Basics & Fundamentals
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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…
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…
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…
Dextrocardia
Key Points Dextrocardia is a congenital condition where the heart is located on the right side of the thorax. Situs inversus totalis refers to complete reversal of all thoracic and…
Atrial Fibrillation with RVR
Key Points Most Common Sustained Arrhythmia: Atrial Fibrillation (AFib) is the most frequently encountered sustained arrhythmia in clinical practice, particularly among the elderly population. Misdiagnosis Risk: AFib is commonly misdiagnosed…
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…
Lead Misplacement
Key Points Proper lead placement is critical to avoid misdiagnoses that can lead to unnecessary interventions and patient harm. Misplaced precordial leads (V1-V6) can mimic ischemia and cause false MI…
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…
Earliest Evidence of Occlusion MI
Key Points Dynamic Nature of ACS: Acute coronary syndromes (ACS) are complex and dynamic, with coronary arteries potentially undergoing reperfusion and reocclusion at any time. The ECG can provide real-time…
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…
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