Effect of Hyperventilation on Periodic Repolarization Dynamics

Heart and lung functions are closely connected, and the interaction is mediated by the autonomic nervous system. Hyperventilation has been demonstrated to especially activate its sympathetic branch. However, there is still a lack of methods to assess autonomic activity within this cardiorespiratory coupling. Periodic repolarization dynamics (PRD) is an ECG-based biomarker mirroring the effect of efferent cardiac sympathetic activity on the ventricular myocardium. Its calculation is based on beat-to-beat variations of the T wave vector (dT degrees). In the present study, we investigated the effects of a standardized hyperventilation maneuver on changes of PRD and its underlyingdT degrees signal in 11 healthy subjects. In response to hyperventilation,dT degrees revealed a characteristic pattern and normalizeddT degrees values increased significantly compared to baseline [0.063 (IQR 0.032) vs. 0.376 (IQR 0.093),p< 0.001] and recovery [0.082 (IQR 0.029) vs. 0.376 (IQR 0.093),p< 0.001]. During recovery,dT degrees remained on a higher level compared to baseline (p= 0.019). When calculating PRD, we found significantly increased PRD values after hyperventilation compared to baseline [3.30 (IQR 2.29) deg(2)vs. 2.76 (IQR 1.43) deg(2),p= 0.018]. Linear regression analysis revealed that the increase in PRD level was independent of heart rate (p= 0.63). Our pilot data provide further insights in the effect of hyperventilation on sympathetic activity associated repolarization instability

Cardiovascular Mortality Can Be Predicted by Heart Rate Turbulence in Hemodialysis Patients

Background: Excess mortality in hemodialysis patients is mostly of cardiovascular origin. We examined the association of heart rate turbulence (HRT), a marker of baroreflex sensitivity, with cardiovascular mortality in hemodialysis patients. Methods: A population of 290 prevalent hemodialysis patients was followed up for a median of 3 years. HRT categories 0 (both turbulence onset [TO] and slope [TS] normal), 1 (TO or TS abnormal), and 2 (both TO and TS abnormal) were obtained from 24 h Holter recordings. The primary end-point was cardiovascular mortality. Associations of HRT categories with the endpoints were analyzed by multivariable Cox regression models including HRT, age, albumin, and the improved Charlson Comorbidity Index for hemodialysis patients. Multivariable linear regression analysis identified factors associated with TO and TS. Results: During the follow-up period, 20 patients died from cardiovascular causes. In patients with HRT categories 0, 1 and 2, cardiovascular mortality was 1, 10, and 22%, respectively. HRT category 2 showed the strongest independent association with cardiovascular mortality with a hazard ratio of 19.3 (95% confidence interval: 3.69-92.03;P < 0.001). Age, calcium phosphate product, and smoking status were associated with TO and TS. Diabetes mellitus and diastolic blood pressure were only associated with TS. Conclusion: Independent of known risk factors, HRT assessment allows identification of hemodialysis patients with low, intermediate, and high risk of cardiovascular mortality. Future prospective studies are needed to translate risk prediction into risk reduction in hemodialysis patients