A 55-year-old man presents with a regular wide-complex tachycardia at 180 bpm. He has a history of previous MI. ECG shows AV dissociation with fusion beats. Which is the MOST likely diagnosis?
- A SVT with aberrant conduction (RBBB)
- B Antidromic AVRT in WPW syndrome
- C Ventricular tachycardia (VT) ✓
- D Accelerated idioventricular rhythm
Explanation
AV dissociation (P waves at a different rate from QRS, unrelated) and fusion beats (hybrid P-QRS morphology when a sinus beat coincides with the VT beat) are pathognomonic of ventricular tachycardia and cannot occur in supraventricular tachycardia. Prior MI history adds further pre-test probability for scar-related re-entry VT. The Brugada algorithm for differentiating VT from SVT-with-aberrancy uses AV dissociation, RS interval >100 ms in precordial leads, and concordance patterns. VT in the setting of structural heart disease is managed with IV amiodarone followed by DC cardioversion if unstable.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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