Combined prognostic value of peak O2 uptake and microvolt level T-wave alternans in patients with idiopathic dilated cardiomyopathy

Background: Despite the great improvement in clinical management of patients with idiopathic dilated cardiomyopathy (DCM), sudden cardiac death (SCD) and death due to worsening heart failure (HF) remain a challenging problem. The assessment of oxygen consumption (peakVO₂) has been recognized as an independent marker of mortality. Nevertheless peakVO₂ is not helpful in the risk stratification of SCD. Given this limitation, the association with another non-invasive test able to predict SCD such as microvolt level T-wave alternans (MTWA) would be useful. Objectives: To determine the combined predictive value of peakVO₂ and MTWA in patients with DCM. Methods: Seventy consecutive DCM patients were prospectively investigated. PeakVO₂ and MTWA were determined during bicycle exercise testing. Primary composite study end-point was defined as major cardiac events (MCE): total cardiac death or documented sustained VT/VF (including appropriate ICD shock). Secondary end-point was defined as arrhythmic events (AE): SCD or documented sustained VT/VF. Results: Thirty-nine patients (55%) had a peakVO₂ <10 ml/kg/min, while 40 patients (57%) showed an abnormal MTWA test. During an average follow-up of 19.2 ± 10.7 months, 11 MCE of which 6 AE have been documented. Among patients with abnormal MTWA and peakVO₂ <10 ml/kg/min 8 MCE of which 5 AE occurred while among patients with normal MTWA and peakVO₂ ≥ 10 ml/kg/min no event occurred. From multivariate analysis, the combined prognostic value of MTWA and peakVO₂ achieved statistical significance for MCE (p = 0.03, HR 0.28, 95% CI 0.12-0.95) and for AE (p = 0.05, HR 0.39, 95% CI 0.18-0.99) while MTWA alone was a significant predictor of AE (p = 0.04, HR 0.32, 95% CI 0.14-0.93). Conclusions: Our results suggest that only the association of MTWA and peakVO₂, but not the two single tests, is a significant prognostic marker of both MCE and AE in DCM patients. However, MTWA alone confirms its predictive power as arrhythmic risk stratifier in this population.