Added value of 18F-FDG-PET/CT and cardiac CTA in suspected transcatheter aortic valve endocarditis.

BACKGROUNDS: Transcatheter-implanted aortic valve infective endocarditis (TAVI-IE) is difficult to diagnose when relying on the Duke Criteria. Our aim was to assess the additional diagnostic value of 18F-fluorodeoxyglucose (18F-FDG) positron emission/computed tomography (PET/CT) and cardiac computed tomography angiography (CTA) in suspected TAVI-IE. METHODS: A multicenter retrospective analysis was performed in all patients who underwent 18F-FDG-PET/CT and/or CTA with suspected TAVI-IE. Patients were first classified with Duke Criteria and after adding 18F-FDG-PET/CT and CTA, they were classified with European Society of Cardiology (ESC) criteria. The final diagnosis was determined by our Endocarditis Team based on ESC guideline recommendations. RESULTS: Thirty patients with suspected TAVI-IE were included. 18F-FDG-PET/CT was performed in all patients and Cardiac CTA in 14/30. Using the Modified Duke Criteria, patients were classified as 3% rejected (1/30), 73% possible (22/30), and 23% definite (7/30) TAVI-IE. Adding 18F-FDG-PET/CT and CTA supported the reclassification of 10 of the 22 possible cases as "definite TAVI-IE" (5/22) or "rejected TAVI-IE" (5/22). This changed the final diagnosis to 20% rejected (6/30), 40% possible (12/30), and 40% definite (12/30) TAVI-IE. CONCLUSIONS: Addition of 18F-FDG-PET/CT and/or CTA changed the final diagnosis in 33% of patients and proved to be a valuable diagnostic tool in patients with suspected TAVI-IE.

Circulating Extracellular Vesicles Contain miRNAs and are Released as Early Biomarkers for Cardiac Injury.

Plasma-circulating microRNAs have been implicated as novel early biomarkers for myocardial infarction (MI) due to their high specificity for cardiac injury. For swift clinical translation of this potential biomarker, it is important to understand their temporal and spatial characteristics upon MI. Therefore, we studied the temporal release, potential source, and transportation of circulating miRNAs in different models of ischemia reperfusion (I/R) injury. We demonstrated that extracellular vesicles are released from the ischemic myocardium upon I/R injury. Moreover, we provided evidence that cardiac and muscle-specific miRNAs are transported by extracellular vesicles and are rapidly detectable in plasma. Since these vesicles are enriched for the released miRNAs and their detection precedes traditional damage markers, they hold great potential as specific early biomarkers for MI.

Necrostatin-1 alleviates reperfusion injury following acute myocardial infarction in pigs.

BACKGROUND: In rodents, it has previously been shown that necrostatin-1 (Nec-1) inhibits RIP1, a central regulator of programmed necrosis, thereby decreasing cell death and reducing infarct size (IS) after ischaemia/reperfusion (I/R) injury. To address unanswered questions on feasibility and efficacy of Nec-1 in a large animal model, we assessed the effects of Nec-1 in a porcine I/R model, relevant to human disease. MATERIALS AND METHODS: In Dalland landrace pigs (69 ± 3 kg), I/R injury was induced by a 75-min surgical ligation of the left circumflex coronary artery (LCx). Ten minutes prior to reperfusion, pigs were randomly allocated to different Nec-1 doses (1.0 mg/kg or 3.3 mg/kg) or vehicle treatment (control, CTRL). Functional endpoints and immunohistological analyses were performed 24 h after reperfusion. RESULTS: Nec-1 3.3 mg/kg significantly reduced IS (n = 6; 24.4 ± 15.6%) compared to Nec-1 1.0 mg/kg (n = 5; 54.8 ± 16.9%) or CTRLs (n = 6; 62.1 ± 26.6%; P = 0.016). In line, LV ejection fraction (LVEF) was significantly higher in Nec-1 3.3 mg/kg, copared to Nec-1 1.0 mg/kg or CTRL treated animals (50.0 ± 12.0% vs. 32.5 ± 12.9% vs. 31.9 ± 6.6%, respectively, P = 0.015). Hemodynamically, a preserved contractility was observed [end-systolic volume at 100 mmHg (ESV100 )] at 24-h follow-up (87.6 ± 17.3 mL vs. 74.5 ± 41.1 mL vs. 56.8 ± 11.8 mL, respectively, P = 0.032), reflecting improved cardiac function. CONCLUSIONS: In the pig model of I/R injury, intravenous administration of Nec-1 prior to reperfusion was an effective and above all practical therapeutic strategy that significantly reduced IS and preserved left ventricular function. These data highlight the potential of cardioprotection as a promising adjuvant therapy in the setting of early reperfusion following I/R injury.

Layer-specific radiofrequency ultrasound-based strain analysis in a porcine model of ischemic cardiomyopathy validated by a geometric model.

Local layer-specific myocardial deformation after myocardial infarction (MI) has not been studied extensively although the sub-endocardium is more vulnerable to ischemia and interstitial fibrosis deposition. Radiofrequency (RF) ultrasound-based analysis could provide superior layer-specific radial strain estimation compared with clinically available deformation imaging techniques. In this study, we used RF-based myocardial deformation measurements to investigate layer-specific differences between healthy and damaged myocardium in a porcine model of chronic MI. RF data were acquired epicardially in healthy (n = 21) and infarcted (n = 5) regions of a porcine chronic MI model 12 wk post-MI. Radial and longitudinal strains were estimated in the sub-endocardial, mid-wall and sub-epicardial layers of the left ventricle. Collagen content was quantified in three layers of healthy and infarcted regions in five pigs. An analytical geometric model of the left ventricle was used to theoretically underpin the radial deformation estimated in different myocardial layers. Means ± standard errors of the peak radial and longitudinal strain estimates of the sub-endocardial, mid-wall and sub-epicardial layers of the healthy and infarcted tissue were: 82.7 ± 5.2% versus 39.9 ± 10.8% (p = 0.002), 63.6 ± 3.3% versus 38.8 ± 7.7% (p = 0.004) and 34.3 ± 3.0% versus 35.1 ± 5.2% (p = 0.9), respectively. The radial strain gradient between the sub-endocardium and the sub-epicardium had decreased 12 wk after MI, and histologic examination revealed the greatest increases in collagen in the sub-endocardial and mid-wall layers. Comparable normal peak radial strain values were found by geometric modeling when input values were derived from the in vivo measurements and literature. In conclusion, the estimated strain values are realistic and indicate that sub-endocardial radial strain in healthy tissue can amount to 80%. This high value can be explained by the cardiac geometry, as was illustrated by geometric modeling. After MI, strain values were decreased and collagen content was increased in the sub-endocardial and mid-wall layers. Layer-specific peak radial strain can be assessed by RF strain estimation and clearly differs between healthy and infarcted tissue. Although the relationship between tissue stiffness and tissue strain is not strictly local, this novel technique provides a valuable way to assess layer-specific regional cardiac function in a variety of myocardial diseases.

Assessment of coronary microvascular resistance in the chronic infarcted pig heart.

Pre-clinical studies aimed at treating ischemic heart disease (i.e. stem cell- and growth factor therapy) often consider restoration of the impaired microvascular circulation as an important treatment goal. However, serial in vivo measurement hereof is often lacking. The purpose of this study was to evaluate the applicability of intracoronary pressure and flow velocity as a measure of microvascular resistance in a large animal model of chronic myocardial infarction (MI). Myocardial infarction was induced in Dalland Landrace pigs (n = 13; 68.9 ± 4.1 kg) by a 75-min. balloon occlusion of the left circumflex artery (LCX). Intracoronary pressure and flow velocity parameters were measured simultaneously at rest and during adenosine-induced hyperemia, using the Combowire (Volcano) before and 4 weeks after MI. Various pressure- and/or flow-derived indices were evaluated. Hyperemic microvascular resistance (HMR) was significantly increased by 28% in the infarct-related artery, based on a significantly decreased peak average peak flow velocity (pAPV) by 20% at 4 weeks post-MI (P = 0.03). Capillary density in the infarct zone was decreased compared to the remote area (658 ± 207/mm(2) versus 1650 ± 304/mm(2) , P = 0.017). In addition, arterioles in the infarct zone showed excessive thickening of the alpha smooth muscle actin (αSMA) positive cell layer compared to the remote area (33.55 ± 4.25 µm versus 14.64 ± 1.39 µm, P = 0.002). Intracoronary measurement of HMR successfully detected increased microvascular resistance that might be caused by the loss of capillaries and arteriolar remodelling in the chronic infarcted pig heart. Thus, HMR may serve as a novel outcome measure in pre-clinical studies for serial assessment of microvascular circulation.

Intracoronary infusion of allogeneic mesenchymal precursor cells directly after experimental acute myocardial infarction reduces infarct size, abrogates adverse remodeling, and improves cardiac function.

RATIONALE: Mesenchymal precursor cells (MPCs) are a specific Stro-3+ subpopulation of mesenchymal stem cells isolated from bone marrow. MPCs exert extensive cardioprotective effects, and are considered to be immune privileged. OBJECTIVE: This study assessed the safety, feasibility, and efficacy of intracoronary delivery of allogeneic MPCs directly after acute myocardial infarction in sheep. METHODS AND RESULTS: Initially, intracoronary delivery conditions were optimized in 20 sheep. These conditions were applied in a randomized study of 68 sheep with an anterior acute myocardial infarction. Coronary flow was monitored during MPC infusion, and cardiac function was assessed using invasive hemodynamics and echocardiography at baseline and during 8 weeks follow-up. Coronary flow remained within thrombolysis in myocardial infarction III definitions in all sheep during MPC infusion. Global left ventricular ejection fraction as measured by pressure-volume loop analysis deteriorated in controls to 40.7±2.6% after 8 weeks. In contrast, MPC treatment improved cardiac function to 52.8±0.7%. Echocardiography revealed significant improvement of both global and regional cardiac functions. Infarct size decreased by 40% in treated sheep, whereas infarct and border zone thickness were enhanced. Left ventricular adverse remodeling was abrogated by MPC therapy, resulting in a marked reduction of left ventricular volumes. Blood vessel density increased by >50% in the infarct and border areas. Compensatory cardiomyocyte hypertrophy was reduced in border and remote segments, accompanied by reduced collagen deposition and apoptosis. No microinfarctions in remote myocardial segments or histological abnormalities in unrelated organs were found. CONCLUSIONS: Intracoronary infusion of allogeneic MPCs is safe, feasible, and markedly effective in a large animal model of acute myocardial infarction.

Transendocardial cell injection is not superior to intracoronary infusion in a porcine model of ischaemic cardiomyopathy: a study on delivery efficiency.

Stem cell therapy is a new strategy for chronic ischaemic heart disease in patients. However, no consensus exists on the most optimal delivery strategy. This randomized study was designed to assess cell delivery efficiency of three clinically relevant strategies: intracoronary (IC) and transendocardial (TE) using electromechanical mapping guidance (NOGA) compared to surgical delivery in a chronic pig model of ischaemic cardiomyopathy. Twenty-four animals underwent delivery of 10(7) autologous Indium-oxine-labelled bone marrow-derived mesenchymal stem cells (MSC) 4 weeks after infarction and were randomized to one of three groups (n = 8 each group): IC, TE or surgical delivery (reference group). Primary endpoint was defined as percentage (%) of injected dose per organ and assessed by in vivo gamma-emission counting. In addition, troponin and coronary flow were assessed before and after MSC injection. Blinded endpoint analysis showed no significant difference in efficiency after surgical (16 ± 4%), IC (11 ± 1%) and TE (11 ± 3%) (P = 0.52) injections. IC showed less variability in efficiency compared with TE and surgical injection. Overall, TE injection showed less distribution of MSC to visceral organs compared with other modalities. Troponin rise and IC flow did not differ between the percutaneous groups. This randomized study showed no significant difference in cell delivery efficiency to the myocardium in a clinically relevant ischaemic large animal model between IC and TE delivery. In addition, no differences in safety profile were observed. These results are important in view of the choice of percutaneous cell delivery modality in future clinical stem cell trials.

Advanced measurement techniques of regional myocardial function to assess the effects of cardiac regenerative therapy in different models of ischaemic cardiomyopathy.

Cardiac regenerative therapy is still not used in daily clinical practice. A reason for this might be the modest effect on relevant global clinical endpoints [i.e. ejection fraction (EF)] in preclinical studies. To introduce proper improvement strategies, it is important to extend the focus from clinical endpoints to more detailed local measures of cardiac function. In this review, we discuss the measurement principles of all invasive and non-invasive techniques that are used to assess the local effects of cardiac regenerative therapy in order to improve feedback to researchers unravelling the dominant pathways that lead to effective cardiac regeneration. Generally adopted mechanisms of cardiac regenerative therapy are: (i) vasculogenesis, (ii) cardiomyogenesis, and (iii) matrix-assisted myocardium stabilization. Since direct in vivo measures of these mechanisms do not exist, we discuss the measurement techniques of local microvascular resistance, myocardial perfusion, viability, fibrosis, and deformation imaging. The ability of these techniques to reflect the mechanism of cardiac regenerative therapy, and the results of applications in stem cell studies are discussed, and critically commented upon. Special attention is given to applications of deformation imaging, since this has recently been suggested and used as a potential new technique to assess local changes of cardiac biomechanics, which requires special knowledge about cardiac physiology. We conclude that besides the clinically relevant EF measurements, detailed measures of local cardiac function provide information about the local changes induced by cardiac regenerative therapy. In particular, combination of deformation imaging, by ultrasound or magnetic resonance imaging, with simultaneously measured local geometry and pressure measurements is a promising approach to assess the effects of cardiac regenerative therapy on local cardiac biomechanics. This approach provides information about local tissue contractility, stiffness, and thereby remodelling. We recommend that researchers use this comprehensive approach in future studies.

Surgical left ventricular radius enlargement by patch insertion on the beating heart: a new experimental aneurysm model.

We presented a novel experimental aneurysm model for studies in left ventricular (LV) reconstruction techniques and assessed LV function. In eight pigs, the LV radius and geometry were enlarged surgically on the beating heart by inserting an aortic allograft construct. Haemodynamics and LV dimensions were assessed by echocardiography at baseline and under dobutamine stress. Surgery was successfully performed without lethal blood loss or arrhythmias. LV end-diastolic and end-systolic short-axis areas increased from 13.0 ± 1.7 to 17.0 ± 4.3 cm(2) (P = 0.001) and from 4.0 ± 0.9 to 13.0 ± 2.6 cm(2) (P = 0.001), respectively. Stroke volume decreased from 56 ± 11 to 33 ± 16 ml (P = 0.001). Incremental dobutamine infusion concurred with a biphasic response on fractional area shortening. Mitral valve insufficiency ranging from grades 2 to 4 was observed. In the pig, a novel, reproducible aneurysm model for acute cardiac dysfunction was created on the beating heart. Innovative (surgical) strategies for (staged) reconfiguration of the ventricle, e.g. adjustable Dor procedures and stepwise volume restraining cardiac support devices, can be tested for efficacy using this acute model.

Human relevance of pre-clinical studies in stem cell therapy: systematic review and meta-analysis of large animal models of ischaemic heart disease.

AIMS: Stem cell therapy is a treatment strategy for ischaemic heart disease patients. Meta-analysis of randomized human trials showed <5% improvement in left ventricular ejection fraction (LVEF). Meta-analysis of available pre-clinical data of ischaemic heart disease could provide important clues to design human clinical trials. METHODS AND RESULTS: Random-effects meta-analysis was performed on pig, dog, or sheep studies investigating the effect of cardiac stem cell therapy in ischaemic cardiomyopathy (52 studies; n = 888 animals). Endpoints were LVEF and death. Ischaemia/reperfusion infarction was performed in 23 studies and chronic occlusion in 29 studies. Pooled analysis showed a LVEF difference of 7.5% at follow-up after cell therapy vs. control (95% confidence interval, 6.2-8.9%; P < 0.001). By exploratory multivariable meta-regression, significant predictors of LVEF improvement were: cell type [bone marrow mononuclear cells (BM-MNC) showed less effect than other cell types, e.g. mesenchymal stem cells; P = 0.040] and type of infarction (left anterior descending artery 8.0 vs. left circumflex artery 5.8%; P = 0.045). Cell therapy was not associated with increased mortality (P = 0.68). Sensitivity analysis showed trends towards more improvement with higher cell number (≥10(7)), chronic occlusion models, and late injections (>1 week). After follow-up of 8 weeks, the effect of cell therapy decreased to 6%. CONCLUSION: This meta-analysis showed that large animal models are valid to predict the outcome of clinical trials. Our results showed that cell therapy is safe and leads to a preserved LVEF. Future trials should focus on cell types other than BM-MNC, large infarction, and strategies to obtain sustained effects.

Non-surgical stem cell delivery strategies and in vivo cell tracking to injured myocardium.

Heart failure is a major economic and public health problem. Despite the recent advances in drug therapy and coronary revascularization, the lost cardiomyocytes due to necrosis and apoptosis are not replaced by new myocardial tissue. Cell therapy is an interesting therapeutic option as it potentially improves contractility and restores regional ventricular function. Early clinical data demonstrated that cell transplantation, mainly delivered through non-surgical methods, is safe and feasible. However, several important issues need to be elucidated. This includes, next to determining the best cell type, the optimal delivery strategy, the biodistribution and the survival of implanted stem cells after transplantation. In this view, pre-clinical animal experiments are indispensable. Reporter genes, magnetic or radioactive labeling of stem cells have been developed to observe the fate and the distribution of transplanted cells using non-invasive imaging techniques. Several studies have demonstrated that these direct and non-direct labeling techniques may become an important tool in cell therapy. Integration of cell delivery and cell tracking will probably be a key for the success of cell therapy in patients. This review will provide a comprehensive overview on the various cell tracking and non-surgical cell delivery techniques, which are highly important in view of experimental and clinical studies.

Transmural myocardial mechanics during isovolumic contraction.

OBJECTIVES: We sought to resolve the 3-dimensional transmural heterogeneity in myocardial mechanics observed during the isovolumic contraction (IC) phase. BACKGROUND: Although myocardial deformation during IC is expected to be little, recent tissue Doppler imaging studies suggest dynamic myocardial motions during this phase with biphasic longitudinal tissue velocities in left ventricular (LV) long-axis views. A unifying understanding of myocardial mechanics that would account for these dynamic aspects of IC is lacking. METHODS: We determined the time course of 3-dimensional finite strains in the anterior LV of 14 adult mongrel dogs in vivo during IC and ejection with biplane cineradiography of implanted transmural markers. Transmural fiber orientations were histologically measured in the heart tissue postmortem. The strain time course was determined in the subepicardial, midwall, and subendocardial layers referenced to the end-diastolic configuration. RESULTS: During IC, there was circumferential stretch in the subepicardial layer, whereas circumferential shortening was observed in the midwall and the subendocardial layer. There was significant longitudinal shortening and wall thickening across the wall. Although longitudinal tissue velocity showed a biphasic profile; tissue deformation in the longitudinal as well as other directions was almost linear during IC. Subendocardial fibers shortened, whereas subepicardial fibers lengthened. During ejection, all strain components showed a significant change over time that was greater in magnitude than that of IC. Significant transmural gradient was observed in all normal strains. CONCLUSIONS: IC is a dynamic phase characterized by deformation in circumferential, longitudinal, and radial directions. Tissue mechanics during IC, including fiber shortening, appear uninterrupted by rapid longitudinal motion created by mitral valve closure. This study is the first to report layer-dependent deformation of circumferential strain, which results from layer-dependent deformation of myofibers during IC. Complex myofiber mechanics provide the mechanism of brief clockwise LV rotation (untwisting) and significant wall thickening during IC within the isovolumic constraint.