Computed tomography imaging in myocardial infarction

Visualization of Myocardial Infarction in Postmortem Multiphase Computed Tomography Angiography: A Feasibility Study

Recent studies have indicated that multiphase postmortem computed tomography angiography (MPMCTA) allows detection of a pathological enhancement of the myocardium in regions that correlate with the localization of the infarction at histology. The aim of this study was to verify this hypothesis by examining MPMCTA images in cases of myocardial infarction. Therefore, we investigated 10 autopsy cases where death was attributed to myocardial infarction or which showed cardiovascular pathology. As a control group, we selected 10 cases of non-natural (namely, not cardiac) death. The MPMCTA was performed in both groups to ascertain whether a pathological enhancement could be observed. We detected a myocardial enhancement in all cardiac death cases, in the same region that showed infarction at histology. No enhancement was observed in control cases. These results have important implications in the routine management of sudden cardiac death cases. In fact, MPMCTA can not only orient about the cause of death before autopsy, but can especially help to identify affected regions for guiding and improving the sampling for microscopic examination.

Magnetic resonance imaging and multi-detector computed tomography assessment of extracellular compartment in ischemic and non-ischemic myocardial pathologies

Myocardial pathologies are major causes of morbidity and mortality worldwide. Early detection of loss of cellular integrity and expansion in extracellular volume (ECV) in myocardium is critical to initiate effective treatment. The three compartments in healthy myocardium are: intravascular (approximately 10% of tissue volume), interstitium (approximately 15%) and intracellular (approximately 75%). Myocardial cells, fibroblasts and vascular endothelial/smooth muscle cells represent intracellular compartment and the main proteins in the interstitium are types I/III collagens. Microscopic studies have shown that expansion of ECV is an important feature of diffuse physiologic fibrosis (e.g., aging and obesity) and pathologic fibrosis [heart failure, aortic valve disease, hypertrophic cardiomyopathy, myocarditis, dilated cardiomyopathy, amyloidosis, congenital heart disease, aortic stenosis, restrictive cardiomyopathy (hypereosinophilic and idiopathic types), arrythmogenic right ventricular dysplasia and hypertension]. This review addresses recent advances in measuring of ECV in ischemic and non-ischemic myocardial pathologies. Magnetic resonance imaging (MRI) has the ability to characterize tissue proton relaxation times (T1, T2, and T2*). Proton relaxation times reflect the physical and chemical environments of water protons in myocardium. Delayed contrast enhanced-MRI (DE-MRI) and multi-detector computed tomography (DE-MDCT) demonstrated hyper-enhanced infarct, hypo-enhanced microvascular obstruction zone and moderately enhanced peri-infarct zone, but are limited for visualizing diffuse fibrosis and patchy microinfarct despite the increase in ECV. ECV can be measured on equilibrium contrast enhanced MRI/MDCT and MRI longitudinal relaxation time mapping. Equilibrium contrast enhanced MRI/MDCT and MRI T1 mapping is currently used, but at a lower scale, as an alternative to invasive sub-endomyocardial biopsies to eliminate the need for anesthesia, coronary catheterization and possibility of tissue sampling error. Similar to delayed contrast enhancement, equilibrium contrast enhanced MRI/MDCT and T1 mapping is completely noninvasive and may play a specialized role in diagnosis of subclinical and other myocardial pathologies. DE-MRI and when T1-mapping demonstrated sub-epicardium, sub-endocardial and patchy mid-myocardial enhancement in myocarditis, Behcet’s disease and sarcoidosis, respectively. Furthermore, recent studies showed that the combined technique of cine, T2-weighted and DE-MRI technique has high diagnostic accuracy for detecting myocarditis. When the tomographic techniques are coupled with myocardial perfusion and left ventricular function they can provide valuable information on the progression of myocardial pathologies and effectiveness of new therapies.

Spectral CT imaging of myocardial infarction: preliminary animal experience

OBJECTIVES

To evaluate the capability of spectral CT imaging to detect the different stages and angiogenesis of myocardial infarction (MI).

METHODS

MI was surgically induced in 40 rabbits that were evenly divided into four stages of MI: 6 h (6H), 3 days (3D), 7 days (7D) and 14 days (14D). Spectral CT was performed at 10 s, 1 min and 3 min after intravenous contrast medium administration. CD31 immunohistochemistry was used for the microvessel density (MVD) measurement. Iodine concentrations in the myocardium were measured and normalised to the aorta as nIC. The relationships between infarcted myocardial nIC and MVD were analysed.

RESULTS

The nIC of infarct myocardium decreased at 10 s and increased in late-phase CT images. There were significant differences between the 6H and other groups (P ( 6H-3D )  = 0.01, P ( 6H-7D )  = 0.01, P ( 6H-14D )  = 0.00). There was a significant difference in the MVD of infarct myocardium between the two groups except in the 7D and 14D groups (P = 0.08). In the 10-s phase, the nIC of infarct myocardium was negatively correlated with MVD (r = -0.54, P = 0.00), whereas in the late phases, there was a positive correlation between them (r = 0.57, P = 0.00 in the 1-min phase, r = 0.48, P = 0.00 in the 3-min phase).

CONCLUSION

Spectral CT imaging of the myocardium can be used to evaluate the different stages and angiogenesis of MI.

CT of coronary heart disease: Part 2, Dual-phase MDCT evaluates late symptom recurrence in ST-segment elevation myocardial infarction patients after revascularization

OBJECTIVE

The purpose of the study was to investigate dual-phase MDCT for assessing obstructive lesions and the extent and severity of the subtending myocardium at risk in patients presenting with chest pain syndromes 9 or more months after having undergone revascularization for the treatment of ST-segment elevation myocardial infarction (STEMI).

MATERIALS AND METHODS

Dual-phase 64-MDCT was performed on 135 patients with recurring chest symptoms 9 months or more after revascularization (mean ± SD, 23 ± 11 months after index invasive angiogram for treatment of STEMI). Obstructive lesions (≥ 50% stenosis) were detected by MDCT angiography and the extent of myocardium at risk was detected by delayed phase 3D myocardium maps. A myocardium at-risk score based on MDCT findings was defined as the extent of myocardium at risk governed by the coronary lesion and weighted by lesion severity. Results were compared with stress-redistribution (201)Tl-SPECT and invasive angiography.

RESULTS

In restenotic, new, progressive, and previously obstructive lesions that are not currently progressive, analysis of assessable segments (1966/2025, 97.1%) obtained true-positive detection rates of 88.1%, 88.6%, 82.9%, and 100%, respectively; false-negative detection rates were 5.3%, 1.6%, 2.9%, and 8.8%. In 124 patients (91.9%) in whom all segments were assessable, the MDCT-based myocardium at-risk score correlated with the SPECT-based summed difference score (SDS) (r = 0.841, p < 0.001). For detecting SPECT-based SDS ≥ 1 and SDS > 3, areas under the receiver operating characteristic curve for the MDCT-based myocardium at-risk score were 0.874 (95% CI, 0.805-0.942) and 0.938 (95% CI, 0.895-0.981), with optimal cutoff values of 2.68 and 5.01, respectively.

CONCLUSION

Dual-phase MDCT is useful in detecting different patterns of obstructive lesions and the extent of myocardium at risk as an alternative for therapeutic planning in patients presenting with late symptoms after treatment for acute myocardial infarction.