Scenario: This rhythm strip was obtained in an 18-year-old woman admitted to the intensive care unit (ICU) following a motor vehicle accident; her sister, the passenger, was dead on arrival. Although the patient was in critical condition, she was hemodynamically stable with mechanical ventilation and sedation. Unexpectedly, the central monitor alarmed for the ECG strip below. Immediate assessment of the patient revealed that she had no palpable carotid pulse.

Interpretation: Sinus tachycardia at 120 beats per minute with sustained pulseless ventricular tachycardia triggered by R-on-T.

Careful evaluation of the T waves reveals that there is some variability from beat to beat. For example, the offset of the T wave is distinct with some beats, whereas the offset of the T wave actually extends into the P wave of some beats. Such lengthening extends the relative refractory period of repolarization,...

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