Relation between Gd-DTPA contrast enhancement and regional inotropic response in the periphery and center of myocardial infarction

Background-Od-DTPA contrast-enhanced (CE) MRI identifies patterns of early hypoenhancement and delayed hyperenhancement in acute myocardial infarction , but their clinical significance for the prediction of myocardial viabilit y remains controversial. Therefore, we closely examined the relationship be tween these CE patterns and regional inotropic response to low-dose dobutam ine infusion at a regional level. Methods and Results-Thirteen dogs underwent CE and tagged MRI at rest and d uring 5 mug.kg(-1).min(-1) dobutamine 48 hours after MI. CE patterns and 3D regional strains were measured in 96 segments per animal. Segments were ca tegorized as being normofunctional (n = 828) if resting circumferential sho rtening was within the range of remote myocardium, or dysfunctional (n=420) if not. Inotropic response in resting dysfunctional segments was assessed according to CE patterns. Significant improvement of radial thickening (fro m +12 +/- 1% [mean +/- SEM] to +22 +/- 2%, P < 0.05) and circumferential sh ortening (from +1 <plus/minus> 1% to -5 +/- 1%, P < 0.05) strains occurred in dysfunctional myocardium with normal CE pattern but not in myocardium. w ith early hypoenhancement. Delayed hyperenhanced myocardium displayed a mor e complex behavior. Circumferential stretching improved in the peripheral r egions (from +4 <plus/minus> 1% to -2 +/- 2%, P < 0.05), where the infarct was nontransmural (38 <plus/minus> 3% transmurality), but not in centrally hyperenhanced regions (from +4 +/- 1% to +1 +/- 1% P = NS), where the- infa rct was 66 +/- 3% transmural. Conclusions-Inotropic reserve was confined to dysfunctional myocardium with normal contrast enhancement but not to myocardium. with early hypoenhancem ent. Inotropic response in delayed hyperenhanced myocardium is influenced b y transmurality of necrosis. These observations support the use of CE MRI f or the clinical detection of myocardial viability.