Indices of Sudden Cardiac Death

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, is strongly correlated with the onset of lethal ventricular tachyarrhythmia and sudden cardiac death (SCD). QRS alternans, which is also evident in the current scenario, provides less prognostic information, and resembles an accessory atrioventricular (AV) connection during narrow complex tachycardia.More recently, very small microscopic alterations, usually referred to as microvolt TWA, can be detected by modern ECG machines and can be used to risk stratify patients after myocardial infarction to initiate proper SCD prevention measures (eg, implantable cardioverter defibrillator). This firefighter’s case is interesting because his baseline ECG (upper ECG strip) is normal and he is apparently healthy and without any cardiac history, although he has important risk factors for heart disease including high BMI and smoking. Current evidence suggests that TWA plays a pathologic role in SCD in athletes. Given the high prevalence of on-duty cardiac death in professional firefighters and the athletic nature of the job, attention needs to be directed toward the role of TWA as a risk stratifier in this high risk population.The results of this routine screening ETT warrant examination for coronary artery disease risk factors (obesity and smoking) and proper management to lower these risk factors. A referral to a cardiologist for more comprehensive evaluation (eg, electrophysiology testing and angiography) for any underlying cardiac pathology is also indicated.