ECG Differential Diagnosis

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:

• Sinus tachycardia
• Supraventricular tachycardia
• Atrial flutter

Narrow-complex irregular rhythm:

• Atrial fibrillation
• Atrial flutter with variable block
• Multifocal atrial tachycardia

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

• Left anterior fascicular block
• Left bundle branch block
• Inferior myocardial infarction
• Left ventricular hypertrophy
• Ventricular ectopy
• Paced beats
• Wolff-Parkinson-White syndrome

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)

• Hypokalaemia*
• Hypomagnesaemia
• Hypocalcaemia
• Myocardial ischemia
• Elevated intracranial pressure
• Sodium-channel blockers
• Hypothermia
• Congenital prolonged QT syndrome

*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”)

Poor R-wave progression (PRWP)

• Prior anteroseptal MI
• LVH
• Abnormally high placement of the mid-precordial electrodes
• Normal variant

Prominent R-wave in lead V1 (R/S ratio >1)

• WPW
• Posterior MI
• RBBB (or incomplete RBBB)
• Ventricular ectopy
• RVH
• Acute right ventricular dilatation (right ventricular “strain,” e.g. massive PE)
• Hypertrophic cardiomyopathy
• Progressive muscular dystrophy
• Dextrocardia
• Misplaced precordial electrodes
• Paediatric ECG
• Normal variant (rare)

Prominent T-wave

• Acute myocardial ischemia (i.e. hyperacute STEMI)
• Hyperkalaemia
• Acute pericarditis
• LVH
• Benign early repolarization
• Bundle branch block (LBBB / RBBB)
• Preexcitation syndromes

Rightward axis

• Left posterior fascicular block (LPFB)
• Lateral myocardial infarction
• Right ventricular hypertrophy (RVH)
• Acute lung disease (e.g. Pulmonary Embolus)
• Chronic lung disease (e.g. COPD)
• Ventricular ectopy
• Hyperkalaemia
• Sodium-channel blocker toxicity
• Normal in children or thin adults with a horizontally positioned heart

ST-segment elevation

Important causes of ST elevation

• Acute myocardial infarction (AMI)
• Coronary vasospasm (Printzmetal’s angina)
• Pericarditis and myocarditis
• Benign early repolarisation (BER)
• Left bundle branch block (LBBB)
• Left ventricular hypertrophy (LVH)
• Ventricular aneurysm
• Brugada syndrome
• Ventricular paced rhythm
• Raised intracranial pressure (ICP)

ST segment elevation in V1

• Left Ventricular Hypertrophy (LVH)
• Left Bundle Branch Block (LBBB)
• Anteroseptal MI
• Right ventricular MI
• Brugada syndrome
• Pulmonary embolism (PE, PTE)

Diffuse ST-segment elevation

• Extensive myocardial infarction
• Acute pericarditis
• Benign early repolarization (BER)
• Ventricular aneurysm
• Coronary vasospasm

Advanced Reading

Further reading

• Wiesbauer F. Atrial Fibrillation Management Essentials. Medmastery

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.
• Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest