Killer Differentials
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Must-Know 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…
Acute Chest Pain: DDx
Key Points In patients presenting with acute chest pain, identifying life-threatening conditions is essential. Use a systematic ECG approach alongside clinical context to evaluate for high-risk diagnoses that require immediate…
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…
Tall R wave in aVR: DDx
Key Points Normal expectation: In aVR, the QRS is usually negative (deep S wave). A dominant or tall R wave (R > S) is abnormal and should prompt investigation. Mechanism:…
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…
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…
VT vs SVT with Aberrancy: DDx
Key Points ECG alone cannot reliably distinguish VT from SVT-aberrancy in many cases. Use ECG features to rule in VT, not to exclude it. Default: treat regular WCT as VT…
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…
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…
Right Axis Deviation + ST Elevation: 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…
Indeterminate Axis: DDx
Key Points An indeterminate axis, sometimes referred to as an “extreme” or “undetermined” axis, is suspected when the QRS complexes are isoelectric or nearly biphasic in both Lead I and…
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 see new RAD in an adult, immediately consider life-threatening etiologies: Acute Right Heart Strain Pulmonary embolism until proven otherwise…
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…
No Clear P Waves: DDx
Key Points Absence of Sinus Rhythm: The lack of clear P waves before the QRS complexes suggests loss or dysfunction of sinus activity. Potential Causes: This pattern can result from…
Left Bundle Branch Block (LBBB): DDx
Key Point Overview: Left bundle branch block (LBBB) is an intraventricular conduction delay that results from a block in the left bundle branch of the heart’s electrical conduction system. It…
T Wave Inversion DDx
Key Points: Ischemia Isn’t Everything: While T wave inversions often raise concern for ischemia, many non-ischemic processes (e.g., pulmonary pathology, neurologic conditions, repolarization variants) can produce similar findings. Clinical Correlation:…
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