ELECTROCARDIOGRAPHY

✓ Medically ReviewedINVESTIGATIONID: MDBT0296🚨 TRIAGE: EMERGENCYICD-10: R94.31

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Definition

CLINICAL DEFINITION

Electrocardiography is the graphical recording of electrical potential differences generated by cardiac depolarization and repolarization, detected at prescribed sites on the body surface. The standard resting 12-lead electrocardiogram records these potentials from 10 electrodes, producing 12 leads that view the heart from different planar orientations. It is the most commonly performed cardiovascular diagnostic procedure and is essential for the diagnosis and management of acute coronary syndromes, arrhythmias, and intraventricular conduction disturbances.

IN PLAIN ENGLISH

Electrocardiography is a painless test that records the heart's electrical activity. It produces a tracing called an electrocardiogram, which doctors use to check the heart's rhythm and look for signs of heart attack, abnormal rhythms, or other heart problems.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Electrocardiography is NOT a test of cardiac structure or mechanical function; it records electrical activity only. It does not directly measure ejection fraction, valve function, or myocardial wall motion. A normal ECG does not exclude structural heart disease, and an abnormal ECG does not always indicate a cardiac cause.

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Word Breakdown

electro-

=electricity (from Greek 'ēlektron', amber; associated with electrical phenomena)

-graphy

=process of recording (from Greek 'graphein', to write)

Literal Meaning: The process of recording electrical activity

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Abbreviations

ECG=Electrocardiogram — the graphical record produced by electrocardiography; the most commonly used abbreviation in clinical practice.

EKG=Electrocardiogram — alternative abbreviation derived from the German spelling 'Elektrokardiogramm'; used interchangeably with ECG.

12-lead ECG=Standard 12-lead electrocardiogram — the routine resting ECG comprising 3 bipolar limb leads, 3 augmented unipolar limb leads, and 6 precordial leads.

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Synonyms & Variants

Electrocardiogram›ECG›EKG›

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Category-Specific Context

Electrocardiography is classified as an Investigation because it is a diagnostic procedure used to gather physiological data, not a therapeutic intervention. Within cardiology, it sits alongside other diagnostic modalities such as echocardiography and cardiac biomarkers, but uniquely provides a real-time electrical map of the heart. Its results are described in a standardised diagnostic statement list to promote uniformity of interpretation.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentCardiology Outpatient ClinicGeneral Medicine WardCritical Care UnitPreoperative Assessment ClinicAmbulatory Monitoring Service

USAGE & DOCUMENTATION NOTES

In clinical documentation, electrocardiography is commonly recorded as '12-lead ECG' or simply 'ECG'. Reports typically begin with the rate, rhythm, and axis, followed by intervals, chamber enlargement, and ST-T changes. In emergency notes, the time of ECG acquisition relative to symptom onset is often stated. Serial ECGs are documented with timestamps to demonstrate dynamic change.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Electrocardiography detects the extracellular potential differences generated by myocardial cells during depolarization and repolarization. When cardiac muscle cells depolarize, sodium ions enter the cell, creating an electrical dipole that spreads through the myocardium. The body surface electrodes detect the sum of these dipoles from different orientations, producing the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization). The timing and morphology of these waveforms reflect the sequence and speed of electrical conduction through the atria, atrioventricular node, His-Purkinje system, and ventricles. Abnormalities in electrolyte concentrations, myocardial ischaemia, or conduction tissue disease alter these potentials and produce characteristic ECG patterns.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

ST-segment elevation meeting guideline criteria in a patient with ongoing chest pain — consider acute coronary occlusion and activate the reperfusion pathway according to local protocol; ECG findings alone do not confirm occlusion but mandate urgent clinical assessment.
New wide-complex tachycardia in a haemodynamically unstable patient — treat as ventricular tachycardia until proven otherwise and proceed to urgent electrical or pharmacological cardioversion per resuscitation guidelines.

URGENT EVALUATION TRIGGERS

Chest pain with ST-segment elevation or new left bundle branch block on ECG
Syncope with an abnormal ECG (e.g., high-grade AV block, ventricular tachyarrhythmia, pre-excitation)
Palpitations with haemodynamic compromise or a wide-complex tachycardia on ECG
Suspected drug overdose with QT prolongation or conduction disturbance on ECG

Contraindications & Precautions

SPECIAL PRECAUTIONS

Ensure electrodes are placed on intact
clean
dry skin; avoid wounded or inflamed areas to reduce skin irritation and poor signal quality.
In patients with known adhesive or electrode allergies
use hypoallergenic electrodes and monitor for skin reactions.
Remove ECG electrodes carefully
particularly in neonates and patients with fragile skin
to avoid skin erosion.

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Reference Ranges

NORMAL RANGEPR interval 120–200 ms; QRS duration <120 ms; QT interval rate-dependent (QTc <440 ms in men, <460 ms in women, though thresholds vary by population and guideline).

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Echocardiography

Both are cardiac investigations with similar abbreviations; echocardiography assesses structure and function using ultrasound, whereas electrocardiography records electrical activity.

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Clinical Pearls

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Read every ECG systematically (rate, rhythm, axis, intervals, hypertrophy, ischaemia/infarction) rather than focusing on a single striking feature; optical-illusion-like perceptual traps can cause serious misdiagnosis.

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Artifact from motion, tremor, poor electrode contact, or electrical interference can mimic arrhythmia or ischaemia; if a finding is unexpected, check lead placement and repeat the tracing before acting on it.

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A normal initial ECG does not exclude acute coronary syndrome; serial ECGs and cardiac troponin measurement are required when clinical suspicion persists.

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Lead reversal (e.g., arm-leg reversal) can produce dramatic but recognisable patterns; a negative P wave in lead I with an abnormal QRS axis should prompt verification of limb lead placement.

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Example Usage & SOAP

CLINICAL SENTENCE

"A 12-lead ECG was obtained within 10 minutes of arrival and showed sinus rhythm at 78 bpm with 1 mm ST-segment elevation in leads V2–V4."

IN A SOAP NOTE

S: 58-year-old man with 45 minutes of central chest pain radiating to the left arm. O: BP 145/90 mmHg, HR 92 bpm, SpO2 96% on room air. 12-lead ECG: sinus tachycardia, 2 mm ST-segment elevation in leads II, III, and aVF. A: Suspected inferior ST-elevation myocardial infarction. P: Activate cath lab, aspirin 300 mg chewed, prepare for primary percutaneous coronary intervention.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for an ECG showing ST-segment elevation: (1) acute myocardial infarction — convex ST elevation with reciprocal depression, correlated with troponin and symptoms; (2) pericarditis — widespread concave ST elevation with PR depression; (3) early repolarization — concave ST elevation with J-point notching, stable over time; (4) left ventricular aneurysm — persistent ST elevation after prior infarction; (5) Brugada pattern — coved ST elevation in V1–V2 with negative T wave, unrelated to ischaemia.

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References & Coding

ICD-10 DIAGNOSTIC CODE

R94.31

LITERATURE CITATIONS & GUIDELINES

[1]Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram: part I: the electrocardiogram and its technology: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation. 2007;115(10):1306–1324.

[2]Kadish AH, Buxton AE, Kennedy HL, et al. ACC/AHA clinical competence statement on electrocardiography and ambulatory electrocardiography: a report of the ACC/AHA/ACP-ASIM Task Force on Clinical Competence (ACC/AHA Committee to Develop a Clinical Competence Statement on Electrocardiography and Ambulatory Electrocardiography). Circulation. 2001;104(25):3169–3178.

[3]Shen WK, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2017;70(5):e39–e110.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.