Percutaneous Mechanical Unloading Simultaneously With Reperfusion Induces Increased Myocardial Salvage in Experimental Acute Myocardial Infarction

Reperfusion Injury in Patients With Acute Myocardial Infarction: JACC Scientific Statement

Despite impressive improvements in the care of patients with ST-segment elevation myocardial infarction, mortality remains high. Reperfusion is necessary for myocardial salvage, but the abrupt return of flow sets off a cascade of injurious processes that can lead to further necrosis. This has been termed myocardial ischemia-reperfusion injury and is the subject of this review. The pathologic and molecular bases for myocardial ischemia-reperfusion injury are increasingly understood and include injury from reactive oxygen species, inflammation, calcium overload, endothelial dysfunction, and impaired microvascular flow. A variety of pharmacologic strategies have been developed that have worked well in preclinical models and some have shown promise in the clinical setting. In addition, there are newer mechanical approaches including mechanical unloading of the heart prior to reperfusion that are in current clinical trials.

Mechanical Unloading of the Left Ventricle before Coronary Reperfusion in Preclinical Models of Myocardial Infarction without Cardiogenic Shock: A Meta-Analysis

Aim: to compare a conventional primary reperfusion strategy with a primary unloading approach before reperfusion in preclinical studies. Methods: we performed a meta-analysis of preclinical studies. The primary endpoint was infarct size (IS). Secondary endpoints were left ventricle end-diastolic pressure (LVEDP), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO). We calculated mean differences (MDs) and associated 95% confidence intervals (CIs). Sensitivity and subgroup analyses on the primary and secondary endpoints, as well as a meta-regression on the primary endpoint using the year of publication as a covariate, were also conducted. Results: 11 studies (n = 142) were selected and entered in the meta-analysis. Primary unloading reduced IS (MD −28.82, 95% CI −35.78 to −21.86, I2 96%, p < 0.01) and LVEDP (MD −3.88, 95% CI −5.33 to −2.44, I2 56%, p = 0.02) and increased MAP (MD 7.26, 95% CI 1.40 to 13.12, I2 43%, p < 0.01) and HR (MD 5.26, 95% CI 1.97 to 8.55, I2 1%, p < 0.01), while being neutral on CO (MD −0.11, 95% CI −0.95 to 0.72, I2 88%, p = 0.79). Sensitivity and subgroup analyses showed, overall, consistent results. The meta-regression on the primary endpoint demonstrated a significant influence of the year of publication on effect estimate. Conclusions: in animal models of myocardial infarction, a primary unloading significantly reduces IS and exerts beneficial hemodynamic effects compared to a primary reperfusion.

Left Ventricular Assist Devices for Acute Myocardial Infarct Size Reduction: Meta-analysis

We conducted a meta-analysis of preclinical studies that tested left ventricular assist device (LVAD) therapy for reducing myocardial infarct size in experimental acute myocardial infarction (AMI). Twenty-six articles were included with a total of 488 experimental animal subjects. The meta-analysis showed that infarct size was significantly decreased by LVAD support compared to control animals (SDM, - 2.19; 95% CI, - 2.70 to - 1.69; P < 0.001). The meta-regression analysis demonstrated a high degree of heterogeneity associated with time from coronary artery occlusion to LVAD support, which correlated positively with infarct size. Subgroup analysis suggested smaller infarct size in LVAD therapies that withdrew blood from left heart than those from right heart. The proportion of left ventricular support relative to total cardiac output was positively correlated with infarct size reduction in Impella studies. Thus, early initiation of LVAD after ischemia and effective left ventricular venting may be important factors to reduce infarct size in AMI.

Veno-occlusive unloading of the heart reduces infarct size in experimental ischemia-reperfusion

Mechanical unloading of the left ventricle reduces infarct size after acute myocardial infarction by reducing cardiac work. Left ventricular veno-occlusive unloading reduces cardiac work and may reduce ischemia and reperfusion injury. In a porcine model of myocardial ischemia-reperfusion injury we randomized 18 pigs to either control or veno-occlusive unloading using a balloon engaged from the femoral vein into the inferior caval vein and inflated at onset of ischemia. Evans blue and 2,3,5-triphenyltetrazolium chloride were used to determine the myocardial area at risk and infarct size, respectively. Pressure-volume loops were recorded to calculate cardiac work, left ventricular (LV) volumes and ejection fraction. Veno-occlusive unloading reduced infarct size compared with controls (Unloading 13.9 ± 8.2% versus Control 22.4 ± 6.6%; p = 0.04). Unloading increased myocardial salvage (54.8 ± 23.4% vs 28.5 ± 14.0%; p = 0.02), while the area at risk was similar (28.4 ± 6.7% vs 27.4 ± 5.8%; p = 0.74). LV ejection fraction was preserved in the unloaded group, while the control group showed a reduced LV ejection fraction. Veno-occlusive unloading reduced myocardial infarct size and preserved LV ejection fraction in an experimental acute ischemia-reperfusion model. This proof-of-concept study demonstrated the potential of veno-occlusive unloading as an adjunctive cardioprotective therapy in patients undergoing revascularization for acute myocardial infarction.

Door-to-unload: left ventricular unloading before reperfusion in ST-elevation myocardial infarction

ST-elevation myocardial infarction treatment in the modern era has focused on minimizing time of ischemia by reducing door-to-balloon time to limit infarct size and improve survival. Although there have been significant improvements in minimizing time to coronary reperfusion, the incidence of heart failure following a myocardial infarction has remained high. Preclinical studies have shown that unloading the left ventricle for 30 min prior to coronary reperfusion can reduce infarct size and promote myocardial recovery. The DTU-STEMI randomized prospective trial will test the hypothesis that left ventricular unloading for at least 30 min prior to coronary reperfusion will improve infarct size and heart failure-related events as compared with the current standard of care.

Large Animal Models of Heart Failure: A Translational Bridge to Clinical Success

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Preclinical large animal models play a critical and expanding role in translating basic science findings to the development and clinical approval of novel cardiovascular therapeutics.

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This state-of-the-art review outlines existing methodologies and physiological phenotypes of several HF models developed in large animals. A comprehensive list of porcine, ovine, and canine models of disease are presented, and the translational importance of these studies to clinical success is highlighted through a brief overview of recent devices approved by the FDA alongside associated clinical trials and preclinical animal reports.

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Increasing the use of large animal models of HF holds significant potential for identifying new mechanisms underlying this disease and providing valuable information regarding the safety and efficacy of new therapies, thus, improving physiological and economical translation of animal research to the successful treatment of human HF.

Preclinical large animal models of heart failure (HF) play a critical and expanding role in translating basic science findings to the development and clinical approval of novel therapeutics and devices. The complex combination of cardiovascular events and risk factors leading to HF has proved challenging for the development of new treatments for these patients. This state-of-the-art review presents historical and recent studies in porcine, ovine, and canine models of HF and outlines existing methodologies and physiological phenotypes. The translational importance of large animal studies to clinical success is also highlighted with an overview of recent devices approved by the Food and Drug Administration, together with preclinical HF animal studies used to aid both development and safety and/or efficacy testing. Increasing the use of large animal models of HF holds significant potential for identifying the novel mechanisms underlying the clinical condition and to improving physiological and economical translation of animal research to successfully treat human HF.