Basics & Fundamentals
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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 see new RAD in an adult, immediately consider life-threatening etiologies: Acute Right Heart Strain Pulmonary embolism until proven otherwise…
Normal QRS Axis
Key Points Normal Axis Range: –30° to +90° Lead I: QRS complex is positive Lead aVF: QRS complex is positive → This combination confirms a normal QRS axis Frontal plane…
Bifascicular Block
Key Points Definition: Conduction block in any two of the three fascicles: right bundle branch (RBB), left anterior fascicle (LAF), or left posterior fascicle (LPF). High-Risk OMI Pattern: New RBBB…
Bundle Branch Blocks
Key Point Types: The two main BBBs are Right Bundle Branch Block (RBBB) and Left Bundle Branch Block (LBBB). Impact on ECG: Both widen the QRS (>120 ms) and produce…
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…
Interval Interpretation
Key Points: Intervals are your ECG safety rails. Before you get seduced by ST segments and T waves, lock down PR, QRS, and QT/QTc. They frequently reveal the real danger…
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) —…
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…
Left Bundle Branch Block (LBBB)
Key Points: Definition: LBBB occurs when electrical conduction through the left bundle branch is delayed or blocked, resulting in asynchronous and delayed activation of the left ventricle (LV) and a…
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…
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