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Sinus Node Dysfunction
(Sick Sinus Syndrome, “Brady-Tachy” Syndrome)

Key Points Spectrum of Arrhythmias: Sinus node dysfunction produces alternating periods of inappropriate bradycardia (sinus bradycardia, pauses, arrest) and paroxysmal atrial tachyarrhythmias (AF, atrial flutter, atrial tachycardia). Symptom Driver: Transient…

Wellens Syndrome

Key Points Diagnosis: Wellens syndrome is a clinical diagnosis that requires more than just the presence of Wellens waves; it necessitates a thorough history and consideration of other potential causes…

Slow Atrial Fibrillation

Key Points Definition: Atrial fibrillation with a slow ventricular response, usually < 60 bpm. ECG: Irregularly irregular rhythm, no discrete P waves, slow R-R intervals. Common causes: AV-nodal blockers (digoxin,…

Occlusion MI – STEMI Criteria & Beyond

Key Points A STAT ECG is the most important initial test in patients with suspected acute coronary syndrome (ACS), enabling rapid identification of acute coronary occlusion myocardial infarction (OMI), a…

Aslanger Pattern (OMI Pattern)

Key Points STEMI Diagnosis and Contiguous Leads: While current guidelines typically require ST elevation (STE) in at least two contiguous leads for the diagnosis of STEMI, this practice is not…

Precordial Swirl (OMI Pattern)

Key Points Definition: The precordial swirl sign refers to a rotational pattern of ST-segment abnormalities across the precordial leads, suggesting a dynamic and evolving occlusion myocardial infarction (OMI). It is…

Digoxin Toxicity

Key Points Narrow therapeutic window: Small dosing errors or renal decline can push serum digoxin above the safe range. Excess automaticity + AV block: Toxicity increases atrial and ventricular irritability…

High-Risk Pulmonary Embolism

Key Points High-Risk PE: High-risk pulmonary embolism (PE) is a life-threatening condition requiring immediate recognition and treatment. The ECG can provide early, life-saving clues in the diagnosis of high-risk PE. Critical…

Pericardial Tamponade

Key Points Beyond Electrical Alternans: Although classically linked to tamponade, electrical alternans is present in fewer than 30% of confirmed cases. It’s abscence should never rule out tamponade. Low Voltage…

Post-Cardiac Arrest ECGs

Key Points Coronary Occlusion After Shockable Arrest: ~30% of patients resuscitated from ventricular fibrillation (VF) arrest have an acute coronary occlusion and present with STEMI on ECG. Among patients without…

Second-Degree AV Block Type I
(Mobitz I/Wenckebach)

Key Points Definition: Progressive lengthening of the PR interval until one atrial impulse fails to conduct to the ventricles (a dropped QRS complex). Site of Block: Typically within the AV…

Second-Degree AV Block with 2:1 Conduction

Key Points Definition: A form of second-degree AV block in which every other atrial impulse is blocked, producing a 2:1 atrioventricular conduction ratio. Diagnostic Challenge: Differentiating between Mobitz I and…

Second-Degree AV Block, High-Grade
(Advanced AV Block)

Key Points Definition: A severe form of second-degree AV block—most often Mobitz II—characterized by multiple consecutive non-conducted P waves (e.g., 3:1 or 4:1 conduction). PR Intervals: Constant before conducted beats,…

Second-Degree AV Block Type II (Mobitz II)

Key Points Definition: Mobitz II is a type of second-degree AV block defined by sudden, intermittent failure of atrial impulses to conduct to the ventricles, without progressive PR interval lengthening…

Atrial Flutter 1:1 Conduction

Key Points Rapid Ventricular Rates: Atrial flutter with 1:1 conduction is associated with very rapid ventricular rates (250-320 bpm), leading to significant symptoms and rapid hemodynamic compromise. This rhythm is…

Electrical Alternans

Key Points Classically associated with pericardial tamponade but seen in fewer than 30% of confirmed cases. Combination of low-voltage QRS + sinus tachycardia strongly suggests pericardial effusion/tamponade. Always perform rapid…

Torsades de Pointes (TdP)

Key Points Definition: TdP is a specific subtype of polymorphic ventricular tachycardia associated with a prolonged QTc interval. It often presents with a “twisting” pattern on ECG but can be…

Polymorphic Ventricular Tachycardia (PMVT)

Key Points Definition: PMVT is a ventricular tachycardia characterized by beat-to-beat variations in QRS morphology, axis, and duration, reflecting multiple ventricular foci or reentrant circuits. Clinical Importance: PMVT is often…

Computer Interpreted “Normal” ECGs

Key Points Do not fully trust computer interpretations of “normal” ECGs—they may miss significant abnormalities. Computer algorithms can miss early ischemic signs such as reciprocal changes in aVL and hyperacute…

Posterior STEMI Criteria

Key Points High Risk of Missed Diagnosis: Isolated posterior occlusion MI is frequently missed due to the absence of ST elevation on standard 12-lead ECG. Instead, ST depression in V1–V3…

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