ECG Case 139

This is a regular broad-complex tachycardia at 143 beats per minute with a QRS duration of about 170 ms. In a 71-year-old man, a regular broad-complex tachycardia is ventricular tachycardia until proven otherwise. The rhythm strip contains capture and fusion beats, proving atrioventricular dissociation, which in a broad-complex tachycardia establishes VT. SVT with aberrancy can produce a broad QRS but cannot produce AV dissociation.

Capture beats are narrow complexes that appear when a sinus impulse conducts to the ventricles between tachycardia beats. A fusion beat has an intermediate morphology produced by simultaneous activation from both the sinus impulse and the ventricular focus. Together they prove that the atria and ventricles are operating independently, which in a broad-complex tachycardia effectively proves ventricular tachycardia. A wide QRS alone does not exclude aberrant conduction.

The 2022 ESC ventricular arrhythmia guideline recommends synchronised electrical cardioversion as first-line treatment for haemodynamically tolerated sustained monomorphic VT with known or suspected structural heart disease, provided the sedation risk is acceptable (Class I). Intravenous procainamide should be considered (Class IIa) and intravenous amiodarone may be considered (Class IIb). The reflex to reach for amiodarone because the patient is stable is common but is a weaker recommendation than cardioversion. The Resuscitation Council UK adult tachycardia algorithm still names amiodarone for stable broad-complex tachycardia, so practice varies between guidelines.

There are QS complexes across V1 to V4 with no R-wave progression through the anterior chest leads, indicating a previous anterior myocardial infarction. The T waves are upright in V3 to V6 and there is no acute ST elevation, distinguishing this from an acute event. The QRS is narrow at 74 ms, excluding a bundle branch block.

Monomorphic ventricular tachycardia in the setting of a healed myocardial infarction is typically scar-mediated re-entry. The infarct scar provides the slow conduction zone that sustains the tachycardia circuit. This patient requires cardiology assessment, echocardiography to assess left ventricular function, and consideration of an implantable cardioverter-defibrillator for secondary prevention of sustained VT.