Contrast-enhanced cardiac MRI in myocardial infarction

The clinical utility of new cardiac imaging modalities in Australasian clinical practice

Cardiac imaging is a rapidly evolving field, with improvements in the diagnostic capabilities of non-invasive cardiac assessment. We review the two main emerging technologies in cardiac imaging: computed tomography coronary angiography (CTCA) to evaluate chest symptoms and to exclude coronary artery disease; and cardiovascular magnetic resonance (CMR) for evaluating cardiac morphology, function and presence of scar. CTCA is an excellent "rule out" test, with a negative predictive value approaching 100%. Radiation exposure is no longer a concern for CTCA, with doses routinely < 5 mSv, and as low as < 1 mSv in selected patients. CTCA is useful for excluding coronary artery disease, investigating the anatomy of coronary anomalies or fistulae, and for the patency of coronary bypass grafts. CMR is the reference test for the accurate quantitation of left ventricular and right ventricular size and function. CMR has no ionising radiation, making it particularly suitable for patients with heart failure or congenital heart disease who require longitudinal follow-up. Evaluation of cardiomyopathies (hypertrophic, ischaemic, infiltrative, myocarditis, iron overload or idiopathic) is a unique strength of CMR. Stress perfusion CMR has a strong evidence base and improved spatial and temporal resolution compared with nuclear single-photon emission computed tomography.

Late gadolinium enhancement does occur in Tako-tsubo cardiomyopathy - A quantitative cardiac magnetic resonance and speckle tracking strain study

Background

Late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMR) has been recommended to distinguish Tako-tsubo cardiomyopathy (TTC) from either acute myocardial infarction or myocarditis.

Method

44 consecutive patients with confirmed Mayo Clinic criteria for TTC underwent CMR imaging at 1.5 Tesla during the acute phase. 10 patients who had CMRI to exclude scar related ventricular tachycardia, and had negative studies, were used as negative controls. LGE was quantitated at two signal intensity thresholds (CircleCVi software) at > 2 and > 5 standard-deviations (SD) above reference myocardium, and compared to biomarkers.

Findings

Mean door-to-CMR time was 57 hours. 18 patients (41%) had LGE > 2 SD localized to the area of abnormal wall motion, representing 28.9 ± 11.2% LV mass. In 16 of these 18 patients (89%) LGE signal intensity was > 5 SD above normal myocardium, representing 12.1 ± 10% LV mass. LGE signal intensity was significantly greater in TTC than in matched controls (p < 0.05) but lower than in STEMI patients (p < 0.05). Mean troponin was significantly higher in LGE positive patients (2.5 ± 1.8 vs 4.4 ± 6.9, p = 0.001). Mean ejection fraction (EF) by CMR was 45% ± 8.7 in LGE-negative, and 40% ± 7.1 in LGE-positive patients (p = 0.37). Recovery of segmental function was confirmed at follow-up, mean EF was 59% in both groups.

Conclusion

LGE was present in 41% of cases of TTC, 89% of which had intense enhancement > 5 SD above normal myocardium. Presence of LGE was associated with worse myocardial injury in the acute setting, with no difference in recovery of function.

Postinfarct Left Ventricular Remodelling: A Prevailing Cause of Heart Failure

Heart failure is a chronic disease with high morbidity and mortality, which represents a growing challenge in medicine. A major risk factor for heart failure with reduced ejection fraction is a history of myocardial infarction. The expansion of a large infarct scar and subsequent regional ventricular dilatation can cause postinfarct remodelling, leading to significant enlargement of the left ventricular chamber. It has a negative prognostic value, because it precedes the clinical manifestations of heart failure. The characteristics of the infarcted myocardium predicting postinfarct remodelling can be studied with cardiac magnetic resonance and experimental imaging modalities such as diffusion tensor imaging can identify the changes in the architecture of myocardial fibers. This review discusses all the aspects related to postinfarct left ventricular remodelling: definition, pathogenesis, diagnosis, consequences, and available therapies, together with experimental interventions that show promising results against postinfarct remodelling and heart failure.

Late gadolinium enhancement cardiac imaging on a 3T scanner with parallel RF transmission technique: prospective comparison of 3D-PSIR and 3D-IR

OBJECTIVE

To qualitatively and quantitatively compare different late gadolinium enhancement (LGE) sequences acquired at 3T with a parallel RF transmission technique.

METHODS

One hundred and sixty participants prospectively enrolled underwent a 3T cardiac MRI with 3 different LGE sequences: 3D Phase-Sensitive Inversion-Recovery (3D-PSIR) acquired 5 minutes after injection, 3D Inversion-Recovery (3D-IR) at 9 minutes and 3D-PSIR at 13 minutes. All LGE-positive patients were qualitatively evaluated both independently and blindly by two radiologists using a 4-level scale, and quantitatively assessed with measurement of contrast-to-noise ratio and LGE maximal surface. Statistical analyses were calculated under a Bayesian paradigm using MCMC methods.

RESULTS

Fifty patients (70 % men, 56yo ± 19) exhibited LGE (62 % were post-ischemic, 30 % related to cardiomyopathy and 8 % post-myocarditis). Early and late 3D-PSIR were superior to 3D-IR sequences (global quality, estimated coefficient IR > early-PSIR : -2.37 CI = [-3.46 ; -1.38], prob(coef > 0) = 0 % and late-PSIR > IR : 3.12 CI = [0.62 ; 4.41], prob(coef > 0) = 100 %), LGE surface estimated coefficient IR > early-PSIR: -0.09 CI = [-1.11; -0.74], prob(coef > 0) = 0 % and late-PSIR > IR : 0.96 CI = [0.77; 1.15], prob(coef > 0) = 100 %). Probabilities for late PSIR being superior to early PSIR concerning global quality and CNR were over 90 %, regardless of the aetiological subgroup.

CONCLUSIONS

In 3T cardiac MRI acquired with parallel RF transmission technique, 3D-PSIR is qualitatively and quantitatively superior to 3D-IR.

KEY POINTS

• Late gadolinium enhancement is an essential part of a cardiac MRI examination • PSIR and IR sequences are the two possible options for LGE imaging • At 3T with parallel RF transmission, PSIR sequences are significantly better • One LGE sequence is sufficient, allowing an optimization of the acquisition time.