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Electrocardiogram (ECG) – Cardiac Diagnosis Explained

An electrocardiogram (ECG) is a diagnostic test that records the electrical activity of the heart. It helps doctors detect arrhythmias, heart attacks, and other cardiac conditions quickly and non-invasively.

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Things worth knowing about "Electrocardiogram"

An electrocardiogram (ECG) is a diagnostic test that records the electrical activity of the heart. It helps doctors detect arrhythmias, heart attacks, and other cardiac conditions quickly and non-invasively.

What Is an Electrocardiogram?

An electrocardiogram (ECG) is a medical diagnostic procedure that measures and graphically records the electrical signals produced by the heart. Every heartbeat is triggered by an electrical impulse that travels through the heart muscle. These impulses are detected by electrodes placed on the skin and displayed as a characteristic wave pattern. The ECG is one of the most widely used tools in cardiology and emergency medicine worldwide.

How Does an ECG Work?

During a standard ECG, adhesive electrodes are placed at specific locations on the body – typically on the arms, legs, and chest. These electrodes capture the electrical activity of the heart from multiple angles, known as leads. The recorded curve shows characteristic deflections labeled with letters:

P wave: Electrical activation of the atria
QRS complex: Electrical activation of the ventricles
T wave: Recovery (repolarization) of the ventricles

A standard 12-lead resting ECG takes only a few minutes and is completely painless. In addition to the resting ECG, other types include the stress ECG (performed during physical exercise) and the Holter ECG (worn continuously for 24 to 48 hours).

When Is an ECG Used?

An ECG is ordered for a wide range of clinical situations, including:

Suspected heart attack or unstable angina
Evaluation of cardiac arrhythmias (e.g., atrial fibrillation, atrial flutter, ventricular tachycardia)
Monitoring of known heart conditions such as heart failure or cardiomyopathy
Assessing the effects of cardiac medications
Pre-operative routine assessment
Investigation of symptoms such as chest pain, palpitations, dizziness, or fainting

What Can an ECG Detect?

An ECG provides essential information about:

Heart rate and heart rhythm
The electrical axis of the heart
Signs of reduced blood flow to the heart muscle (ischemia, infarction patterns)
Enlargement of the heart chambers or atria
Conduction abnormalities such as bundle branch blocks or AV blocks
Electrolyte imbalances affecting cardiac function (e.g., low potassium or calcium levels)

Types of ECG

Resting ECG

The resting ECG is the standard form of the test, performed while the patient lies still. It takes only a few minutes and is the most commonly used form of cardiac recording.

Stress ECG

During a stress ECG (exercise ECG or ergometry), the heart is monitored under controlled physical exertion – typically on a stationary bicycle or treadmill. This can reveal blood flow abnormalities that are not apparent at rest.

Holter ECG (Long-Term ECG)

The Holter ECG records heart activity continuously over 24 to 48 hours or longer. It is particularly useful for detecting intermittent arrhythmias that may not be captured during a brief office visit.

Event ECG

An event ECG is triggered by the patient when symptoms occur, allowing for targeted recording of palpitations or irregular heartbeats during daily activities.

How Is an ECG Interpreted?

ECG interpretation is performed by a physician, typically a cardiologist or internist. Modern ECG devices can generate automated computer-assisted pre-interpretations, but these must always be reviewed and confirmed by a qualified doctor. The evaluation includes assessing the regularity of the heart rhythm, the duration and shape of individual waveform segments, and any ST-segment changes that may indicate myocardial injury or ischemia.

Risks and Limitations

The ECG is a risk-free, non-invasive procedure with no radiation exposure. However, a normal resting ECG does not completely rule out heart disease – some abnormalities are only detectable under stress or over extended periods. Motion artifacts or incorrectly placed electrodes can also affect the quality of the recording.

References

Thaler, M. S. – The Only EKG Book You'll Ever Need, 9th Edition, Wolters Kluwer, 2019.
European Society of Cardiology (ESC) – Guidelines for the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death, 2022. Available at: https://www.escardio.org
World Health Organization (WHO) – Cardiovascular Diseases: Diagnosis and Management. Available at: https://www.who.int/health-topics/cardiovascular-diseases

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