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T2-imaging of area-at-risk predicts recovery of cardiac function in a canine model of acute myocardial infarction

Introduction

Infarct size is the strongest predictor of subsequent outcomes and remains an important therapeutic target. Myocardial edema measured by T2-weighted magnetic resonance (MR) imaging identifies the ischemic area-at-risk and predicts infarct size, allows more accurate evaluation of novel anti-ischemic therapies, and may be associated with stunning and long-term recovery of function.

Purpose

We sought to identify the extent of infarcted and at-risk myocardium and correlate these markers with post-infarct recovery of myocardial function.

Methods

Five dogs (mean weight 18.9 kgs) underwent successful 2-hour complete occlusion of the left-circumflex artery and collaterals after baseline functional cine imaging. They subsequently underwent 48-hour and 4-week complete left-ventricular (LV) short-axis MR imaging on a 1.5 Tesla scanner using SSFP-cine (TE 1.4 ms, TR 35.3 ms, voxel size 0.6 × 1 × 7 mm3), ACUTE T2-weighted (TE 1.9 ms, TR 168.1 ms, voxel size 0.6 × 0.9 × 7 mm3), and phase-sensitive, inversion recovery late Gadolinium (0.15 mmol/kg Magnevist) enhancement sequences (LGE, TE 3.4 ms, TR 548 ms, voxel size 0.5 × 0.8 × 7 mm3). The percentages of LGE and T2 hyperenhacement were identified through intensity threshold testing, 5 standard devitations (SDs) and 2 SDs above the reference myocardium respectively. All outcome variables were given as mean percentages ± SDs.

Results

The mean percentage LGE was extensive at 44.1 ± 5.9%. T2-imaging identified a large area-at-risk measuring 68.5 ± 7.1% of the myocardium. The mean LV ejection fraction (LVEF) at 48 hours was 23.7 ± 2.8%. Significant recovery of function was seen at four weeks (mean LVEF increased to 42.7 ± 7.3%), likely in large part due to the significant stunning present and low LGE/T2 hyperenhancement ratio (0.65 ± 0.13) at 48 hours. This ratio was found to moderately correlate negatively with the percent LVEF improvement (r = -0.57). Figure 1.

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Figure 1

Conclusion

The area-at-risk estimated by T2-weighted MR imaging correlates with recovery of myocardial infarction in an acute-MI canine model. Further evaluation of this method will maximize our ability to prognosticate and guide therapy post-infarction. Increasing the proportion of myocardial salvage from the initial area-at-risk should serve as an important therapeutic target. This imaging technique may become a significant marker of treatment efficacy and prognosis.

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Correspondence to Jamieson M Bourque.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Bourque, J.M., Glover, D.K., Goodman, C.C. et al. T2-imaging of area-at-risk predicts recovery of cardiac function in a canine model of acute myocardial infarction. J Cardiovasc Magn Reson 11, P43 (2009). https://doi.org/10.1186/1532-429X-11-S1-P43

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Keywords

  • Acute Myocardial Infarction
  • Infarct Size
  • Canine Model
  • Cine Imaging
  • Myocardial Edema