962-67 Dobutamine Stress has a Limited Value for Enhancing Flow Heterogeneity in the Presence of a Moderate Stenosis When Used in Conjunction with Tc99m-Sestamibi Imaging

Dobutamine (DOB) is used as an alternative to exercise in conjunction with Tc99m-sestamibi (MB) SPECT perfusion imaging; however, the utility of quantitative DOB MB SPECT to enhance flow heterogeneity is not established, To validate this approach, we injected MB and radiolabeled microspheres in 6 open chest dogs during DOB stress in the presence of a flow limiting LCX stenosis (STEN). The proximal LCX was partially occluded, so as to create a 30 mmHg gradient across the STEN. Radiolabeled microspheres were injected at baseline (BASE), during STEN, and during DOB stress (10 μg/kg/min). MB was injected i.v. at peak DOB. Hearts were excised 20 min after MB injection for postmortem analysis. Hearts were cut into 96 or 192 segments for gamma well counting, for determination of myocardial MB activity and microsphere flow (μFL). The moderate stenosis resulted in impairment of CFR in response to i.c. adenosine (18 μ g) during STEN (pre-STEN: 2.44 ± 0.21; STEN: 1.24 ± 0.05, P l 0.005)as measured by an epicardial flow probe. DOB increased heart rate significantly (Pre-DOB: 112 ± 8 bpm; DOB: 141 ± 8 bpm, p l 0.001), and did not significantly reduce mean aortic pressure (Pre-DOB: 80 ± 5; DOB: 95 ± 7, P = ns). Measured μFL (ml/min/gm) and MB activity for nonischemic (NI) and ischemic (lS) regions are shown below (mean ± SEM): 1S μFL NI μFL IS/NI μFL MB(%NI) BASE 0.88 ± 0.13 0.96 ± 0.18 0.93 ± 0.02 - STEN 0.58 ± 0.14 0.97 ± 0.11 0.59 ± 0.10 - DaB 1.02 ± 0.37 1.87 ± 0.32 * 0.52 ± 0.12 # 0.70 ± 0.06 † * p l 0.05 vs STEN † P l 0.05 vs IS/NI μFL # P = ns vs STEN DOB increased flow in both the NI and IS regions. Myocardial MB activity (%Nl) correlated with flow (MB = 0.69FL + 0.47, r = 0.66, n = 417) when flow was less than 1 ml/min/gm. However, at higher flow ranges (1 to 4.5 ml/min/gm) MB activity did not correlate with flow (MB = 0.04FL + 0.94, r = 0.13, n = 543). This resulted in the underestimation of the relative flow deficit by MB Thus, DOB may have limited value for the enhancement of flow heterogeneity, since (1) DOB does not augment the flow heterogeneity in the presence of a moderate flow limiting STEN (49% reduction CFR), and (2) myocardial MB activity does not correlate with μFL at higher flows induced by DOB.