Killer Differentials
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Not Enough P Waves (P:QRS < 1): DDx
Key Points: Fewer visible P waves than QRS complexes means some ventricular beats are not preceded by an identifiable sinus P wave. This usually reflects: Premature junctional or ventricular beats…
No Clear P Waves: DDx
Key Points: “No clear P waves” is an ECG finding, not a diagnosis. P waves may be truly absent, replaced by abnormal atrial activity, buried within the QRS or T…
Too Many P Waves (P:QRS>1): DDx
Key Points: More P waves than QRS complexes means that some atrial impulses are not activating the ventricles. The cause may be a premature atrial impulse that arrives while the…
Wide QRS Complex: DDx
Key Points: A QRS duration greater than 120 ms reflects delayed or abnormal ventricular depolarization. A wide QRS may be chronic and benign in context, or it may be the…
ST Elevation in aVR: DDx
Key Points: ST elevation (STE) in aVR with diffuse ST depression most often reflects global subendocardial ischemia, not focal transmural infarction. High-risk coronary disease is one cause, not the only…
Must-Know Differentials (DDx) Hub
Key Points: The Must-Know DDx hub is your rapid reference for ECG-centered differential diagnosis in acute care. Use it when you recognize an ECG abnormality but need a focused list…
T Wave Inversion in V1-V3: DDx
Key Points: Anterior T wave inversion in V1-V3 is not synonymous with “anteroseptal ischemia.” The differential includes ACS, right heart strain, conduction/structural disease, and normal variants. In acute care, the…
STEMI vs LVH: DDx
Key Points: Left ventricular hypertrophy (LVH) with strain is one of the most common and dangerous STEMI mimics, particularly in the anterior leads, and is a frequent cause of false-positive…
ST Depression: DDx
Key Points: ST depression is a pattern, not a diagnosis. It can represent ischemia, reciprocal change, baseline repolarization abnormalities, or noncardiac physiology. First split: regional (territorial) ST depression vs diffuse…
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 Elevation: DDx
Key Points: ST elevation describes an ECG finding, not a diagnosis. It reflects abnormal ventricular repolarization and can arise from ischemic, structural, metabolic, electrical, or extracardiac processes. Occlusion MI is…
Diffuse ST Elevation: DDx
Key Points: ST-segment elevation (STE) is an ECG finding, not a diagnosis. Multiple ischemic and non-ischemic processes can produce STE. Diffuse STE is often non-ischemic, in contrast to the regional…
STEMI vs Early Repolarization: DDx
Key Points: Early repolarization (ER) is a common, benign ECG pattern that most often appears in young, healthy patients. It can closely resemble acute anterior STEMI, creating a high-risk diagnostic…
STEMI vs LV Aneurysm: DDx
Key Points: LV aneurysm pattern is a post MI scar pattern with persistent ST elevation in the prior infarct territory, usually with pathologic Q waves and a stable, non evolving…
STEMI Mimics: DDx
Key Points: ST elevation is a pattern, not a diagnosis. STEMI represents one cause of ST elevation and requires correlation with ECG morphology, distribution, evolution, and clinical context. Most ED…
STEMI vs Severe Hyperkalemia: DDx
Key Points: Severe hyperkalemia is a true ECG chameleon. It can produce ST elevation, wide QRS complexes, axis shifts, and conduction blocks that closely mimic STEMI or ventricular tachycardia. New…
STEMI vs Takotsubo Cardiomyopathy: 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…
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…
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…
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