747-6 Myocardial Blood Flow in Aortic Regurgitation: Comparison of Global and Regional Blood Flow to Regional Wall Stresses

The impact of regional wall stress (WS) abnormalities on regional coronary flow (CBF) in aortic regurgitation (AR) is not known. However, the existence of such a relation is of potential importance since it might account in part for LV dysfunction and myocardial fibrosis seen in AR, and could suggest therapeutic strategies. We have previously developed and validated a method for calculating regional WS in the radial, circumferential and meridional directions from mid wall (MW) to apex (AP) and endocardium (ENDO) to epicardium (EPI) using a 4000 element model of the LV To define the relation of regional WS and CSF in AR, we applied our LV model in 5 normal (NL) and 4 AR rabbits in which regional CBF was measured using fluorescent microspheres. CBF and radial WS were as follows:CBF (ml/min/gm)Radial WS (×103dynes/cm2)MWAPMWAPNLEPI2.491.308329*ENDO2.090.74133133*AREPI1.821.82*8638*ENDO1.410.77*133133**=p<0.001 (EPI vs ENDO for CSF, EPI to ENDO gradient in AR vs NL for radial WS)Thus, in AR, transmural CBF distribution varies significantly at the apex, while this tendency is less marked and less consistent in NL. No discernable transmural variation was apparent elsewhere in either group. These differences paralleled inversely the transmural variations in radial WS in AR vs NL. In contrast, meridional WS and circumferential WS were uniformly and significantly higher in AR than NL at apex and base (all p < 0.001), a pattern which bore no relation to regional CSF pattern. Thus, regional radial WS influences regional transmural CBF pattern in AR. The importance of this relation to regional LV function and regional myocardial fibrosis in AR now must be assessed

901-102 Atherosclerotic Plaques Imaged by Tc-99m-Labeled Synthetic Peptide

1–123 SP-4. a synthetic oligopeptide fragment of apolipoprotein B, identifies aortic atherosclerosis in a hyperlipidemic rabbit model by external gamma camera imaging. Because Tc-99m is preferable to 1–123 for imaging, we have studied 3 Tc-99m-labeled SP-4-derived peptides, each coinjected with 1–125 SP-4 into normal (NL) or cholesterol-fed (CF) New Zealand White Rabbits, sacrificed at 15–30 min (6 NL; 6 CF) or 2hr (11 NL;12 CF) later. Aortas in CF rabbits invariably revealed high atherosclerotic lesion density, while atherosclerotic lesions were absent from NL rabbit aortas. After sacrifice, the aorta was excised and divided into upper, middle and lower segments and percent injected dose per gram (%ID/gm) was determined. At 30min NL and CF did not differ, but at 2hrs %ID/gm values were as follows:AortaTimeP352P302P380SP-4UpperNL 2hr0.005730.002080.003320.00088CF 2hr0.005340.002380.007480.00296*MiddleNL 2hr0.003590.001940.002730.00078CF 2hr0004590002120.00722*0.00203*‡LowerNL 2hr0.003670001620001880.00061CF 2hr0.003000001950.00806*0.00209*†*p<0.05 vs NL.†p<0.02 vs P380.‡p<0.008 vs P380Tc-99m P380 showed greater absolute uptake in plaque than SP-4, and relatively similar CF-to-NL ratios. We conclude that P380 shows particular affinity for the atherosclerotic aorta. comparable to that apparent with 1-123 SP-4. Given the favorable imaging characteristics of 99mTc vs 123l, P380 holds particular promise for clinical imaging