Scenario: Nurses working in the telemetry unit were alerted to a “patient check” by the monitor watcher based on the ECG shown here. The patient, a 78-year-old man admitted with syncope and bradycardia, was being paced with an external pacemaker until the cardiac catheterization laboratory was ready. When the nurses arrived, they learned that the patient’s cardiologist, who was at the bedside, had temporarily paused the external pacemaker in order to determine the underlying rhythm.

The initial rhythm shows atrial flutter (atrial rate = 300/min) with ventricular pacing at 50/min. After the fourth paced beat is a premature contraction (junction with delayed conduction vs ventricular) followed by a 4½-second pause, caused by cessation of external pacing, and then an escape beat.

In this example, whereas the flutter waves, or F waves, do not display the classic “sawtooth” waveform pattern, typically seen best in...

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