METABOLIC RESPONSE OF NORMAL HUMAN MYOCARDIUM TO HIGH-DOSE ATROPINE-DOBUTAMINE STRESS STUDIED BY P-31-MRS

Background P-31-MRS during cardiac stress may provide (patho)physiolog ical insights into the high-energy phosphate metabolism of the myocard ium. Accordingly, the purpose of the present study was to determine th e metabolic response of normal human myocardium to severe atropine-dob utamine (A-D) stress. To corroborate the results from the present in v ivo study, a P-31-MRS experiment was performed with a moving phantom t o simulate respiratory motion. Methods and Results The phantom experim ent showed no relation (P=.371) between the intensity ratio of two sep arate phosphate peaks and amplitude of phantom excursions. The phospho creatine (PCr) and ATP signal strength and the PCr/ATP ratio were dete rmined from the left ventricular wall in 20 healthy subjects (posttest likelihood for coronary artery disease was <2.5%) with P-31-MRS at re st and during high-dose A-D stress (rate-pressure product increased th reefold). Stress-induced changes were -21% for PCr (P<.001) and -9% fo r ATP (P<.05). The average PCr/ATP value at rest was 1.42+/-0.18 and d ecreased by 14% to 1.22+/-0.20 during stress (P<.001). Conclusions The phantom experiment shows that the in vivo decrease of myocardial PCr/ ATP due to high-dose A-D stress we observed is not a motion artifact. Consequently, this indicates that myocardial high-energy phosphate met abolism of the normal human heart is altered at high workloads.