Identification of impaired metabolic reserve by atrial pacing in patients with significant coronary artery stenosis.

We investigated myocardial 11C-palmitate clearance kinetics at a resting heart rate (control) and during pacing using positron-emission tomography in 10 patients with significant coronary artery stenosis (greater than 70%) and evidence of exercise-induced ischemia. Serial 11C-palmitate images acquired at control and during pacing revealed biexponential myocardial 11C clearance both in myocardium supplied by a stenotic coronary artery (myocardium "at risk") and in myocardium supplied by a normal coronary artery (normal myocardium). At control, the average rate of myocardial 11C clearance from the early rapid curve component (the clearance half-time) was similar in normal myocardium and in that at risk (22.2 +/- 5.2 vs 21.0 +/- 5.4 min, NS), as was the amount of myocardial 11C activity at the end of the early rapid phase (residual fraction 56.3 +/- 7.2% vs 54.7 +/- 7.3%, NS). Thus, myocardial clearance was homogeneous at control, suggesting a similar rate and amount of 11C-palmitate oxidation in normal myoc...