ANTIMYOSIN ANTIBODY IMAGING IN EXPERIMENTAL AORTIC REGURGITATION

Background. Fiber dropout and myocyte necrosis precede heart failure i n experimental aortic regurgitation (AR), The current study aimed to d etermine whether this process can be detected by noninvasive scintigra phic imaging. Methods and Results. In-111-labeled antimyosin antibody Fab fragment (1 to 1.5 mCi) (Myoscint) was administered to each of 34 New Zealand White rabbits: 11 early (3 to 5 weeks) after surgical AR i nduction; 9 late (98 to 128 weeks) after AR induction; 5 normal and 3 sham-operated age-matched with early AR; and 3 normal and 3 sham-opera ted age-matched with late AR, Echocardiographic fractional shortening was indistinguishable among control, early AR, and late AR groups, In vivo gamma camera imaging 24 and 48 hours after isotope administration , post-mortem heart activity determination (percentage injected dose p er gram), and autoradiography were performed, At 24 and 48 hours, hear t-to-lung counts-per-pixel ratios from in vivo images were greater (p < 0.05) in the late AR rabbits than in each of the three other groups, No significant differences were found when early AR and older or youn ger control rabbits were compared, Heart activity (percentage injected dose per gram) in late AR rabbits trended toward higher values than i n age-matched control rabbits (p = 0.057), but in early AR it was indi stinguishable from that in the corresponding control (p = 0.413, diffe rence not significant), The autoradiographic endocardial/epicardial ac tivity ratio in late AR rabbits was greater than in control and early AR rabbits (1.27 +/- 0.13 vs 1.06 +/- 0.09 and vs 1.13 +/- 0.10, respe ctively, p < 0.02). Conclusions. Whereas isotope uptake in late AR rab bits differed from that in control and early AR rabbits, systolic func tion was indistinguishable. Thus In-111-labeled antimyosin antibody im aging may permit noninvasive detection of AR-induced myocardial damage before functional deterioration.