Altered heart rate variability in long QT syndrome assessed by 24 hour holter recordings

Purpose of the Study: Conventional heart rate variability (HRV) parameters in long QT syndrome (LQTS) have only been studied in small cohorts and results were conflicting. Therefore we evaluated HRV parameters in a large cohort of genotyped LQTS patients. Methods: We included 68 LQTS patients (22 LQT1, 39 LQT2 and 7 LQT3) and 55 controls comprised of 31 genotype negative family members of LQTS probands and 24 additional controls to balance the groups. All individuals underwent 2 channel 24 hour holter recordings with HRV analysis (Synescope, ELA medical). Parameters were assessed both over 24 hours and during daytime (8AM-9 PM) and nighttime (11PM-6AM) separately. The included parameters were both time domain measures (SDNN, SDANN, RMSSD, SDNN index and PNN50) and frequency domain measures of HRV (normalized high frequency (HFn) and low frequency (LFn) power). LQTS patients and controls were compared using a unpaired student T-test. LQT1 and LQT2 were compared with controls using One-way ANOVA. Patients with LQT3 were not included in this genotype analysis since the low number of patients (N=7). Summary of Results: LQTS patients were more often treated with beta-blockers (37% versus 20%; p=0.04), while age and gender were comparable. RMSSD (52 ± 31 ms versus 39 ± 19 ms; p=0.008), PNN50 (18 ± 15 % versus 11 ± 9 %; p=0.004), SDNN (157 ± 47 ms versus 141 ± 36 ms; p=0.03) and HFn (27 ± 12 ms versus 22 ± 10 ms; p=0.01) were significantly increased, while LFn (60 ± 12 ms versus 66 ± 10 ms; p=0.006) was significantly reduced during 24 hour measurements in LQTS compared to controls. These observations remained significant during daytime, but during nighttime this was only true for RMSSD, PNN50 and HFn. Subgroup analysis revealed that the difference for RMSSD, PNN50, SDNN and LFn remained significant in the LQT2 patients, but not in the LQT1 patients compared to controls. There was no difference in any of the HRV parameters in the LQTS patients taking beta-blockers (N=25) compared to those that did not (N=43). Since there were only 8 symptomatic LQTS patients in this cohort, evaluation of the value in risk stratification was not feasible. Conclusion: Patients with LQTS, and especially LQT2, showed a modulation of the autonomic tone of the sinus node. Whether these markers can help in risk stratification should be evaluated in a cohort with more symptomatic patients.

Jaar van publicatie:2016