Scenario: This 12-lead electrocardiogram (ECG) was obtained by prehospital providers on a 70-year-old woman who called 911 because her internal cardiac defibrillator “fired” multiple times. The patient was alert but complained of dizziness. She said she had not felt well for a few days but stated that she had not had any chest pain or shortness of breath. She has a complex medical history that includes hypertension, chronic obstructive pulmonary disease, obstructive sleep apnea, coronary artery disease, previous myocardial infarction, ischemic cardiomyopathy, chronic heart failure, and psychological depression. She was alert and oriented, her blood pressure was 80/40 mm Hg, and peripheral and central pulses were present.

Wide-complex tachycardia (WCT) with undetermined origin. Top differential diagnoses: (1) ventricular tachycardia with right bundle branch block (BBB) type pattern; (2) supraventricular tachycardia with aberrancy; or (3) supraventricular tachycardia with preexisting BBB.

The width of the QRS complex is a key feature...

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