Scenario: This 12-lead electrocardiogram (ECG) was obtained by paramedics on an 81-year-old man with chief complaints of dizziness, weakness, nausea, and vomiting for 2 days. The patient reported that he had experienced 2 similar near-syncopal episodes the preceding week. The patient denied chest pain or shortness of breath. He had a complex medical history that included coronary artery disease, arrhythmias, and renal failure. During the prehospital evaluation, the patient was lethargic, had a weak pulse at 28 beats per minute, and his blood pressure was undetectable.

Atrial flutter with complete heart block and 4 ventricular escape beats of multifocal origin. Although the fourth beat looks narrow, it is unlikely to be of supraventricular origin given the lack of distinctive waveform morphology in leads V4 through V6.

The 4 QRS complexes (ie, heartbeats) seen in this rhythm (arrows) are mostly...

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