Deceleration Capacity of Heart Rate in Long-QT Syndrome

Objectives: Risk stratification in patients with the long-QT (LQT) syndrome is of critical importance. Previous studies demonstrated a link between alterations of cardiac autonomic function and malignant arrhythmias in LQT-syndrome. Deceleration Capacity (DC) of heart rate is a novel autonomic ECG-based marker that specifically captures deceleration-related oscillations of heart rate. Impaired DC has established as strong and independent predictor of mortality in post-infarction patients which is superior to standard measures of heart rate variability (HRV). The potential prognostic value of DC in LQT-patients is unknown. This is the first study to investigate DC in LQT-patients.

Methods: We included 20 patients (age: 24 ± 10 years, 5 males) with genetically confirmed LQT-syndrome from our outpatient clinic who were compared with 20 age- and gender-matched controls. In all subjects, a 30-minute high-resolution resting ECG was performed in supine position and under resting conditions. DC of heart rate as well as all established measures of HRV in time and frequency domain (mean heart rate, SDNN, RMSSD, VLF, LF, HF) were assessed according to previously published technologies.

Results: In LQT-patients, we noted a significantly reduced resting heart rate (65 ± 8 bpm vs. 74 ± 9 bpm, p< 0.05), presumably due to chronic beta-blockade in 17 of the 20 LQT patients. DC was lower in LQT compared with controls (6.0 ± 5.0ms vs. 8.1 ± 3.3ms, p = 0.054). This difference aggravated when Results were adjusted for underlying heart rate (p = 0.016). Interestingly, all other markers of heart rate variability showed no difference between LQT-patients and controls, whether adjusted for underlying heart rate or not.

Conclusion: DC is reduced in LQT-patients compared with control, particularly when adjusted to underlying heart rate. Future studies should test whether impaired DC is associated with the clinical phenotype.