Killer Differentials
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Tall R wave in V1 DDx
Key Points Normal expectation: In V1, the S wave is typically larger than the R wave. A tall or dominant R wave (R/S > 1) is abnormal and should prompt…
Wide & Regular Tachydysrhythmia DDx
Key Points Definition: Wide complex tachycardia (WCT) = QRS >120 ms with a steady R-R interval. This section focuses on regular WCT (RWCT). Wide & irregular rhythms are covered separately…
ST Elevation in aVR DDx
Key Points Global Subendocardial Ischemia: ST elevation (STE) in aVR with diffuse ST depression elsewhere usually reflects global subendocardial ischemia. Proximal Occlusion or Severe CAD: Common in left main (LMCA)…
ST Elevation DDx
Key Points Definition: ST elevation refers to upward displacement of the ST segment above baseline, often signaling acute myocardial injury. Clinical Importance: While most concerning for ST-Elevation Myocardial Infarction (STEMI)…
Diffuse ST Elevation DDx
Key Points ST-Segment Elevation (STE): It’s crucial to recognize that several conditions beyond STEMI can cause ST-segment elevation (STE) on an ECG. Identifying these differentials is vital to avoid misdiagnosis…
Wide QRS Complex DDx
Key Points A QRS duration greater than 120 ms indicates abnormal ventricular depolarization. A wide QRS can signal conditions that range from benign to immediately life-threatening. Developing a focused differential…
Clumped or Grouped Beats DDx
Key Points Clumped or grouped beats can cause irregular rhythms, often leading to misdiagnosis as atrial fibrillation. Misdiagnosing atrial fibrillation may lead to inappropriate rate/rhythm control or unnecessary anticoagulation in…
Narrow QRS Bradycardia DDx
Key Point Narrow QRS bradycardias are often related to vagal tone or reversible causes, but not always benign. Certain AV blocks and conduction abnormalities may still carry significant risk, even…
Must-Know Differential Diagnoses (DDx)
Key Points Definition: A differential diagnosis is the structured process of considering multiple possible conditions that could explain a patient’s symptoms and ECG findings. Purpose: The goal is to narrow…
Wide & Irregular Tachycardia DDx
Key Points Definition: QRS >120 ms with an irregular ventricular rate. Clinical Priority: Always first consider AF with accessory pathway (AF + WPW) and polymorphic VT (PMVT, including torsades) —…
Narrow & Irregular Tachycardia DDx
Key Points Narrow irregular tachycardia = QRS <120 ms with variable R–R interval. The big three DDx: Atrial fibrillation (AF) with RVR, atrial flutter with variable block, multifocal atrial tachycardia…
Narrow & Regular Tachycardia DDx
Key Points Narrow regular tachycardia = QRS <120 ms with a steady R–R interval. The big three DDx: sinus tachycardia, SVT (AVNRT/AVRT/junctional), and atrial flutter with fixed AV conduction (commonly…
Ventricular Tachycardia (VT) Mimics
Key Points Initial Assumption: Any wide (QRS >120 ms), regular tachycardia should be considered ventricular tachycardia (VT) until clearly proven otherwise. VT Characteristics: VT generally has a ventricular rate of…
Syncope DDx
Key Points Syncope and the ECG: Syncope is a transient loss of consciousness and postural tone, characterized by rapid onset, brief duration, and spontaneous recovery without medical intervention. Cardiac syncope…
Right Axis Deviation + STE DDx
Key Points RAD combined with ST-segment elevation (STE) is an uncommon but high-risk finding. While STE often suggests acute coronary occlusion, this pattern rarely reflects classic STEMI. Several non-ischemic conditions…
Extreme Axis Deviation DDx
Key Points Definition: Extreme axis deviation is present when the QRS axis lies between –90° and ±180°. This is sometimes referred to as the “northwest axis.” ECG Pattern: QRS is…
Left Axis Deviation DDx
Key Points Definition: Left axis deviation (LAD) is defined as a QRS axis between –30° and –90°. ECG Clue: QRS complex is positive in Lead I and negative in Lead…
Right Axis Deviation DDx
Top 3 Emergent Causes of New Rightward Axis Deviation: When you encounter new right axis deviation on an ECG, immediately consider the following life-threatening conditions: Acute Right Heart Strain or…
Cerebral T Waves
Key Points Definition: Cerebral T waves, sometimes called “roller coaster T waves”, are dramatic ECG abnormalities linked to acute brain pathology. They are characterized by deep, symmetric T wave inversions…
Not Enough P Waves (P:QRS < 1) DDx
Key Points Fewer P waves than QRS complexes: This means impulses are originating from below the atria (junctional, ventricular, or paced), or from ectopy interrupting sinus rhythm. Clinical relevance: In…
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