Distinction between open and occluded infarct-related arteries using contrast-enhanced magnetic resonance imaging

Multidetector row computed tomography can identify and characterize the occlusive culprit lesions in patients early (within 24 hours) after acute myocardial infarction

BACKGROUND

The reliable noninvasive assessment of occluded disrupted plaques and thromboses in culprit vessels could constitute an important step forward in risk stratification of patients early after acute myocardial infarction (AMI). However, noninvasive identification of patency of culprit vessels remains a challenging issue. This prospective study was designed to identify the occluded culprit vessels by multidetector row computed tomography (MDCT) and to compare the stenotic and occlusive culprit lesions by MDCT in patients early (within 24 hours) after AMI.

METHODS

We enrolled 62 patients with first Q-wave AMI (54 males). Multidetector row computed tomography was performed 16.5 +/- 7.1 hours after the onset of chest pain without any complication. Coronary angiography was done within 6 hours after MDCT. Patients were divided into 2 groups according to angiographic findings: stenotic group (35 patients) and occluded group (27 patients). The following MDCT data were collected: luminal artery stenosis, remodeling index, plaque burden, and lesion attenuation.

RESULTS

Compared to coronary angiography, MDCT detected occluded culprit vessels with sensitivity, specificity, negative predict value, and positive predict value of 92.6%, 88.6%, 93.9%, and 86.2%, respectively. Compared with the stenotic group, culprit lesions in the occlusive group had significantly longer length (18.9 +/- 9.7 vs 11.9 +/- 6.2 mm; P = .024) and higher MDCT lesion attenuation (38.8 +/- 15.6 vs 29.2 +/- 12.9 Hounsfield unit; P = .008). Multidetector row computed tomography attenuation was negatively correlated with thrombolysis in myocardial infarction flow (Spearman rho = -0.46; P < .001).

CONCLUSIONS

Multidetector row computed tomography could accurately and safely identify occluded culprit lesions in patients early after AMI, providing important information to aid in risk stratification.

MR imaging in assessing cardiovascular interventions and myocardial injury

Performing an MR-guided endovascular intervention requires (1) real-time tracking and guidance of catheters/guide wires to the target, (2) high-resolution images of the target and its surroundings in order to define the extent of the target, (3) performing a therapeutic procedure (delivery of stent or injection of gene or cells) and (4) evaluating the outcome of the therapeutic procedure. The combination of X-ray and MR imaging (XMR) in a single suite was designed for new interventional procedures. MR contrast media can be used to delineate myocardial infarcts and microvascular obstruction, thereby defining the target for local delivery of therapeutic agents under MR-guidance. Iron particles, or gadolinium- or dysprosium-chelates are mixed with the soluble injectates or stem cells in order to track intramyocardial delivery and distribution. Preliminary results show that genes encoded for vascular endothelial and fibroblast growth factor and cells are effective in promoting angiogenesis, arteriogenesis, perfusion and LV function. Angiogenic growth factors, genes and cells administered under MR-guided minimally invasive catheter-based procedures will open up new avenues in treating end-stage ischemic heart disease. The optimum dose of the therapeutic agents, delivery devices and real-time imaging techniques to guide the delivery are currently the subject of ongoing research. The aim of this review is to (1) provide an updated review of experiences using MR imaging to guide transcatheter therapy, (2) address the potential of cardiovascular magnetic resonance (MR) imaging and MR contrast media in assessing myocardial injury at a molecular level and labeling cells and (3) illustrate the applicability of the non-invasive MR imaging in the field of angiogenic therapies through recent clinical and experimental publications.

Importance of perfusion in myocardial viability studies using delayed contrast-enhanced magnetic resonance imaging

PURPOSE

To investigate whether an extracellular gadolinium-(Gd)-based contrast agent (CA) enters nonperfused myocardium during acute coronary occlusion, and whether nonperfused myocardium presents as hyperintense in delayed contrast-enhanced (DE) MR images in the absence of CA in that region.

MATERIALS AND METHODS

The left anterior descending coronary artery (LAD) was occluded for 200 minutes in six pigs. The longitudinal relaxation rate (R(1)) in blood, perfused myocardium, and nonperfused myocardium was repeatedly measured using a Look-Locker sequence before and during the first hour after administration of Gd-DTPA-BMA.

RESULTS

While blood and perfused myocardium showed a major increase in R(1) after CA administration, nonperfused myocardium did not. R(1) in nonperfused myocardium was significantly lower than in blood and perfused myocardium during the first hour after CA administration. When the signal from perfused myocardium was nulled, demarcation of the hyperintense nonperfused myocardium was achieved in all of the study animals.

CONCLUSION

Gd-DTPA-BMA does not enter ischemic myocardium within one hour after administration during acute coronary occlusion. The ischemic region with complete absence of CA still appears bright when the signal from perfused myocardium is nulled using inversion-recovery DE-MRI. This finding is important for understanding the basic pathophysiology of inversion-recovery viability imaging, as well as for imaging of acute coronary syndromes.

MRI of acute myocarditis: a comprehensive approach based on various imaging sequences

STUDY OBJECTIVES

To explore the diagnostic performance of MRI for the diagnosis of acute myocarditis, using a comprehensive imaging approach.

DESIGN AND SETTINGS

Twenty patients with myocarditis and 7 age-matched and gender-matched control subjects underwent comprehensive MRI. Magnetic resonance (MR) examinations included axial T2-weighted sequences, precontrast and postcontrast ECG-gated T1-weighted sequences in axial and short heart axis, cine-MRI, and serial dynamic turbo fast low-angle shot (turboFLASH) acquisitions in the short axis following Gd injection for a period of 2 min. Precontrast and postcontrast images were postprocessed using subtraction. Two observers read all images qualitatively and quantitatively. Myocardial enhancement was compared between patients and control subjects.

PATIENTS

Myocardial involvement was focal in 6 patients examined within 1 week from clinical onset, and diffuse in the remaining 14 patients examined later.

RESULTS

Qualitatively, contrast-enhanced T1-weighted subtracted images had 100% sensitivity and specificity for myocardial involvement. Postcontrast T1-weighted images were able to discriminate the early phase (nodular enhancement) from the later phase of myocarditis (diffuse enhancement). Quantitatively, myocardial enhancement was 56% +/- 3.2% in patients, vs 29% +/- 3.1% in control subjects using T1-weighted MRI (p < 0.0001). Serial turboFLASH images displayed greater myocardial enhancement between 25 s and 120 s in patients than in control subjects (p < 0.0001); however, there was marked enhancement of skeletal muscles in both early and late stages of myocarditis compared to control subjects (p < 0.0001).

CONCLUSION

On the basis of subtracted cardiac-gated T1-weighted images and serial postinjection turboFLASH images, our study shows that myocarditis is largely, at least in the early stages, a focal process in the myocardium. It also provides evidence of transient skeletal muscle involvement, which may actually be useful for diagnosis.