title: The heart rate performance curve and left ventricular function during exercise in patients after myocardial infarction.
abstract: OBJECTIVE
  The aim of the study was to investigate the heart rate turn point (HRTP) in the time course of the heart rate performance curve (HRPC) in patients after myocardial infarction, and the relationship between the HRTP, the left ventricular function, and the second lactate turn point (LTP2).
  
  
  METHODS
  We studied the degree and the direction of the HRPC and the left ventricular ejection fraction (LVEF) in 49 male patients 57 +/- 8 d after their first posterior wall infarction (MI). An incremental cycle ergometer test was performed and three phases of energy supply were defined (I: aerobic; II: aerobic-anaerobic transition; III: anaerobic) via blood lactate LA concentration. HRTP and LVEF-turn points (LVEFTP) were assessed by linear turn point analysis. The degree and direction of the deflection of HRPC were described as factor k (k > 0.1: downward deflection; -0.1 < k < 0.1: linear time curse; k < -0.1: upward deflection). The LVEF was determined by RNA. The difference between Pmax and LTP2 was calculated for LVEF (delta LVEF).
  
  
  RESULTS
  An HRTP could be found in 44 and a LVEFTP in 47 cases. The HRTP occurred at 85 +/- 17 Watt (W), which correlated (r = 0.95; P < 0.001) with the LTP2 (84 +/- 17 W) and the LVEFTP (84 +/- 17 W, r = 0.93; P < 0.001). From LTP2 to Pmax a significant decrease in LVEF was found. There was a correlation between the percentage of HRmax at the HRTP and k (r = 0.70), as well as delta LVEF (r = 0.56).
  
  
  CONCLUSIONS
  To prevent myocardial overloading, it seems to be useful to determine the HRTP, which indicate the workload where LVEF decreases.
authors.affiliation: Department of Sport Physiology University of Vienna, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Pokan
authors.forename: P
authors.initials: P
authors.lastname: Hofmann
authors.forename: S P
authors.initials: SP
authors.lastname: von Duvillard
authors.forename: F
authors.initials: F
authors.lastname: Beaufort
authors.forename: G
authors.initials: G
authors.lastname: Smekal
authors.forename: R
authors.initials: R
authors.lastname: Gasser
authors.forename: W
authors.initials: W
authors.lastname: Klein
authors.forename: B
authors.initials: B
authors.lastname: Eber
authors.forename: N
authors.initials: N
authors.lastname: Bachl
authors.forename: P
authors.initials: P
authors.lastname: Schmid
mesh_terms: D015308:Anaerobic Threshold / Q000502:physiology; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology; D004452:Echocardiography; D018618:Echocardiography, Doppler, Color; D005080:Exercise Test; D015637:Gated Blood-Pool Imaging; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000000981:diagnostic imaging / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology*
chemical_list: D007773:Lactates