ECG Differential Diagnosis

Sun, 21 Dec 2025 00:00:00 +0000

Lists of differential diagnoses of specific ECG findings based on from ECGs for the Emergency Physician 1 and ECGs for the Emergency Physician 2

Atrial fibrillation with slow ventricular response

Severe AV nodal disease
Hypothermia
Medications: Digoxin toxicity, Calcium-channel blocker / beta-blocker toxicity

Tachydysrhythmias

Narrow-complex regular rhythm:

Narrow-complex irregular rhythm:

Wide-complex regular rhythm:

Ventricular tachycardia
Sinus tachycardia with aberrant conduction
SVT with aberrant conduction
Atrial flutter with aberrant conduction

Wide-complex irregular rhythm:

Atrial fibrillation with aberrant conduction (for example bundle branch block)
Atrial flutter with variable block and aberrant conduction
Multifocal atrial tachycardia with aberrant conduction
Atrial fibrillation with WPW
Polymorphic ventricular tachycardia / Torsades de Pointes

Leftward axis

Low voltage

Myxoedema
Large pericardial effusion
Large pleural effusion
End-stage dilated cardiomyopathy
Severe chronic obstructive pulmonary disease
Severe obesity
Infiltrative myocardial diseases (i.e. restrictive cardiomyopathy)
Constrictive pericarditis
Prior massive MI
Low gain settings on ECG machine

Increased QRS Duration

Hypothermia
Hyperkalaemia
WPW
Aberrant intraventricular conduction (for example bundle branch block)
Ventricular ectopy
Paced beats
Drugs, particularly those with sodium-channel blocking effects

Increased QT-interval (and QTc-interval)

*Hypokalemia — the actual QT-interval is normal; the QT-interval appears prolonged because of the presence of fusion of the T-wave with a U-wave (a “T-U fusion complex”)

Atrial Fibrillation on ECG Library – LITFL Basics