title: Isovolumic acceleration at rest and during exercise in children normal values for the left ventricle and first noninvasive demonstration of exercise-induced force-frequency relationships.
abstract: OBJECTIVE
  This study aimed to determine the normal variation of left ventricular (LV) isovolumic acceleration (IVA) in healthy children and to assess the feasibility of an entirely noninvasive method for demonstration of the LV force-frequency relationship (FFR).
  
  
  BACKGROUND
  Pediatric cardiologists continue to seek noninvasive, load-independent indexes for the assessment of LV contractility and myocardial reserve.
  
  
  METHODS
  Resting LV IVA was measured by echocardiogram in 236 healthy children and compared with their clinical characteristics. Further measurements were made in 51 children at incremental heart rates during semi-recumbent exercise. For these, FFRs were constructed by plotting LV IVA against heart rate. To assess potential clinical applications, pilot FFR data were collected from 16 children previously treated with anthracyclines.
  
  
  RESULTS
  In healthy children, median resting LV IVA was 1.2 m/s(2), interquartile range 0.9 to 1.6 m/s(2). Resting LV IVA was unaffected by age, sex, weight, height, and body surface area but associated with baseline heart rate (r = 0.18, p = 0.0006). Noninvasive evaluation of the LV FFR was possible in 98% of subjects. Positive FFRs were confirmed in all the healthy children. By comparison, several of the children with anthracycline exposure demonstrated flattened force-frequency curves that were largely independent of resting LV ejection fraction and suggest reduced contractile reserve.
  
  
  CONCLUSIONS
  In children over 7 years, it is possible to demonstrate the LV FFR by interval measurement of IVA during exercise. The availability of pediatric normal values for both this relation and resting LV IVA might facilitate future investigation of LV contractility and myocardial contractile reserve during childhood.
authors.affiliation: The Labatt Family Heart Centre, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Susan Lucy
authors.initials: SL
authors.lastname: Roche
authors.forename: Michael
authors.initials: M
authors.lastname: Vogel
authors.forename: Oli
authors.initials: O
authors.lastname: Pitkänen
authors.forename: Brian
authors.initials: B
authors.lastname: Grant
authors.forename: Cameron
authors.initials: C
authors.lastname: Slorach
authors.forename: Cheryl
authors.initials: C
authors.lastname: Fackoury
authors.forename: Derek
authors.initials: D
authors.lastname: Stephens
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Smallhorn
authors.forename: Lee N
authors.initials: LN
authors.lastname: Benson
authors.forename: Paul F
authors.initials: PF
authors.lastname: Kantor
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Redington
mesh_terms: D000054:Acceleration; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004452:Echocardiography; D015444:Exercise / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D012016:Reference Values; D012146:Rest / Q000502:physiology*; D013318:Stroke Volume; D016277:Ventricular Function, Left / Q000502:physiology*