title: Intact skeletal muscle mitochondrial enzyme activity but diminished exercise capacity in advanced heart failure patients on optimal medical and device therapy.
abstract: BACKGROUND
  A skeletal myopathy, perhaps attributable to neuro-endocrine excitation or disuse, has been described in heart failure (HF) patients, and is thought to contribute to their exercise limitation. Our purpose was to assess biochemical and morphometric characteristics of skeletal muscles of HF patients on optimal HF therapy. A secondary purpose was to explore the effects of clonidine, which interrupts the neuro-endocrine excitation, on these same muscle characteristics.
  
  
  RESULTS
  Eleven HF patients (50.8 ± 3.4 years, peak VO2 11.6 ± 2.5 ml/kg/min) underwent two vastus lateralis biopsies (pre/post clonidine). Baseline values were compared to biopsies in 11 age-matched, healthy controls. Scatter plots of individual values for each mitochondrial enzyme revealed almost complete overlap between HF and control groups; mean values, although tending to be greater in controls versus HF patients, were not significantly different. The proportion of type 1 fibers was diminished in 10 of 11 patients. There was no difference in any of the variables after 3 months clonidine versus placebo.
  
  
  CONCLUSIONS
  In HF patients treated with optimal medical and device therapy, characteristic abnormalities of mitochondrial enzyme activity are not found, but muscle fiber type shifts are present. The remaining severe impairment in exercise capacity cannot be attributed to mitochondrial abnormalities.
authors.affiliation: Division of Cardiology, Department of Medicine, David Geffen School of Medicine at UCLA, A2-237 CHS, 10833 Le Conte Avenue, Los Angeles, CA, 90095, USA. hmiddlekauff@mednet.ucla.edu
authors.forename: Holly R
authors.initials: HR
authors.lastname: Middlekauff
authors.forename: M Anthony
authors.initials: MA
authors.lastname: Verity
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Horwich
authors.forename: Gregg C
authors.initials: GC
authors.lastname: Fonarow
authors.forename: Michele A
authors.initials: MA
authors.lastname: Hamilton
authors.forename: Perry
authors.initials: P
authors.lastname: Shieh
mesh_terms: D001706:Biopsy; D016022:Case-Control Studies; D003000:Clonidine / Q000494:pharmacology*; D004311:Double-Blind Method; D017079:Exercise Tolerance; D005260:Female; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000201:enzymology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D013565:Sympatholytics / Q000494:pharmacology*
chemical_list: D013565:Sympatholytics; D003000:Clonidine