Defining the transmurality of a chronic myocardial infarction by ultrasonic strain-rate imaging - Implications for identifying intramural viability an experimental study

Background-In a correlative functional/histopathologic study, we investigated the regional deformation characteristics of both chronic nontransmural and transmural infarctions before and after a dobutamine challenge. Methods and Results-After stenosing copper-coated stent implantation to produce circumflex artery endothelial proliferation, 18 pigs were followed up for 5 weeks. Posteuthanasia histology showed 10 to have a nontransmural and 8 a transmural infarction. Eight nonstented animals served as controls. Regional radial function was monitored by measuring ultrasound-derived peak systolic strain rates (SRSYS) and systolic strains (epsilon(SYS)) (1) before stent implantation and (2) at 5 weeks, at baseline (bs) and during an incremental dobutamine infusion. In controls, dobutamine induced a linear increase in SRSYS (dobutamine: bs, 4.8+/-0.4 s(-1); 20 mug . kg(-1) . min(-1), 9.9+/-0.7 s(-1); P<0.0001) and an initial increase of ε(SYS) at low dose (bs, 58+/-5%; at 5 μg . kg(-1) . min(-1),78+/-6%; P<0.05) but a subsequent decrease during higher infusion rates. In the nontransmural group, bs SRSYS and epsilon(SYS) were significantly lower than prestent values (SRSYS, 2.9+/-0.5 s(-1) and epsilon(SYS), 32+/-6%, P<0.05 versus prestent). During dobutamine infusion, SRSYS increased slightly at 5 μg . kg(-1) . min(-1) (4.7+/-0.6 s(-1), P<0.05) but fell during higher infusion rates, whereas epsilon(SYS) showed no change. For nontransmural infarctions, transmural scar extension correlated closely with epsilon(SYS) at bs (r=0.88). For transmural infarctions, SRSYS at bs was significantly reduced and epsilon(SYS) was almost not measurable (SRSYS, 1.8+/-0.3 s(-1); epsilon(SYS), 3+/-4%). Both deformation parameters showed no further change during the incremental dobutamine infusion. Conclusions-Ultrasonic deformation values could clearly differentiate chronic nontransmural from transmural myocardial infarction. The transmural extension of the scar could be defined by the regional deformation response.