Scenario: These ECG tracings (lead II) were obtained during a symptom-limited exercise treadmill test (ETT) of a 45-year-old, male professional firefighter during a routine annual check-up. He showed no angina symptoms during the ETT and reached his maximum heart rate after 12 minutes of starting the test. This firefighter has no significant medical history, is in good athletic shape, and was cleared for duty by his health care provider. However, his body mass index (BMI) is 29 kg/m2 (overweight) and he is an active tobacco smoker.

Sinus tachycardia with T wave alternans (TWA)

Repolarization alternans or TWA is seen in every other beat as a variation in the amplitude or morphology of the T wave (lower ECG strip). Consistent with the current scenario, these morphological alterations are commonly seen during exercise rather than rest. Visually detected TWA (macroscopic), first described 100 years ago,...

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