title: The effect of heart rate on wave reflections may be determined by the level of aortic stiffness: clinical and technical implications.
abstract: BACKGROUND
  Augmentation Index (AIx) is related to cardiovascular diseases, risk, and mortality. AIx is associated with heart rate but the effect of aortic stiffness on this relationship has not been studied. The purpose of our study was to investigate the relationship between AIx and heart rate at different aortic stiffness levels.
  
  
  METHODS
  The study consisted of 425 normotensive and untreated hypertensive subjects. Wave reflections and pulse-wave velocity (PWV) were determined by the Sphygmocor and the Complior systems, respectively.
  
  
  RESULTS
  AIx was independently associated with heart rate, age, gender, height, mean blood pressure (BP) and the effective reflection site distance (ERD). The population was divided into three groups of those with different PWV levels (tertiles). The regression lines for AIx with heart rate differed significantly between the 3rd and the other two tertiles of PWV (P = 0.039 for slopes and P = 0.002 for intercepts). This difference remained significant even after adjustment for age, gender, height, mean BP, and distance of wave reflections.
  
  
  CONCLUSIONS
  A significantly stronger correlation of AIx with heart rate was observed in subjects with higher levels of aortic stiffness as compared to those with lower levels; namely, the same increase in the heart rate between subjects, induced a greater decrease in the AIx at higher compared to lower PWV levels. The correction of AIx for heart rate should be reconsidered based on the aortic stiffness level. This finding has implications for interventional studies that aim to improve central hemodynamics but simultaneously affect heart rate. Further studies that show acute modifications of heart rate at different arterial stiffness levels are required to support these findings.
authors.affiliation: First Department of Cardiology, Unit of Biomedical Engineering and Hypertension Unit, Hippokration Hospital, Medical School, National & Kapodistrian University of Athens, Greece. theopap@mail.ntua.gr
authors.forename: Theodore G
authors.initials: TG
authors.lastname: Papaioannou
authors.forename: Charalambos V
authors.initials: CV
authors.lastname: Vlachopoulos
authors.forename: Nikolaos A
authors.initials: NA
authors.lastname: Alexopoulos
authors.forename: Ioanna
authors.initials: I
authors.lastname: Dima
authors.forename: Panagiota G
authors.initials: PG
authors.lastname: Pietri
authors.forename: Athanassios D
authors.initials: AD
authors.lastname: Protogerou
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Vyssoulis
authors.forename: Christodoulos I
authors.initials: CI
authors.lastname: Stefanadis
mesh_terms: D000328:Adult; D001011:Aorta / Q000502:physiology* / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology*; D001916:Brachial Artery / Q000502:physiology / Q000503:physiopathology; D016022:Case-Control Studies; D004548:Elasticity; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011673:Pulsatile Flow / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology