Relation Between Gd-DTPA Contrast Enhancement and Regional Inotropic Response in the Periphery and Center of Myocardial Infarction

Abstract

Background-Gd-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 viability remains controversial. Therefore, we closely examined the relationship between these CE patterns and regional inotropic response to low-dose dobutamine infusion at a regional level. Methods and Results-Thirteen dogs underwent CE and tagged MRI at rest and during 5 g · kg Ϫ1 · min Ϫ1 dobutamine 48 hours after MI. CE patterns and 3D regional strains were measured in 96 segments per animal. Segments were categorized as being normofunctional (nϭ828) if resting circumferential shortening was within the range of remote myocardium, or dysfunctional (nϭ420) if not. Inotropic response in resting dysfunctional segments was assessed according to CE patterns. Significant improvement of radial thickening (from ϩ12Ϯ1% [meanϮSEM] to ϩ22Ϯ2%, PϽ0.05) and circumferential shortening (from ϩ1Ϯ1% to Ϫ5Ϯ1%, PϽ0.05) strains occurred in dysfunctional myocardium with normal CE pattern but not in myocardium with early hypoenhancement. Delayed hyperenhanced myocardium displayed a more complex behavior. Circumferential stretching improved in the peripheral regions (from ϩ4Ϯ1% to Ϫ2Ϯ2%, PϽ0.05), where the infarct was nontransmural (38Ϯ3% transmurality), but not in centrally hyperenhanced regions (from ϩ4Ϯ1% to ϩ1Ϯ1% PϭNS), where the infarct was 66Ϯ3% transmural. Conclusions-Inotropic reserve was confined to dysfunctional myocardium with normal contrast enhancement but not to myocardium with early hypoenhancement. Inotropic response in delayed hyperenhanced myocardium is influenced by transmurality of necrosis. These observations support the use of CE MRI for the clinical detection of myocardial viability.

Segmentation of non-viable myocardium in delayed enhancement magnetic resonance images

“…Then, threshold values were defined as either 2*SD above the mean image intensity of viable myocardium (for the Mean+2SD Semi algorithm), as described pre viously [7,[11][12][13], or 3*SD above the mean image intensity of viable myocardium (for the Mean+ 3SD Semi algorithm), also described previously [8,14]. Figure 1.…”

“…These algorithms have been described and implemented in several previous studies [7,8,[11][12][13][14]. Although the Mean+3SD Semi algorithm did differ significantly from the manual technique, Percent Scar differed by <10% in 80% (55 of 69) of images using this technique, with an overall bias of only )3%.…”

“…Semi-automatic segmentation techniques, based on the image intensity characteristics of viable myocardium, have been used extensively [7,8,[11][12][13][14], but have not been validated previously in the literature. However, given the marked contrast between via ble and non-viable tissue in DE images, with an almost fivefold intensity difference between regions [7,15], near-automatic segmentation of non-viable tissue may be possible.…”

The Automatic Identification of Hibernating Myocardium

“…In the literature, techniques have typically employed intensity thresholding to distinguish areas of scar. Intensity thresholds have been identified manually [5], from manually identified non-scar areas [9], using properties of the histogram [10], using kmeans clustering [11] and also fuzzy k-means clustering [12]. In a comparison of these different thresholding techniques with manually identified areas of scar, fuzzy k-means clustering produced the best results [13].…”

Head‐to‐head comparison between delayed enhancement and percent infarct mapping for assessment of myocardial infarct size in a canine model

“…This determination is achieved due to a delayed and somewhat sustained accumulation of CA into irreversibly injured areas of the myocardium due to loss of membrane integrity and increase in the distribution volume of extracellular contrast agents (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Thus, the delayed contrast enhancement (DE) method of ceMRI is now widely accepted for the determination of infarct size (8,11,13,15,18 -22).…”