Validity of estimates of myocardial oxidative metabolism with carbon-11 acetate and positron emission tomography despite altered patterns of substrate utilization.

We recently demonstrated that the myocardial turnover rate constant (k) measured noninvasively with positron emission tomography (PET) after intravenous administration of [11C]acetate provides a reliable index of myocardial oxidative metabolism (MVO2) theoretically independent of the pattern of myocardial substrate use. However, because estimates of metabolism with other metabolic tracers are sensitive to substrate use, we measured k in 12 dogs during baseline conditions and again after infusion of either glucose (n = 8) or Intralipid (n = 4), interventions that raised arterial glucose or fatty acids by more than fivefold with concomitant changes in myocardial substrate use. Following glucose administration k increased, but no difference was detected after compensation for changes in hemodynamics and myocardial work induced by the infusion (0.18 +/- 0.03 min-1 (t1/2 = 3.9 min) at baseline compared with 0.22 +/- 0.06 min-1 (t1/2 = 3.2 min, p = N.S.). k was not affected by Intralipid infusion (k = 0.15 +/- 0.06 min-1 at baseline and 0.14 +/- 0.04 min-1 during infusion), and correlated closely with MVO2 measured directly (n = 19 comparisons, r = 0.89). The results indicate that estimates of MVO2 using [11C]acetate and PET are valid despite changes in the pattern of myocardial substrate utilization.