Killer Differentials
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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…
Too Many P Waves (P:QRS>1) DDx
Key Points Non-conducted P waves (too many P waves) occur when atrial impulses fail to conduct to the ventricles. Automated ECG interpretations are unreliable in irregular rhythms and with non-conducted…
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…
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: Always…
Bradycardia DDx
Key Points Common Offenders: Beta-blockers, calcium channel blockers, and digoxin often top the list of medication-induced bradycardia. High Vagal Tone or AV Block can arise from structural heart disease, ischemia,…
Abnormal P Wave Axis DDx
Key Points Normal Sinus Rhythm: In a normal rhythm, the sinus node initiates atrial depolarization, resulting in a P wave with a normal axis: upright in lead II, inverted in…
Low Voltage QRS DDx
Key Points Definition: Low voltage QRS complexes reflect decreased myocardial electrical amplitude on ECG. Sensitive Definition (Preferred): Limb leads (I + II + III) sum < 15 mm OR precordial…
Wide QRS Bradyarrhythmia DDx
Key Point Wide QRS bradycardias usually reflect infranodal conduction disease (His–Purkinje or below), making them much more dangerous than narrow QRS bradycardias. These rhythms often lead to hemodynamic instability and…
Acute Chest Pain DDx
Key Point In patients presenting with acute chest pain, rapidly identifying life-threatening conditions is essential. Use a systematic ECG approach alongside clinical context to evaluate for high-risk diagnoses that require…
Prolonged QT Interval DDx
Key Points Definition: The QT interval reflects the time it takes for total ventricular depolarization and repolarization (Q wave onset to T wave end). Clinical Relevance: QT prolongation increases the…
ST Depression in V1-V4 DDx
Key Point ST segment depression in V1–V4 is often misattributed to anterior ischemia or NSTEMI. In patients with ACS symptoms, this pattern should first raise concern for isolated posterior occlusion…
T Wave Inversion in V1-V3 DDx
Key Points Common Misconception: T-wave inversions (TWIs) in V1–V3 are often prematurely labeled as “anteroseptal ischemia,” but there’s a much broader differential. Essential Differentials: Pulmonary causes (e.g., PE), Arrhythmogenic RV…
Large T Wave DDx
Key Point Large T waves on an ECG can have several different etiologies, ranging from benign to life-threatening conditions. It’s essential to interpret them in the clinical context and with…
Poor R Wave Progression DDx
Key Points Poor R Wave Progression (PRWP): This refers to a situation where the R waves in the precordial leads (V1 to V6) fail to increase in amplitude as expected….
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