Postreperfusion myocardial technetium-99m-sestamibi defect corresponds to area at risk: experimental results from an ischemia-reperfusion porcine model

Towards stratifying ischemic components by cardiac MRI and multifunctional stainings in a rabbit model of myocardial infarction

OBJECTIVES

We sought to identify critical components of myocardial infarction (MI) including area at risk (AAR), MI-core and salvageable zone (SZ) by using cardiac magnetic resonance imaging (cMRI) and multifunctional stainings in rabbits.

MATERIALS AND METHODS

Fifteen rabbits received 90-min coronary artery (CA) ligation and reopening to induce reperfused MI. First-pass perfusion weighted imaging (PWI(90')) was performed immediately before CA reperfusion. Necrosis avid dye Evans blue (EB) was intravenously injected for later MI-core detection. One-day later, cMRI with T2-weighted imaging (T2WI), PWI(24h) and delayed enhancement (DE) T1WI was performed at a 3.0T clinical scanner. The heart was excised and CA was re-ligated with aorta infused by red-iodized-oil (RIO). The heart was sliced into 3-mm sections for digital radiography (DR), histology and planimetry with myocardial salvage index (MSI) and perfusion density rate (PDR) calculated.

RESULTS

There was no significant difference between MI-cores defined by DE-T1WI and EB-staining (31.13±8.55% vs 29.80±7.97%; p=0.74). The AAR was defined similarly by PWI90' (39.93±9.51%), RIO (38.82±14.41%) and DR (38.17±15.98%), underestimated by PWI(24h) (36.44±5.31%), but overestimated (p<0.01) by T2WI (56.93±8.87%). Corresponding MSI turned out to be 24.17±9.5% (PWI(90')), 21.97±9.41% (DR) and 22.68±9.65% (RIO), which were significantly (p<0.01) higher and lower than that with PWI(24h) (15.15±7.34%) and T2WI (45.52±7.5%) respectively. The PDR differed significantly (p<0.001) between normal myocardium (350.6±33.1%) and the AAR (31.2±15%), suggesting 11-times greater blood perfusion in normal myocardium over the AAR.

CONCLUSION

The introduced rabbit platform and new staining techniques together with the use of a 3.0T clinical scanner for cMRI enabled visualization of MI components and may contribute to translational cardiac imaging research for improved theranostic management of ischemic heart disease.

Bifunctional staining for ex vivo determination of area at risk in rabbits with reperfused myocardial infarction

AIM: To develop a method for studying myocardial area at risk (AAR) in ischemic heart disease in correlation with cardiac magnetic resonance imaging (cMRI).

METHODS: Nine rabbits were anesthetized, intubated and subjected to occlusion and reperfusion of the left circumflex coronary artery (LCx) to induce myocardial infarction (MI). ECG-triggered cMRI with delayed enhancement was performed at 3.0 T. After euthanasia, the heart was excised with the LCx re-ligated. Bifunctional staining was performed by perfusing the aorta with a homemade red-iodized-oil (RIO) dye. The heart was then agar-embedded for ex vivo magnetic resonance imaging and sliced into 3 mm-sections. The AAR was defined by RIO-staining and digital radiography (DR). The perfusion density rate (PDR) was derived from DR for the AAR and normal myocardium. The MI was measured by in vivo delayed enhancement (iDE) and ex vivo delayed enhancement (eDE) cMRI. The AAR and MI were compared to validate the bifunctional straining for cardiac imaging research. Linear regression with Bland-Altman agreement, one way-ANOVA with Bonferroni’s multiple comparison, and paired t tests were applied for statistics.

RESULTS: All rabbits tolerated well the surgical procedure and subsequent cMRI sessions. The open-chest occlusion and close-chest reperfusion of the LCx, double suture method and bifunctional staining were successfully applied in all animals. The percentage MI volumes globally (n = 6) and by slice (n = 25) were 36.59% ± 13.68% and 32.88% ± 12.38% on iDE, and 35.41% ± 12.25% and 32.40% ± 12.34% on eDE. There were no significant differences for MI determination with excellent linear regression correspondence (r_global = 0.89; r_slice = 0.9) between iDE and eDE. The percentage AAR volumes globally (n = 6) and by slice (n = 25) were 44.82% ± 15.18% and 40.04% ± 13.64% with RIO-staining, and 44.74% ± 15.98% and 40.48% ± 13.26% by DR showing high correlation in linear regression analysis (r_global = 0.99; r_slice = 1.0). The mean differences of the two AAR measurements on Bland-Altman were almost zero, indicating RIO-staining and DR were essentially equivalent or inter-replaceable. The AAR was significantly larger than MI both globally and slice-by-slice (P < 0.01). After correction with the background and the blank heart without bifunctional staining (n = 3), the PDR for the AAR and normal myocardium was 32% ± 15% and 35.5% ± 35%, respectively, which is significantly different (P < 0.001), suggesting that blood perfusion to the AAR probably by collateral circulation was only less than 10% of that in the normal myocardium.

CONCLUSION: The myocardial area at risk in ischemic heart disease could be accurately determined postmortem by this novel bifunctional staining, which may substantially contribute to translational cardiac imaging research.

Cell injury after ischemia and reperfusion in the porcine kidney evaluated by radiolabelled microspheres, sestamibi, and lactadherin

Background

The purpose of the present study was to quantify renal cell injury after ischemia and reperfusion in a pig model using ^99mTc-lactadherin as a marker of apoptosis and ^99mTc-sestamibi as a marker of mitochondrial dysfunction.

Methods

Thirty-four pigs were randomized into unilateral renal warm ischemia of 120 (WI₁₂₀) or 240 min (WI₂₄₀). The glomerular filtration rate (GFR) was calculated by renal clearance of ⁵¹Cr-ethylenediaminetetraacetic acid, and apoptosis was quantified by immunohistochemical detection of caspase-3. After 240 min of reperfusion, intravenous ^99mTc-lactadherin or ^99mTc-sestamibi was injected simultaneously with ¹⁵³Gd microspheres into the aorta. Ex-vivo static planar images of the kidneys were acquired for determination of the differential renal function of tracer distribution using a gamma camera.

Results

In WI₁₂₀, there was no significant difference in the uptake of microspheres in the ischemic and contralateral normal kidney indicating adequate perfusion (uptake in ischemic kidney relative to the sum of uptake in both kidneys; 46% ± 12% and 51% ± 5%). In WI₂₄₀, the uptake of microspheres was severely reduced in both groups (17% ± 11% and 27% ± 17%). GFR was severely reduced in the post ischemic kidney in both groups.

In both groups, the uptake of lactadherin was reduced (41% ± 8%, 17% ± 13%) but not different from the uptake of ¹⁵³Gd microspheres. Caspase-3-positive cell profiles were increased in the post-ischemic kidneys (p < 0.001) and increased as the length of ischemia increased (p = 0.003). In both WI₁₂₀ and WI₂₄₀, the amount of ^99mTc-sestamibi in the ischemic kidney was significantly lower than the amount of ¹⁵³Gd microspheres (40 ± 5 versus 51 ± 5 and 20 ± 11 versus 27 ± 17; p < 0.05).

Conclusions

In an established pig model with unilateral renal warm ischemia, we found significantly reduced ^99mTc-sestamibi uptake relative to perfusion in the kidneys exposed to ischemia indicating a potential ability to detect renal ischemic and reperfusion injuries. However, apoptosis was not detected using ^99mTc-lactadherin in the post-ischemic kidneys despite increased number of caspase-3-positive cell profiles.

Trial registration

This study is approved by the Danish Inspectorate of Animal Experiments (2010/561-1837).