Quantitative myocardial infarction on delayed enhancement MRI. Part I: Animal validation of an automated feature analysis and combined thresholding infarct sizing algorithm

Infarct tissue heterogeneity by magnetic resonance imaging identifies enhanced cardiac arrhythmia susceptibility in patients with left ventricular dysfunction

BACKGROUND

The extent of the peri-infarct zone by magnetic resonance imaging (MRI) has been related to all-cause mortality in patients with coronary artery disease. This relationship may result from arrhythmogenesis in the infarct border. However, the relationship between tissue heterogeneity in the infarct periphery and arrhythmic substrate has not been investigated. In the present study, we quantify myocardial infarct heterogeneity by contrast-enhanced MRI and relate it to an electrophysiological marker of arrhythmic substrate in patients with left ventricular (LV) systolic dysfunction undergoing prophylactic implantable cardioverter defibrillator placement.

METHODS AND RESULTS

Before implantable cardioverter defibrillator implantation for primary prevention of sudden cardiac death, 47 patients underwent cine and contrast-enhanced MRI to measure LV function, volumes, mass, and infarct size. A method for quantifying the heterogeneous infarct periphery and the denser infarct core is described. MRI indices were related to inducibility of sustained monomorphic ventricular tachycardia during electrophysiological or device testing. For the noninducible versus inducible patients, LV ejection fraction (30+/-10% versus 29+/-7%, P=0.79), LV end-diastolic volume (220+/-70 versus 228+/-57 mL, P=0.68), and infarct size by standard contrast-enhanced MRI definitions (P=NS) were similar. Quantification of tissue heterogeneity at the infarct periphery was strongly associated with inducibility for monomorphic ventricular tachycardia (noninducible versus inducible: 13+/-9 versus 19+/-8 g, P=0.015) and was the single significant factor in a stepwise logistic regression.

CONCLUSIONS

Tissue heterogeneity is present and quantifiable within human infarcts. More extensive tissue heterogeneity correlates with increased ventricular irritability by programmed electrical stimulation. These findings support the hypothesis that anatomic tissue heterogeneity increases susceptibility to ventricular arrhythmias in patients with prior myocardial infarction and LV dysfunction.

The endocardial extent of reperfused first-time myocardial infarction is more predictive of pathologic Q waves than is infarct transmurality: a magnetic resonance imaging study

BACKGROUND

Historically, Q-wave myocardial infarction (MI) has been equated with transmural MI. This association have, however, recently been rejected. The endocardial extent of MI is another potential determinant of pathological Q waves, since the first part of the QRS complex where the Q wave appears reflects depolarization of subendocardial myocardium. Therefore, the aim of the present study was to test the hypothesis that endocardial extent of MI is more predictive of pathological Q waves than is MI transmurality and to investigate the relationship between QRS scoring of the ECG and MI characteristics.

METHODS

Twenty-nine patients with reperfused first-time MI were prospectively enrolled. One week after admission, delayed contrast-enhanced magnetic resonance imaging (DE-MRI) was performed and 12-lead ECG was recorded. Size, transmurality and endocardial extent of MI were assessed by DE-MRI. Q waves were identified with Minnesota coding and electrocardiographic MI size was estimated by QRS scoring of the ECG.

RESULTS

There was a significant difference between patients with and without Q waves with regard to MI size (P = 0.03) and endocardial extent of MI (P = 0.01), but not to mean and maximum MI transmurality (P = 0.09 and P = 0.14). Endocardial extent was the only independent predictor of pathological Q waves. Endocardial extent of MI was most strongly correlated to QRS score (r = 0.86, P<0.001) of the MI variables tested.

CONCLUSION

The endocardial extent of reperfused first-time acute MI is more predictive of pathological Q waves than is MI transmurality.

Quantitation of infarct size in patients with chronic coronary artery disease using rest-redistribution Tl-201 myocardial perfusion SPECT: correlation with contrast-enhanced cardiac magnetic resonance

BACKGROUND

Rest and rest-redistribution thallium 201 myocardial perfusion single photon emission computed tomography (SPECT) (MPS) has been incompletely validated in patients for determination of the total amount of scarred myocardium. We sought to determine whether rest or redistribution Tl-201 MPS provides an accurate determination of infarct size as defined by delayed contrast-enhanced cardiac magnetic resonance (CMR).

METHODS AND RESULTS

We studied patients (n = 44) with chronic coronary artery disease referred for rest-redistribution Tl-201 MPS, who were also studied by contrast-enhanced CMR within 3 +/- 4 days. Patients were considered retrospectively based on a series of patients referred for clinically indicated MPS. Defect size, as a percent of left ventricular mass (% LV), was determined by quantitative perfusion SPECT (QPS) and compared with the volume of delayed hyperenhancement on contrast-enhanced CMR, normalized to LV mass. Infarct size varied from 0% to 43% LV. Rest QPS defect size correlated with the amount of nonviable myocardium assessed by contrast-enhanced CMR (r = 0.76; mean difference, 4.3% +/- 8.0% LV). When delayed thallium data were considered, redistribution QPS was superior to rest QPS for determination of infarct size (redistribution r = 0.90; mean difference, 2.4% +/- 5.2% LV; P = .03 vs rest).

CONCLUSION

Rest-redistribution Tl-201 MPS provides a more accurate measurement of total infarct size than rest-only Tl-201 MPS and correlates with contrast-enhanced CMR.

Retrospective determination of the area at risk for reperfused acute myocardial infarction with T2-weighted cardiac magnetic resonance imaging: histopathological and displacement encoding with stimulated echoes (DENSE) functional validations

BACKGROUND

The aim of this study was to determine whether edema imaging by T2-weighted cardiac magnetic resonance (CMR) imaging could retrospectively delineate the area at risk in reperfused myocardial infarction. We hypothesized that the size of the area at risk during a transient occlusion would be similar to the T2-weighted hyperintense region observed 2 days later, that the T2-weighted hyperintense myocardium would show partial functional recovery after 2 months, and that the T2 abnormality would resolve over 2 months.

METHODS AND RESULTS

Seventeen dogs underwent a 90-minute coronary artery occlusion, followed by reperfusion. The area at risk, as measured with microspheres (9 animals), was comparable to the size of the hyperintense zone on T2-weighted images 2 days later (43.4+/-3.3% versus 43.0+/-3.4% of the left ventricle; P=NS), and the 2 measures correlated (R=0.84). The infarcted zone was significantly smaller (23.1+/-3.7; both P<0.001). To test whether the hyperintense myocardium would exhibit partial functional recovery over time, 8 animals were imaged on day 2 and 2 months later. Systolic strain was mapped with displacement encoding with stimulated echoes. Edema, as detected by a hyperintense zone on T2-weighted images, resolved, and regional radial systolic strain partially improved from 4.9+/-0.7 to 13.1+/-1.5 (P=0.001) over 2 months.

CONCLUSIONS

These findings are consistent with the premise that the T2 abnormality depicts the area at risk, a zone of reversibly and irreversibly injured myocardium associated with reperfused subendocardial infarctions. The persistence of postischemic edema allows T2-weighted CMR to delineate the area at risk 2 days after reperfused myocardial infarction.