Abstract 55: The Natural Course of Myocardial Infarction in Large Animal Models; a Systematic Review and Meta-analysis

Background: Large animal models of myocardial infarction (MI) are essential for the development of novel therapeutic strategies. However, it is unclear which experimental factors are independent determinants of disease progression outcomes and the fidelity with which these models resemble MI in humans. The aim of this study was to investigate systematically what independently influences the outcome after MI in large animal models and determine which methodological factors influence primary endpoints and disease progression.

Methods: We used control animal data from two meta-analyses of large animal models of MI. We performed univariable and multivariable meta-regression to analyze if potential relevant variables were influencing outcomes; infarct size as a ratio of the area at risk (IS/AAR), as a ratio of the left ventricle (IS/LV) and ejection fraction (EF). Pre-defined independent variables were species, sex, weight, ischemia model (open vs closed), occlusion type (temporary vs permanent), occluded vessel, follow-up duration, use of co-medication, use of immunosuppression and study quality. Outcomes and variables were complemented per dataset if needed.

Results: Our analyses yielded 246 relevant studies, reporting 1500, 1221 and 775 control animals for IS/AAR, IS/LV and EF respectively. Multivariable meta-regression showed IS/AAR was influenced by species (p<0.001), sex (p=0.03), co-medication (p=0.01), occlusion type (p<0.001), occluded vessel (p=0.002) and follow-up (p=0.001). For IS/LV occlusion type (p=0.03), occluded vessel (p=0.03) and study quality (p=0.03) showed significant effects. EF measurements revealed that species (p=0.04), sex (p=0.04) and occluded vessel (p=0.05) were independent predictors. Using these variables, we can partially predict these outcomes for certain study setups.

Conclusion: Many methodological variations exist in the design of large animal MI studies. This should be taken into account when selecting a model to study therapy efficacy. We provide evidence that disease manifestation and progression greatly depend on certain biological characteristics, e.g. location of MI and sex of the patient. It is therefore possible that therapies have a different effect in specific patient populations.

Translational failure of anti-inflammatory compounds for myocardial infarction: a meta-analysis of large animal models

AIMS

Numerous anti-inflammatory drugs have been tested in large animal studies of myocardial infarction (MI). Despite positive results, translation of anti-inflammatory strategies into clinical practice has proved to be difficult. Critical disparities between preclinical and clinical study design that influence efficacy may partly be responsible for this translational failure. The aim of the present systematic review was to better understand which factors underlie the failure of transition towards the clinic.

METHODS AND RESULTS

Meta-analysis and regression of large animal studies were performed to identify sources that influenced effect size of anti-inflammatory compounds in large animal models of MI. We included 183 studies, containing 3331 large animals. Infarct size (IS) as a ratio of the area at risk (12.7%; 95% confidence interval, CI 11.1-14.4%, P < 0.001) and IS as a ratio of the left ventricle (3.9%; 95% CI 3.1-4.7%, P < 0.001) were reduced in treatment compared with control groups. Effect size was higher when outcome was assessed early after MI (P = 0.013) and where studies included only male animals (P < 0.001). Mortality in treated animals was higher in studies that blinded the investigator during the experiment (P = 0.041) and depended on the type of drug used (P < 0.001).

CONCLUSIONS

As expected, treatment with anti-inflammatory drugs leads to smaller infarct size in large animal MI models. Timing of outcome assessment, sex, and study quality are significantly associated with outcome and may explain part of the translational failure in clinical settings. Effect size depends on the type of drug used, enabling identification of compounds for future clinical testing.

Endogenous assessment of chronic myocardial infarction with T(1ρ)-mapping in patients

BACKGROUND

Detection of cardiac fibrosis based on endogenous magnetic resonance (MR) characteristics of the myocardium would yield a measurement that can provide quantitative information, is independent of contrast agent concentration, renal function and timing. In ex vivo myocardial infarction (MI) tissue, it has been shown that a significantly higher T(1ρ) is found in the MI region, and studies in animal models of chronic MI showed the first in vivo evidence for the ability to detect myocardial fibrosis with native T(1ρ)-mapping. In this study we aimed to translate and validate T(1ρ)-mapping for endogenous detection of chronic MI in patients.

METHODS

We first performed a study in a porcine animal model of chronic MI to validate the implementation of T(1ρ)-mapping on a clinical cardiovascular MR scanner and studied the correlation with histology. Subsequently a clinical protocol was developed, to assess the feasibility of scar tissue detection with native T(1ρ)-mapping in patients (n = 21) with chronic MI, and correlated with gold standard late gadolinium enhancement (LGE) CMR. Four T1ρ-weighted images were acquired using a spin-lock preparation pulse with varying duration (0, 13, 27, 45 ms) and an amplitude of 750 Hz, and a T(1ρ)-map was calculated. The resulting T(1ρ)-maps and LGE images were scored qualitatively for the presence and extent of myocardial scarring using the 17-segment AHA model.

RESULTS

In the animal model (n = 9) a significantly higher T(1ρ) relaxation time was found in the infarct region (61 ± 11 ms), compared to healthy remote myocardium (36 ± 4 ms) . In patients a higher T(1ρ) relaxation time (79 ± 11 ms) was found in the infarct region than in remote myocardium (54 ± 6 ms). Overlap in the scoring of scar tissue on LGE images and T(1ρ)-maps was 74%.

CONCLUSION

We have shown the feasibility of native T(1ρ)-mapping for detection of infarct area in patients with a chronic myocardial infarction. In the near future, improvements on the T(1ρ)-mapping sequence could provide a higher sensitivity and specificity. This endogenous method could be an alternative for LGE imaging, and provide additional quantitative information on myocardial tissue characteristics.

Admittance-based pressure-volume loops versus gold standard cardiac magnetic resonance imaging in a porcine model of myocardial infarction

A novel admittance‐based pressure–volume system (AS) has recently been developed and introduced. Thus far, the new technique has been validated predominantly in small animals. In large animals it has only been compared to three‐dimensional echocardiography (3DE) where the AS showed to overestimate left ventricular (LV) volumes. To fully determine the accuracy of this device, we compared the AS with gold standard cardiac magnetic resonance imaging (CMRI) in a porcine model of chronic myocardial infarction (MI). Fourteen pigs were subjected to 90 min closed chest balloon occlusion of the left anterior descending artery. After 8 weeks of follow up, pigs were consecutively subjected to LV volume measurements by the AS, CMRI, and 3DE under general anesthesia. The AS overestimated end diastolic volume (EDV; +20.9 ± 30.6 mL, P = 0.024) and end systolic volume (ESV; +17.7 ± 29.4 mL, P = 0.042) but not ejection fraction (EF; +2.46 ± 6.16%, P = NS) compared to CMRI. Good correlations of EDV (R = 0.626, P = 0.017) and EF (R = 0.704, P = 0.005) between the AS and CMRI were observed. EF measured by the AS and 3DE also correlated significantly (R = 0.624, P = 0.030). After subjection of pigs to MI, the AS very moderately overestimates LV volumes and shows accurate measurements for EF compared to CMRI. This makes the AS a useful tool to determine cardiac function and dynamic changes in large animal models of cardiac disease.

Is the novel admittance‐based pressure–volume loop system reliable for the assessment of left ventricular volumes compared to gold standard cardiac magnetic resonance imaging in a porcine model of myocardial infarction? In the postinfarction remodeled heart, admittance‐based pressure–volume loop measurements accurately measure ejection fraction and very moderately overestimate end diastolic and end systolic volumes compared to gold standard cardiac magnetic resonance imaging, making it a very useful technique for cardiac function assessment in experimental studies.