Correlation Between Heart Rate Variability Indices and QT Durations in Heart Failure

Reduced heart rate variability (HRV) is consistently observed and is accepted to be due to autonomic dysfunction in patients with heart failure. The duration of QT interval and QT dispersion (QTd) is also known to be influenced by autonomic nervous system. The aim of this study is to evaluate the correlation between QT interval and QTd with HRV indices. Thirty-nine patients with heart failure were enrolled in the study in order to monitor 24-hour Holter recordings. The HRV indices and QT interval dynamicity were analyzed in the same recordings. QTd measurements were evaluated manually in the 12-lead electrocardiograms. The low-frequency (LF) and high frequency (HF) power were expressed in normalized units(nu). Corrected QT (QTc) intervals were found to be correlated with HF(nu) (r=0.36, p=0.02), however was negatively correlated with LF/HF ratio (r =-0.43, p=0.005) and SDNN (r=-0.37, p=0.01). There was no correlation between LF(nu) and QTc intervals. In patients with prolonged QTc interval (QTc ?440 msn); HF(nu) was significantly higher (16±10 to 9±5, p=0.01) and LF/HF ratio was significantly lower (1.7±0.6 to 3.1±1.6, p= 0.008) compared with patients without prolonged QTc interval. There was no significant difference in the LF(nu) values between patients with prolonged and normal QTc interval. In the reduced SDNN group (SDNN <100 msn); QTc interval was significantly longer (442±49 msn to 402±32 msn, p=0.001) and corrected QT dispersion (QTcd) was significantly increased (47±15 to 29±18, p=0.002). Among HRV indices, only SDNN showed significant correlation with QTcd. In conclusion; we observed a significant correlation between QT interval and HRV indices that may support autonomic modulation affecting the QT interval. These influences can be detected on electrocardiograms in patients with heart failure. (Türk Kardiyol Dern Arş 2004; 32: 232-238)