Prolonged QT interval is an independent risk factor for sudden cardiac death. Our recent study demonstrated that acquired long QT syndrome (ALQTS) is common in patients with left ventricular hypertrophy (LVH). In this study, we tested a hypothesis that cardiac autonomic nervous system is altered in ALQTS patients with essential hypertensive LVH (EHTN-LVH).Design and method:
In a retrospective study, ambulatory ECGs (24-hour Holter) were analyzed in 156 patients (age 58 ± 14 years, male 64%) diagnosed with EHTN-LVH. All study subjects met the ECG criteria for LVH defined by Sokolow-Lyon Voltage, Cornell Voltage or Cornell Voltage Products. ECG parameters including heart rate (HR) and QT interval (QTc by Bazett's) were evaluated. QTc prolongation was defined by QTc ≥ 450ms. The function of autonomic nervous system was assessed by heart rate variability (HRV) with SDNN (standard deviation of RR intervals), SDANN (standard deviation of the means of all corrected RR intervals calculated at 5-minute intervals), rMSSD ( the square root of the mean squared differences of successive RR intervals), pNN50 (percentage of difference between successive normal RR intervals that were > 50 ms computed over the entire Holter recording), HF (high frequency), LF (low frequency) and LF/HF ratio analyzed.Results:
Prolonged QTc was seen in 33 (21%) patients. Compared to patients with normal QTc, there were significantly decreased SDNN, rMSSD, PNN50, LF, and HF in the ALQTS subjects (Table 1). Moreover, patients in ALQTS group had a faster HR [72 (67, 80) vs 64 (59, 71) bpm, P < 0.01].Conclusions:
The decreased HRV and increased HR indicate that EHTN-LVH patients with QT prolongation have a higher cardiac sympathetic drive. Whether there is a causative relationship between the dysfunction of cardiac autonomic nervous system and prolonged QT interval in EHTN-LVH warrant further investigation.