Delayed calf muscle phosphocreatine recovery after exercise identifies peripheral arterial disease

OBJECTIVES In this study we intend to characterize phosphocreatine (PCr) recovery kinetics with phosphoms-31 (P-31) magnetic resonance spectroscopy in symptomatic peripheral arterial disease (PAD) patients compared with control subjects and determine the diagnostic value and reproducibility of this parameter. BACKGROUND Due to the inconsistent relationship between flow and function in PAD, novel techniques focused on the end-organ are needed to assess disease severity and measure therapeutic response. METHODS Fourteen normal subjects (5 men, age 45 +/- 14 years) and 20 patients with mild-to-moderate symptomatic PAD (12 men, age 67 10 years, mean ankle brachial index 0.62 +/- 0.13) were studied. Subjects exercised one leg to exhaustion while supine in a 1.5-T magnetic resonance scanner using a custom-built plantar flexion device. Surface coil-localized, free induction decay acquisition localized to the mid-calf was used. Each P-31 spectrum consisted of 25 signal averages at a repetition time of 550 ms. The PCr recovery time constant was calculated by monoexponential fit of PCr versus time, beginning at exercise completion. RESULTS Median exercise time was 195.0 s in normal subjects and 162.5 s in PAD patients (p = 0.06). Despite shorter exercise times in patients, the median recovery time constant of PCr was 34.7 s in normal subjects and 91.0 s in PAD patients. Area under the receiver-operating characteristic curve was 0.925 +/- 0.045. Test-retest reliability was excellent. CONCLUSIONS The PCr recovery time constant is prolonged in patients wish symptomatic PAD compared with normal subjects. The method is reproducible and may be useful in the identification of disease. Further study of this parameter's ability to track response to therapy as well as its prognostic capability is warranted.