Electrical alternans detection during exercise and prediction of future cardiac health

The authors describe a noninvasive technique for the detection of electrical alternans from surface ECG recordings during exercise testing. For 35 patients aged 45 to 65, the mean alternans ratio was calculated for the QRS complex, ST segment and T-wave. Patients were grouped according to the response of the alternans ratio to the change in heart rate during exercise and recovery. The subsequent medical histories of the patients identified those that later suffered from cardiac problems. The positive group contained 63.6% of the patients that subsequently suffered from heart disease (HD). 91.7% of patients that were not later diagnosed as having HD were not part of the positive group. All patients suffering sudden cardiac death (SCD) were members of the positive group