title: Hypertrophic cardiomyopathy in childhood: disease natural history, impact of obstruction, and its influence on survival.
abstract: BACKGROUND
  We investigated the natural history, outcomes of myectomy, and impact on survival of obstructive hypertrophic cardiomyopathy (HCM) in childhood.
  
  
  METHODS
  All 120 children diagnosed with HCM between 1971 and 2006 were studied. Available echocardiograms (n=685) were incorporated in regression analyses adjusted for repeated measures. Multiphase parametric models and competing risks methodology were used to define outcomes.
  
  
  RESULTS
  Left ventricular outflow tract (LVOT) obstruction (peak gradient>30 mm Hg) developed in 61 (50%) of the cohort. Onset of obstructive features occurred during 2 discrete periods of risk; either during infancy (within 3 years of age), or otherwise later during early adolescence and beyond. Among children with obstructive HCM, the following 2 distinct groups were apparent: (1) those with peak LVOT gradients less than 65 mm Hg showed hemodynamic improvement (p<0.001) with medical strategies; and (2) those with peak gradients greater than 65 mm Hg instead had accelerated septal hypertrophy (p<0.001) with progression of peak gradients (p<0.01), and therefore underwent myectomy. Myectomy restored the gradient (mean 57 mm Hg reduction, 95% confidence interval 25 to 88, p<0.01) to nonobstructive levels. Furthermore, peak gradients and septal hypertrophy did not progress thereafter; they instead mirrored the natural history of nonobstructive HCM. Overall, in our experience, obstructive disease (or need for myectomy) did not influence late risk of death compared with children with nonobstructive HCM.
  
  
  CONCLUSIONS
  Obstructive HCM is phenotypically heterogeneous in childhood. Peak gradients less than 65 mm Hg respond well to nonsurgical management. The patient subset with higher gradients (>65 mm Hg) instead responds poorly and early myectomy should be pursued. Reassuringly, late survival in this cohort was not compromised by development of obstructive symptoms.
authors.affiliation: Division of Cardiovascular Surgery, Department of Surgery, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Hickey
authors.forename: Brian W
authors.initials: BW
authors.lastname: McCrindle
authors.forename: Signe-Holm
authors.initials: SH
authors.lastname: Larsen
authors.forename: Lee
authors.initials: L
authors.lastname: Benson
authors.forename: Cedric
authors.initials: C
authors.lastname: Manlhiot
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Caldarone
authors.forename: Glen S
authors.initials: GS
authors.lastname: Van Arsdell
authors.forename: Brett M
authors.initials: BM
authors.lastname: McCrindle
authors.forename: William G
authors.initials: WG
authors.lastname: Williams
mesh_terms: D000293:Adolescent; D000328:Adult; D002312:Cardiomyopathy, Hypertrophic / Q000150:complications* / Q000401:mortality / Q000601:surgery; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D014694:Ventricular Outflow Obstruction / Q000209:etiology*; D055815:Young Adult