Intramyocardial Sprouting Tip Cells Specify Coronary Arterialization.

BACKGROUND: The elaborate patterning of coronary arteries critically supports the high metabolic activity of the beating heart. How coronary endothelial cells coordinate hierarchical vascular remodeling and achieve arteriovenous specification remains largely unknown. Understanding the molecular and cellular cues that pattern coronary arteries is crucial to develop innovative therapeutic strategies that restore functional perfusion within the ischemic heart. METHODS: Single-cell transcriptomics and histological validation were used to delineate heterogeneous transcriptional states of the developing and mature coronary endothelium with a focus on sprouting endothelium and arterial cell specification. Genetic lineage tracing and high-resolution 3-dimensional imaging were used to characterize the origin and mechanisms of coronary angiogenic sprouting, as well as to fate-map selective endothelial lineages. Integration of single-cell transcriptomic data from ischemic adult mouse hearts and human embryonic data served to assess the conservation of transcriptional states across development, disease, and species. RESULTS: We discover that coronary arteries originate from cells that have previously transitioned through a specific tip cell phenotype. We identify nonoverlapping intramyocardial and subepicardial tip cell populations with differential gene expression profiles and regulatory pathways. Esm1-lineage tracing confirmed that intramyocardial tip cells selectively contribute to coronary arteries and endocardial tunnels, but not veins. Notably, prearterial cells are detected from development stages to adulthood, increasingly in response to ischemic injury, and in human embryos, suggesting that tip cell-to-artery specification is a conserved mechanism. CONCLUSIONS: A tip cell-to-artery specification mechanism drives arterialization of the intramyocardial plexus and endocardial tunnels throughout life and is reactivated upon ischemic injury. Differential sprouting programs govern the formation and specification of the venous and arterial coronary plexus.

Contribution of VEGF-B-Induced Endocardial Endothelial Cell Lineage in Physiological Versus Pathological Cardiac Hypertrophy.

BACKGROUND: Preclinical studies have shown the therapeutic potential of VEGF-B (vascular endothelial growth factor B) in revascularization of the ischemic myocardium, but the associated cardiac hypertrophy and adverse side effects remain a concern. To understand the importance of endothelial proliferation and migration for the beneficial versus adverse effects of VEGF-B in the heart, we explored the cardiac effects of autocrine versus paracrine VEGF-B expression in transgenic and gene-transduced mice. METHODS: We used single-cell RNA sequencing to compare cardiac endothelial gene expression in VEGF-B transgenic mouse models. Lineage tracing was used to identify the origin of a VEGF-B-induced novel endothelial cell population and adeno-associated virus-mediated gene delivery to compare the effects of VEGF-B isoforms. Cardiac function was investigated using echocardiography, magnetic resonance imaging, and micro-computed tomography. RESULTS: Unlike in physiological cardiac hypertrophy driven by a cardiomyocyte-specific VEGF-B transgene (myosin heavy chain alpha-VEGF-B), autocrine VEGF-B expression in cardiac endothelium (aP2 [adipocyte protein 2]-VEGF-B) was associated with septal defects and failure to increase perfused subendocardial capillaries postnatally. Paracrine VEGF-B led to robust proliferation and myocardial migration of a novel cardiac endothelial cell lineage (VEGF-B-induced endothelial cells) of endocardial origin, whereas autocrine VEGF-B increased proliferation of VEGF-B-induced endothelial cells but failed to promote their migration and efficient contribution to myocardial capillaries. The surviving aP2-VEGF-B offspring showed an altered ratio of secreted VEGF-B isoforms and developed massive pathological cardiac hypertrophy with a distinct cardiac vessel pattern. In the normal heart, we found a small VEGF-B-induced endothelial cell population that was only minimally expanded during myocardial infarction but not during physiological cardiac hypertrophy associated with mouse pregnancy. CONCLUSIONS: Paracrine and autocrine secretions of VEGF-B induce expansion of a specific endocardium-derived endothelial cell population with distinct angiogenic markers. However, autocrine VEGF-B signaling fails to promote VEGF-B-induced endothelial cell migration and contribution to myocardial capillaries, predisposing to septal defects and inducing a mismatch between angiogenesis and myocardial growth, which results in pathological cardiac hypertrophy.

Coronary Artery Calcification: Current Concepts and Clinical Implications.

Coronary artery calcification (CAC) accompanies the development of advanced atherosclerosis. Its role in atherosclerosis holds great interest because the presence and burden of coronary calcification provide direct evidence of the presence and extent of coronary artery disease; furthermore, CAC predicts future events independently of concomitant conventional cardiovascular risk factors and to a greater extent than any other noninvasive biomarker of this disease. Nevertheless, the relationship between CAC and the susceptibility of a plaque to provoke a thrombotic event remains incompletely understood. This review summarizes the current understanding and literature on CAC. It outlines the pathophysiology of CAC and reviews laboratory, histopathological, and genetic studies, as well as imaging findings, to characterize different types of calcification and to elucidate their implications. Some patterns of calcification such as microcalcification portend increased risk of rupture and cardiovascular events and may improve prognosis assessment noninvasively. However, contemporary computed tomography cannot assess early microcalcification. Limited spatial resolution and blooming artifacts may hinder estimation of degree of coronary artery stenosis. Technical advances such as photon counting detectors and combination with nuclear approaches (eg, NaF imaging) promise to improve the performance of cardiac computed tomography. These innovations may speed achieving the ultimate goal of providing noninvasively specific and clinically actionable information.

Heterogeneous pdgfrb+ cells regulate coronary vessel development and revascularization during heart regeneration.

Endothelial cells emerge from the atrioventricular canal to form coronary blood vessels in juvenile zebrafish hearts. We find that pdgfrb is first expressed in the epicardium around the atrioventricular canal and later becomes localized mainly in the mural cells. pdgfrb mutant fish show severe defects in mural cell recruitment and coronary vessel development. Single-cell RNA sequencing analyses identified pdgfrb+ cells as epicardium-derived cells (EPDCs) and mural cells. Mural cells associated with coronary arteries also express cxcl12b and smooth muscle cell markers. Interestingly, these mural cells remain associated with coronary arteries even in the absence of Pdgfrß, although smooth muscle gene expression is downregulated. We find that pdgfrb expression dynamically changes in EPDCs of regenerating hearts. Differential gene expression analyses of pdgfrb+ EPDCs and mural cells suggest that they express genes that are important for regeneration after heart injuries. mdka was identified as a highly upregulated gene in pdgfrb+ cells during heart regeneration. However, pdgfrb but not mdka mutants show defects in heart regeneration after amputation. Our results demonstrate that heterogeneous pdgfrb+ cells are essential for coronary development and heart regeneration.

Cardiac Vagal Nerve Activity Increases During Exercise to Enhance Coronary Blood Flow.

BACKGROUND: The phrase complete vagal withdrawal is often used when discussing autonomic control of the heart during exercise. However, more recent studies have challenged this assumption. We hypothesized that cardiac vagal activity increases during exercise and maintains cardiac function via transmitters other than acetylcholine. METHODS: Chronic direct recordings of cardiac vagal nerve activity, cardiac output, coronary artery blood flow, and heart rate were recorded in conscious adult sheep during whole-body treadmill exercise. Cardiac innervation of the left cardiac vagal branch was confirmed with lipophilic tracer dyes (DiO). Sheep were exercised with pharmacological blockers of acetylcholine (atropine, 250 mg), VIP (vasoactive intestinal peptide; [4Cl-D-Phe6,Leu17]VIP 25 µg), or saline control, randomized on different days. In a subset of sheep, the left cardiac vagal branch was denervated. RESULTS: Neural innervation from the cardiac vagal branch is seen at major cardiac ganglionic plexi, and within the fat pads associated with the coronary arteries. Directly recorded cardiac vagal nerve activity increased during exercise. Left cardiac vagal branch denervation attenuated the maximum changes in coronary artery blood flow (maximum exercise, control: 63.5±5.9 mL/min, n=8; cardiac vagal denervated: 32.7±5.6 mL/min, n=6, P=2.5×10-7), cardiac output, and heart rate during exercise. Atropine did not affect any cardiac parameters during exercise, but VIP antagonism significantly reduced coronary artery blood flow during exercise to a similar level to vagal denervation. CONCLUSIONS: Our study demonstrates that cardiac vagal nerve activity actually increases and is crucial for maintaining cardiac function during exercise. Furthermore, our findings show the dynamic modulation of coronary artery blood flow during exercise is mediated by VIP.

Sox7-positive endothelial progenitors establish coronary arteries and govern ventricular compaction.

The cardiac endothelium influences ventricular chamber development by coordinating trabeculation and compaction. However, the endothelial-specific molecular mechanisms mediating this coordination are not fully understood. Here, we identify the Sox7 transcription factor as a critical cue instructing cardiac endothelium identity during ventricular chamber development. Endothelial-specific loss of Sox7 function in mice results in cardiac ventricular defects similar to non-compaction cardiomyopathy, with a change in the proportions of trabecular and compact cardiomyocytes in the mutant hearts. This phenotype is paralleled by abnormal coronary artery formation. Loss of Sox7 function disrupts the transcriptional regulation of the Notch pathway and connexins 37 and 40, which govern coronary arterial specification. Upon Sox7 endothelial-specific deletion, single-nuclei transcriptomics analysis identifies the depletion of a subset of Sox9/Gpc3-positive endocardial progenitor cells and an increase in erythro-myeloid cell lineages. Fate mapping analysis reveals that a subset of Sox7-null endothelial cells transdifferentiate into hematopoietic but not cardiomyocyte lineages. Our findings determine that Sox7 maintains cardiac endothelial cell identity, which is crucial to the cellular cross-talk that drives ventricular compaction and coronary artery development.

Radiation-Induced Macrovessel/Microvessel Disease.

Radiation therapy (RT) is a cornerstone in cancer treatment (used in 50% of cases), yet challenges persist because damage to normal tissue through direct impact of radiation or bystander effects is inevitable. Injury of macrovessels by RT manifests as obstructive disease, which is akin to atherosclerotic disease. Historically observed in coronary arteries of patients treated for breast cancer and lymphoma, it also affects patients receiving contemporary therapy for lung and chest cancers. Moreover, radiation at various sites can lead to peripheral vascular disease. An aspect of radiation-induced injury that has received little attention is microvascular injury, which typically results from damage to the endothelium and is considered the primary driver of RT-induced toxicity in the skin, kidney, and brain. This review delves into the clinical manifestations of RT-induced vascular disease, signaling pathways, cellular targets affected by radiation injury, and preclinical models of RT-induced vascular injury. The goal is to inspire the development of innovative strategies to prevent RT-related cardiovascular disease.

Associations Between Flavonoid Intake and Subclinical Atherosclerosis: The Multi-Ethnic Study of Atherosclerosis.

BACKGROUND: Flavonoids may play a role in mitigating atherosclerotic cardiovascular diseases, with evidence suggesting effects may differ between vascular beds. Studies examining associations with subclinical markers of atherosclerosis between subpopulations with different underlying risks of atherosclerosis are lacking. METHODS: Among 5599 participants from the MESA (Multi-Ethnic Study of Atherosclerosis), associations between dietary flavonoid intakes (estimated from a food frequency questionnaire) and subclinical measures of atherosclerosis (ankle-brachial index, carotid plaques and intima-media thickness, and coronary artery calcification) were examined using repeated measures models. Exposures and outcomes were measured at exam 1 (2000-2002) and exam 5 (2010-2011). Stratified analyses and interaction terms were used to explore effect modification by time, sex, race/ethnicity, and smoking status. RESULTS: In the analytic population, at baseline, ≈46% were men with a median age of 62 (interquartile range, 53-70) years and total flavonoid intakes of 182 (interquartile range, 98-308) mg/d. After multivariable adjustments, participants with the highest (quartile 4) versus lowest (quartile 1) total flavonoid intakes had 26% lower odds of having an ankle-brachial index <1 (odds ratio, 0.74 [95% CI, 0.60-0.92]) and 18% lower odds of having a carotid plaque (odds ratio, 0.82 [95% CI, 0.69-0.99]), averaged over exams 1 and 5. Moderate (quartile 3) to high (quartile 4) intakes of flavonols, flavanol monomers, and anthocyanins were associated with 19% to 34% lower odds of having an ankle-brachial index <1 and 18% to 20% lower odds of having carotid plaque. Participants with the highest intakes of anthocyanins (quartile 4) at baseline had a marginally slower rate of carotid plaque progression than those with moderate intakes (quartiles 2 and 3). There were no significant associations with intima-media thickness or coronary artery calcification. Observed associations did not differ by sex, race/ethnicity, or smoking status. CONCLUSIONS: In this multi-ethnic population, higher dietary flavonoid intakes were associated with lower odds of peripheral and carotid artery atherosclerosis. Increasing intakes of healthy, flavonoid-rich foods may protect against atherosclerosis in the peripheral and carotid arteries.

Coronary Artery Disease Risk Variant Dampens the Expression of CALCRL by Reducing HSF Binding to Shear Stress Responsive Enhancer in Endothelial Cells In Vitro.

BACKGROUND: CALCRL (calcitonin receptor-like) protein is an important mediator of the endothelial fluid shear stress response, which is associated with the genetic risk of coronary artery disease. In this study, we functionally characterized the noncoding regulatory elements carrying coronary artery disease that risks single-nucleotide polymorphisms and studied their role in the regulation of CALCRL expression in endothelial cells. METHODS: To functionally characterize the coronary artery disease single-nucleotide polymorphisms harbored around the gene CALCRL, we applied an integrative approach encompassing statistical, transcriptional (RNA-seq), and epigenetic (ATAC-seq [transposase-accessible chromatin with sequencing], chromatin immunoprecipitation assay-quantitative polymerase chain reaction, and electromobility shift assay) analyses, alongside luciferase reporter assays, and targeted gene and enhancer perturbations (siRNA and clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9) in human aortic endothelial cells. RESULTS: We demonstrate that the regulatory element harboring rs880890 exhibits high enhancer activity and shows significant allelic bias. The A allele was favored over the G allele, particularly under shear stress conditions, mediated through alterations in the HSF1 (heat shock factor 1) motif and binding. CRISPR deletion of rs880890 enhancer resulted in downregulation of CALCRL expression, whereas HSF1 knockdown resulted in a significant decrease in rs880890-enhancer activity and CALCRL expression. A significant decrease in HSF1 binding to the enhancer region in endothelial cells was observed under disturbed flow compared with unidirectional flow. CALCRL knockdown and variant perturbation experiments indicated the role of CALCRL in mediating eNOS (endothelial nitric oxide synthase), APLN (apelin), angiopoietin, prostaglandins, and EDN1 (endothelin-1) signaling pathways leading to a decrease in cell proliferation, tube formation, and NO production. CONCLUSIONS: Overall, our results demonstrate the existence of an endothelial-specific HSF (heat shock factor)-regulated transcriptional enhancer that mediates CALCRL expression. A better understanding of CALCRL gene regulation and the role of single-nucleotide polymorphisms in the modulation of CALCRL expression could provide important steps toward understanding the genetic regulation of shear stress signaling responses.

Whys and Wherefores of Coronary Arterial Positive Remodeling.

Positive remodeling (PR) is an atherosclerotic plaque feature defined as an increase in arterial caliber at the level of an atheroma, in response to increasing plaque burden. The mechanisms that lead to its formation are incompletely understood, but its role in coronary atherosclerosis has major clinical implications. Indeed, plaques with PR have elevated risk of provoking acute cardiac events. Hence, PR figures among the high-risk plaque features that cardiac imaging studies should report. This review aims to provide an overview of the current literature on coronary PR. It outlines the pathophysiology of PR, the different techniques used to assess its presence, and the imaging findings associated to PR, on both noninvasive and invasive studies. This review also summarizes clinical observations, trials, and studies, focused on the impact of PR on clinical outcome.

Methods for dynamic and whole volume imaging of the zebrafish heart.

Tissue development and regeneration are dynamic processes involving complex cell migration and cell-cell interactions. We have developed a protocol for complementary time-lapse and three-dimensional (3D) imaging of tissue for developmental and regeneration studies which we apply here to the zebrafish cardiac vasculature. 3D imaging of fixed specimens is used to first define the subject at high resolution then live imaging captures how it changes dynamically. Hearts from adult and juvenile zebrafish are extracted and cleaned in preparation for the different imaging modalities. For whole-mount 3D confocal imaging, single or multiple hearts with native fluorescence or immuno-labeling are prepared for stabilization or clearing, and then imaged. For live imaging, hearts are placed in a prefabricated fluidic device and set on a temperature-controlled microscope for culture and imaging over several days. This protocol allows complete visualization of morphogenic processes in a 3D context and provides the ability to follow cell behaviors to complement in vivo and fixed tissue studies. This culture and imaging protocol can be applied to different cell and tissue types. Here, we have used it to observe zebrafish coronary vasculature and the migration of coronary endothelial cells during heart regeneration.

Low-Density Lipoprotein Cholesterol Is Predominantly Associated With Atherosclerotic Cardiovascular Disease Events in Patients With Evidence of Coronary Atherosclerosis: The Western Denmark Heart Registry.

BACKGROUND: Low-density lipoprotein cholesterol (LDL-C) is an important causal risk factor for atherosclerotic cardiovascular disease (ASCVD). However, a sizable proportion of middle-aged individuals with elevated LDL-C level have not developed coronary atherosclerosis as assessed by coronary artery calcification (CAC). Whether presence of CAC modifies the association of LDL-C with ASCVD risk is unknown. We evaluated the association of LDL-C with future ASCVD events in patients with and without CAC. METHODS: The study included 23 132 consecutive symptomatic patients evaluated for coronary artery disease using coronary computed tomography angiography (CTA) from the Western Denmark Heart Registry, a seminational, multicenter-based registry with longitudinal registration of patient and procedure data. We assessed the association of LDL-C level obtained before CTA with ASCVD (myocardial infarction and ischemic stroke) events occurring during follow-up stratified by CAC>0 versus CAC=0 using Cox regression models adjusted for baseline characteristics. Outcomes were identified through linkage among national registries covering all hospitals in Denmark. We replicated our results in the National Heart, Lung, and Blood Institute-funded Multi-Ethnic Study of Atherosclerosis. RESULTS: During a median follow-up of 4.3 years, 552 patients experienced a first ASCVD event. In the overall population, LDL-C (per 38.7 mg/dL increase) was associated with ASCVD events occurring during follow-up (adjusted hazard ratio [aHR], 1.14 [95% CI, 1.04-1.24]). When stratified by the presence or absence of baseline CAC, LDL-C was only associated with ASCVD in the 10 792/23 132 patients (47%) with CAC>0 (aHR, 1.18 [95% CI, 1.06-1.31]); no association was observed among the 12 340/23 132 patients (53%) with CAC=0 (aHR, 1.02 [95% CI, 0.87-1.18]). Similarly, a very high LDL-C level (>193 mg/dL) versus LDL-C <116 mg/dL was associated with ASCVD in patients with CAC>0 (aHR, 2.42 [95% CI, 1.59-3.67]) but not in those without CAC (aHR, 0.92 [0.48-1.79]). In patients with CAC=0, diabetes, current smoking, and low high-density lipoprotein cholesterol levels were associated with future ASCVD events. The principal findings were replicated in the Multi-Ethnic Study of Atherosclerosis. CONCLUSIONS: LDL-C appears to be almost exclusively associated with ASCVD events over ≈5 years of follow-up in middle-aged individuals with versus without evidence of coronary atherosclerosis. This information is valuable for individualized risk assessment among middle-aged people with or without coronary atherosclerosis.

A Vegfc-Emilin2a-Cxcl8a Signaling Axis Required for Zebrafish Cardiac Regeneration.

BACKGROUND: Ischemic heart disease following the obstruction of coronary vessels leads to the death of cardiac tissue and the formation of a fibrotic scar. In contrast to adult mammals, zebrafish can regenerate their heart after injury, enabling the study of the underlying mechanisms. One of the earliest responses following cardiac injury in adult zebrafish is coronary revascularization. Defects in this process lead to impaired cardiomyocyte repopulation and scarring. Hence, identifying and investigating factors that promote coronary revascularization holds great therapeutic potential. METHODS: We used wholemount imaging, immunohistochemistry and histology to assess various aspects of zebrafish cardiac regeneration. Deep transcriptomic analysis allowed us to identify targets and potential effectors of Vegfc (vascular endothelial growth factor C) signaling. We used newly generated loss- and gain-of-function genetic tools to investigate the role of Emilin2a (elastin microfibril interfacer 2a) and Cxcl8a (chemokine (C-X-C) motif ligand 8a)-Cxcr1 (chemokine (C-X-C) motif receptor 1) signaling in cardiac regeneration. RESULTS: We first show that regenerating coronary endothelial cells upregulate vegfc upon cardiac injury in adult zebrafish and that Vegfc signaling is required for their proliferation during regeneration. Notably, blocking Vegfc signaling also significantly reduces cardiomyocyte dedifferentiation and proliferation. Using transcriptomic analyses, we identified emilin2a as a target of Vegfc signaling and found that manipulation of emilin2a expression can modulate coronary revascularization as well as cardiomyocyte proliferation. Mechanistically, Emilin2a induces the expression of the chemokine gene cxcl8a in epicardium-derived cells, while cxcr1, the Cxcl8a receptor gene, is expressed in coronary endothelial cells. We further show that Cxcl8a-Cxcr1 signaling is also required for coronary endothelial cell proliferation during cardiac regeneration. CONCLUSIONS: These data show that after cardiac injury, coronary endothelial cells upregulate vegfc to promote coronary network reestablishment and cardiac regeneration. Mechanistically, Vegfc signaling upregulates epicardial emilin2a and cxcl8a expression to promote cardiac regeneration. These studies aid in understanding the mechanisms underlying coronary revascularization in zebrafish, with potential therapeutic implications to enhance revascularization and regeneration in injured human hearts.

Coronary Arterial Function and Disease in Women With No Obstructive Coronary Arteries.

Ischemic heart disease (IHD) is the leading cause of mortality in women. While traditional cardiovascular risk factors play an important role in the development of IHD in women, women may experience sex-specific IHD risk factors and pathophysiology, and thus female-specific risk stratification is needed for IHD prevention, diagnosis, and treatment. Emerging data from the past 2 decades have significantly improved the understanding of IHD in women, including mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries. Despite this progress, sex differences in IHD outcomes persist, particularly in young women. This review highlights the contemporary understanding of coronary arterial function and disease in women with no obstructive coronary arteries, including coronary anatomy and physiology, mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries, noninvasive and invasive diagnostic strategies, and management of IHD.

Feasibility of virtual non-iodine coronary calcium scoring on dual source photon-counting coronary CT angiography: a dynamic phantom study.

BACKGROUND: The aim of our current systematic dynamic phantom study was first, to optimize reconstruction parameters of coronary CTA (CCTA) acquired on photon counting CT (PCCT) for coronary artery calcium (CAC) scoring, and second, to assess the feasibility of calculating CAC scores from CCTA, in comparison to reference calcium scoring CT (CSCT) scans. METHODS: In this phantom study, an artificial coronary artery was translated at velocities corresponding to 0, < 60, and 60-75 beats per minute (bpm) within an anthropomorphic phantom. The density of calcifications was 100 (very low), 200 (low), 400 (medium), and 800 (high) mgHA/cm3, respectively. CCTA was reconstructed with the following parameters: virtual non-iodine (VNI), with and without iterative reconstruction (QIR level 2, QIR off, respectively); kernels Qr36 and Qr44f; slice thickness/increment 3.0/1.5 mm and 0.4/0.2 mm. The agreement in risk group classification between CACCCTA and CACCSCT scoring was measured using Cohen weighted linear κ with 95% CI. RESULTS: For CCTA reconstructed with 0.4 mm slice thickness, calcium detectability was perfect (100%). At < 60 bpm, CACCCTA of low, and medium density calcification was underestimated by 53%, and 15%, respectively. However, CACCCTA was not significantly different from CACCSCT of very low, and high-density calcifications. The best risk agreement was achieved when CCTA was reconstructed with QIR off, Qr44f, and 0.4 mm slice thickness (κ = 0.762, 95% CI 0.671-0.853). CONCLUSION: In this dynamic phantom study, the detection of calcifications with different densities was excellent with CCTA on PCCT using thin-slice VNI reconstruction. Agatston scores were underestimated compared to CSCT but agreement in risk classification was substantial. CLINICAL RELEVANCE STATEMENT: Photon counting CT may enable the implementation of coronary artery calcium scoring from coronary CTA in daily clinical practice. KEY POINTS: Photon-counting CTA allows for excellent detectability of low-density calcifications at all heart rates. Coronary artery calcium scoring from coronary CTA acquired on photon counting CT is feasible, although improvement is needed. Adoption of the standard acquisition and reconstruction protocol for calcium scoring is needed for improved quantification of coronary artery calcium to fully employ the potential of photon counting CT.

Optimizing coronary CT angiography quality with motion-compensated reconstruction for second-generation dual-layer spectral detector CT.

OBJECTIVES: To investigate the effect of motion-compensated reconstruction (MCR) algorithm on improving the image quality of coronary computed tomography angiography (CCTA) using second-generation dual-layer spectral detector computed tomography (DLCT), and to evaluate the influence of heart rate (HR) on the motion-correction efficacy of this algorithm. MATERIALS AND METHODS: We retrospectively enrolled 127 patients who underwent CCTA for suspected coronary artery disease using second-generation DLCT. We divided the patients into two subgroups according to their average HR during scanning: the "HR < 75 bpm" group and the "HR ≥ 75 bpm" group. All images were reconstructed by the standard (STD) algorithm and MCR algorithm. Subjective image quality (4-point Likert scale), interpretability, and objective image quality between the STD and MCR in the whole population and within each subgroup were compared. RESULTS: MCR showed significantly higher Likert scores and interpretability than STD on the per-segment (3.58 ± 0.69 vs. 2.82 ± 0.93, 98.4% vs. 91.9%), per-vessel (3.12 ± 0.81 vs. 2.12 ± 0.74, 96.3% vs. 78.7%) and per-patient (2.57 ± 0.76 vs. 1.62 ± 0.55, 90.6% vs. 59.1%) levels (all p < 0.001). In the analysis of HR subgroups on a per-vessel basis of interpretability, significant differences were observed only in the right coronary artery in the low HR group, whereas significant differences were noted in three major coronary arteries in the high HR group. For objective image quality assessment, MCR significantly improved the SNR (13.22 ± 4.06 vs. 12.72 ± 4.06) and the contrast-to-noise ratio (15.84 ± 4.82 vs. 15.39 ± 4.38) compared to STD (both p < 0.001). CONCLUSION: MCR significantly improves the subjective image quality, interpretability, and objective image quality of CCTA, especially in patients with higher HRs. CLINICAL RELEVANCE STATEMENT: The motion-compensated reconstruction algorithm of the second-generation dual-layer spectral detector computed tomography is helpful in improving the image quality of coronary computed tomography angiography in clinical practice, especially in patients with higher heart rates. KEY POINTS: Motion artifacts from cardiac movement affect the quality and interpretability of coronary computed tomography angiography (CCTA). This motion-compensated reconstruction (MCR) algorithm significantly improves the image quality of CCTA in clinical practice. Image quality improvement by using MCR was more significant in the high heart rate group.

The influence of motion-compensated reconstruction on coronary artery analysis for a dual-layer detector CT system: a dynamic phantom study.

OBJECTIVES: Cardiac motion artifacts hinder the assessment of coronary arteries in coronary computed tomography angiography (CCTA). We investigated the impact of motion compensation reconstruction (MCR) on motion artifacts in CCTA at various heart rates (HR) using a dynamic phantom. MATERIALS AND METHODS: An artificial hollow coronary artery (5-mm diameter lumen) filled with iodinated contrast agent (400 HU at 120 kVp), positioned centrally in an anthropomorphic chest phantom, was scanned using a dual-layer spectral detector CT. The artery was translated at constant horizontal velocities (0-80 mm/s, increment of 10 mm/s). For each velocity, five CCTA scans were repeated using a clinical protocol. Motion artifacts were quantified using the in-plane motion area. Regression analysis was performed to calculate the reduction in motion artifacts provided by MCR, by division of the slopes of non-MCR and MCR fitted lines. RESULTS: Reference mean (95% confidence interval) motion artifact area was 24.9 mm2 (23.8, 26.0). Without MCR, motion artifact areas for velocities exceeding 20 mm/s were significantly larger (up to 57.2 mm2 (40.1, 74.2)) than the reference. With MCR, no significant differences compared to the reference were shown for all velocities, except for 70 mm/s (29.0 mm2 (27.0, 31.0)). The slopes of the fitted data were 0.44 and 0.04 for standard and MCR reconstructions, respectively, resulting in an 11-time motion artifact reduction. CONCLUSION: MCR may improve CCTA assessment in patients by reducing coronary artery motion artifacts, especially in those with elevated HR who cannot receive beta blockers or do not attain the targeted HR. CLINICAL RELEVANCE STATEMENT: This vendor-specific motion compensation reconstruction may improve coronary computed tomography angiography assessment in patients by reduction of coronary artery motion artifacts, especially in those with elevated various heart rates (HR) who cannot receive beta blockers or do not attain the targeted HR. KEY POINTS: • Motion artifacts are known to hinder the assessment of coronary arteries on coronary CT angiography (CCTA), leading to more non-diagnostic scans. • This dynamic phantom study shows that motion compensation reconstruction (MCR) reduces motion artifacts at various velocities, which may help to decrease the number of non-diagnostic scans. • MCR in this study showed to reduce motion artifacts 11-fold.

Epicardial adipose tissue dispersion at CT and recurrent atrial fibrillation after pulmonary vein isolation.

OBJECTIVES: Epicardial adipose tissue (EAT) remodeling is associated with atrial fibrillation (AF). Left atrial (LA) EAT dispersion on cardiac CT is a non-invasive imaging biomarker reflecting EAT heterogeneity. We aimed to investigate the association of LA EAT dispersion with AF recurrence after pulmonary vein isolation (PVI). METHODS: In a prospective registry of consecutive patients undergoing first PVI, mean EAT attenuation values were measured on contrast-enhanced cardiac CT scans in Hounsfield units (HU) within low (- 195 to - 45 HU) and high (- 44 to - 15 HU) threshold EAT compartments around the left atrium (LA). EAT dispersion was defined as the difference between the mean HU values within the two EAT compartments. Continuous variables were compared between groups using the Mann-Whitney U test and cox proportional hazard models were used to calculate hazard ratios of predictors of 1-year AF recurrence. RESULTS: A total of 208 patients were included, 135 with paroxysmal AF and 73 with persistent AF. LA EAT dispersion was significantly larger in patients with persistent compared to paroxysmal AF (52.6 HU vs. 49.9 HU; p = 0.001). After 1 year of follow-up, LA EAT dispersion above the mean (> 50.8 HU) was associated with a higher risk of AF recurrence (HR 2.3, 95% CI 1.5-3.6; p < 0.001). It retained its predictive value when corrected for age, sex, body mass index, LA volume, and AF type (HR 2.8, 95% CI 1.6-4.6; p < 0.001). CONCLUSION: A larger LA EAT dispersion on contrast-enhanced cardiac CT scans, reflecting EAT heterogeneity, is independently associated with AF recurrence after PVI. CLINICAL RELEVANCE STATEMENT: Based on LA EAT dispersion assessment, a more accurate risk stratification and patient selection may be possible based on a pre-procedural cardiac CT when planning PVI. KEY POINTS: • Epicardial adipose tissue (EAT) remodeling is associated with atrial fibrillation (AF). • A larger left atrial EAT dispersion in a pre-procedural cardiac CT was associated with a higher 1-year AF recurrence risk after pulmonary vein isolation. • A pre-procedural cardiac CT with left atrial EAT dispersion assessment may provide a more accurate risk stratification and patient selection for PVI.

The Contractile Machines of the Heart.

This chapter will describe basic structural and functional features of the contractile apparatus of muscle cells of the heart, namely, cardiomyocytes and smooth muscle cells. Cardiomyocytes form the contractile myocardium of the heart, while smooth muscle cells form the contractile coronary vessels. Both muscle types have distinct properties and will be considered with respect to their cellular appearance (brick-like cross-striated versus spindle-like smooth), arrangement of contractile proteins (sarcomeric versus non-sarcomeric organization), calcium activation mechanisms (thin-filament versus thick-filament regulation), contractile features (fast and phasic versus slow and tonic), energy metabolism (high oxygen versus low oxygen demand), molecular motors (type II myosin isoenzymes with high adenosine diphosphate [ADP]-release rate versus myosin isoenzymes with low ADP-release rates), chemomechanical energy conversion (high adenosine triphosphate [ATP] consumption and short duty ratio versus low ATP consumption and high duty ratio of myosin II cross-bridges [XBs]), and excitation-contraction coupling (calcium-induced calcium release versus pharmacomechanical coupling). Part of the work has been published (Neuroscience - From Molecules to Behavior", Chap. 22, Galizia and Lledo eds 2013, Springer-Verlag; with kind permission from Springer Science + Business Media).

Correlation between peripheral immature platelet level and coronary immature platelet levels in coronary artery disease: an observational study in cardiac referral centre in East Java, Indonesia.

OBJECTIVE: To investigate the correlation between peripheral and coronary immature platelet, and factors that may predict coronary immature platelet levels. METHODS: The cross-sectional, observational, analytical study was conducted at the Cardiovascular Diagnostic and Intervention Centre of Dr Soetomo General Academic Hospital, Surabaya, Indonesia, from November 2017 to January 2018, and comprised patients of either gender with coronary artery disease. Peripheral and coronary blood samples were retrieved during coronary catheterisation. Immature platelet fraction was acquired by examining whole blood samples analysed through automated flow cytometry. Relationship between peripheral and coronary immature platelet fractions and counts were analysed using parametric correlation test, followed by linear regression analysis model of variables that influenced coronary immature platelet fraction. The statistical analysis was carried out using SPSS Statistics for Windows, Version 25.0 (IBM Corp, Armonk, NY, USA). RESULTS: Of the 70 patients, 55(78.6%) were males and 15(21.4%) were females. The overall mean age was 57±5.32 years. There were 35(50%) patients with a history of smoking, and 34(48.6%) had hypertension and dyslipidaemia. Mean peripheral immature platelet fraction was 3.86±1.84% and mean coronary immature platelet fraction was 3.63±1.7%. There was a robust positive and significant correlation (r=0.882; p<0.001) between immature platelet levels in peripheral and coronary blood. Peripheral immature platelet and glycated haemoglobin >7.5 were independent predictors of coronary immature platelet (p=0.001). CONCLUSIONS: There was a strong correlation between immature platelet levels in peripheral and coronary blood.