Effects of dobutamine at maximally tolerated dose on myocardial blood flow in humans with ischemic heart disease

Background: This study tests the hypothesis in humans with ischemic heart disease that myocardial blood flow response to dobutamine is linearly correlated with blood flow response to adenosine. Methods and Results: PET with [¹³N]ammonia was used to measure myocardial blood flow at rest and during adenosine and dobutamine at the maximally tolerated dose. Myocardial segments were defined physiologically on the basis of blood flow response to adenosine: normal, ≤2 mL · min^-1 · g^-1; abnormal, <2 mL · min^-1 · g^-1; and 'steal,' decline versus baseline ≤0.15 mL · min^-1 · g^-1. The patient population consisted of 11 men and 2 women. Dobutamine increased heart rate (79 ± 22 to 115 ± 28 bpm) and rate-pressure product (9748 ± 2862 to 15 157 ± 3433 mm Hg/min) significantly (both P<.01). Myocardial blood flow at rest in abnormal segments (0.50 ± 0.23 mL · min^-1 · g^{- 1}) was reduced (P<.001) versus normal (0.90 ± 0.45) and steal (0.92 ± 0,60). Nevertheless, in abnormal segments, blood flow increased versus rest (P<.001) with dobutamine (0.83 ± 0.43) and adenosine (0.90 ± 0.49). In steal segments, myocardial blood flow declined versus baseline (P<.001) with dobutamine (0.68 ± 0.46) and adenosine (0.50 ± 0.45). In normal segments, myocardial blood flow increased (P<.001) with dobutamine (2.16 ± 0.99) and adenosine (3.10 ± 0.90). Over the range of flows, the correlation between adenosine and dobutamine was good (r=.78, P<.0001). Although flow with dobutamine in normal segments correlated with rate-pressure product (r=.81, P<.05), the slope of the line was 2.7 ± 0.8 (P<.02), and normalized blood flow (3.3 ± 2.5 xrest) exceeded normalized rate-pressure product (1.9 ± 0.8 xrest; P<.05). Conclusions: In humans with ischemic heart disease, myocardial blood flow responses to dobutamine and adenosine are linearly correlated over a wide range. The hyperemic response to dobutamine is in excess of that predicted by rate-pressure product and reflects the unmeasured inotropic, oxygen-wasting, and β₂-agonist effects of the drug. Dobutamine induces coronary steal with a frequency approaching that of adenosine.