Removal of endothelial surface-associated von villebrand factor suppresses accelerate datherosclerosis after myocardial infarction

BACKGROUND

Thromboinflammation involving platelet adhesion to endothelial surface-associated von Willebrand factor (VWF) has been implicated in the accelerated progression of non-culprit plaques after MI. The aim of this study was to use arterial endothelial molecular imaging to mechanistically evaluate endothelial-associated VWF as a therapeutic target for reducing remote plaque activation after myocardial infarction (MI).

METHODS

Hyperlipidemic mice deficient for the low-density lipoprotein receptor and Apobec-1 underwent closed-chest MI and were treated chronically with either: (i) recombinant ADAMTS13 which is responsible for proteolytic removal of VWF from the endothelial surface, (ii) N-acetylcysteine (NAC) which removes VWF by disulfide bond reduction, (iii) function-blocking anti-factor XI (FXI) antibody, or (iv) no therapy. Non-ischemic controls were also studied. At day 3 and 21, ultrasound molecular imaging was performed with probes targeted to endothelial-associated VWF A1-domain, platelet GPIbα, P-selectin and vascular cell adhesion molecule-1 (VCAM-1) at lesion-prone sites of the aorta. Histology was performed at day 21.

RESULTS

Aortic signal for P-selectin, VCAM-1, VWF, and platelet-GPIbα were all increased several-fold (p < 0.01) in post-MI mice versus sham-treated animals at day 3 and 21. Treatment with NAC and ADAMTS13 significantly attenuated the post-MI increase for all four molecular targets by > 50% (p < 0.05 vs. non-treated at day 3 and 21). On aortic root histology, mice undergoing MI versus controls had 2-4 fold greater plaque size and macrophage content (p < 0.05), approximately 20-fold greater platelet adhesion (p < 0.05), and increased staining for markers of platelet transforming growth factor-β1 signaling. Accelerated plaque growth and inflammatory activation was almost entirely prevented by ADAMTS13 and NAC. Inhibition of FXI had no significant effect on molecular imaging signal or plaque morphology.

CONCLUSIONS

Plaque inflammatory activation in remote arteries after MI is strongly influenced by VWF-mediated platelet adhesion to the endothelium. These findings support investigation into new secondary preventive therapies for reducing non-culprit artery events after MI.

Influence of Atherosclerotic Risk Factors on the Effectiveness of Therapeutic Ultrasound Cavitation for Flow Augmentation

BACKGROUND

Shear created by inertial cavitation of microbubbles by ultrasound augments limb and myocardial perfusion and can reverse tissue ischemia. Our aim was to determine whether this therapeutic bioeffect is attenuated by atherosclerotic risk factors that are known to impair shear-mediated vasodilation and adversely affect microvascular reactivity.

METHODS

In mice, lipid-stabilized decafluorobutane microbubbles (2 × 108) were administered intravenously while exposing a proximal hind limb to ultrasound (1.3 MHz, 1.3 mechanical index, pulsing interval 5 seconds) for 10 minutes. Murine strains included wild-type mice and severely hyperlipidemic mice at 15, 35, or 52 weeks of age as a model of aging and elevated cholesterol, and obese db/db mice (≈15 weeks) with severe insulin resistance. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess microvascular perfusion in the control and ultrasound-exposed limb. An in situ electrochemical probe and in vivo biophotonic imaging were used to assess limb nitric oxide (NO) and adenosine triphosphosphate concentrations, respectively.

RESULTS

Microvascular perfusion was significantly increased by several fold in the cavitation-exposed limb versus control limb for all murine strains and ages (P < .001). In wild-type and hyperlipidemic mice, hyperemia from cavitation was attenuated in the 2 older age groups (P < .01). In young mice (15 weeks), perfusion in cavitation-exposed muscle was less in both the hyperlipidemic mice and the obese db/db mice compared with corresponding wild-type mice. Using young hyperlipidemic mice as a model for flow impairment, limb NO production after cavitation was reduced but adenosine triphosphosphate production was unaltered when compared with age-matched wild-type mice.

CONCLUSIONS

In mice, ultrasound cavitation of microbubbles increases limb perfusion by several fold even in the presence of traditional atherosclerotic risk factors. However, older age, hyperlipidemia, and insulin resistance modestly attenuate the degree of flow augmentation, which could impact the degree of flow response in current clinical trials in patients with critical limb ischemia.

Activation of coagulation FXI promotes endothelial inflammation and amplifies platelet activation in a nonhuman primate model of hyperlipidemia

Background

Hyperlipidemia is associated with chronic inflammation and thromboinflammation. This is an underlying cause of several cardiovascular diseases, including atherosclerosis. In diseased blood vessels, rampant thrombin generation results in the initiation of the coagulation cascade, activation of platelets, and endothelial cell dysfunction. Coagulation factor (F) XI represents a promising therapeutic target to reduce thromboinflammation, as it is uniquely positioned at an intersection between inflammation and thrombin generation.

Objectives

This study aimed to investigate the role of FXI in promoting platelet and endothelial cell activation in a model of hyperlipidemia.

Methods

Nonhuman primates (NHPs) were fed a standard chow diet (lean, n = 6) or a high-fat diet (obese, n = 8) to establish a model of hyperlipidemia. Obese NHPs were intravenously administered a FXI blocking antibody (2 mg/kg) and studied at baseline and at 1, 7, 14, 21, and 28 days after drug administration. Platelet activation and inflammatory markers were measured using fluorescence-activated cell sorting or enzyme-linked immunosorbent assay. Molecular imaging was used to quantify vascular cell adhesion molecule 1 (VCAM-1) expression at the carotid bifurcation.

Results

Obese NHPs demonstrated increased sensitivity for platelet P-selectin expression and phosphatidylserine exposure in response to platelet GPVI or PAR agonists compared with lean NHPs. Obese NHPs exhibited elevated levels of C-reactive protein, cathepsin D, and myeloperoxidase compared with lean NHPs. Following pharmacological inhibition of FIX activation by FXIa, platelet priming for activation by GPVI or PAR agonists, C-reactive protein levels, and endothelial VCAM-1 levels were reduced in obese NHPs.

Conclusion

FXI activation promotes the proinflammatory phenotype of hyperlipidemia by priming platelet activation and inciting endothelial cell dysfunction.

Contrast Echocardiography for Assessing Myocardial Perfusion

PURPOSE OF REVIEW

Improvements in ultrasound methods for detecting microbubble ultrasound enhancing agents have led to an increase in the use of perfusion imaging with myocardial contrast echocardiography (MCE). This technique is now beginning to play an important role in specific clinical scenarios, which is the focus of this review.

RECENT FINDINGS

MCE was originally conceived as a technique for detecting resting perfusion abnormalities related to ischemia at rest or during stress from coronary artery disease. More recently, MCE has increasingly been used in circumstances where the technique's ability to provide rapid, quantitative, or bedside assessment of perfusion is advantageous. Quantitative MCE is also increasingly being used as a research technique for evaluating pathobiology and therapy that involve changes in the myocardial microcirculation. While MCE was developed and validated decades ago, it is only now beginning to be used by an increasing number of clinicians due to improvements in imaging technology and recognition of specific situations where the technique is impactful.

Cardiac allograft vasculopathy diagnosed by vasodilator myocardial contrast echocardiography perfusion imaging

Cardiac allograft vasculopathy (CAV) remains a common long-term complication of cardiac transplantation. While invasive coronary angiography is considered the gold standard, it is also invasive and lacks sensitivity to detect early, distal CAV. Although vasodilator stress myocardial contrast echocardiography perfusion imaging (MCE) is used in the detection of microvascular disease in non-transplant patients, there is little data guiding its use in transplant recipients. Herein is a case series of four heart transplant recipients that had vasodilator stress MCE performed in addition to invasive coronary angiography for CAV surveillance. MCE at rest and after regadenason was performed using a continuous infusion of lipid-shelled microbubbles. We describe a case of normal microvascular function, diffuse microvascular dysfunction, patchy sub-endocardial perfusion defects and a focal sub-endocardial perfusion defect. Cardiac allograft vasculopathy can be heralded by several different perfusion patterns on MCE in patients after orthotopic heart transplant. The varying prognoses and potential interventions for these different patterns require further investigation.

Low-density lipoprotein promotes microvascular thrombosis by enhancing von Willebrand factor self-association

von Willebrand factor (VWF) mediates primary hemostasis and thrombosis in response to hydrodynamic forces. We previously showed that high shear promoted self-association of VWF into hyperadhesive strands, which can be attenuated by high-density lipoprotein (HDL) and apolipoprotein A-I. In this study, we show that low-density lipoprotein (LDL) binds VWF under shear and enhances self-association. Vortexing VWF in tubes resulted in its loss from the solution and deposition onto tube surfaces, which was prevented by HDL. At a stabilizing HDL concentration of 1.2 mg/mL, increasing concentrations of LDL progressively increased VWF loss, the effect correlating with the LDL-to-HDL ratio and not the absolute concentration of the lipoproteins. Similarly, HDL diminished deposition of VWF in a post-in-channel microfluidic device, whereas LDL increased both the rate and extent of strand deposition, with both purified VWF and plasma. Hypercholesterolemic human plasma also displayed accelerated VWF accumulation in the microfluidic device. The initial rate of accumulation correlated linearly with the LDL-to-HDL ratio. In Adamts13-/- and Adamts13-/-LDLR-/- mice, high LDL levels enhanced VWF and platelet adhesion to the myocardial microvasculature, reducing cardiac perfusion, impairing systolic function, and producing early signs of cardiomyopathy. In wild-type mice, high plasma LDL concentrations also increased the size and persistence of VWF-platelet thrombi in ionophore-treated mesenteric microvessels, exceeding the accumulation seen in similarly treated ADAMTS13-deficient mice that did not receive LDL infusion. We propose that targeting the interaction of VWF with itself and with LDL may improve the course of thrombotic microangiopathies, atherosclerosis, and other disorders with defective microvascular circulation.

A G1528C Hadha knock-in mouse model recapitulates aspects of human clinical phenotypes for long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a fatty acid oxidation disorder (FAOD) caused by a pathogenic variant, c.1528 G > C, in HADHA encoding the alpha subunit of trifunctional protein (TFPα). Individuals with LCHADD develop chorioretinopathy and peripheral neuropathy not observed in other FAODs in addition to the more ubiquitous symptoms of hypoketotic hypoglycemia, rhabdomyolysis and cardiomyopathy. We report a CRISPR/Cas9 generated knock-in murine model of G1528C in Hadha that recapitulates aspects of the human LCHADD phenotype. Homozygous pups are less numerous than expected from Mendelian probability, but survivors exhibit similar viability with wildtype (WT) littermates. Tissues of LCHADD homozygotes express TFPα protein, but LCHADD mice oxidize less fat and accumulate plasma 3-hydroxyacylcarnitines compared to WT mice. LCHADD mice exhibit lower ketones with fasting, exhaust earlier during treadmill exercise and develop a dilated cardiomyopathy compared to WT mice. In addition, LCHADD mice exhibit decreased visual performance, decreased cone function, and disruption of retinal pigment epithelium. Neurological function is affected, with impaired motor function during wire hang test and reduced open field activity. The G1528C knock-in mouse exhibits a phenotype similar to that observed in human patients; this model will be useful to explore pathophysiology and treatments for LCHADD in the future.

Elevated LDL (Low-Density Lipoprotein) Cholesterol Increases Microvascular Endothelial VWF (von Willebrand Factor) and Thromboinflammation After Myocardial Infarction

BACKGROUND

In reperfused myocardial infarction, VWF (von Willebrand factor)-mediated platelet adhesion contributes to impaired microvascular reflow and possibly also to postmyocardial infarction inflammation. We hypothesized that postischemic thromboinflammatory processes are worsened by elevated LDL (low-density lipoprotein) cholesterol.

METHODS

Myocardial ischemia-reperfusion or sham procedure was performed in wild-type mice and hyperlipidemic mice deficient for the LDL receptor and Apobec-1 (apolipoprotein-B mRNA editing enzyme catalytic polypeptide-1; DKO [double knockout]). DKO subgroups were treated with N-acetylcysteine, which inhibits pro-adhesive VWF multimers or with recombinant ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin motifs-13), which enzymatically cleaves endothelial surface-associated VWF. Myocardial contrast echocardiography perfusion imaging and molecular imaging for VWF, platelet GP Ibα, and leukocyte CD18 were performed 30 minutes post-reperfusion. Histology, infarct sizing, and echocardiography were performed at 1.5 or 72 hours; late echocardiography was performed at day 21.

RESULTS

After ischemia-reperfusion, DKO compared with wild-type mice had ≈2-fold higher (P<0.05) risk area signal for microvascular platelet adhesion, VWF, and CD18; greater impairment in microvascular reflow, and 2-fold larger infarct size. Treatment of DKO mice with N-acetylcysteine and ADAMTS13 reduced molecular imaging signal for microvascular platelet adhesion, VWF, and CD18; improved early microvascular reflow; and reduced eventual infarct size. ADAMTS13 suppressed the postmyocardial infarction neutrophil and monocyte infiltration, enhanced the time-dependent recovery of left ventricular systolic function, and prevented late left ventricular remodeling.

CONCLUSIONS

In reperfused myocardial infarction, elevated LDL cholesterol promotes thromboinflammation through excess microvascular endothelial VWF and platelet adhesion, resulting in less microvascular reflow and larger infarct size. In the presence of elevated LDL cholesterol, therapies that suppress endothelial-associated VWF can promote recovery of left ventricular function and protect against remodeling.

Utilizing Contrast-Enhanced Ultrasonography with Phosphatidylserine Microbubbles to Detect Placental Inflammation in Rhesus Macaques

The ability to comprehensively monitor physiological and detect pathophysiologic processes early during pregnancy can reduce maternal and fetal morbidity and mortality. Contrast-enhanced ultrasound (CEUS) is a non-invasive imaging technology that utilizes the acoustic detection of microbubbles to examine vascular spaces. Furthermore, microbubbles conjugated to specific compounds can focus studies on precise physiological pathways. We hypothesized that CEUS with phosphatidylserine microbubbles (MB-PS) could be employed to monitor placental inflammation. We tested this hypothesis in rhesus macaques (Macaca mulatta), a translational and relevant animal model of human placental health. As placental inflammation impacts many at-risk pregnancies, we performed CEUS with MB-PS in pregnant macaques fed a high-fat diet (e.g., a western-style diet, WSD) in the presence or absence of testosterone (T) to mimic the increased risk of polycystic ovary syndrome and subfertility. We have previously demonstrated a placental inflammation phenotype in this model, and, thus, we related the MB-PS CEUS signal intensity to placental inflammation markers: selectin p and angiopoietins. Testosterone exposure increased the MB-PS signal in the placental microcirculation on the maternal side compared to control animals. We found that T increased placental weight and decreased angiopoietin 2 (ANGPT2) immunoreactivity. Furthermore, a significant inverse correlation was found between MB-PS signal and ANGPT2. This indicated that CEUS with MB-PS can be used to monitor placental parameters. We propose that CEUS with MB-PS could aid in the identification of pregnancies at risk of placental vascular compromise.

Recognized and Unrecognized Value of Echocardiography in Guideline and Consensus Documents Regarding Patients With Chest Pain

Guideline and consensus documents have recently been published on the important topic of the noninvasive evaluation of patients presenting with chest pain (CP) or patients with known acute or chronic coronary syndromes. Authors for these documents have included members representing multispecialty imaging societies, yet the process of generating consensus and the need to produce concise written documents have led to a situation where the particular advantages of echocardiography are overlooked. Broad guidelines such as these can be helpful when it comes to "when to do" noninvasive cardiac testing, but they do not pretend to offer nuances on "how to do" noninvasive cardiac testing. This report details the particular value of echocardiography and potential explanations for its understated role in recent guidelines. This report is categorized into the following sections: (1) impact of the level of evidence on guideline creation; (2) versatility of echocardiography in the assessment of CP and the inimitable role for echo Doppler echocardiography in the assessment of dyspnea; (3) value of point-of-care ultrasound in assessing CP and dyspnea; and (4) the future role of echocardiography in ischemic heart disease.

Increased Susceptibility for Adverse Reactions to Ultrasound Enhancing Agents in Sickle Cell Disease

BACKGROUND

Pain-related adverse events (AEs) to ultrasound enhancing agents (UEAs) have been reported in patients with sickle cell disease (SCD). The aims of this study were to characterize the scope of these AEs in the SCD population and to investigate potential mechanisms on the basis of pathways involved in SCD vaso-occlusive crisis (VOC) and pain.

METHODS

The prevalence and classification of AEs were analyzed from two clinical trials in which high-dose Definity infusions were used in patients with SCD (n = 55) or matched control subjects (n = 43) to study muscle or myocardial microvascular perfusion. Because complement (C') activation can trigger VOC in SCD, C' activation and surface adhesion of C' proteins on lipid UEAs were studied in vitro. C'-mediated UEA attachment to bone marrow immune cells was assessed using flow cytometry in a murine SCD model (Townes mice). Blood from patients receiving Definity was obtained to measure specific lysophospholipid metabolites of lipids in Definity thought to mediate SCD pain.

RESULTS

Moderate or greater AEs, all of which were nociceptive (back or bone pain), occurred in one control subject and nine SCD subjects (2% vs 16%, P = .02). Patients with SCD who had AEs tended to have more severe manifestations of SCD. Three of the subjects with SCD had previously received Definity without complications. In patients with SCD, four AEs were classified as severe in intensity and as serious AEs on the basis of need for medical intervention. AEs were described to be similar to SCD-related pain, but there was no evidence for VOC, hemolysis, hypotension, or hypoxemia. At baseline, markers of C' activation were greater in patients with SCD than control subjects. However, after administration of lipid UEAs, SCD and control subjects were similar with regard to C' activation response, anaphylatoxin production, bone marrow microbubble retention, and production of lysophospholipids. There was a trend toward increased deposition of C3b and C3bi on lipid UEAs exposed to serum from patients with SCD.

CONCLUSIONS

Patients with SCD are particularly susceptible to nociceptive AEs when given Definity at high doses. The mechanism for these AEs remains unclear but most are not related to the triggering of classic VOC.

Resting coronary flow drives the daily pattern in coronary flow reserve in patients with chest pain without obstructive epicardial stenosis

Objectives

Ischemia with no obstructive coronary artery disease (INOCA) is a risk factor for major adverse cardiovascular events and is characterized by abnormal coronary microvascular tone. In patients with INOCA, adverse cardiovascular events most commonly occur in the morning compared to other times of the day and night.

Materials and methods

We tested whether coronary microvascular function varies diurnally with attenuation in the morning in patients with symptomatic coronary artery disease without significant (>50%) epicardial stenosis. We evaluated data from 17 patients studied in the AM (700-1159 h) and 11 patients in the PM (1200-1800 h). Coronary microvascular function was measured using perfusion contrast imaging at rest and after infusion of intravenous regadenoson. We calculated microvascular flow reserve as the ratio of hyperemic to resting flow. Along with independent sample t-tests, we performed bootstrapping procedures to test mean differences between AM and PM groups, using the bias-corrected and accelerated method with 5,000 bootstrapped samples.

Results and conclusion

The AM and PM groups were matched for demographic and existing risk factors. Coronary microvascular flow reserve was ∼33% higher in the AM compared to the PM (P = 0.025, BCa 95% CI [0.25, 1.64]; Hedge's g = 0.89, 95% CI [0.11, 1.66]) as a result of significantly lower resting flow (∼50%) in the AM compared to the PM (P = 0.03, M Diff = -56.65, BCa 95% CI [-118.59, -2.12]; Hedge's g = -0.86, 95% CI [-1.60, -0.06]). Our observations are of clinical value and can influence diagnosis and treatment in the clinic based on the time of day of measurements.

Changes in microvascular perfusion of heart and skeletal muscle in sheep around the time of birth

NEW FINDINGS

What is the central question of this study? How does the microvascular perfusion of striated muscle change during the dynamic developmental period between the late gestation fetus and early neonate? What is the main finding and its importance? In both myocardium and skeletal muscle, perfusion of striated muscle is significantly reduced in the neonate compared to the late term fetus, but flow reserve is unchanged. The results suggest striated muscle capillary networks grow more slowly relative to the myofibres they nourish during the perinatal period.

ABSTRACT

Microvascular perfusion of striated muscle is an important determinant of health throughout life. Birth is a transition with profound effects on the growth and function of striated muscle, but the regulation of microvascular perfusion around this transition is poorly understood. We used contrast-enhanced ultrasound perfusion imaging (CEUS) to study the perfusion of left ventricular myocardium and hindlimb biceps femoris, which are populations of muscle with different degrees of change in pre- to postnatal workloads and different capacities for postnatal proliferative growth. We studied separate groups of lambs in late gestation (135 days' gestational age; 92% of term) and shortly after birth (5 days' postnatal age). We used CEUS to quantify baseline perfusion, perfusion during hyperaemia induced by adenosine infusion (myocardium) or electrically stimulated unloaded exercise (skeletal muscle), flow reserve and oxygen delivery. We found heart-to-body weight ratio was greater in neonates than fetuses. Microvascular volume and overall perfusion were lower in neonates than fetuses in both muscle groups at baseline and with hyperaemia. Flux rate differed with muscle group, with myocardial flux being faster in neonates than fetuses, but skeletal muscle flux being slower. Oxygen delivery to skeletal muscle at baseline was lower in neonates than fetuses, but was not significantly different in myocardium. Flow reserve was not different between ages. Given the significant somatic growth, and the transition from hyperplastic to hypertrophic myocyte growth occurring in the perinatal period, we postulate that the primary driver of lower neonatal striated muscle perfusion is faster growth of myofibres than their associated capillary networks.

Maternal Western-style diet remodels the transcriptional landscape of fetal hematopoietic stem and progenitor cells in rhesus macaques

Maternal obesity adversely impacts the in utero metabolic environment, but its effect on fetal hematopoiesis remains incompletely understood. During late development, the fetal bone marrow (FBM) becomes the major site where macrophages and B lymphocytes are produced via differentiation of hematopoietic stem and progenitor cells (HSPCs). Here, we analyzed the transcriptional landscape of FBM HSPCs at single-cell resolution in fetal macaques exposed to a maternal high-fat Western-style diet (WSD) or a low-fat control diet. We demonstrate that maternal WSD induces a proinflammatory response in FBM HSPCs and fetal macrophages. In addition, maternal WSD consumption suppresses the expression of B cell development genes and decreases the frequency of FBM B cells. Finally, maternal WSD leads to poor engraftment of fetal HSPCs in nonlethally irradiated immunodeficient NOD/SCID/IL2rγ^-/- mice. Collectively, these data demonstrate for the first time that maternal WSD impairs fetal HSPC differentiation and function in a translationally relevant nonhuman primate model.

Coronary conductance in the normal development of sheep during the perinatal period

Birth is associated with substantial shifts in cardiovascular physiology. Little is known about coronary vascular adaptations during this period. We used fetal and neonatal lambs to measure coronary function at late gestation (92% of term) and shortly after birth (5-6 days postnatal age). In each animal we measured unanesthetized myocardial perfusion and oxygen delivery using a circumflex artery flow probe. We used inflatable occluders and adenosine to determine coronary conductance and flow reserve. In a subset of animals, we used myocardial contrast echocardiography (MCE, anesthetized) to assess its utility as a tool for studying changes in regional myocardial perfusion in normal development. Separate age-matched animals were instrumented with aortic and coronary sinus sampling catheters to determine myocardial oxygen extraction (unanesthetized). With an average of 17 days of developmental time separating our neonatal and fetal cohorts we found that heart-to-body weight ratio was significantly greater in neonates than fetuses. In resting animals, we found significant decreases in weight-normalized perfusion of, and oxygen delivery to, neonatal relative to fetal myocardium. Similar results were seen when measuring baseline MCE-derived perfusion. Pressure-flow relationship studies revealed lower baseline and maximal coronary conductance in neonates than fetuses, with similar coronary flow reserve between groups. There was greater oxygen extraction in neonates than fetuses. Combined analysis of oxygen extraction with coronary flow suggested greater oxygen consumption by the fetal than neonatal myocardium. We conclude that, during the immediate perinatal period, cardiac growth outpaces coronary microvascular growth resulting in lower capacity for microvascular perfusion in the early neonate.

Augmentation of Pulmonary Perfusion by Conducted Effects of a Pulmonary Artery Ultrasound Catheter

Ultrasound (US) generated by catheters used clinically for US-facilitated thrombolysis can release shear-dependent vasodilators from endothelial and red blood cells. We hypothesized that catheter-based US in the pulmonary artery (PA) decreases downstream vascular resistance and increases pulmonary blood flow. In rhesus macaques, a U.S. Food and Drug Administration-approved multi-element US catheter was placed in a pulmonary artery. Comprehensive echocardiography was performed (i) at baseline, (ii) during hypoxemia (12% FIO2) to increase pulmonary vascular resistance (PVR) and (c) 15 min after initiating US during hypoxemia. Reduced FIO2 produced intended reductions in oxygen saturation (69 ± 3%) and PaO2 (34 ± 5 mm Hg), yet on echocardiography, hypoxemia did not create the intended model, with only modest hypoxia-related increases in PA systolic pressure (24 ± 4 to 28 ± 4 mm Hg, p = 0.05) and no significant change in PVR or multiparametric right ventricular (RV) function. Although US did not further change total PVR, on 99mTc-macroalbumin aggregate single-photon-emission computed tomography imaging, lung perfusion was significantly higher in the lung ipsilateral to the US catheter versus the contralateral control lung (133 ± 48 cpm vs. 103 ± 43 × 103 cpm, p = 0.01). We conclude that PA catheter-based US increases regional lung perfusion, most likely from vasodilators that are conducted downstream.

Myocardial contrast echocardiography assessment of perfusion abnormalities in hypertrophic cardiomyopathy

Background

Perfusion defects during stress can occur in hypertrophic cardiomyopathy (HCM) from either structural or functional abnormalities of the coronary microcirculation. In this study, vasodilator stress myocardial contrast echocardiography (MCE) was used to quantify and spatially characterize hyperemic myocardial blood flow (MBF) deficits in HCM.

Methods

Regadenoson stress MCE was performed in patients with septal-variant HCM (n = 17) and healthy control subjects (n = 15). The presence and spatial distribution (transmural diffuse, patchy, subendocardial) of perfusion defects was determined by semiquantitative analysis. Kinetic analysis of time-intensity data was used to quantify MBF, microvascular flux rate (β), and microvascular blood volume. In patients undergoing septal myectomy (n = 3), MCE was repeated > 1 years after surgery. 

Results

In HCM subjects, perfusion defects during stress occurred in the septum in 80%, and in non-hypertrophied regions in 40%. The majority of septal defects (83%) were patchy or subendocardial, while 67% of non-hypertrophied defects were transmural and diffuse. On quantitative analysis, hyperemic MBF was approximately 50% lower (p < 0.001) in the hypertrophied and non-hypertrophied regions of those with HCM compared to controls, largely based on an inability to augment β, although hypertrophic regions also had blood volume deficits. There was no correlation between hyperemic MBF and either percent fibrosis on magnetic resonance imaging or outflow gradient, yet those with higher degrees of fibrosis (≥ 5%) or severe gradients all had low septal MBF during regadenoson. Substantial improvement in hyperemic MBF was observed in two of the three subjects undergoing myectomy, both of whom had severe pre-surgical outflow gradients at rest.

Conclusion

Perfusion defects on vasodilator MCE are common in HCM, particularly in those with extensive fibrosis, but have a different spatial pattern for the hypertrophied and non-hypertrophied segments, likely reflecting different contributions of functional and structural abnormalities. Improvement in hyperemic perfusion is possible in those undergoing septal myectomy to relieve obstruction. 

Trial registration

ClinicalTrials.gov NCT02560467.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12947-022-00293-2.

Reduced Proteolytic Cleavage of von Willebrand Factor Leads to Aortic Valve Stenosis and Load-Dependent Ventricular Remodeling

We hypothesized that excess endothelial-associated von Willebrand factor (vWF) and secondary platelet adhesion contribute to aortic valve stenosis (AS). We studied hyperlipidemic mice lacking ADAMTS13 (LDLR ^-/- AD13 ^-/- ), which cleaves endothelial-associated vWF multimers. On echocardiography and molecular imaging, LDLR ^-/- AD13 ^-/- compared with control strains had increased aortic endothelial vWF and platelet adhesion and developed hemodynamically significant AS, arterial stiffening, high valvulo-aortic impedance, and secondary load-dependent reduction in LV systolic function. Histology revealed leaflet thickening and calcification with valve interstitial cell myofibroblastic and osteogenic transformation, and evidence for TGFβ1 pathway activation. We conclude that valve leaflet endothelial vWF-platelet interactions promote AS through juxtacrine platelet signaling.

Ibrutinib Inhibits BMX-Dependent Endothelial VCAM-1 Expression In Vitro and Pro-Atherosclerotic Endothelial Activation and Platelet Adhesion In Vivo

Introduction

Inflammatory activation of the vascular endothelium leads to overexpression of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), contributing to the pro-thrombotic state underpinning atherogenesis. While the role of TEC family kinases (TFKs) in mediating inflammatory cell and platelet activation is well defined, the role of TFKs in vascular endothelial activation remains unclear. We investigated the role of TFKs in endothelial cell activation in vitro and in a nonhuman primate model of diet-induced atherosclerosis in vivo.

Methods and Results

In vitro, we found that ibrutinib blocked activation of the TFK member, BMX, by vascular endothelial growth factors (VEGF)-A in human aortic endothelial cells (HAECs). Blockade of BMX activation with ibrutinib or pharmacologically distinct BMX inhibitors eliminated the ability of VEGF-A to stimulate VCAM-1 expression in HAECs. We validated that treatment with ibrutinib inhibited TFK-mediated platelet activation and aggregation in both human and primate samples as measured using flow cytometry and light transmission aggregometry. We utilized contrast-enhanced ultrasound molecular imaging to measure platelet GPIbα and endothelial VCAM-1 expression in atherosclerosis-prone carotid arteries of obese nonhuman primates. We observed that the TFK inhibitor, ibrutinib, inhibited platelet deposition and endothelial cell activation in vivo.

Conclusion

Herein we found that VEGF-A signals through BMX to induce VCAM-1 expression in endothelial cells, and that VCAM-1 expression is sensitive to ibrutinib in vitro and in atherosclerosis-prone carotid arteries in vivo. These findings suggest that TFKs may contribute to the pathogenesis of atherosclerosis and could represent a novel therapeutic target.

Placental sFlt-1 Gene Delivery in Early Primate Pregnancy Suppresses Uterine Spiral Artery Remodeling

Uterine spiral artery remodeling (SAR) is essential for promoting placental perfusion and fetal development. A defect in SAR results in placental ischemia and increase in placental expression and serum levels of the soluble fms-like tyrosine kinase-1 (sFlt-1) receptor that binds to and suppresses vascular endothelial growth factor (VEGF) bioavailability, thereby leading to maternal vascular dysfunction. We have established a nonhuman primate model of impaired SAR and maternal vascular dysfunction by prematurely elevating estradiol levels in early baboon pregnancy. However, it is unknown whether this primate model of defective SAR involves an increase in placental expression of sFlt-1, which may suppress VEGF bioavailability and thus SAR in the first trimester. Therefore, to establish the role of sFlt-1 in early pregnancy, SAR was quantified in baboons treated on days 25 through 59 of gestation (term = 184 days) with estradiol or with the sFlt-1 gene targeted selectively to the placental basal plate by ultrasound-mediated/microbubble-facilitated gene delivery technology. Placental basal plate sFlt-1 protein expression was 2-fold higher (P < 0.038) and the level of SAR for vessels > 25 µm in diameter was 72% and 63% lower (P < 0.01), respectively, in estradiol-treated and sFlt-1 gene-treated baboons than in untreated animals. In summary, prematurely elevating estradiol levels or sFlt-1 gene delivery increased placental basal plate sFlt-1 protein expression and suppressed SAR in early baboon pregnancy. This study makes the novel discovery that in elevated levels sFlt-1 has a role both in suppressing SAR in early primate pregnancy and maternal vascular endothelial function in late gestation.

Contrast-Enhanced Ultrasound Molecular Imaging in Atherosclerosis Research

The management of cardiovascular conditions will likely be improved by noninvasive in vivo molecular imaging technologies that can provide earlier or more accurate diagnosis. These techniques are already having a positive impact in preclinical research by providing insight into disease pathobiology or efficacy of new therapies. Contrast enhanced ultrasound (CEU) molecular imaging is a technique that relies on the ultrasound detection of targeted microbubble contrast agents to examine molecular or cellular events that occur at the blood pool-endothelial interface. For the most part, targeted contrast agents are composed of encapsulated gas microbubbles (MBs) that are 2-4 μm in diameter, or other acoustically active micro- or nanoparticles. These agents bear several tens of thousands of binding molecules per particle. Because nonadhered agent is cleared rapidly, CEU molecular imaging can be performed in a matter of minutes. MBs are detected using contrast-specific techniques that generate and receive nonlinear signals produced by MB cavitation, thereby increasing signal-to-noise ratio. Dedicated kinetic models for molecular imaging have been generated that permit the elimination of signal from nonadherent agent.

Contrast Ultrasound Assessment of Skeletal Muscle Recruitable Perfusion after Permanent Left Ventricular Assist Device Implantation: Implications for Functional Recovery

BACKGROUND

In heart failure with reduced ejection fraction (HFrEF), abnormal regulation of skeletal muscle perfusion contributes to reduced exercise tolerance. The aim of this study was to test the hypothesis that improvement in functional status after permanent left ventricular assist device (LVAD) implantation in patients with HFrEF is related to improvement in muscle perfusion during work, which was measured using contrast-enhanced ultrasound (CEUS).

METHODS

CEUS perfusion imaging of calf muscle at rest and during low-intensity plantar flexion exercise (20 W, 0.2 Hz) was performed in patients with HFrEF (n = 22) at baseline and 3 months after placement of permanent LVADs. Parametric analysis of CEUS data was used to quantify muscle microvascular blood flow (MBF), blood volume index, and red blood cell flux rate. For subjects alive at 3 months, comparisons were made between those with New York Heart Association functional class I or II (n = 13) versus III or IV (n = 7) status after LVAD. Subjects were followed for a median of 5.7 years for mortality.

RESULTS

Echocardiographic data before and after LVAD placement and LVAD parameters were similar in subjects classified with New York Heart Association functional class I-II versus functional class III-IV after LVAD. Skeletal muscle MBF at rest and during exercise before LVAD implantation was also similar between groups. After LVAD placement, resting MBF remained similar between groups, but during exercise those with New York Heart Association functional class I or II had greater exercise MBF (111 ± 60 vs 52 ± 38 intensity units/sec, P = .03), MBF reserve (median, 4.45 [3.95 to 6.80] vs 2.22 [0.98 to 3.80]; P = .02), and percentage change in exercise MBF (median, 73% [-28% to 83%] vs -45% [-80% to 26%]; P = .03). During exercise, increases in MBF were attributable to faster microvascular flux rate, with little change in blood volume index, indicating impaired exercise-mediated microvascular recruitment. The only clinical or echocardiographic feature that correlated with post-LVAD exercise MBF was a history of diabetes mellitus. There was a trend toward better survival in patients who demonstrated improvement in muscle exercise MBF after LVAD placement (P = .05).

CONCLUSIONS

CEUS perfusion imaging can quantify peripheral vascular responses to advanced therapies for HFrEF. After LVAD implantation, improvement in functional class is seen in patients with improvements in skeletal muscle exercise perfusion and flux rate, implicating a change in vasoactive substances that control resistance arteriolar tone.

Best Practices for Imaging Cardiac Device-Related Infections and Endocarditis: A JACC: Cardiovascular Imaging Expert Panel Statement

The diagnosis of cardiac device infection and, more importantly, accurate localization of the infection site, such as defibrillator pocket, pacemaker lead, along the peripheral driveline or central portion of the left ventricular assist device, prosthetic valve ring abscesses, and perivalvular extensions, remain clinically challenging. Although transthoracic and transesophageal echocardiography are the first-line imaging tests in suspected endocarditis and for assessing hemodynamic complications, recent studies suggest that cardiac computed tomography (CT) or CT angiography and functional imaging with ¹⁸F-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) with CT (FDG PET/CT) may have an incremental role in technically limited or inconclusive cases on echocardiography. One of the key benefits of FDG PET/CT is in its detection of inflammatory cells early in the infection process, before morphological damages ensue. However, there are many unanswered questions in the literature. In this document, we provide consensus on best practices among the various imaging studies, which includes the detection of cardiac device infection, differentiation of infection from inflammation, image-guided patient management, and detailed recommendations on patient preparation, image acquisition, processing, interpretation, and standardized reporting.

Echocardiographic Ischemic Memory Molecular Imaging for Point-of-Care Detection of Myocardial Ischemia

BACKGROUND

Noninvasive molecular imaging of recent ischemia can potentially be used to diagnose acute coronary syndrome (ACS) with high accuracy.

OBJECTIVES

The authors hypothesized that bedside myocardial contrast echocardiography (MCE) ischemic memory imaging could be achieved with phosphatidylserine microbubbles (MB_PS) that are retained in the microcirculation via ischemia-associated endothelial activation.

METHODS

A dose-finding study was performed in healthy volunteers (n = 17) to establish optimal MB_PS dosing. Stable patients with ACS (n = 30) and confirmed antecedent but resolved myocardial ischemia were studied within 2 hours of coronary angiography and percutaneous coronary intervention (PCI) when indicated. MCE molecular imaging was performed 8 minutes after intravenous administration of MB_PS. MCE perfusion imaging was used to assess the status of the postischemic microcirculation.

RESULTS

Based on dose-finding studies, 0.10 or 0.15 mL of MB_PS based on body mass was selected. In patients with ACS, all but 2 underwent primary PCI. MCE molecular imaging signal intensity was greater in the postischemic risk area vs remote territory (median [95% CI]: 56 [33-66] vs 8 [2-17] IU; P < 0.001) with a receiver-operating characteristic curve C-statistic of 0.94 to differentiate post-ischemic from remote territory. Molecular imaging signal in the risk area was not related to type of ACS (unstable angina: 3; non-ST-segment elevation myocardial infarction: 14; ST-segment elevation myocardial infarction: 13), peak troponin, time to PCI, post-PCI myocardial perfusion, GRACE (Global Registry of Acute Coronary Events) score, or HEART score.

CONCLUSIONS

Molecular imaging with point-of-care echocardiography and MB_PS can detect recent but resolved myocardial ischemia. This bedside technique requires only minutes to perform and appears independent of the degree of ischemia. (Ischemic Memory Imaging With Myocardial Contrast Echocardiography; NCT03009266).

Non-invasive Imaging in Coronary Syndromes - Recommendations of the European Association of Cardiovascular Imaging and the American Society of Echocardiography, in Collaboration with the American Society of Nuclear Cardiology, Society of Cardiovascular Computed Tomography and Society for Cardiovascular Magnetic Resonance

Coronary artery disease (CAD) is one of the major causes of mortality and morbidity worldwide, with a high socioeconomic impact.(1) Non-invasive imaging modalities play a fundamental role in the evaluation and management of patients with known or suspected CAD. Imaging end-points have served as surrogate markers in many observational studies and randomized clinical trials that evaluated the benefits of specific therapies for CAD.(2) A number of guidelines and recommendations have been published about coronary syndromes by cardiology societies and associations, but have not focused on the excellent opportunities with cardiac imaging. The recent European Society of Cardiology (ESC) 2019 guideline on chronic coronary syndromes (CCS) and 2020 guideline on acute coronary syndromes in patients presenting with non-ST-segment elevation (NSTE-ACS) highlight the importance of non-invasive imaging in the diagnosis, treatment, and risk assessment of the disease.(3)(4) The purpose of the current recommendations is to present the significant role of non-invasive imaging in coronary syndromes in more detail. These recommendations have been developed by the European Association of Cardiovascular Imaging (EACVI) and the American Society of Echocardiography (ASE), in collaboration with the American Society of Nuclear Cardiology, the Society of Cardiovascular Computed Tomography, and the Society for Cardiovascular Magnetic Resonance, all of which have approved the final document.

Treatment of Limb Ischemia with Conducted Effects of Catheter-Based Endovascular Ultrasound

Ultrasound (US) is known to stimulate endogenous shear-dependent pathways, and can lower microvascular resistance through mediators that are conducted downstream from US exposure. We hypothesized that endovascular US, already in use for thrombolysis in humans, can improve tissue perfusion in the setting of acute limb ischemia through downstream-conducted effects. Models of severe peripheral arterial disease were developed in mice and in rhesus macaques. An endovascular US catheter (2.3 MHz, 0.5-1.1 MPa) was used to expose the limb adductor in mice for 10 min or the femoral artery distal to stenosis in macaques for 15 min. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess flow augmentation in the adductor muscle of mice and the calf muscle of macaques. Microvascular blood flow in the ischemic limb relative to the contralateral control limb was reduced to 22 ± 8% in mice and 36 ± 20% in macaques. US produced immediate 2.3- and 3-fold increases (p < 0.05) in the murine and macaque ischemic limbs, respectively. In macaques, perfusion in the ischemic limb was increased to a normal level. We conclude that non-cavitating US produced by endovascular catheters that are used to enhance thrombolysis in humans can reduce vascular resistance and increase limb perfusion in the setting of acute ischemia.

Ultrasound contrast agent hypersensitivity in patients allergic to polyethylene glycol: position statement by the European Association of Cardiovascular Imaging

The Food and Drug Administration alert enhances our understanding of the mechanism of severe reactions to ultrasound-enhancing agents (UEAs). The known incidence of these reactions remains low and unchanged (1 in 10 000 administrations). Because the risk-to-benefit ratio for ultrasound contrast agents (UCAs) remains extremely low, we do not advise any changes to laboratory policy regarding indications for their use. The use of these agents should continue in situations where they have been shown to be impactful. Lipid-based UCAs (SonoVue and Luminity) are contraindicated in patients who have a history of prior hypersensitivity to these UEAs, to polyethylene glycol (PEG) (macrogol), or to PEG-containing products, such as certain bowel preps for colonoscopy or laxatives.

Arterial Platelet Adhesion in Atherosclerosis-Prone Arteries of Obese, Insulin-Resistant Nonhuman Primates

Background

Platelet–endothelial interactions are thought to contribute to early atherogenesis. These interactions are potentiated by oxidative stress. We used in vivo molecular imaging to test the hypothesis that platelet–endothelial interactions occur at early stages of plaque development in obese, insulin‐resistant nonhuman primates, and are suppressed by NADPH‐oxidase‐2 inhibition.

Methods and Results

Six adult rhesus macaques fed a Western‐style diet for a median of 4.0 years were studied at baseline and after 8 weeks of therapy with the NADPH‐oxidase‐2‐inhibitor apocynin (50 mg/kg per day). Six lean control animals were also studied. Measurements included intravenous glucose tolerance test, body composition by dual‐energy X‐ray absorptiometry, carotid intimal medial thickness, carotid artery contrast ultrasound molecular imaging for platelet GPIbα (glycoprotein‐ Ibα) and vascular cell adhesion molecule‐1, and blood oxidative markers on mass spectrometry. Compared with lean controls, animals on a Western‐style diet were obese (median body mass: 16.0 versus 8.7 kg, P=0.003; median truncal fat: 49% versus 20%, P=0.002), were insulin resistant (4‐fold higher insulin–glucose area under the curve on intravenous glucose tolerance test, P=0.002), had 40% larger carotid intimal medial thickness (P=0.004), and exhibited oxidative signatures on proteomics. In obese but not lean animals, signal enhancement on molecular imaging was significantly elevated for GPIbα and vascular cell adhesion molecule‐1. The signal correlated modestly with intimal medial thickness but not with the degree of insulin resistance. Apocynin significantly (P<0.01) reduced median signal for GPIbα by >80% and vascular cell adhesion molecule‐1 signal by 75%, but did not affect intimal medial thickness, body mass, or intravenous glucose tolerance test results.

Conclusion

In nonhuman primates, diet‐induced obesity and insulin resistance leads to platelet–endothelial adhesion at early atherosclerotic lesion sites, which is associated with the expression of pro‐inflammatory adhesion molecules. These responses appear to be mediated, in part, through oxidative pathways.

Echocardiographic Molecular Imaging of the Effect of Anticytokine Therapy for Atherosclerosis

BACKGROUND

Echocardiographic molecular imaging techniques are beginning to be applied to evaluate preclinical efficacy of new drugs. In a large clinical trial, anti-interleukin-1β (IL-1β) immunotherapy reduced atherosclerotic events, yet treatment effects were modest, and the mechanisms of action were not fully elucidated. We tested the hypothesis that echocardiographic molecular imaging can assess changes in vascular thromboinflammatory status in response to anti-IL-1β therapy.

METHODS

In wild-type and atherosclerotic mice deficient for the low-density lipoprotein-receptor and Apobec-1, closed-chest myocardial infarction (MI) was performed to mimic high-risk clinical cohorts. Control animals had sham surgery. Post-MI animals were randomized to either no therapy or anti-IL-1β immunotherapy, which was continued weekly. At post-MI day 3 or 21, in vivo ultrasound molecular imaging of aortic VCAM-1, P-selectin, von Willebrand factor A1-domain, and platelet GPIbα in the thoracic aorta was performed. Aortic histology and NF-κB activity were assessed in atherosclerotic mice.

RESULTS

In both atherosclerotic and wild-type mice, MI produced a several-fold increase (P < .05) in aortic molecular signals for P-selectin, VCAM-1, von Willebrand factor, and GPIbα. In atherosclerotic mice, signal remained elevated at day 21. Anti-IL-1β therapy completely abolished the post-MI increase in signal for all endothelial targets (P < .05 vs nontreated) at day 3 and 21. In atherosclerotic mice, MI triggered an increase in aortic plaque growth and macrophage content, a decrease in plaque collagen, and elevated aortic NF-κB (P < .05 for all changes). All of these remote plaque adverse changes were inhibited by anti-IL-1β therapy.

CONCLUSIONS

Echocardiographic molecular imaging of the vascular endothelium can quantify the beneficial effects of therapies designed to suppress the proatherosclerotic arterial thromboinflammatory effects of alarmins such as IL-1β. This approach could potentially be used to evaluate the biologic variables that influence response in preclinical studies, and possibly to select patients most likely to benefit from therapy.

Augmentation of Tissue Perfusion with Contrast Ultrasound: Influence of Three-Dimensional Beam Geometry and Conducted Vasodilation

BACKGROUND

Cavitation of microbubble contrast agents with ultrasound produces shear-mediated vasodilation and an increase in tissue perfusion. We investigated the influence of the size of the cavitation volume by comparing flow augmentation produced by two-dimensional (2D) versus three-dimensional (3D) therapeutic ultrasound. We also hypothesized that cavitation could augment flow beyond the ultrasound field through release of vasodilators that are carried downstream.

METHODS

In 11 rhesus macaques, cavitation of intravenously administered lipid-shelled microbubbles was performed in the proximal forearm flexor muscles unilaterally for 10 min. Ultrasound cavitation (1.3 MHz, 1.5 MPa peak negative pressure) was performed with 2D or 3D transmission with beam elevations of 5 and 25 mm, respectively, and pulsing intervals (PIs) sufficient to allow complete postdestruction refill (5 and 12 sec for 2D and 3D, respectively). Contrast ultrasound perfusion imaging was performed before and after cavitation, using multiplane assessment within and beyond the cavitation field in 1.5-cm increments. Cavitation in the hindlimb of mice using 2D ultrasound at a PI of 1 or 5 sec was performed to examine microvascular flow changes from cavitation in only arteries versus the microcirculation.

RESULTS

In primates, the degree of muscle flow augmentation in the center of the cavitation field was similar for 2D and 3D conditions (five- to sixfold increase for both, P < .01 vs baseline). The spatial extent of flow augmentation was only modestly greater for 3D cavitation because of an increase in perfusion with 2D transmission that was detected outside of the cavitation field. In mice, cavitation in the microvascular compartment (PI 5 sec) produced the greatest degree of flow augmentation, yet cavitation in the arterial compartment (PI 1 sec) still produced a three- to fourfold increase in flow (P < .001 vs control). The mechanism for flow augmentation beyond the cavitation zone was investigated by in vitro studies that demonstrated cavitation-related release of vasodilators, including adenosine triphosphate and nitric oxide, from erythrocytes and endothelial cells.

CONCLUSIONS

Compared with 2D transmission, 3D cavitation of microbubbles generates a similar degree of muscle flow augmentation, possibly because of a trade-off between volume of cavitation and PI, and only modestly increases the spatial extent of flow augmentation because of the ability of cavitation to produce conducted effects beyond the ultrasound field.

Microbubble-Facilitated Ultrasound Catheter Ablation Causes Microvascular Damage and Fibrosis

High-intensity ultrasound (US) ablation produces deeper myocardial lesions than radiofrequency ablation. The presence of intravascular microbubble (MB) contrast agents enhances pulsed-wave US ablation via cavitation-related histotripsy, potentially facilitating ablation in persistently perfused/conducting myocardium. US ablation catheters were developed and tested in the presence of MBs using ex vivo and in vivo models. High-frame-rate videomicroscopy and US imaging of gel phantom models confirmed MB destruction by inertial cavitation. MB-facilitated US ablation in an ex vivo perfused myocardium model generated shallow (2 mm) lesions and, in an in vivo murine hindlimb model, reduced perfusion by 42% with perivascular hemorrhage and inflammation, but no myonecrosis.

Arterial Thrombotic Complications of Tyrosine Kinase Inhibitors

Abnormal expression or function of several classes of kinases contribute to the development of many types of solid and hematologic malignancies. TKs (tyrosine kinases) in particular play a role in tumor growth, metastasis, neovascularization, suppression of immune surveillance, and drug resistance. TKIs (tyrosine kinase inhibitors) targeted to TKs such as BCR-ABL1, VEGF receptors, PDGF receptors, have transformed therapy of certain forms of cancer by providing excellent efficacy with relatively low adverse event rates. Yet some of these agents have been associated with high rates of vascular events, presumably from prothrombotic complications that result in myocardial infarction, stroke, and critical limb ischemia. This review describes the scope of the problem evidenced by clinical experience with some of the most commonly used TKIs, with a focus on TKIs targeted to the BCR-ABL1 (breakpoint cluster region-Abelson 1) translocation. We also discuss the potential mechanisms responsible for arterial thrombotic complications that could lead to mitigation strategies or unique TK targeting strategies to reduce adverse event rates without compromising efficacy.

High-intensity ultrasound catheter ablation achieves deep mid-myocardial lesions in vivo

BACKGROUND

Radiofrequency ablation of epicardial and mid-myocardial ventricular arrhythmias is limited by lesion depth.

OBJECTIVE

The purpose of this study was to generate deep mid-interventricular septal (IVS) lesions using high-intensity ultrasound (US) from an endocardial catheter-based approach.

METHODS

Irrigated US catheters (12 F) were fabricated with 3 × 5 mm transducers of 5.0, 6.5, and 8.0 MHz frequencies and compared in an ex vivo perfused myocardial ablation model. In vivo septal ablation in swine (n = 12) was performed via femoral venous access to the right ventricle. Lesions were characterized by echocardiography, cardiac magnetic resonance imaging, and electroanatomic voltage mapping pre- and post-ablation, and at 30 days. Four animals were euthanized immediately post-ablation to compare acute and chronic lesion histology and gross pathology.

RESULTS

In ex vivo models, maximal lesion depth and volume was achieved by 6.5 MHz catheters, which were used in vivo. Lesion depth by gross pathology was similar post-ablation (10.8 mm; 95% confidence interval [CI] 9.9-12.4 mm) and at 30 days (11.2 mm; 95% CI 10.6-12.4 mm) (P = .56). Lesion volume decreased post-ablation to 30 days (from 255 [95% CI 198-440] to 162 [95% CI 133-234] mm³; P = .05), yet transmurality increased from 58% (95% CI 50%-76%) to 81% (95% CI 74%-93%), attributable to a reduction in IVS thickness (from 16.0 ± 1.7 to 10.6 ± 2.4 mm; P = .007). Magnetic resonance imaging confirmed dense septal ablation by delayed enhancement, with increased T1 time post-ablation and at 30 days and increased T2 time only post-ablation. Voltage mapping of both sides of IVS demonstrated reduced unipolar (but not bipolar) voltage along the IVS.

CONCLUSION

High-intensity US catheter ablation may be an effective treatment of mid-myocardial or epicardial ventricular arrhythmias from an endocardial approach.

Contrast echocardiography: current status and future directions

Contrast echocardiography is a family of ultrasound-based procedures, whereby acoustic enhancing agents, usually microbubbles, are administered by intravenous route and detected in order to improve diagnostic performance. This review describes: (1) the agents that have been designed for diagnostic imaging, (2) current clinical applications where either left ventricular opacification or microvascular perfusion imaging with myocardial contrast echocardiography have been demonstrated to provide incremental information to non-contrast echocardiography and (3) future diagnostic and therapeutic applications of contrast ultrasound that rely on unique compositional design of ultrasound-enhancing agents.

Proteolysis of Von Willebrand Factor Influences Inflammatory Endothelial Activation and Vascular Compliance in Atherosclerosis

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In murine models of atherosclerosis, excess endothelial-associated vWF results not only in platelet adhesion, but also endothelial expression of leukocyte adhesion molecules, indicating a role of platelets in endothelial activation.

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The events triggered by excess endothelial-associated vWF lead to accelerated plaque growth and abnormal arterial mechanical properties.

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The cellular and molecular events described herein can be assessed noninvasively through molecular imaging.

This study used in vivo molecular imaging to characterize endotheliall activation attributable to von Willebrand factor (vWF)-mediated platelet adhesion in atherosclerosis. In atherosclerotic mice lacking the low-density lipoprotein receptor on Western diet, the additional genetic deletion of the ADAMTS13, which cleaves endothelial-associated vWF, produced greater aortic molecular imaging signal for not only vWF and platelets, but also for endothelial adhesion molecules VCAM1 and P-selectin, larger plaque size, and lower aortic distensibility. Sustained ADAMTS13 therapy reduced signal for all 4 molecular targets and plaque size. We conclude that excess endothelial-associated vWF contributes to not only platelet adhesion, but also to up-regulation of endothelial cell adhesion molecules.

Regional and Conducted Vascular Effects of Endovascular Ultrasound Catheters

Intra-vascular ultrasound catheters are used clinically to facilitate clot lysis. We hypothesized that these devices could also directly lower microvascular resistance and increase tissue perfusion through established shear-dependent pathways. In mice, either the proximal hind-limb muscles or the upstream femoral artery alone was exposed to an endovascular ultrasound catheter (2.3 MHz, 0.5-1.1 MPa) for 10 min. Quantitative microvascular perfusion imaging in the hind limbs exposed to the endovascular ultrasound system exhibited a more-than-twofold increase in flow (p < 0.01) compared with the contralateral control limb after exposure of either the muscle or the femoral artery alone. Using an in vivo optical imaging reporting system, an eight- to ninefold increase in tissue adenosine triphosphate (ATP) was detected in the region of insonification (p = 0.006). Ultrasound was found to produce an immediate release of ATP from ex vivo erythrocytes (p = 0.03). In situ electrochemical sensing revealed an immediate increase in nitric oxide with initiation of ultrasound which returned to baseline within 5 min of termination, as well as ultrasound-triggered nitric oxide (NO) release from erythrocytes. These data indicate that non-cavitating ultrasound produced by endovascular catheters can reduce vascular resistance and increase flow through recognized shear-dependent vasodilator pathways involving purinergic signaling and NO.