Skeletal muscle ATP kinetics during exercise in patients with systolic heart failure

Abstract

Background Creatine kinase (CK) reaction is the primary energy reserve reaction in skeletal muscle (SM), providing additional ATP during exercise. Although exercise intolerance is a major limitation in systolic heart failure (SHF), the rate of ATP delivery by CK (CK flux) has not been studied during exercise in healthy subjects (HS) or SHF patients. We hypothesized that SM high-energy phosphates and CK flux are reduced at rest and during low intensity plantar flexion exercise (PFE) in mild-moderate SHF patients. Methods 14 non-ischemic SHF patients (EF<40) and 11 HS underwent 31P magnetic resonance spectroscopy with saturation transfer (MRST) measures of gastrocnemius creatine phosphate-to-ATP (PCr/ATP) and CK pseudo-first-order rate constant, k, at rest and during PFE in a Philips 3T MRI/ MRS system. Single-leg PFE involved lifting 0.9 kg/sec on a custom built non-magnetic device for 8.5 minutes. [ATP] (umol/g) was taken as 5.2umol/g for both groups and [PCr](umol/g) was calculated as (PCr/ATP)*(5.2umol/g) and CK flux (umol/g/s) as ([PCr]*k). Comparisons were made with paired and non-paired t-testing using XLSTAT package.