216 Low stress-induced ST segment/Heart rate hysteresis as a predictor of low microvolt T-wave alternans

Background ST segment/heart rate hysteresis can improve the diagnostic performance of the exercise ECG for prediction of coronary artery disease and cardiovascular mortality. As this simple variable integrates the heart-rate adjusted ST segment depression during exercise and recovery phase, ST/HR hysteresis is related both to ischemia and sympathovagal balance. Microvolt T wave alternans (TWA) measurement during stress testing has been suggested as a predictor of life-threatening cardiac arrhythmia. According to the Coumel's triangle hypothesis, the sympathovagal balance could modulate TWA. Dipyridamol-induced ischemia does not disturb significantly this balance. Purpose We aimed to assess the absence of an elevated TWA under a dipyridamol SPECT imaging. Methods and Results All 339 consecutive patients who were referred for a pharmacological stress test with dipyridamol. The maximum TWA was determined with the modified moving average method. Using for ST/HR hysteresis a cutoff of 0.038 mV, yields a 75% negative predictive value for a TWA above the reported threshold of 47 μV (from holter recordings). ST/HR hysteresis negative predictive value was even better reaching 90% to rule out the occurrence of a higher TWA (65 μV derived from ECG stress testing). Conclusion The absence of significant alterations in sympathovagal balance seems to be associated with low T-wave alternans. ST/HR hysteresis might be useful to exclude the possibility of an elevated T wave alternans.