real benefit. For adults without symptoms at intermediate or high risk, the Task Force found the evidence insufficient to recommend for or against. We decide case by case, based on your symptoms, risk factors and medications.
How the test works
You lie on an exam table with your chest, wrists and ankles exposed. A standard 12-lead ECG uses electrodes on the chest and limbs connected by wires to the machine. Occasionally a small patch of chest hair is trimmed so the electrodes stick well. You lie still and breathe normally for a few seconds while the tracing is recorded. The electrodes peel off afterward; some people notice mild skin irritation where they were placed, but there is essentially no other risk.
How to prepare
No real preparation is needed. Avoid oily skin creams and lotions on your chest, arms and legs on the day of the test, since they keep the electrodes from sticking, and wear a top that is easy to remove. Full-length hosiery can get in the way of the ankle electrodes. Bring a list of your medications and supplements, because some affect the tracing, and bring any previous ECGs if you have them. Comparison with an older tracing is often as valuable as the new one.
What results mean
Your physician reviews the tracing and explains it with you. A normal ECG is reassuring for rhythm and conduction at that moment, but it does not rule out coronary artery disease or an intermittent arrhythmia, so persistent symptoms still deserve follow-up. Common findings that lead to a next step include atrial fibrillation, extra beats, a slow rhythm or conduction block, signs of an old heart attack, a prolonged QT interval, or a pattern suggesting a thickened heart muscle. Depending on the finding, we may adjust medications, order an echocardiogram to look at the heart's structure, arrange a stress test or ambulatory monitor, or coordinate with cardiology.
What to expect at your visit
Most ECGs at NYMD Center are done as part of a broader visit: a history of your symptoms and risk factors, a physical examination, blood pressure measurement, and blood work when needed. The ECG itself adds only a few minutes. We review the result with you, and if anything needs further testing, we explain why and schedule it.
When to seek care urgently
Do not wait for an office ECG if you have chest pain or pressure that is severe, lasts more than a few minutes, or comes with shortness of breath, sweating, nausea, or pain spreading to the arm, jaw, neck or back. Call 911. The same applies to fainting, or a racing or very slow heartbeat with lightheadedness or chest discomfort. Emergency crews can perform an ECG on the way to the hospital.
Questions patients ask
How long does an ECG take?
The recording itself takes about ten seconds. With placing and removing the electrodes, the whole test takes only a few minutes. At NYMD Center it is usually done during your office visit, so the result can be reviewed with your physician before you leave. There is no recovery time, and you can return to normal activities immediately.
Can an ECG detect a blocked artery?
Usually not at rest. A resting ECG can show signs of a current or past heart attack, but narrowed arteries often cause no changes until the heart works harder. That is why an exercise stress test, sometimes with imaging, is used to look for reduced blood flow during exertion. A normal resting ECG does not rule out coronary artery disease.
My ECG was normal but I still have palpitations. Why?
A standard ECG records only a few seconds of heart activity. If an irregular rhythm comes and goes, it may simply not have been present during the test. An ambulatory ECG monitor, such as a Holter or patch monitor worn at home for a day or longer, is designed to catch those episodes and link them to your symptoms.
Should everyone get a routine ECG?
No. The U.S. Preventive Services Task Force recommends against screening ECGs in adults without symptoms who are at low risk of heart disease, because the results rarely change care and can lead to unnecessary testing. We order an ECG when you have symptoms, before certain surgeries, when medications could affect heart rhythm, or when your risk profile makes a baseline useful.
How should I prepare for an ECG?
Very little preparation is needed. Avoid oily lotions or creams on your chest, arms and legs that day so the electrodes stick, and wear a top that is easy to remove. Bring a list of your medications and supplements, and any earlier ECGs, since comparing tracings over time is often very helpful.