Conduction
Results:
Second-Degree AV Block Type II (Mobitz II)
Key Points: Mobitz II is defined by sudden failure of AV conduction after at least 2 consecutive conducted beats with fixed PR intervals and no preceding PR prolongation. The block…
Atrial Flutter
Key Points: Atrial flutter is a supraventricular tachyarrhythmia caused by a macro-reentrant circuit, most commonly typical cavotricuspid isthmus-dependent flutter in the right atrium. The atrial rate is usually about 250-350…
Advanced (High-Grade) AV Block
Key Points: Advanced or high-grade AV block is a severe second-degree AV block with 2 or more consecutive non-conducted P waves, such as 3:1 or 4:1 conduction. Do not force…
Preexcitation Pitfalls (Part 3): Wide, Irregular, Fast…Avoid AV Nodal Blockers
A 53-year-old man presents with palpitations and lightheadedness. The following ECG is obtained on arrival and appears very rapid and irregular with changing QRS morphologies. He starts showing signs of…
Preexcitation Pitfalls (Part 2): Wide, Regular, Fast…Treat It Like VT
A young man with recurrent palpitations presents to the emergency department hemodynamically stable during an episode. The arrival ECG shows a wide complex, regular tachycardia and the computer interpretation calls…
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…
Preexcitation Pitfalls (Part 1): The “Inferior STEMI” That Isn’t
A critically ill 38-year-old man presents hypotensive, pale, and diaphoretic with abdominal pain and rectal bleeding. Upright chest X-ray shows free air under the diaphragm, and the patient is headed…
ECG Foundations: Vectors, Leads, & Activation
Key Points: An ECG records voltage differences over time. The ECG tracing is a plot where the horizontal axis is time and the vertical axis is voltage. Leads are viewpoints….
Dr. Mattu’s 5 Favorite ECG Cases of 2025
A 68-year-old man presents after syncope with profound bradycardia. The ECG shows a very slow ventricular rate with high-grade AV block. The reflex move is to focus only on pacing,…
Premature Atrial Complexes (PACs)
Key Points PACs are early atrial depolarizations from an ectopic focus that create a premature P wave with a different morphology and axis than the sinus P wave, usually followed…
Premature Junctional Complexes (PJCs)
Key Points PJCs are premature impulses from ectopic foci in or near the AV junction. ECG hallmark is a narrow premature beat with an absent or retrograde P wave. Retrograde…
Blocked Premature Atrial Complexes (PACs)
Key Points Definition: early ectopic atrial beats that do not conduct to the ventricles. You see a premature P wave with no following QRS and a pause that is usually…
Premature Complexes (PACs, PJCs, & PVCs) Overview
Key Points: Premature complexes are early depolarizations arising from the atrium, AV junction, or ventricle which interrupt the expected sinus rhythm. Rapid classification by origin: look for a P wave…
Premature Ventricular Complexes (PVCs)
Key Points PVCs are early ventricular depolarizations that produce a wide QRS with secondary ST-T changes and are usually followed by a full compensatory pause. No preceding P wave. A…
Fascicular Blocks
Key Points Definition: Delay/block within the left bundle’s fascicles—left anterior (LAF) or left posterior (LPF)—alters ventricular activation and the QRS axis. Types: LAFB (common) → left axis deviation; LPFB (rare)…
Left Anterior Fascicular Block (LAFB)
Key Points: LAFB occurs when conduction through the left anterior fascicle is delayed or blocked. Ventricular activation travels preferentially down the left posterior fascicle, then spreads inferior-to-superior and rightward-to-leftward across…
Left Posterior Fascicular Block (LPFB)
Key Points: LPFB occurs when conduction through the left posterior fascicle is delayed or blocked. LV activation travels preferentially through the left anterior fascicle, then spreads superior-to-inferior and left-to-right toward…
Fascicular Ventricular Tachycardia (Idiopathic Left Fascicular VT)
Key Points Idiopathic reentrant VT arising within the left Purkinje system, most often the left posterior fascicle. Patients are usually young and lack structural heart disease. Signature ECG: RBBB-like morphology…
Beta-Blocker and Calcium Channel Blocker Toxicity
Key Point BBs and CCBs are widely prescribed but overdoses can cause life-threatening bradycardia, AV block, hypotension, and shock. Differentiating between them is important, but both require early recognition, aggressive…
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…
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