Conduction
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UMEM Cases, Part 4: When the Computer Misses the Rhythm and Flutter Fakes a STEMI
A 44-year-old man with severe cardiomyopathy, an LVAD, chronic amiodarone therapy, and an AICD presents with palpitations. His ECG shows a regular wide-complex tachycardia, but the rate is only 135….
Junctional Tachycardia
Key Points: Junctional tachycardia is an uncommon supraventricular tachycardia arising from the AV junction, usually due to enhanced automaticity rather than reentry. It is usually a regular narrow-complex tachycardia, although…
Junctional Rhythms
Key Points: Junctional rhythms arise from the AV junction, usually the AV node or proximal His bundle, when the sinus node slows, fails, or impulses do not reach the ventricles…
UMEM Cases, Part 2: When the ECG Conceals and When It Reveals
An 81-year-old woman presents with lightheadedness and marked bradycardia. Her ECG shows more P waves than QRS complexes, but the mechanism is not immediately clear. The key question is whether…
Three ECG Traps You Cannot Afford to Miss
A 60-year-old woman presents with palpitations and an irregular wide-complex tachycardia. The computer calls atrial fibrillation with a left bundle branch block, but a subtle clue in the precordial leads…
Pacemaker Syndrome
Key Points: Pacemaker syndrome is a hemodynamic problem caused by loss of proper atrioventricular (AV) synchrony. Most commonly occurs with ventricular pacing that produces retrograde atrial activation, but can also…
Ventricular Paced Rhythms
Key Points: Ventricular pacing changes depolarization and repolarization, so ST-T segments often look abnormal. In most paced rhythms, some discordant ST deviation is expected and should not be mistaken for…
Atrioventricular (AV) Block: Comprehensive Summary
Key Points: AV block refers specifically to delayed or failed conduction of impulses from the atria to the ventricles. AV block is classified by the ECG pattern of conduction: First-degree…
Occlusion MI in Left Bundle Branch Block (LBBB): STEMI Equivalent Pattern
Key Points: LBBB does not exclude acute coronary occlusion. LBBB produces abnormal depolarization and expected secondary ST-T changes, which can mask or mimic ischemia. Acute OMI can still be recognized…
The Syncope ECG With Too Much P
A 68-year-old man has syncope, then has a second syncopal episode while lying still on a stretcher during evaluation at an outpatient clinic. He is sent emergently to the ED….
Isorhythmic AV Dissociation
Key Points: Isorhythmic AV dissociation is a form of AV dissociation in which the sinus rate and junctional or ventricular escape rate are nearly identical, making the P waves and…
Third-Degree AV Block (Complete Heart Block)
Key Points: Third-degree AV block is complete failure of atrial impulses to conduct to the ventricles. The defining ECG feature is AV dissociation with no conducted P waves. The atrial…
Second-Degree AV Block Type I (Mobitz I/Wenckebach)
Key Points: Mobitz I is defined by progressive PR prolongation until a single P wave fails to conduct, after which the cycle resets. The block is usually at the AV…
Second-Degree AV Block with 2:1 Conduction
Key Points: Second-degree AV block with 2:1 conduction means every other P wave conducts and every other P wave is blocked. A single ECG with 2:1 conduction usually cannot be…
First-Degree AV Block
Key Points: First-degree AV block is defined by a PR interval greater than 200 ms with fixed 1:1 AV conduction and no dropped QRS complexes. It usually reflects delayed conduction,…
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…
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