Conduction
Results:
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…
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…
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…
Not Enough P Waves (P:QRS < 1): DDx
Key Points Fewer P waves than QRS complexes: This means impulses are originating from below the atria (junctional, ventricular, or paced), or from ectopy interrupting sinus rhythm. Clinical relevance: In…
No Clear P Waves: DDx
Key Points Absence of Sinus Rhythm: The lack of clear P waves before the QRS complexes suggests loss or dysfunction of sinus activity. Potential Causes: This pattern can result from…
Too Many P Waves (P:QRS>1): DDx
Key Points Non-conducted P waves (too many P waves) occur when atrial impulses fail to conduct to the ventricles. Automated ECG interpretations are unreliable in irregular rhythms and with non-conducted…
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;…
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…
Occlusion MI in Left Bundle Branch Block: STEMI Equivalent Pattern
Key Points LBBB Does Not Exclude Acute Coronary Occlusion: LBBB alters ventricular activation, leading to expected secondary ST/T abnormalities. However, acute occlusion myocardial infarction (OMI) can and must still be…
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:…
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…
Left Bundle Branch Block (LBBB): DDx
Key Point Overview: Left bundle branch block (LBBB) is an intraventricular conduction delay that results from a block in the left bundle branch of the heart’s electrical conduction system. It…
ECG Foundations: Waveforms, Intervals, Conduction, and Leads
Key Points: Electrocardiography Defined: An ECG records the heart’s electrical activity in real time, offering a rapid window into rate, rhythm and conduction. The ECG measures changes in voltage between…
Sodium Channel Blocker Toxicity
Key Points Recognizing the Danger: Sodium channel blocker toxicity can present with a variety of ECG changes that are critical to recognize, especially in patients with altered mental status or…
New RBBB and LAFB in ACS: OMI Pattern
Key Points Pattern Recognition: New-onset Right Bundle Branch Block (RBBB) and Left Anterior Fascicular Block (LAFB) occurring together is a high-risk ECG finding. Often associated with proximal Left Anterior Descending…
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…
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