Understanding LV remodeling following myocardial infarction: are T1 maps by CMR the new guide?

Cardiac αVβ3 integrin expression following acute myocardial infarction in humans

Objective

Maladaptive repair contributes towards the development of heart failure following myocardial infarction (MI). The α_vβ₃ integrin receptor is a key mediator and determinant of cardiac repair. We aimed to establish whether α_vβ₃ integrin expression determines myocardial recovery following MI.

Methods

¹⁸F-Fluciclatide (a novel α_vβ₃-selective radiotracer) positron emission tomography (PET) and CT imaging and gadolinium-enhanced MRI (CMR) were performed in 21 patients 2 weeks after ST-segment elevation MI (anterior, n=16; lateral, n=4; inferior, n=1). CMR was repeated 9 months after MI. 7 stable patients with chronic total occlusion (CTO) of a major coronary vessel and nine healthy volunteers underwent a single PET/CT and CMR.

Results

¹⁸F-Fluciclatide uptake was increased at sites of acute infarction compared with remote myocardium (tissue-to-background ratio (TBR_mean) 1.34±0.22 vs 0.85±0.17; p<0.001) and myocardium of healthy volunteers (TBR_mean 1.34±0.22 vs 0.70±0.03; p<0.001). There was no ¹⁸F-fluciclatide uptake at sites of established prior infarction in patients with CTO, with activity similar to the myocardium of healthy volunteers (TBR_mean 0.71±0.06 vs 0.70±0.03, p=0.83). ¹⁸F-Fluciclatide uptake occurred at sites of regional wall hypokinesia (wall motion index≥1 vs 0; TBR_mean 0.93±0.31 vs 0.80±0.26 respectively, p<0.001) and subendocardial infarction. Importantly, although there was no correlation with infarct size (r=0.03, p=0.90) or inflammation (C reactive protein, r=−0.20, p=0.38), ¹⁸F-fluciclatide uptake was increased in segments displaying functional recovery (TBR_mean 0.95±0.33 vs 0.81±0.27, p=0.002) and associated with increase in probability of regional recovery.

Conclusion

¹⁸F-Fluciclatide uptake is increased at sites of recent MI acting as a biomarker of cardiac repair and predicting regions of recovery.

Trial registration number

NCT01813045; Post-results.

Modified look-locker inversion recovery T1 mapping indices: assessment of accuracy and reproducibility between magnetic resonance scanners

BACKGROUND

Cardiovascular magnetic resonance (CMR) T1 mapping indices, such as T1 time and partition coefficient (λ), have shown potential to assess diffuse myocardial fibrosis. The purpose of this study was to investigate how scanner and field strength variation affect the accuracy and precision/reproducibility of T1 mapping indices.

METHODS

CMR studies were performed on two 1.5T and three 3T scanners. Eight phantoms were made to mimic the T1/T2 of pre- and post-contrast myocardium and blood at 1.5T and 3T. T1 mapping using MOLLI was performed with simulated heart rate of 40-100 bpm. Inversion recovery spin echo (IR-SE) was the reference standard for T1 determination. Accuracy was defined as the percent error between MOLLI and IR-SE, and scan/re-scan reproducibility was defined as the relative percent mean difference between repeat MOLLI scans. Partition coefficient was estimated by ΔR1myocardium phantom/ΔR1blood phantom. Generalized linear mixed model was used to compare the accuracy and precision/reproducibility of T1 and λ across field strength, scanners, and protocols.

RESULTS

Field strength significantly affected MOLLI T1 accuracy (6.3% error for 1.5T vs. 10.8% error for 3T, p<0.001) but not λ accuracy (8.8% error for 1.5T vs. 8.0% error for 3T, p=0.11). Partition coefficients of MOLLI were not different between two 1.5T scanners (47.2% vs. 47.9%, p=0.13), and showed only slight variation across three 3T scanners (49.2% vs. 49.8% vs. 49.9%, p=0.016). Partition coefficient also had significantly lower percent error for precision (better scan/re-scan reproducibility) than measurement of individual T1 values (3.6% for λ vs. 4.3%-4.8% for T1 values, approximately, for pre/post blood and myocardium values).

CONCLUSION

Based on phantom studies, T1 errors using MOLLI ranged from 6-14% across various MR scanners while errors for partition coefficient were less (6-10%). Compared with absolute T1 times, partition coefficient showed less variability across platforms and field strengths as well as higher precision.