CARDIAC AND NON-CARDIAC RISK STRATIFICATION BY USING HEART RATE AND ITS VARIABILITY - VALIDATION STUDY
Background: Previously, we have demonstrated (on the cohort of 1455 post-infarction patients) that heart rate (HR) contributes to the predictive power of heart rate variability (HRV), moreover, by using simple modifications of the HRV dependence on HR we have been able to differentiate those at risk of cardiac and non-cardiac death. Specifically, we have shown that the very low frequency component highly dependent on HR (‘VLF-dependent’) is more powerful in predicting cardiac death than non-cardiac death, but the very low frequency component independent of HR (‘VLF-independent’) is the strongest predictor of non-cardiac mortality.
The aim of the present study was to validate the principal findings of our previous research.
Method: We analyzed a separate group of 946 post-infarction patients. Twenty one of them were not eligible for the spectral HRV analysis due to artifacts and arrhythmias in their Holter recordings and were excluded. The excluded group exhibited the same risk of death as the remaining patients (p=0.93), thus this exclusion should not bias the study results. During a 5-year follow-up period, 48 (5.2%) patients died, i.e. 28 (3.0%) from cardiac and 20 (2.2%) from non-cardiac causes. Spectral HRV indices were estimated from 512 RR interval segments of Holter recordings and then averaged for each patient. ‘VLF-dependent’ was calculated by multiplication of standard VLF by average RR interval to the power of 16, but ‘VLF-independent’ was obtained by division of standard VLF by average RR interval to the power of 4. The cut-off points for ‘VLF-dependent’ (i.e. 4.00E+47ms^18) in predicting cardiac death and for ‘VLF-independent’ (i.e. 6.61E-10/ms^2) in predicting non-cardiac death were pre-specified on the basis of our previous study.
Figure 72.1. Kaplan-Meier curves of cardiac, non-cardiac and all-cause death for patients stratified according to the 'VLF-dependent' and 'VLF-independent'
Results: Figure shows cumulative cardiac, non-cardiac and all-cause mortality curves for the patients classified by the "‘VLF-dependent" and "VLF-independent".
Conclusion: the "VLF-dependent" proves to be a significant predictor of cardiac death, whereas the "VLF-independent" predicts non-cardiac death - the combination of both indices stratifies all-cause mortality. Thus, the analysis of the validation cohort confirmed principal findings of our previous study.