RESUMO
The objective of this scientific work was to evaluate the extent and severity of perfusion abnormalities on myocardial perfusion scintigraphy (MPS) at rest and with sublingual nitroglycerine, in relation to the presence and anatomical location of collaterals demonstrated by selective coronary angiography (SCA). Twenty-eight patients with unstable angina underwent selective coronary angiography. Eighteen of them were diagnosed with myocardial infarction (MI) 2-15 days prior to examination. Presence or absence of collaterals was noted, with anatomical depiction of donor and recipient arteries as well as evaluation of degree of collateral flow. As an inclusion criterion, collateral flow had to be grade 2 (partial epicardial filling of the occluded artery) or 3 (complete epicardial filling of the occluded artery) in accordance with the Rentrop collateral flow classification. Flow was noted as follows: Complete antegrade (CA), complete retrograde (CR), partial antegrade (PA), and partial retrograde (PR). Myocardial perfusion scintigraphy using Tc-99m Sestamibi at rest and after sublingual administration of nitroglycerine was performed according to a 2-day protocol. Perfusion abnormalities, which were quantified using the 20-segments model and visual 5-point system (0, normal perfusion; 4, absent perfusion), were analyzed according to donor's and recipient's territories, as well as territories with limited or without collateral flow (PA/PR, grade 0-1 flow). A total of 84 arteries were analyzed, with stenosis in 79 of them. Arteries were divided into three groups: Donors (group I), recipients (group II), and arteries with limited or without collaterals (group III). In group I, there were 28 donor arteries, with mean severity of stenosis 71.3 ± 0.65%. In group II, there were 36 recipient arteries and mean severity of stenosis was 94.8 ± 0.26%. In group III, there were 20 arteries, and all of them had either no or poorly developed collaterals (mean severity of stenosis 60.4 ± 2%). In 3 cases, 2 donor arteries gave collaterals to 1 recipient artery, while in 11 cases, a single donor artery gave collaterals to 2 recipient arteries, and in 11 cases there was 1 donor to 1 recipient artery. A total of 1120 MPS segments were analyzed (560 at rest and 560 after nitroglycerine). The number of segments in groups I, II, and III were 204, 242, and 144, respectively. Mean number of segments per donor artery was 7.2 ± 0.7, mean number of segments per recipient artery was 7.0 ± 0.3, and mean number of segments in the territory of arteries without collaterals was 5.5 ± 0.5. In the territory of donor arteries, the mean number of segments with normal, decreased, and absent perfusion at rest was 1.6 ± 0.07, 5.67 ± 0.07, and 0.6 ± 0.03, respectively. After nitroglycerine administration, the mean number of above-mentioned segments was 1.2 ± 0.07, 6.07 ± 0.06, and 2.3 ± 0.06, respectively. There was no significant difference in the mean number of segments with normal and decreased perfusion at rest and after nitroglycerine administration (P = 0.4). However, the increase of mean segments with absent perfusion that appeared after nitroglycerine administration in donor arteries was statistically significant in comparison to MPS at rest (P < 0.0001). In the territory of recipient arteries, there was statistically significant increase in the mean number of segments with normal perfusion from 0.5 ± 0.02 at rest to 2.7 ± 0.06 with nitroglycerine (P < 0.0001), decrease in mean number of segments with decreased perfusion from 6.5 ± 0.06 at rest to 4.19 ± 0.06 with nitroglycerine (P < 0.0001), and decrease in the mean number of segments with absent perfusion from 2.3 ± 0.06 to 0.7 ± 0.03 (P = 0.003). In Group III, there was increase in mean segments with normal perfusion from 2.4 ± 0.5 to 3.2 ± 0.5, decrease in mean segments with decreased perfusion from 3.15 ± 0.5 to 2.35 ± 0.5, and absent tracer uptake from 1.1 ± 0.5 to 0.45 ± 0.3. However, these changes were not statistically significant (P = 0.3, P = 0.4, and P = 0.2, respectively). There was also statistically significant improvement of perfusion in the recipient territories from mean severity score at rest of 2.67 ± 0.08 to 1.6 ± 0.09 with nitroglycerine (P < 0.0001), in territories of poorly collateralized arteries from mean severity score at rest of 1.5 ± 0.14 to 0.8 ± 0.12 with nitroglycerine (P < 0.0008), as well as significant deterioration of myocardial perfusion in donor artery territories from mean severity score at rest of 1.7 ± 0.06 to 2.4 ± 0.06 with nitroglycerine (P < 0.0001). Based on the results of the study, we concluded that nitroglycerine administration in patients with multiple vessel coronary artery disease and well-developed collaterals can reduce myocardial perfusion to the areas supplied by donor arteries, even resulting in apparent absent perfusion, probably due to "steal syndrome," although these arteries were less stenosed angiographically and deemed viable on MPS at rest. It appears that MPS in patients on nitroglycerine medication may result in an inappropriate decision by interventionists and surgeons to forgo revascularization. Hence, in cases where large and severe perfusion abnormalities are noted, MPS should be repeated after omitting nitrates.
