Basics & Fundamentals
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Fusion Beats
Key Points Definition: A fusion beat occurs when two impulses — one from the normal conduction system (typically supraventricular) and one from an ectopic ventricular focus (e.g., during VT) —…
QRS Morphology & Proportionality
Key Points QRS Morphology Reflects Conduction Pathways: The shape and width of the QRS complex help differentiate between normal conduction, conduction delays, and ventricular-origin rhythms. QRS–T Wave Proportionality Signals Repolarization…
Normal Sinus Rhythm
Key Points Definition: Normal sinus rhythm (NSR) refers to the heart’s rhythm when impulses originate from the sinoatrial (SA) node, the heart’s primary pacemaker. This rhythm suggests that electrical impulses…
Normal Cardiac Conduction
Key Points SA Node: Initiates electrical impulses; primary pacemaker (60–100 bpm). AV Node: Slows conduction to permit ventricular filling. Bundle of His: Transmits impulses from the AV node to ventricles;…
History of the “STAT ECG”
Key Points The ECG is a cornerstone of acute care medicine, offering immediate, non-invasive insight into cardiac function in critically ill patients. Its evolution spans over a century, from rudimentary…
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…
Pseudonormalization of T Waves
Key Points Definition: Pseudonormalization is the apparent normalization of previously inverted T waves, often signaling reocclusion of a coronary artery that had recently reperfused. Mechanism: During reperfusion, ischemic T wave…
Right Bundle Branch Block (RBBB)
Key Points RBBB delays right ventricular activation. The left ventricle depolarizes normally via the left bundle; the right ventricle is activated late through myocardial spread. ECG hallmark: wide QRS and…
Escape-Capture Bigeminy
Key Points Escape-capture bigeminy is a unique rhythm characterized by alternating escape beats and normally conducted sinus beats, resulting in a bigeminal (paired) rhythm pattern. It typically occurs in patients…
Modified Sgarbossa Criteria: STEMI Equivalent Pattern
Key Points Wide QRS Rhythms Can Mask OMI: Left bundle branch block (LBBB) and right ventricular (RV)-paced rhythms alter ventricular depolarization, producing expected secondary ST/T changes. However, acute occlusion MI…
Ventricular Escape Rhythms
Key Points Wide QRS Complex Rhythm: Ventricular escape rhythms (aka idioventricular rhythms) are characterized by a wide QRS duration (>120 ms), absent or dissociated P-waves, and a regular, slow ventricular…
Appropriate Discordance
Key Points: Definition: Appropriate discordance is a normal repolarization pattern in which the ST segment and T wave are directed opposite to the main QRS vector. It reflects expected changes…
Junctional Escape Rhythms
Key Points Narrow QRS Complexes typically indicate junctional escape rhythms, originating near the AV node or proximal His-Purkinje system. These generally have a more favorable prognosis. Wide QRS Complexes suggest…
The Bix Rule (Unmasking Atrial Flutter)
Key Points The Bix Rule refers to a simple but powerful ECG clue: if you observe a consistent P wave located exactly halfway between two QRS complexes, suspect concealed atrial…
Sinus Tachycardia
Key Points Definition: Sinus tachycardia is a regular rhythm originating from the sinoatrial (SA) node, defined by a heart rate >100 bpm in adults or above age-adjusted norms in children….
Ashman Phenomenon
Key Points Definition: Ashman phenomenon is an aberrant intraventricular conduction pattern triggered by cycle-length variation. It is most often seen in atrial fibrillation but can appear in any supraventricular rhythm….
Sinoatrial Nodal Reentry Tachycardia (SANRT)
Key Points Mechanism: SANRT is a rare type of paroxysmal supraventricular tachycardia (SVT) that operates through a similar mechanism as AV nodal reentry tachycardia (AVNRT), with the reentry loop occurring…
Junctional Tachycardia
Key Points Origin: Junctional tachycardia is a rare type of paroxysmal supraventricular tachycardia (SVT) that originates from the AV node or the bundle of His. Mechanism: The arrhythmia is caused…
Atrial Tachycardia
Key Points: Definition: Atrial tachycardia is a supraventricular arrhythmia characterized by rapid atrial depolarizations from one or more ectopic foci outside the SA node. Atrial Rate: > 100 bpm, typically…
Trifascicular Block
Key Points Definition: Trifascicular block describes ECG evidence of impaired conduction across all three fascicles: right bundle branch (RBB), left anterior fascicle (LAF), and left posterior fascicle (LPF). Common Usage:…
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