[Show abstract][Hide abstract] ABSTRACT: OBJECTIVES: The aim of this study was to ascertain the relationship of 9p21 locus with: 1) angiographic coronary artery disease (CAD) burden; and 2) myocardial infarction (MI) in individuals with underlying CAD. BACKGROUND: Chromosome 9p21 variants have been robustly associated with coronary heart disease, but questions remain on the mechanism of risk, specifically whether the locus contributes to coronary atheroma burden or plaque instability. METHODS: We established a collaboration of 21 studies consisting of 33,673 subjects with information on both CAD (clinical or angiographic) and MI status along with 9p21 genotype. Tabular data are provided for each cohort on the presence and burden of angiographic CAD, MI cases with underlying CAD, and the diabetic status of all subjects. RESULTS: We first confirmed an association between 9p21 and CAD with angiographically defined cases and control subjects (pooled odds ratio [OR]: 1.31, 95% confidence interval [CI]: 1.20 to 1.43). Among subjects with angiographic CAD (n = 20,987), random-effects model identified an association with multivessel CAD, compared with those with single-vessel disease (OR: 1.10, 95% CI: 1.04 to 1.17)/copy of risk allele). Genotypic models showed an OR of 1.15, 95% CI: 1.04 to 1.26 for heterozygous carrier and OR: 1.23, 95% CI: 1.08 to 1.39 for homozygous carrier. Finally, there was no significant association between 9p21 and prevalent MI when both cases (n = 17,791) and control subjects (n = 15,882) had underlying CAD (OR: 0.99, 95% CI: 0.95 to 1.03)/risk allele. CONCLUSIONS: The 9p21 locus shows convincing association with greater burden of CAD but not with MI in the presence of underlying CAD. This adds further weight to the hypothesis that 9p21 locus primarily mediates an atherosclerotic phenotype.
Journal of the American College of Cardiology 01/2013; · 14.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous studies have demonstrated significant heterogeneity in responses to antiplatelet therapy (APT), and high residual platelet reactivity is associated with the risk of ischaemic events, including stent thrombosis (ST). The prevalence of APT hyporesponsiveness in a 'real world' registry of ST patients and the feasibility of personalising APT are reported.
39 consecutive patients admitted to a single regional cardiothoracic centre with definite ST were prospectively evaluated.
Response to aspirin and clopidogrel was measured following discharge using short thrombelastography (TEG), a rapid, well validated near patient platelet function test. Treatment modification in hyporesponders comprised an increase in aspirin dose and/or changing clopidogrel to prasugrel or ticagrelor. Short TEG was repeated following treatment modification to ensure an adequate response had been achieved.
12 (31%) patients had an adequate response to both aspirin and clopidogrel, 16 (41%) were hyporesponsive to clopidogrel alone, one (3%) was hyporesponsive to aspirin alone and 10 (26%) were hyporesponsive to both aspirin and clopidogrel. Following treatment modification, an adequate response to aspirin and P2Y12 agent was achieved in 10 (91%) and 22 (85%) patients, respectively. None has presented with a further ST episode.
There is a high prevalence of hyporesponsiveness to APT in patients with ST. Improved APT efficacy can be achieved by tailored therapy. Short TEG is a plausible platelet function test that can be used to deliver point of care personalised APT.
[Show abstract][Hide abstract] ABSTRACT: To evaluate the associations of emergent genome-wide-association study-derived coronary heart disease (CHD)-associated single nucleotide polymorphisms (SNPs) with established and emerging risk factors, and the association of genome-wide-association study-derived lipid-associated SNPs with other risk factors and CHD events.
Using two case-control studies, three cross-sectional, and seven prospective studies with up to 25 000 individuals and 5794 CHD events we evaluated associations of 34 genome-wide-association study-identified SNPs with CHD risk and 16 CHD-associated risk factors or biomarkers. The Ch9p21 SNPs rs1333049 (OR 1.17; 95% confidence limits 1.11-1.24) and rs10757274 (OR 1.17; 1.09-1.26), MIA3 rs17465637 (OR 1.10; 1.04-1.15), Ch2q36 rs2943634 (OR 1.08; 1.03-1.14), APC rs383830 (OR 1.10; 1.02, 1.18), MTHFD1L rs6922269 (OR 1.10; 1.03, 1.16), CXCL12 rs501120 (OR 1.12; 1.04, 1.20), and SMAD3 rs17228212 (OR 1.11; 1.05, 1.17) were all associated with CHD risk, but not with the CHD biomarkers and risk factors measured. Among the 20 blood lipid-related SNPs, LPL rs17411031 was associated with a lower risk of CHD (OR 0.91; 0.84-0.97), an increase in Apolipoprotein AI and HDL-cholesterol, and reduced triglycerides. SORT1 rs599839 was associated with CHD risk (OR 1.20; 1.15-1.26) as well as total- and LDL-cholesterol, and apolipoprotein B. ANGPTL3 rs12042319 was associated with CHD risk (OR 1.11; 1.03, 1.19), total- and LDL-cholesterol, triglycerides, and interleukin-6.
Several SNPs predicting CHD events appear to involve pathways not currently indexed by the established or emerging risk factors; others involved changes in blood lipids including triglycerides or HDL-cholesterol as well as LDL-cholesterol. The overlapping association of SNPs with multiple risk factors and biomarkers supports the existence of shared points of regulation for these phenotypes.
European Heart Journal 07/2011; 33(3):393-407. · 14.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The optimal duration of clopidogrel treatment, particularly following drug-eluting stent (DES) implantation, remains contentious. Previous studies have observed a clustering of adverse events following clopidogrel cessation 1 year after DES, the aetiology of which is poorly understood.
To investigate, in the prospective CESSATION study, the effect of clopidogrel withdrawal at 1 year after DES implantation on (i) arachidonic acid (AA)- and adenosine diphosphate (ADP)-induced platelet aggregation, and (ii) biomarkers of vascular inflammation, including soluble CD40 ligand (sCD40L), high-sensitivity C-reactive protein (hsCRP) and interleukin 6 (IL-6).
The prospective CESSATION study was undertaken in 33 patients receiving aspirin and due to discontinue clopidogrel 1 year after DES. Platetet reactivity was measured using short thromboelastography, and compliance with aspirin determined from serum thromboxane B(2) (TXB(2)) levels. Venesection was performed at 4 weeks and 24 h before, and at 24 h, 48 h, 1, 2 and 4 weeks after, clopidogrel cessation. Following clopidogrel withdrawal, there was (i) a predictable increase in ADP-induced platelet aggregation (ii) an unexpected significant increase in AA-induced platelet aggregation (iii) a decline in IL-6 and hsCRP at 1 week and 4 weeks respectively; and (iv) a non-significant increase in sCD40L at 4 weeks TXB(2) levels were consistently suppressed, indicating complete inhibition of cyclo-oxygenase-1 by aspirin.
An aspirin-independent, time-dependent increase in AA-induced platelet activation following clopidogrel withdrawal in patients with a DES has been described. New insights into a potential mechanism for the observed clustering of adverse events that occur early after clopidogrel cessation have been provided. These findings raise the question as to whether AA-induced clotting is an appropriate test of aspirin sensitivity.
[Show abstract][Hide abstract] ABSTRACT: IntroductionA clustering of adverse events, in particular stent thrombosis (ST) has been observed following clopidogrel cessation 1-year after drug-eluting stenting (DES), the aetiology of which is poorly understood. We investigated the effect of withdrawing clopidogrel in DES patients using a simple, rapid, reproducible near-patient platelet function test known as short Thrombelastography (s-TEG) that has been developed and validated by this group.Methods33 patients on aspirin and due to stop clopidogrel at 1 year following DES were investigated. Venesection was performed at (i) 4 weeks and 24 h pre clopidogrel cessation (ii) 24 h, 48 h, 1, 2 and 4 weeks post clopidogrel cessation. At all time-points, platelet reactivity was determined using s-TEG and thromboxane (TX) B2, IL-6, CD40 ligand and high sensitivity CRP were measured.ResultsClopidogrel cessation produced (i) a predictable increase in ADP-induced platelet aggregation, and (ii) an unexpected and significant rise in AA-induced platelet aggregation. TXB2 was consistently suppressed confirming inhibition of COX by aspirin.Conclusion
We have described for the first time an aspirin-independent increase in AA-induced clotting following clopidogrel withdrawal in DES patients. As well as potentially helping to explain the observed clustering of ST events early after clopidogrel withdrawal, these findings raise the question as to whether AA-induced clotting is an appropriate test of aspirin sensitivity. Our results also confirm s-TEG as a plausible candidate for near-patient platelet function testing in this field.
[Show abstract][Hide abstract] ABSTRACT: Whether triglyceride-mediated pathways are causally relevant to coronary heart disease is uncertain. We studied a genetic variant that regulates triglyceride concentration to help judge likelihood of causality.
We assessed the -1131T>C (rs662799) promoter polymorphism of the apolipoprotein A5 (APOA5) gene in relation to triglyceride concentration, several other risk factors, and risk of coronary heart disease. We compared disease risk for genetically-raised triglyceride concentration (20,842 patients with coronary heart disease, 35,206 controls) with that recorded for equivalent differences in circulating triglyceride concentration in prospective studies (302 430 participants with no history of cardiovascular disease; 12,785 incident cases of coronary heart disease during 2.79 million person-years at risk). We analysed -1131T>C in 1795 people without a history of cardiovascular disease who had information about lipoprotein concentration and diameter obtained by nuclear magnetic resonance spectroscopy.
The minor allele frequency of -1131T>C was 8% (95% CI 7-9). -1131T>C was not significantly associated with several non-lipid risk factors or LDL cholesterol, and it was modestly associated with lower HDL cholesterol (mean difference per C allele 3.5% [95% CI 2.6-4.6]; 0.053 mmol/L [0.039-0.068]), lower apolipoprotein AI (1.3% [0.3-2.3]; 0.023 g/L [0.005-0.041]), and higher apolipoprotein B (3.2% [1.3-5.1]; 0.027 g/L [0.011-0.043]). By contrast, for every C allele inherited, mean triglyceride concentration was 16.0% (95% CI 12.9-18.7), or 0.25 mmol/L (0.20-0.29), higher (p=4.4x10(-24)). The odds ratio for coronary heart disease was 1.18 (95% CI 1.11-1.26; p=2.6x10(-7)) per C allele, which was concordant with the hazard ratio of 1.10 (95% CI 1.08-1.12) per 16% higher triglyceride concentration recorded in prospective studies. -1131T>C was significantly associated with higher VLDL particle concentration (mean difference per C allele 12.2 nmol/L [95% CI 7.7-16.7]; p=9.3x10(-8)) and smaller HDL particle size (0.14 nm [0.08-0.20]; p=7.0x10(-5)), factors that could mediate the effects of triglyceride.
These data are consistent with a causal association between triglyceride-mediated pathways and coronary heart disease.
British Heart Foundation, UK Medical Research Council, Novartis.
The Lancet 05/2010; 375(9726):1634-9. · 39.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A-disintegrin-and-metalloproteinase-domains (ADAMs) are membrane-anchored glycoproteins involved in cell adhesion, cell migration and proteolysis. ADAM15 has been implicated in atherosclerosis, with an effect on vascular smooth muscle cell migration. We investigated whether ADAM33, which is evolutionally closely related to ADAM15, was expressed in atheromas and whether it had an effect on vascular smooth muscle migration. We also tested whether ADAM33 gene variation had an influence on the extent of atherosclerosis in patients with coronary artery disease. Immunohistochemical analyses showed that ADAM33 was expressed in smooth muscle cells in the arterial wall and that the expression was increased in smooth muscle cells in atheromas. ADAM33 immunostaining on inflammatory cells in atheromas was also observed. Primary vascular smooth muscle cells in culture were also found to express ADAM33. Boyden chamber assays showed that a neutralising antibody against ADAM33 increased the ability of arterial smooth muscle cells to migrate through a reconstituted basement membrane, suggesting that ADAM33 has an inhibitory effect on vascular smooth muscle migration. Moreover, we detected an association between ADAM33 genotype and the extent of atherosclerosis in a large cohort of coronary artery disease patients. These findings suggest that ADAM33 is implicated in the pathogenesis of atherosclerosis.
[Show abstract][Hide abstract] ABSTRACT: Atherosclerotic lesions express matrix metalloproteinase (MMP)8, which possesses proteolytic activity on matrix proteins particularly fibrillar collagens and on nonmatrix proteins such as angiotensin (Ang) I.
We studied whether MMP8 plays a role in atherogenesis.
In atherosclerosis-prone apolipoprotein E-deficient mice, inactivating MMP8 resulted in a substantial reduction in atherosclerotic lesion formation. Immunohistochemical examinations showed that atherosclerotic lesions in MMP8-deficient mice had significantly fewer macrophages but increased collagen content. In line with results of in vitro assays showing that Ang I cleavage by MMP8 generated Ang II, MMP8 knockout mice had lower Ang II levels and lower blood pressure. In addition, we found that products of Ang I cleavage by MMP8 increased vascular cell adhesion molecule (VCAM)-1 expression and that MMP8-deficient mice had reduced VCAM-1 expression in atherosclerotic lesions. Intravital microscopy analysis showed that leukocyte rolling and adhesion on vascular endothelium was reduced in MMP8 knockout mice. Furthermore, we detected an association between MMP8 gene variation and extent of coronary atherosclerosis in patients with coronary artery disease. A relationship among MMP8 gene variation, plasma VCAM-1 level, and atherosclerosis progression was also observed in a population-based, prospective study.
These results indicate that MMP8 is an important player in atherosclerosis.
Circulation Research 10/2009; 105(9):921-9. · 11.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Prosthetic heart valve thrombosis is a potentially life-threatening complication of low anticoagulation. We present a case of acute prosthetic mitral valve thrombosis in a patient whose anticoagulation was inadequate after phenindione was changed to low molecular weight heparin. We discuss the diagnosis and treatment of this condition and highlight the danger of long-term low molecular weight heparin use in patients with prosthetic heart valves, especially those in the mitral position. We review the current guidelines for anticoagulation of prosthetic heart valves and discuss potential treatment options if adequate anticoagulation is not achieved by oral anticoagulant alone.
Journal of the American Society of Echocardiography: official publication of the American Society of Echocardiography 09/2007; 20(8):1010.e7-9. · 2.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We sought to compare the feasibility and accuracy of transthoracic real-time 3-dimensional echocardiography (RT-3DE) with transesophageal echocardiography (TEE) for the preoperative functional assessment of patients with mitral valve prolapse.
In 44 patients with severe mitral regurgitation caused by type 2 valve dysfunction, TEE and RT-3DE were performed 24 hours before surgery and analyzed by two separate observers. TEE and RT-3DE images were acquired digitally and stored for offline analysis. The echocardiographic results were validated intraoperatively.
Five patients did not have image quality suitable for analysis with RT-3DE and were excluded from analysis, leaving a sample size of 39. In total, 54 of 334 analyzed mitral valve segments were diseased. Prolapse of a single mitral valve segment was present in 25 patients and 14 patients had complex disease involving two or more segments. Sensitivity, specificity, and accuracy for TEE in identification of diseased segments were 94%, 100%, and 96%, respectively. The same values for RT-3DE were 91%, 100%, and 94%, respectively. The differences were not statistically significant. Accuracies were not significantly different according to segment location. Interobserver agreement was 92% for TEE and 88% for RT-3DE (P = nonsignificant).
RT-3DE is feasible with comparative accuracy to TEE for precise anatomic localization of prolapsing mitral valve segments. However, the technique is limited by poor image quality in 11% of patients.
Journal of the American Society of Echocardiography: official publication of the American Society of Echocardiography 09/2007; 20(8):934-40. · 2.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ATP-binding-cassette-transporter-A1 (ABCA1) plays a pivotal role in intracellular cholesterol removal, exerting a protective effect against atherosclerosis. ABCA1 gene severe mutations underlie Tangier disease, a rare Mendelian disorder that can lead to premature coronary artery disease (CAD), with age of CAD onset being two decades earlier in mutant homozygotes and one decade earlier in heterozygotes than in mutation non-carriers. It is unknown whether common polymorphisms in ABCA1 could influence age of symptom onset of CAD in the general population. We examined common promoter and non-synonymous coding polymorphisms in relation to age of symptom onset in a group of CAD patients (n = 1164), and also carried out in vitro assays to test effects of the promoter variations on ABCA1 promoter transcriptional activity and effects of the coding variations on ABCA1 function in mediating cellular cholesterol efflux. Age of symptom onset was found to be associated with the promoter - 407G > C polymorphism, being 2.82 years higher in C allele homozygotes than in G allele homozygotes and intermediate in heterozygotes (61.54, 59.79 and 58.72 years, respectively; P = 0.002). In agreement, patients carrying ABCA1 haplotypes containing the -407C allele had higher age of symptom onset. Patients of the G/G or G/C genotype of the -407G > C polymorphism had significant coronary artery stenosis (>75%) at a younger age than those of the C/C genotype (P = 0.003). Reporter gene assays showed that ABCA1 haplotypes bearing the -407C allele had higher promoter activity than haplotypes with the -407G allele. Functional analyses of the coding polymorphisms showed an effect of the V825I substitution on ABCA1 function, with the 825I variant having higher activity in mediating cholesterol efflux than the wild-type (825V). A trend towards higher symptom onset age in 825I allele carriers was observed. The data indicate an influence of common ABCA1 functional polymorphisms on age of symptom onset in CAD patients.
Human Molecular Genetics 06/2007; 16(12):1412-22. · 7.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have developed a mutation-scanning approach suitable for whole population screening for unknown mutations. The method, meltMADGE, combines thermal ramp electrophoresis with MADGE to achieve suitable cost efficiency and throughput. The sensitivity was tested in blind trials using 54 amplicons representing the BRCA1 coding region and a panel of 94 unrelated family breast cancer risk consultands previously screened in a clinical diagnostic laboratory. All 10 common polymorphisms, 15/15 previously identified disease-causing mutations, and three previously untested single base changes were identified. Assays of LDLR exons 3 and 8 were validated in 460 familial hypercholesteremics and detected 8/9 known variants. We then applied the exon 3 assay in several DNA banks representing approximately 8000 subjects with known cholesterol values and applied both assays in one DNA bank (n = 3600). In exon 3 we identified one previously reported moderate mutation, P84S (n = 1), also associated with moderate hypercholesteremia in this subject; an unreported silent variant, N76N (n = 1); and known severe hypercholesteremia splice mutation 313+1G-->A (n = 2). Around exon 8 we identified a paucimorphism (n = 35) at the splice site 1061-8T-->C (known to be in complete linkage disequilibrium with T705I) and unreported sequence variants 1186+11G-->A (n = 1) and D335N G-->A (n = 1). The cholesterol value for D335N was on the 96.2 percentile and for T705I, 2/35 carriers were above the 99th percentile. Thus, variants with predicted severe, moderate, and no effect were identified at the population level. In contrast with case collections, CpG mutations predominated. MeltMADGE will enable definition of the full population spectrum of rare, paucimorphic, severe, moderate (forme fruste), and silent mutations and effects.
Genome Research 07/2005; 15(7):967-77. · 14.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVE: To test the hypothesis that gene-gene interaction of the renin-angiotensin system is associated with an effect on the extent of coronary atherosclerosis. SETTING AND RESULTS: A cohort of 1162 patients with coronary artery disease were genotyped for genetic polymorphisms in the renin-angiotensin system. Patients carrying the D allele of the angiotensin I converting enzyme (ACE) gene had greater coronary extent scores (defined as the number of coronary segments with 5% to 75% stenosis) than those not carrying this allele (p = 0.006 in non-parametric analysis and p = 0.019 in parametric analysis). This association remained significant after adjusting for age, body mass index, hypertension, and diabetes, which were also significantly associated with coronary extent scores. There was a significant interaction (p = 0.033) between genotypes of ACE and angiotensin II type 1 receptor (AGTR1). The association between the ACE gene D allele and increased coronary extent scores was significant (p = 0.008 in non-parametric and p = 0.027 in parametric analysis) in those carrying the +1166 C allele of the AGTR1 gene, but was absent in those not carrying the AGTR1 gene +1166 C allele. CONCLUSION: These findings suggest that variation in the ACE and AGTR1 genes and their interaction may not only contribute to susceptibility of coronary artery disease as previously found but also modify the disease process, thus contributing to interindividual differences in severity of the disease.
[Show abstract][Hide abstract] ABSTRACT: A number of studies have shown that coronary artery disease severity is associated with the epsilon 2/ epsilon 3/ epsilon 4 polymorphism in the coding region of the apolipoprotein E gene. In this study, we investigated whether the severity of the disease was also influenced by a functional polymorphism (-219 G>T) in the promoter of the gene, and if so, whether the effects of the two polymorphisms were independent. A cohort of 1170 patients with angiographically documented coronary artery disease were genotyped for the two polymorphisms. The frequency of the epsilon 4 allele of the epsilon 2/ epsilon 3/ epsilon 4 polymorphism increased linearly with increasing number of diseased vessels, so did the -219T allele of the -219 G>T polymorphism. In the sample as a whole, logistic regression analyses indicated that compared with the G/G genotype, the T/T genotype conferred an odds ratio of 1.598 (95% CI=1.161-2.201, P=0.004) in favor of increased disease severity, and the relationship remained significant after adjustment for epsilon 2/ epsilon 3/ epsilon 4 polymorphism genotypes, plasma cholesterol and triglyceride levels, and other risk factors. The effect of the T/T genotype on disease severity was more significant in patients who did not carry the epsilon 4 allele (OR=1.510, 95% CI=1.028-2.221) than in epsilon 4 allele carriers (OR=1.303, 95% CI=0.619-2.742). There was considerable linkage disequilibrium between the two polymorphisms (rho=0.9, P<0.001). Logistic regression analysis showed that the -219T- epsilon 4 haplotype conferred an odds ratio of 1.488 (95% CI=1.133-1.954). These findings suggest that the -219 G>T and epsilon 2/ epsilon 3/ epsilon 4 polymorphisms, which may affect respectively the quantity and quality of apoE, have independent and possibly additive effects on coronary artery disease severity.
European Journal of HumanGenetics 06/2003; 11(6):437-43. · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: On behalf of the British Hypertension Society 1 , the British Cardiovascular Intervention Society 2 , the British Society for Interventional Radiology 3 , National Institute for Clinical Outcomes Research 4 , the British Cardiovascular Society 5 , and the Renal Association 6 . Background to the Joint Societies' Statement on Renal Denervation. Renal denervation for proven resistant hypertension is a new procedure with an emerging evidence base of effectiveness and safety 1,2,3 . This Joint Societies' Consensus Statement was prepared to support the National Institute of Health and Clinical Excellence Interventional Procedure Guidance on Renal Denervation (NICE IP923) by representatives of key stakeholder societies. Eligiblity for renal denervation. We recommend that we rely upon the current evidence-base to select patients with resistant hypertension who may be eligible for this therapy. In the trials, resistant hypertension was defined as a sustained clinic systolic blood pressure of ≥ 160 mm Hg (≥ 150 mm Hg in Type 2 Diabetes) in patients on 3 or more anti-hypertensive medications. This is equivalent to stage 2 hypertension which is an average clinic blood pressure >160 mm Hg and equivalent to a daytime average on ambulatory blood pressure >150 mm Hg as defined by the 2011 National Institute of Health and Clinical Excellence (CG 127) Hypertension Guideline 4 . We further recommend that to be eligible for renal denervation patients should have progressed through the medications recommended at step 4 in the NICE/British Hypertension Society Treatment Algorithm in CG 127 4 . Confirmation of sustained raised blood pressure using ambulatory blood pressure monitoring is essential (as above). It will allow detection of a "white coat", or alerting response which may be a cause of apparently resistant hypertension. The multi-disciplinary team of hypertension specialists and interventionalists. The selection, treatment and follow up of patients for this intervention requires a multidisciplinary team which must include hypertension specialists who can demonstrate active involvement in the routine investigation and care of patients with resistant hypertension. They will provide detailed assessment of the eligibility of the patients to receive this procedure, excluding non-compliance, secondary causes of hypertension and ensuring that a full range of lifestyle and therapeutic options have been carefully tried. The intervention may be undertaken by interventional cardiologists or radiologists who have been trained in the procedure and are competent to manage complications such as dissection of the renal artery.