Killer Differentials
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Short QT Interval: DDx
Key Points: Short QT Interval: A QT interval is considered short when the corrected QT (QTc) interval is less than 350 ms. A short QT interval on the ECG can…
Prolonged QT Interval: DDx
Key Points: The QT interval reflects the time it takes for total ventricular depolarization and repolarization (Q wave onset to T wave end). QT prolongation increases the risk of torsades…
ST Depression in V1-V4: DDx
Key Points: Do not reflexively label ST depression in V1–V4 as “anterior ischemia/NSTEMI.” In ACS symptoms, posterior OMI is a major concern when the depression is most prominent in V1–V3…
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 STEMI due to acute…
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…
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…
Large T Wave: DDx
Key Points Large T waves are not a single diagnosis. Clinical context and associated ECG findings determine whether the cause is benign, metabolic, or a high-risk OMI pattern. The most…
STEMI Mimics: DDx
Key Points Context Matters: ECGs must be interpreted in the clinical setting. Chest pain, shock, or ACS risk factors increase pretest probability of STEMI/OMI, while atypical presentations lower it. Prevalence:…
Poor R Wave Progression (PRWP): DDx
Key Points PRWP is a pattern, not a diagnosis. Use clinical context and compare with prior ECGs before acting. Practical definition: R in V3 less than 3 mm or a…
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…
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)…
Takotsubo Cardiomyopathy vs STEMI: DDx
Key Points Takotsubo (stress) cardiomyopathy is a transient, non-ischemic LV dysfunction—classically apical ballooning with basal hyperkinesis—often after emotional or physical stress. Presentation mimics occlusion MI (chest pain, ECG changes, elevated…
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…
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…
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