OBJECTIVETo evaluate the direct effects of dobutamine as compared to adenosine on the coronary microcirculation in both normal and stenotic segments using myocardial contrast echocardiography (MCE).

METHODSLeft anterior descending (LAD) coronary artery stenosis, which was not flow limiting at rest, was established in 9 dogs. At the baseline and during intracoronary infusion of dobutamine (2 mg.kg(-1).min(-1)) and adenosine (5 mg.kg(-1).min(-1)), the radiolabeled microsphere (RM)-derived myocardial blood flow (MBF) were determined, and the double product (DP) and myocardial vascular resistance (MVR) were calculated. MCE was performed to determine the myocardial blood volume (MBV, represented by A) and microbubble velocity (beta).

RESULTSAs compared to the baseline level, the MBF increased and MVR decreased significantly in both the normal and abnormal beds during infusion of both drugs (P<0.05). In the normal bed, adenosine had no effect on MBV, the decrease in MVR was the result of decreased arteriolar (plus venular) resistance, and the increase in MBF was predominately due to the increase in b (deltabeta/ deltaA=13.6). Dobutamine caused a 28% increase in MBV, responsible for 32% of the decrease in the total MVR, but the increase in MBF arose mainly from the increase in b (deltabeta/deltaA=5.9). In the abnormal bed, both the drugs caused a similar increase in MBF entirely by increasing b, and 14% and 15% of the increases in capillary resistance were associated with the capillary derecruitment during administration of dobutamine and adenosine, respectively.

CONCLUSIONThe direct effects of intracoronary dobutamine infusion on the coronary microcirculation are similar to that of adenosine, and the increase in MBF occurs mostly as the result of increased myocardial blood velocity.