Late Hypoenhancement Research Articles

Role of first pass and delayed enhancement in assessment of segmental functional recovery after acute myocardial infarction

Assessing myocardial viability is crucial in decision making and prognostic restratification after acute myocardial infarction (MI). A number of noninvasive imaging modalities have been employed in viability identification, but contrast-enhanced magnetic resonance (MR) imaging has been shown to be extremely accurate because of its transmural resolution and precise definition of microvascular obstruction. Our purpose was to assess functional recovery after acute MI, with special focus on the role of infarct transmurality and microvascular obstruction. Forty-six consecutive patients with first acute MI, reperfused by primary percutaneous transluminal coronary angioplasty (PTCA) (n=40) or fibrinolysis (n=6), underwent MR imaging within the first week to assess oedema, microvascular obstruction, function and viability and then again after 4-6 months to assess functional recovery and scar. At first MR examination, postcontrast images were analysed according to three patterns, based on a combination of first-pass and delayed-enhancement data: pattern 1 (normal first pass and late hyperenhancement <50% thickness) identified viable myocardium, whereas pattern 2 (late hyperenhancement >50% thickness, with or without first-pass perfusion defect) and pattern 3 (perfusion defect at first pass and late hypoenhancement) recognised nonviable myocardium, with 93% sensitivity, 75% specificity, 92% positive predictive value and 78% negative predictive value for identifying viable tissue. Furthermore, by dividing pattern 2 into two subpatterns, 2A and 2B, based on absence or presence of microvascular obstruction in >50% transmural infarcts, we were able to better identify the segments without recovery or that were nonviable with a 1.39 relative risk of failed recovery. After acute MI, not all infarcts with transmurality >50% can be considered nonviable; microvascular obstruction detected at first pass can help to better stratify these cases.

The Contribution of Intramyocardial Hemorrhage to the “No‐Reflow Phenomenon”: A Study Performed by Cardiac Magnetic Resonance

Percutaneous coronary intervention (PCI) in acute myocardial infarction (AMI) is sometimes complicated by microvascular damage and hemorrhage. Hemoglobin degradation products have magnetic susceptibility effects which help in detecting hemorrhagic AMI by T₂ -weighted cardiac magnetic resonance (CMR) images. To investigate the possibility to detect intramyocardial hemorrhage after AMI and to assess its contribution to the delayed hypoenhanced core on late gadolinium enhancement (LGE) CMR, a feature traditionally referred to as microvascular obstruction. Consecutive patients with AMI who underwent PCI and CMR were investigated. Hypointense zones T₂ -weighted images were labelled as "hemorrhagic" AMI. Areas of late hypoenhancement on LGE CMR were considered as regions of persistent microvascular damage (PMD). Only transmural AMI were considered. A total number of 108 transmural AMI patients were eventually enrolled and divided into two groups according to the presence of hypoenhancement on T₂ images. Thirty-two patients showed an hypointense stria within the high signal intensity zone on T₂ -weighted images; all these patients showed midmural PMD on LGE. Among the remaining 76 patients, only 14 (18.4%) showed PMD in the subendocardial region. The angiographic outcome was worse in patients with hemorrhagic AMI, with a lower prevalence of TIMI 3 (65.6% vs. 96.1%, P = 0.017) and higher prevalence of myocardial blush grade 0 (84.4% vs. 13.2%, P < 0.001) post-PCI. T₂ -weighted CMR in reperfused AMI allows identification of hemorrhage, related to PMD areas on LGE images and to a worse reperfusion profile on angiography. These features open new avenues of investigation for prognostic assessment of reperfused AMI.

Assessment of Microvascular Obstruction and Prediction of Short-term Remodeling after Acute Myocardial Infarction: Cardiac MR Imaging Study

To evaluate which cardiac magnetic resonance (MR) imaging technique for detection of microvascular obstruction (MVO) best predicts left ventricular (LV) remodeling after acute myocardial infarction (MI). This study had local ethics committee approval; all patients gave written informed consent. Sixty-three patients with first acute MI, treated with primary stent placement and optimal medical therapy, underwent cine MR imaging at 4-7 days and at 4 months after MI. Presence of MVO was qualitatively evaluated at baseline by using three techniques: (a) a single-shot saturation-recovery gradient-echo first-pass perfusion sequence (early hypoenhancement), mean time, 1.09 minutes +/- 0.07 (standard deviation) after contrast material administration; (b) a three-dimensional segmented saturation-recovery gradient-echo sequence (intermediate hypoenhancement), mean time, 2.17 minutes +/- 0.26; and (c) a two-dimensional segmented inversion-recovery gradient-echo late gadolinium enhancement sequence (late hypoenhancement), mean time, 13.32 minutes +/- 1.26. Contrast-to-noise ratios (CNRs) were calculated from the signal-to-noise ratios of the infarcted myocardium and MVO areas. Univariable linear regression analysis was used to identify the predictive value of each MR imaging technique. Early hypoenhancement was detected in 44 (70%) of 63 patients; intermediate hypoenhancement, in 39 (62%); and late hypoenhancement, in 37 (59%). Late hypoenhancement was the strongest predictor of change in LV end-diastolic and end-systolic volumes over time (beta = 14.3, r = 0.40, P = .001 and beta = 11.3, r = 0.44, P < .001, respectively), whereas intermediate and late hypoenhancement had comparable predictive values of change in LV ejection fraction (beta = -3.1, r = -0.29, P = .02 and beta = -2.8, r = -0.27, P = .04, respectively). CNR corrected for spatial resolution was significantly superior for late enhancement compared with the other sequences (P < .001). By using cardiac MR imaging, late hypoenhancement is the best prognostic marker of LV remodeling, with highest CNR between the infarcted myocardium and MVO regions.

Reperfused Myocardial Infarction: Contrast-enhanced 64-Section CT in Comparison to MR Imaging

To prospectively compare 64-section multidetector computed tomography (CT) and cardiac magnetic resonance (MR) imaging for the early assessment of myocardial enhancement and infarct size after acute reperfused myocardial infarction (MI). The study was HIPAA compliant and was approved by the institutional review board. All participants gave written informed consent. Twenty-one patients (18 men; mean age, 60 years +/- 13 [standard deviation]) were examined with 64-section multidetector CT and cardiac MR imaging 5 days or fewer after a first reperfused MI. Multidetector CT was performed during the first pass of contrast material to assess myocardial perfusion and detect microvascular obstruction (no reflow). In 15 patients, a second scan was performed 7 minutes later to assess total infarct size by using delayed hyperenhancement. Early hypoenhancement and delayed hyperenhancement were compared between multidetector CT and cardiac MR imaging with Pearson correlation coefficient and Bland-Altman analysis. Early hypoenhancement was recognized on all multidetector CT and cardiac MR images. Delayed hyperenhancement was observed with cardiac MR imaging at all examinations and with multidetector CT at 11 of 15 examinations. While signal intensity differences between hypoperfused and normal myocardium were comparable for first-pass multidetector CT and cardiac MR imaging, cardiac MR imaging had a far better contrast-to-noise ratio (CNR) for delayed acquisitions than did CT (P < .001). Hypoenhanced areas (as a percentage of left ventricular mass) at first-pass multidetector CT (11% +/- 6) correlated well with those at first-pass cardiac MR imaging (7% +/- 4, R(2) = 0.72). Delayed-enhancement multidetector CT (13% +/- 9) correlated well with delayed-enhancement cardiac MR imaging (15% +/- 7, R(2) = 0.55). Quantification of delayed hypoenhancement (n = 12) had very good correlation between multidetector CT (4% +/- 4) and cardiac MR imaging (3% +/- 2) (R(2) = 0.85). Early and late hypoenhancement showed good CNR and correlated well between multidetector CT and cardiac MR imaging.

Periprocedural Abciximab Administration in ST Elevation Myocardial Infarction Patients

Objectives: The impact of periprocedural (before primary percutaneous coronary angioplasty, PCI) abciximab administration on microvascular obstruction in patients with occluded infarct-related artery (IRA) is unknown. Methods: We studied 36 consecutive patients with first ST elevation myocardial infarction (STEMI) and occluded IRA treated with successful primary PCI within 12 h from symptom onset, who received intravenous abciximab immediately before PCI and 49 matched patients who did not receive abciximab as controls. All patients underwent delayed-enhanced magnetic resonance (DE-MR) 6 ± 2 days after PCI. Necrosis was judged as transmural when DE was extended to ≧75% of left ventricular (LV) segment thickness. Severe microvascular obstruction was identified as areas of late hypoenhancement surrounded by DE. Results: Time to treatment was comparable in the two groups (182 ± 60 vs. 188 ± 110 min, respectively). Transmurality and severe microvascular obstruction were present in 3.03 ± 2.8 versus 3.09 ± 2.9 (p = 0.9) and 1.05 ± 1.5 versus 1.06 ± 1.8 (p = 0.6) of LV segments, respectively, in the abciximab group versus controls. At multivariate analysis, severe microvascular obstruction was independently associated only with transmural necrosis (OR 1.5, p < 0.001) and age (OR 1.1, p = 0.02) but not with the use of abciximab. Conclusions: Severe microvascular obstruction after primary PCI of STEMI patients with occluded IRA is related to transmural necrosis but not to the use of abciximab.

Influence of Transmurality, Infarct Size, and Severe Microvascular Obstruction on Left Ventricular Remodeling and Function After Primary Coronary Angioplasty

Infarct size has been considered an established marker of left ventricular (LV) remodeling. We assessed the predictive value of myocardial/microvascular injury assessed by delayed enhanced magnetic resonance imaging (MRI) on LV remodeling and LV ejection fraction after primary coronary intervention (PCI) compared with peak troponin levels, an established index of myocardial infarct size. We performed MRI in 76 patients with first acute myocardial infarction 6 +/- 2 days after successful PCI. Necrosis was judged as transmural when delayed enhancement was extended to >or=75% of LV segment thickness. Severe microvascular obstruction was identified as areas of late hypoenhancement surrounded by delayed enhancement. Infarct size was expressed as an index by dividing the total percentage of delayed enhancement involvement by the number of LV segments. LV end-diastolic volume index and function were quantified by 2-dimensional echocardiography at 6 +/- 1 months after acute myocardial infarction. Remodeling was evaluated as a change in LV end-diastolic volume index at follow-up compared with baseline. At univariate analyses, transmural necrosis, severe microvascular obstruction, infarct size, and troponin level were correlated directly with remodeling and inversely with LV function at follow-up (p <0.001). At multiple regression, only transmural necrosis and troponin level remained independent predictors of LV remodeling and function. With respect to troponin, transmural necrosis improved the predictive power of LV remodeling (R2 for change = 0.19) and function (R2 for change = 0.16). In conclusion, in patients with acute myocardial infarction undergoing PCI, the amount of transmural necrosis as assessed by MRI is a major determinant of LV remodeling and function, with significant additional predictive value to infarct size and severe microvascular obstruction.

Duration of Ischemia Is a Major Determinant of Transmurality and Severe Microvascular Obstruction After Primary Angioplasty: A Study Performed With Contrast-Enhanced Magnetic Resonance

This study sought to assess the relationship between duration of ischemia and both myocardial transmural necrosis (TN) and severe microvascular obstruction (SMO), by contrast-enhanced magnetic resonance (CE-MR), in patients with acute myocardial infarction (AMI) treated with angioplasty (PCI), and to estimate the risk of TN and SMO with the duration of ischemia. The impact of ischemic time on myocardial and microvascular injury is not well characterized in people. We performed CE-MR in 77 patients with first AMI, 5 +/- 3 days after successful PCI. The AMI was labeled as transmural if hyperenhancement at CE-MR was extended to > or =75% of the thickness in two or more ventricular segments. The SMO was identified as areas of late hypoenhancement surrounded by hyperenhanced tissue. The relationship between ischemic time and CE-MR evidence of SMO or TN was evaluated by logistic regression. Thirteen patients were excluded because of preprocedural Thrombolysis In Myocardial Infarction (TIMI) flow grade 3 of the infarct-related artery. For the remaining 64 patients, the mean time to treatment was 190 +/- 110 min, 45 (65%) patients had TN and 23 (39%) had SMO. Mean pain to balloon time was 90 +/- 40 min, 110 +/- 107 min, and 137 +/- 97 min in patients without TN and SMO, with TN but without SMO, or with both TN and SMO, respectively (p = 0.001). Multivariate analysis showed that time delay was significantly associated both with TN (odds ratio per 30 min, 1.37, p = 0.032), and SMO (odds ratio per 30 min, 1.21; p = 0.021). In AMI patients with impaired coronary perfusion undergoing PCI, the risk of TN and SMO increases with the duration of the ischemic time.