Electrocardiogram
Also known as: electrocardiogram, 12-lead ECG, heart tracing
Ten sticky electrodes on the chest and limbs record the heart's electrical activity from twelve angles over ten seconds. The tracing shows rhythm, rate, the direction of electrical spread and signs of muscle strain, damage or blocked blood supply.
- Canonical name
- Electrocardiogram
- Abbreviations
- ECG, EKG
- Kind
- Physiological or functional test
- Categories
- Cardiovascular
- Specimen
- No specimen
- Method
- Electrophysiological recording
- Terminology
- LOINC 11524-6
- Type
- Cardiac recording
- Sample
- No sample; ten electrodes on the chest and limbs
- Used for
- Chest pain, palpitations, blackouts, rhythm problems, screening
- Measures
- The heart's electrical rhythm and conduction from twelve angles over ten seconds
- Result
- A tracing read for rate, rhythm, intervals and waveform changes, with an automated interpretation checked by a clinician
Why is it used?
- Chest pain (within 10 minutes of arrival)
- Palpitations, blackouts, breathlessness
- Screening before surgery or in athletes
- Electrolyte problems and drug monitoring
- Suspected pulmonary embolism, pericarditis, heart failure
What does it measure?
| Component | What it measures | A higher value may be seen in | A lower value may be seen in |
|---|---|---|---|
| Rate and rhythm | How fast and how regularly the heart beats | Sinus tachycardia, atrial fibrillation or flutter, supraventricular and ventricular tachycardias | Sinus bradycardia, heart block, sick sinus syndrome |
| P wave and PR interval PR | Atrial activation and conduction through the AV node | Long PR: first-degree heart block | Short PR: pre-excitation (Wolff–Parkinson–White) |
| QRS complex QRS | Ventricular activation | Wide QRS: bundle branch block, ventricular rhythms, high potassium; tall complexes: hypertrophy; Q waves: old infarction | Small complexes: obesity, pericardial fluid, lung disease |
| ST segment and T wave ST/T | Ventricular recovery; the part most changed by ischaemia | ST elevation: acute infarction (STEMI) or pericarditis; tall T waves: high potassium | ST depression and T inversion: ischaemia, strain, digoxin, low potassium |
| QT interval QTc | Total time for ventricular activation and recovery, corrected for heart rate | Long QT: inherited syndromes, many medicines, low potassium, magnesium or calcium; risk of dangerous rhythms | Short QT: rare inherited syndromes, high calcium |
A high or low value can be associated with several different situations; the result is interpreted with other results, symptoms, history and clinical findings.
How is it performed?
Lie still for a minute while the machine prints; painless, no electricity goes into the body.
Specimen. None: a recording of the heart's electrical activity from skin electrodes
Do I need to prepare?
None; chest hair may be shaved for contact.
What do the results generally mean?
| Finding | What it may indicate |
|---|---|
| ST elevation in two adjacent leads | STEMI: an artery is blocked, needs emergency angioplasty |
| Irregularly irregular rhythm, no P waves | Atrial fibrillation |
| Tall peaked T waves | High potassium, needs immediate treatment |
| Normal ECG | Reassuring but does not exclude a heart attack or intermittent rhythm problems |
What can affect the result?
- Electrode placement, movement, shivering and electrical interference
- Body shape, lung disease and pericardial fluid change voltages
- Electrolyte levels (potassium, calcium, magnesium) and many medicines
- Heart rate, which changes the corrected QT
- Timing: a tracing between episodes of an intermittent arrhythmia is often normal
Medicines. Many medicines prolong the QT interval (some antibiotics including macrolides, antipsychotics, antidepressants, antiemetics); digoxin, beta blockers and calcium channel blockers slow conduction; sodium channel blockers widen the QRS.
What can the test not tell you?
- Whether a heart attack has occurred when the first tracing is normal (a third of infarctions are); serial ECGs and troponin are needed
- How well the heart pumps or whether the valves work (echocardiography)
- Whether the coronary arteries are narrowed when the person is at rest (stress testing or angiography)
- Intermittent rhythm problems that were not happening during the ten seconds recorded
A ten-second snapshot: intermittent arrhythmias need longer monitoring, and a third of heart attacks have a normal first ECG.
Other tests commonly used with it
Medicines monitored with this test
Each medicine page cites the official document that names this test in its monitoring plan.
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.