Basics & Fundamentals
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Pacemaker Syndrome
Key Points: Pacemaker syndrome is a hemodynamic problem caused by loss of proper atrioventricular (AV) synchrony. Most commonly occurs with ventricular pacing that produces retrograde atrial activation, but can also…
Ventricular Paced Rhythms
Key Points: Ventricular pacing changes depolarization and repolarization, so ST-T segments often look abnormal. In most paced rhythms, some discordant ST deviation is expected and should not be mistaken for…
ECG Basics & Fundamentals Hub
Key Points: This hub organizes ECG basics and fundamentals into three complementary “start here” pathways: ECG definitions and measurement, how ECGs work and are generated, and the acute care STAT…
Electrical Alternans
Key Points: Electrical alternans is a beat-to-beat alternation in QRS amplitude, axis, or both. It is classically associated with a large pericardial effusion and may support concern for tamponade, but…
Pericardial Effusion
Key Points: Pericardial effusion is the accumulation of fluid in the pericardial sac. ECG may provide clues, but it is not sensitive enough to exclude effusion. Important ECG clues include…
Left Ventricular Hypertrophy (LVH)
Key Points: LVH reflects increased left ventricular muscle mass, usually from chronic pressure overload. Common causes include longstanding hypertension and aortic stenosis. ECG diagnosis is imperfect. Voltage criteria are specific…
Modified Sgarbossa Criteria: STEMI Equivalent Pattern
Key Points: LBBB and ventricular-paced rhythms can hide acute coronary occlusion because abnormal depolarization creates expected secondary ST-T changes. Occlusion MI can still be recognized when those ST changes are…
Persistent Juvenile T Wave Pattern
Key Points: Persistent juvenile T wave pattern is a benign normal variant that most often appears as shallow asymmetric T wave inversion in the right precordial leads, usually V1 to…
Appropriate Discordance
Key Points: Appropriate discordance refers to the expected secondary ST segment and T wave pattern seen with abnormal ventricular depolarization, especially LBBB and ventricular-paced rhythm. The ST segment and T…
QRS Morphology and ST-T Interpretation: Basics
Key Points: Read the QRS before you read the ST segment or T wave. Ventricular depolarization shapes repolarization. Narrow QRS usually reflects normal His-Purkinje conduction. Wide QRS suggests abnormal ventricular…
Preexcitation Syndromes: Overview
Key Points: Pre-excitation means an accessory pathway allows atrial impulses to reach the ventricle without traversing the AV node, producing early ventricular activation. A delta wave is the defining ECG…
Delta Waves: Basics
Key Points: Definition: A delta wave is a slurred upstroke at the very start of the QRS. It reflects early ventricular activation through an accessory pathway that bypasses the AV…
Short QT Syndrome
Key Points: Short QT Syndrome (SQTS) is a rare condition characterized by a shortened QT interval on the ECG, increasing the risk of atrial and ventricular arrhythmias, including sudden cardiac…
WPW Syndrome and Pseudo-MI Patterns
Key Points: WPW alters ventricular depolarization, producing secondary repolarization abnormalities that can mimic or mask myocardial infarction. ST-segment deviation in WPW is often non-ischemic, driven by abnormal activation via the…
WPW with Antidromic SVT (Antidromic AVRT)
Key Points: Antidromic AVRT is an AV re-entrant tachycardia that conducts antegrade down the accessory pathway and returns retrograde through the AV node (or another pathway), producing a regular wide-complex…
WPW with Orthodromic SVT (Orthodromic AVRT)
Key Points: Orthodromic AVRT is the most common tachyarrhythmia in WPW and presents as a regular narrow-complex SVT that is indistinguishable from AVNRT during the tachycardia. Mechanism: antegrade conduction down…
ECG Foundations: Vectors, Leads, & Activation
Key Points: An ECG records voltage differences over time. The ECG tracing is a plot where the horizontal axis is time and the vertical axis is voltage. Leads are viewpoints….
P Wave: Basics
Key Points: Definition and measurement: The P wave is atrial depolarization. Measure duration from initial deflection to return to baseline and amplitude from baseline to peak. Normal values: Duration <120…
Third-Degree AV Block (Complete Heart Block)
Key Points: Definition: Third-degree AV block is complete failure of conduction from atria to ventricles, resulting in independent atrial and ventricular activity—known as AV dissociation. Hallmark Feature: No P waves…
Second-Degree AV Block Type I (Mobitz I/Wenckebach)
Key Points: Definition: Progressive PR interval prolongation until one atrial impulse fails to conduct to the ventricles (P wave is non-conducted), after which the cycle repeats. Site of Block: Typically…
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