The effects of cardiac resynchronization treatment on autonomic functions aside from functional status in heart failure

Objective: Cardiac resynchronization therapy (CRT) improves heart rate variability (HRV) and heart rate turbulence (HRT) parameters. Herein, our aim was to compare these parameters with intracardiac- cardioverter defibrillator (ICD) patients with similar functional status to detect possible additional benefits of CRT on autonomic functions. Methods: Patients who had systolic HF (NYHA class II and III) with an ejection fraction <35% were enrolled in this observational, cross-sectional study. These patients were implanted either an ICD or a CRT device. A 24-hour Holter recording was obtained to assess HRV and HRT parameters in 2 groups. Unpaired t-test and Chi-square test were used for comparisons between 2 groups. Logistic regression analysis was performed to determine the variables affecting functional status. Results: Of 105 patients included in the study; 55 had CRT and 50 had ICD device. The baseline characteristics of the patients were similar in both groups. SDNN, SDANN, SDNN index, and LFnu were similar in both groups; however, RMSSD, pNN50, HFnu, LF/HF ratio, turbulence slope and albeit to a non-significant value turbulence onset were better in CRT group. When the HRV and HRT parameters were compared according to functional status, patients in functional class II had significantly better HRV and HRT parameters when compared to the ones in class III (p<0.05 for all). Regression analysis showed that only SDNN was associated with functional class [OR: 0.89 (95% CI: 0.80-0.98), p=0.03]. After the covariance analysis to eliminate the effects of functional status on HRV and HRT parameters; the parameters mostly related with the parasympathetic system activity, namely RMSSD, pNN50, HFnu, LF/HF ratio, turbulence onset and turbulence slope were still better in CRT group. Conclusion: The most striking finding in our study is that HRV and HRT values related with parasympathetic activation are better in CRT patients when compared to ICD patients with similar functional status. Therefore, upgrading to CRT may have additional benefits on autonomic functions, which needs further investigation.