An electrocardiogram (ECG) is one of the most important and commonly used tests in cardiology. It records the electrical activity of the heart and provides essential information about heart rhythm, heart rate, and how electrical signals travel through the heart muscle.
The ECG is quick, painless, non-invasive, and often the first test performed when someone presents with chest pain, palpitations, shortness of breath, dizziness, or fainting.
What Does an ECG Show?
Every heartbeat begins with an electrical signal. The ECG captures these signals as they travel through the heart and displays them as a tracing on paper or a screen.
From an ECG, doctors can evaluate:
- Heart rate and rhythm
- Whether the rhythm is regular or irregular
- Signs of abnormal electrical pathways
- Evidence of heart muscle strain or damage
- Conduction delays or blocks
- Patterns suggesting inherited or acquired heart conditions
Although the ECG records electrical activity—not heart structure—it can strongly suggest when something is wrong and guide further testing or treatment.
Why Is an ECG Performed?
An ECG may be performed for many reasons, including:
- Palpitations or a racing heartbeat
- Chest pain or pressure
- Shortness of breath or reduced exercise tolerance
- Dizziness, lightheadedness, or fainting
- Suspected heart rhythm disorders
- Evaluation before procedures or surgery
- Monitoring known heart disease or medication effects
In emergency situations, the ECG is often critical for rapid diagnosis and decision-making.
How Is an ECG Performed?
During a standard ECG, small adhesive electrodes are placed on the chest, arms, and legs. These electrodes detect the heart’s electrical signals.
The test usually takes only a few minutes. You are asked to lie still and breathe normally while the recording is made. There is no electrical shock and no discomfort.
The most common form is the 12-lead ECG, which provides views of the heart’s electrical activity from multiple angles, allowing a comprehensive assessment.
What Will I Feel During an ECG?
You will not feel the electrical activity being recorded. The test is painless. The only sensation may be the removal of adhesive electrodes afterward, similar to removing a bandage.
What Can an ECG Diagnose?
An ECG can identify or strongly suggest many heart conditions, including:
Arrhythmias
ECG is essential for diagnosing arrhythmias such as atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia, bradycardia, and premature beats.
Heart Attacks and Ischemia
ECG changes can indicate an ongoing or previous heart attack and help identify reduced blood flow to the heart muscle.
Conduction Disorders
ECG can detect heart blocks and delays in electrical conduction that may require monitoring or treatment.
Structural and Inherited Conditions
Certain ECG patterns may suggest conditions such as hypertrophic cardiomyopathy, Brugada syndrome, long QT syndrome, or electrolyte abnormalities.
What an ECG Cannot Show
While extremely powerful, an ECG has limitations. It does not directly show:
- Heart valve function
- Pumping strength of the heart
- Coronary artery blockages unless they cause electrical changes
Because heart rhythm problems can be intermittent, a normal ECG does not always rule out a heart condition. In such cases, longer monitoring or additional tests may be needed.
Different Types of ECG Testing
Because heart rhythm problems may occur only occasionally, a single ECG snapshot is not always enough. For this reason, several types of ECG-based monitoring are used to record the heart’s electrical activity over longer periods or under specific conditions.
Standard 12-Lead Electrocardiogram (ECG)
The standard ECG records the heart’s electrical activity over a few seconds while the patient is resting. It is most useful when symptoms are present at the time of the test or when evaluating ongoing conditions such as atrial fibrillation, heart attack, or conduction abnormalities.
Because it captures only a brief moment in time, a normal ECG does not rule out rhythm problems that occur intermittently.
Continuous In-Hospital ECG Monitoring (Telemetry)
Continuous ECG monitoring, often called telemetry, is used in hospitalized patients. Electrodes remain attached to the chest, allowing the heart rhythm to be monitored continuously over hours or days.
This type of monitoring is especially useful after procedures, during medication adjustments, or when symptoms such as palpitations or fainting are frequent and unpredictable.
Holter Monitor
A Holter monitor is a portable ECG device worn continuously, usually for 24 to 48 hours. It records every heartbeat during normal daily activities and sleep.
Holter monitoring is helpful when symptoms occur daily or every few days. Patients are typically asked to keep a symptom diary to correlate symptoms with recorded heart rhythms.
Extended Event Monitor
Event monitors are wearable ECG devices used for longer periods, often from one week up to several weeks. Unlike a Holter monitor, these devices may record continuously or be triggered automatically or manually when symptoms occur.
They are particularly useful when symptoms are less frequent and may not appear during a short monitoring period.
Patch-Based ECG Monitors
Patch monitors are small, adhesive ECG devices placed on the chest and worn continuously for up to one or two weeks. They are lightweight, water-resistant, and generally more comfortable than traditional monitors.
These devices are well suited for detecting intermittent arrhythmias while allowing patients to maintain normal daily routines.
Implantable Loop Recorder (Insertable Cardiac Monitor)
An implantable loop recorder is a very small ECG device placed just under the skin of the chest during a minor procedure. It can monitor heart rhythms continuously for months to years.
This type of monitoring is used when symptoms such as unexplained fainting or rare palpitations occur infrequently and have not been captured by external monitors.
ECG Monitoring During Stress Testing
In some cases, ECG recording is combined with physical exercise or medication that simulates exercise. This allows doctors to observe how the heart’s electrical system responds to increased workload.
Stress ECG testing is commonly used to evaluate exercise-related symptoms or suspected coronary artery disease.
Choosing the Right Type of ECG Monitoring
The choice of ECG test depends on how often symptoms occur, how severe they are, and what information is needed. Short-term tests are useful for frequent symptoms, while long-term monitoring is essential for rare or unexplained events.
Your doctor selects the most appropriate method to maximize the chance of capturing the abnormal rhythm.
ECG in Daily Clinical Practice
The ECG is used not only to diagnose disease but also to:
- Monitor response to medications
- Guide emergency treatment decisions
- Assess safety before procedures
- Track progression of known heart conditions
Because it is fast and widely available, the ECG plays a central role in both outpatient and emergency care.
Is an ECG Safe?
Yes. ECG testing is completely safe. It does not expose you to radiation and does not send electricity into your body. It simply records the heart’s natural electrical signals.
In Summary
An electrocardiogram (ECG) is a fundamental heart test that records the electrical activity of the heart. It is quick, painless, and provides critical information about heart rhythm, rate, and electrical conduction. While it does not replace imaging or longer-term monitoring, the ECG is often the first and most important step in evaluating heart symptoms and guiding further care.
Reference: Electrocardiogram
