Basics & Fundamentals
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Sinus Arrhythmia
Key Points Definition: Phasic variation in sinus rate with respiration. P-P intervals shorten on inspiration and lengthen on expiration, producing a mild, patterned irregularity. Diagnostic threshold: Difference between the shortest…
Slow Ventricular Tachycardia (VT)
Key Points Definition: Slow ventricular tachycardia is defined as a wide complex tachycardia with a ventricular rate between 100–120 bpm. Distinction: Typical sustained VT usually exceeds 120 bpm. When encountering…
The Lewis Lead (Unmasking Atrial Activity)
Key Points Purpose: The Lewis Lead (modified S5 lead) is a bedside ECG modification designed to enhance visualization of atrial activity. It is particularly useful for differentiating VT from SVT…
Multifocal Atrial Tachycardia (MAT)
Key Points Definition: Multifocal Atrial Tachycardia (MAT) is a rare type of irregularly irregular supraventricular tachycardia (SVT) characterized by the presence of at least three or more different P wave…
Abnormal STAT ECG
Key Points Clinical Context: Abnormal ECGs must be interpreted within the patient’s presentation. Not all abnormalities are life-threatening, and high-risk conditions can still appear subtle or even “normal.” Serial Monitoring:…
STEMI Mimics
Key Points Context Matters: ECGs must be interpreted in the clinical setting. Chest pain, shock, or ACS risk factors increase pretest probability of STEMI/OMI, while atypical presentations lower it. Prevalence:…
Ventricular Tachycardia (VT)
Key Points Definition: VT is a wide complex tachycardia arising from the ventricles, defined as ≥3 consecutive ventricular beats, QRS duration >120 ms, with rapid heart rate typically 120-250 bpm….
Supraventricular Tachycardias (SVTs)
Key Points Definition: SVT refers to any tachyarrhythmia that originates above the ventricles (atria, AV node, or bundle of His). Most present as regular narrow-complex tachycardias, although aberrant conduction can…
STAT ECG 101: The Basics
Key Points Rapid, Non-Invasive, High-Yield Tool: The STAT ECG is the single best screening test in acute care medicine. It is inexpensive, minimally invasive, and immediately available. Within seconds, it…
Atrial Flutter 2:1 Conduction
Key Points Mechanism: Atrial flutter results from a macro re-entry circuit typically located within the right atrium, causing rapid and regular atrial activation (~300 bpm commonly). ECG Appearance: Classic “saw-tooth”…
Atrial Flutter
Key Points Definition: Atrial flutter is a common type of supraventricular tachycardia caused by a re-entry circuit within the right atrium. Atrial Rate: Typically around ~300 bpm, ranging from 240-360…
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…
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. Typing Limitation: Differentiating between Mobitz I and…
Second-Degree AV Block Type II (Mobitz II)
Key Points Definition: Sudden failure of AV conduction after at least two consecutive conducted beats with identical PR intervals, followed by a single non‑conducted P wave. Sinus rate: P–P interval…
Terminal QRS Distortion (OMI Pattern)
Key Points What it is: In V2 or V3, there is no S wave (the R does not descend below the PQ baseline) and no J wave (no notch/slur at…
QRS Axis Basics
Key Points Definition: The QRS axis reflects the net direction of ventricular depolarization and is expressed in degrees on the frontal plane. Why It Matters: Axis assessment is a fast,…
Extreme Axis Deviation Basics
Key Points Definition: Extreme axis deviation (aka “Northwest Axis”) occurs when the QRS axis is between –90° and ±180°. ECG Clue: QRS negative in Lead I QRS negative in Lead…
Indeterminate Axis DDx
Key Points An indeterminate axis, sometimes referred to as an “extreme” or “undetermined” axis, is suspected when the QRS complexes are isoelectric or nearly biphasic in both Lead I and…
Left Axis Deviation Basics
Key Points Definition: LAD occurs when the QRS axis is between –30° and –90°. ECG Pattern: QRS positive in Lead I QRS negative in Lead aVF Clinical Use: LAD can…
VT vs. SVT with Aberrancy
Key Points Basic Distinction: SVTs typically have narrow QRS complexes (<120 ms) but may present with wide complexes if aberrantly conducted (e.g., with existing bundle branch block). Clinical Importance: Differentiating…
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