Killer Differentials
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Must-Know Syncope: DDx
Key Points: Syncope and the ECG: Syncope is a transient loss of consciousness caused by transient global cerebral hypoperfusion, with rapid onset, brief duration, and spontaneous complete recovery. Cardiac syncope…
T Wave Inversions 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…
T Wave Inversion: DDx
Key Points: T wave inversion is a nonspecific ECG finding, not a diagnosis. The differential ranges from benign normal variants to life-threatening cardiac, pulmonary, and neurologic disease. First determine whether…
Clumped or Grouped Beats: DDx
Key Points: Clumped or grouped beats produce an organized, often regularly irregular rhythm and can be mistaken for atrial fibrillation. The major differential includes premature beats, AV block, escape-capture rhythms,…
Inverted P Waves in V1: DDx
Key Points: Know What Is Normal: The sinus P wave in V1 is often biphasic, with an initial positive and terminal negative component. A predominantly or completely negative P wave…
Diffuse ST Elevation: DDx
Key Points: ST segment elevation (STE) is an ECG finding, not a diagnosis. Multiple ischemic and non-ischemic conditions can produce diffuse STE. Diffuse STE is more commonly non-ischemic than ischemic,…
Ventricular Tachycardia (VT) Mimics
Key Points: Default assumption: A regular wide-complex tachycardia should be considered VT until another diagnosis is more likely. Rate modifies the differential, not the diagnosis. Typical monomorphic VT is often…
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 considerations: regional (territorial) ST depression vs diffuse…
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…
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…
STEMI vs Early Repolarization: DDx
Key Points: Early repolarization (ER) is one of the most common non-ischemic causes of ST elevation and one of the most frequent ECG mimics of acute anterior coronary occlusion. 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…
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…
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…
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