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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…
Sinus Arrest
Key Points Definition: Sinus pause/arrest is failure of the sinus node to generate an impulse, producing a transient absence of P waves. On ECG the pause does not equal an…
R-on-T Phenomenon
Key Points Definition: The R on T phenomenon occurs when an ectopic impulse (often a PVC or cardioversion shock) falls on the T wave of the preceding beat. Mechanism: Interrupting…
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:…
Right Ventricular STEMI: Criteria & Pitfalls
Key Points RV involvement accompanies up to ~40% of inferior STEMIs; isolated RV infarction is uncommon but high-impact when missed. Think RV MI when inferior STEMI is present and you…
STAT ECG 101: The Acute Care ECG Approach
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…
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…
Toxicologic Emergencies
Key Points ECG as a Critical Diagnostic Tool: In toxicology, the ECG is often the first and most reliable clue. Early recognition of drug-induced conduction disturbances or arrhythmias can guide…
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…
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…
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…
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…
Indeterminate QRS Axis: Basics
Key Points Definition: An indeterminate QRS axis (also called “no man’s land”) occurs when the frontal QRS vector lies between –90° and ±180°, but no dominant direction is evident. ECG…
Right Axis Deviation: Basics
Key Points Definition: Right Axis Deviation (RAD) occurs when the QRS axis is > +90°, typically up to +180°. ECG Criteria: Negative QRS in Lead I Positive QRS in Lead…
Right Axis Deviation: DDx
Top 3 Emergent Causes of New Rightward Axis Deviation: When you encounter new right axis deviation on an ECG, immediately consider the following life-threatening conditions: Acute Right Heart Strain or…
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