Basics & Fundamentals
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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…
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:…
Sinus Bradycardia
Key Points Definition: Sinus bradycardia is a rhythm originating from the sinoatrial (SA) node with a rate < 60 bpm. Physiological Occurrence: Common in young, healthy adults, athletes, and during…
Sinus Node Dysfunction (Sick Sinus / Brady-Tachy Syndrome)
Key Points Spectrum, not one rhythm: Look for sinus brady, pauses, arrest, alternating atrial tachyarrhythmias (AF, flutter, ATach). Symptoms matter: Syncope, presyncope, fatigue usually come from cerebral/systemic hypoperfusion, especially after…
Right Atrial Enlargement (RAE)
Key Points Definition: Right atrial enlargement (RAE) is an increase in the size of the right atrium, typically resulting from chronic pressure or volume overload, commonly related to cardiac or…
Left Atrial Enlargement (LAE)
Key Points Definition: Left atrial enlargement (LAE) occurs when the left atrium dilates due to chronic pressure or volume overload. It commonly reflects underlying structural heart disease, particularly involving the…
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,…
Sinoatrial Exit Block
Key Points Definition: SA exit block occurs when the sinus node generates impulses that are blocked before they can activate the right atrium, leading to dropped P waves on the…
Unifasicular Block
Key Points Definition: Unifascicular block refers to conduction delay or interruption in a single fascicle of the ventricular conduction system: the right bundle branch (RBB), left anterior fascicle (LAF), or…
Pulmonary Embolism (PE)
Key Points ECG Findings in PE: No single ECG pattern is diagnostic of acute PE, and ECG findings are typically nonspecific. However, certain ECG patterns, especially those indicating right heart…
Atrial Flutter with Variable Conduction
Key Points: Mechanism: Typical atrial flutter arises from a large re-entry circuit in the right atrium. The atrial rate is usually near 300 beats per minute. ECG hallmark: Continuous “saw-tooth”…
QRS Voltage: Basics
Key Points: Definition: QRS voltage represents the amplitude (height) of the QRS complex on ECG, reflecting ventricular electrical activity during depolarization. High Voltage: Increased QRS voltage typically indicates ventricular hypertrophy—most…
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…
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