Influence of the atrio-ventricular delay optimization on the intra left ventricular delay in cardiac resynchronization therapy

The severity index is a new echocardiographic measure that is thought to be an accurate indicator of aortic leaflet pathology in patients with AS. However, it has not been validated against cardiac catheterization or Doppler echocardiographic measures of AS severity nor has it been applied to patients with aortic sclerosis. The purposes of this study were to compare the severity index to invasive hemodynamics and Doppler echocardiography across the spectrum of calcific aortic valve disease, including aortic sclerosis and AS. 48 patients with aortic sclerosis and AS undergoing echocardiography and cardiac catheterization comprised the study population. The aortic valve leaflets were assessed for mobility (scale 1 to 6) and calcification (scale 1 to 4) and the severity index was calculated as the sum of the mobility and calcification scores according to the methods of Bahler et al. The severity index increased with increasing severity of aortic valve disease; the severity indices for patients with aortic sclerosis, mild to moderate AS and severe AS were 3.38 ± 1.06, 6.45 ± 2.16 and 8.38 ± 1.41, respectively. The aortic jet velocity by echocardiography and the square root of the maximum aortic valve gradient by cardiac catheterization correlated well with the severity index (r = 0.84, p < 0.0001; r = 0.84, p < 0.0001, respectively). These results confirm that the severity index correlates with hemodynamic severity of aortic valve disease and may prove to be a useful measure in patients with aortic sclerosis and AS.     

A calcified polymeric valve for valve-in-valve applications

The prevalence of aortic valve stenosis (AS) is increasing in the aging society. More recently, novel treatments and devices for AS, especially transcatheter aortic valve replacement (TAVR) have significantly changed the therapeutic approach to this disease. Research and development related to TAVR require testing these devices in the calcified heart valves that closely mimic a native calcific valve. However, no animal model of AS has yet been available. Alternatively, animals with normal aortic valve that are currently used for TAVR experiments do not closely replicate the aortic valve pathology required for proper testing of these devices. To solve this limitation, for the first time, we developed a novel polymeric valve whose leaflets possess calcium hydroxyapatite inclusions immersed in them. This study reports the characteristics and feasibility of these valves. Two types of the polymeric valve, i.e., moderate and severe calcified AS models were developed and tested by deploying a transcatheter valve in those and measuring the related hemodynamics. The valves were tested in a heart flow simulator, and were studied using echocardiography. Our results showed high echogenicity of the polymeric valve, that was correlated to the severity of the calcification. Aortic valve area of the polymeric valves was measured, and the severity of stenosis was defined according to the clinical guidelines. Accordingly, we showed that these novel polymeric valves closely mimic AS, and can be a desired cost-saving solution for testing the performance of the transcatheter aortic valve systems in vitro.     

Prediction of stenting related adverse events through patient-specific finite element modelling

Right ventricular outflow tract (RVOT) calcific obstruction is frequent after homograft conduit implantation to treat congenital heart disease. Stenting and percutaneous pulmonary valve implantation (PPVI) can relieve the obstruction and prolong the conduit lifespan, but require accurate pre-procedural evaluation to minimize the risk of coronary artery (CA) compression, stent fracture, conduit injury or arterial distortion.Herein, we test patient-specific finite element (FE) modeling as a tool to assess stenting feasibility and investigate clinically relevant risks associated to the percutaneous intervention.Three patients undergoing attempted PPVI due to calcific RVOT conduit failure were enrolled; the calcific RVOT, the aortic root and the proximal CA were segmented on CT scans for each patient. We numerically reproduced RVOT balloon angioplasty to test procedure feasibility and the subsequent RVOT pre-stenting expanding the stent through a balloon-in-balloon delivery system.Our FE framework predicted the occurrence of CA compression in the patient excluded from the real procedure. In the two patients undergoing RVOT stenting, numerical results were consistent with intraprocedural in-vivo fluoroscopic evidences. Furthermore, it quantified the stresses on the stent and on the relevant native structures, highlighting their marked dependence on the extent, shape and location of the calcific deposits. Stent deployment induced displacement and mechanical loading of the calcific deposits, also impacting on the adjacent anatomical structures.This novel workflow has the potential to tackle the analysis of complex RVOT clinical scenarios, pinpointing the procedure impact on the dysfunctional anatomy and elucidating potential periprocedural complications.     

Interleukin-32 plays an essential role in human calcified aortic valve cells

Interleukin-32 (IL-32) is an inflammatory cytokine produced mainly by T, natural killer, and epithelial cells. Previous studies on IL-32 have primarily investigated its proinflammatory properties. The IL-32 also has been described as an activator of the p38 mitogen-activated protein kinase (MAPK) and NF-κB, and induces several cytokines. In this study, we hypothesized that the inflammatory regulators NF-κB, MAP kinase, STAT1, and STAT3 are associated with the expression of the IL-32 protein in human calcified aortic valve cells. This study comprised aortic valve sclerotic patients and control group patients without calcified aortic valve. Increased IL-32 expression in calcified aortic valvular tissue was shown by immunohistochemical staining and western blotting. There was an increase in NF-κB p65 level, p-ERK, p-JNK, and p-p38 MAPK activation underlying IL-32 expression in the study. The level of p-STAT3 but not p-STAT1 was found to be increased in calcified aortic valve tissue. In cultured primary human aortic valve interstitial cells, inhibition of NF-κB or MAPK kinase pathways results in a decrease of IL-32 expression. Treatment of recombinant IL-32 induced the levels of TNF-α, IL-6, IL-1β, and IL-8. Our findings demonstrate that IL-32 may be an important pro-inflammatory molecule involved in calcific aortic valve disease.     

Hemodynamic Changes following Aortic Valve Bypass: A Mathematical Approach

Aortic valve bypass (AVB) has been shown to be a viable solution for patients with severe aortic stenosis (AS). Under this circumstance, the left ventricle (LV) has a double outlet. The objective was to develop a mathematical model capable of evaluating the hemodynamic performance following the AVB surgery. A mathematical model that captures the interaction between LV, AS, arterial system, and AVB was developed. This model uses a limited number of parameters that all can be non-invasively measured using patient data. The model was validated using in vivo data from the literature. The model was used to determine the effect of different AVB and AS configurations on flow proportion and pressure of the aortic valve and the AVB. Results showed that the AVB leads to a significant reduction in transvalvular pressure gradient. The percentage of flow through the AVB can range from 55.47% to 69.43% following AVB with a severe AS. LV stroke work was also significantly reduced following the AVB surgery and reached a value of around 1.2 J for several AS severities. Findings of this study suggest: 1) the AVB leads to a significant reduction in transvalvular pressure gradients; 2) flow distribution between the AS and the AVB is significantly affected by the conduit valve size; 3) the AVB leads to a significant reduction in LV stroke work; and 4) hemodynamic performance variations can be estimated using the model.     

A computational fluid-structure interaction analysis of a fiber-reinforced stentless aortic valve

The importance of the aortic root compliance in the aortic valve performance has most frequently been ignored in computational valve modeling, although it has a significant contribution to the functionality of the valve. Aortic root aneurysm or (calcific) stiffening severely affects the aortic valve behavior and, consequently, the cardiovascular regulation. The compromised mechanical and hemodynamical performance of the valve are difficult to study both 'in vivo' and 'in vitro'. Computational analysis of the valve enables a study on system responses that are difficult to obtain otherwise. In this paper a numerical model of a fiber-reinforced stentless aortic valve is presented. In the computational evaluation of its clinical functioning the interaction of the valve with the blood is essential. Hence, the blood-tissue interaction is incorporated in the model using a combined fictitious domain/arbitrary Lagrange-Euler formulation, which is integrated within the Galerkin finite element method. The model can serve as a diagnostic tool for clinical purposes and as a design tool for improving existing valve prostheses or developing new concepts. Structural mechanical and fluid dynamical aspects are analyzed during the systolic course of the cardiac cycle. Results show that aortic root compliance largely influences the valve opening and closing configurations. Stresses in the delicate parts of the leaflets are substantially reduced if fiber-reinforcement is applied and the aortic root is able to expand.     

Inoperable aortic stenosis in the elderly: benefit from percutaneous transluminal valvuloplasty.

Eight patients with severe symptomatic calcific aortic stenosis were considered to be unsuitable for valve replacement. Four were admitted with pulmonary oedema and three in cardiogenic shock and one had angina at rest. With the use of echocardiographic and radiographic guidance percutaneous transluminal aortic valvuloplasty was carried out. Aortic gradients were reduced by an average of 40%. All four patients who presented with cardiac failure improved immediately and remained well six months later. The patient with angina was symptom free at nine months. Two of the three patients who presented in cardiogenic shock improved immediately and were well nine and three months later. The other patient died four hours after the procedure. Doppler echocardiographic studies showed a slight initial increase in aortic incompetence, but this did not worsen and valvar gradients remained improved three and six months later. Percutaneous valvuloplasty of the aortic valve is an effective therapeutic option in patients with severe calcific aortic stenosis who are unfit for surgery. Its role as an alternative to surgery has not been considered and should be investigated in a controlled clinical trial.     

Ultrasonic Decalcification of Calcified Cardiac Valves and Annuli

Heavily calcified annuli increase the incidence of complications after prosthetic valve replacement—heart block, separation of the aorta or the atrium from the ventricle, late aneurysm formation, paravalvular leak, and haemolysis. An ultrasonic calculus-disintegrator has been developed to remove calcific deposits. The instrument is portable, robust, easily sterilized, inexpensive, and provides nebulized water at the ultrasonic tip which keeps the tissues cool, helps to break up the calculus by cavitation, and washes the calcific debris into the sucker. Preliminary trial on excised calcific valves showed the ultrasound instrument to be capable of removing most forms of calcification. In clinical prosthetic replacement of valves it enabled good clearance of the annulus to be performed in six out of seven cases, in one of which earlier operation had been unsuccessful because of calcification. Two elderly patients with pure calcific aortic stenosis were successfully treated by debridement of the aortic valve with ultrasound.     

A ventricular-vascular coupling model in presence of aortic stenosis

In patients with aortic stenosis, the left ventricular afterload is determined by the degree of valvular obstruction and the systemic arterial system. We developed an explicit mathematical model formulated with a limited number of independent parameters that describes the interaction among the left ventricle, an aortic stenosis, and the arterial system. This ventricular-valvular-vascular (V(3)) model consists of the combination of the time-varying elastance model for the left ventricle, the instantaneous transvalvular pressure-flow relationship for the aortic valve, and the three-element windkessel representation of the vascular system. The objective of this study was to validate the V(3) model by using pressure-volume loop data obtained in six patients with severe aortic stenosis before and after aortic valve replacement. There was very good agreement between the estimated and the measured left ventricular and aortic pressure waveforms. The total relative error between estimated and measured pressures was on average (standard deviation) 7.5% (SD 2.3) and the equation of the corresponding regression line was y = 0.99x - 2.36 with a coefficient of determination r(2) = 0.98. There was also very good agreement between estimated and measured stroke volumes (y = 1.03x + 2.2, r(2) = 0.96, SEE = 2.8 ml). Hence, this mathematical V(3) model can be used to describe the hemodynamic interaction among the left ventricle, the aortic valve, and the systemic arterial system.     

Balloon aortic valvuloplasty as a bridge to aortic valve replacement in a patient with severe calcific aortic stenosis

This case report describes a patient with severe calcific aortic stenosis who was initially considered inoperable because of a very poor left ventricular function and severe pulmonary hypertension. After balloon aortic valvuloplasty, the clinical and haemodynamic status of the patient improved to such an extent that subsequent aortic valve replacement was considered possible and eventually proved to be successful. Balloon aortic valvuloplasty has value as a potential bridge to aortic valve replacement when the risks for surgery are considered to be too high.     

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage^1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease⁴. The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve⁵. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves^6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage¹⁰, bone¹¹ and bladder¹². The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.Download video file.^{(44M, mov)}     

Modification of the Secretion Pattern of Proteases,Inflammatory Mediators,and Extracellular Matrix Proteins by Human Aortic Valve is Key in Severe Aortic Stenosis

One of the major challenges in cardiovascular medicine is to identify candidate biomarker proteins. Secretome analysis is particularly relevant in this search as it focuses on a subset of proteins released by a cell or tissue under certain conditions. The sample can be considered as a plasma subproteome and it provides a more direct approximation to the in vivo situation. Degenerative aortic stenosis is the most common worldwide cause of valve replacement. Using a proteomic analysis of the secretome from aortic stenosis valves we could identify candidate markers related to this pathology, which may facilitate early diagnosis and treatment. For this purpose, we have designed a method to validate the origin of secreted proteins, demonstrating their synthesis and release by the tissue and ruling out blood origin. The nLC-MS/MS analysis showed the labeling of 61 proteins, 82% of which incorporated the label in only one group. Western blot and selective reaction monitoring differential analysis, revealed a notable role of the extracellular matrix. Variation in particular proteins such as PEDF, cystatin and clusterin emphasizes the link between aortic stenosis and atherosclerosis. In particular, certain proteins variation in secretome levels correlates well, not only with label incorporation trend (only labeled in aortic stenosis group) but, more importantly, with alterations found in plasma from an independent cohort of samples, pointing to specific candidate markers to follow up in diagnosis, prognosis, and therapeutic intervention.Degenerative aortic stenosis (AS)¹ is currently the most common cause of valve replacement in Western countries, and a significant increase in its prevalence is expected in the future because of increasing longevity (1). At the same time that our population age increases it can be expected that cardiac valve disease, and AS in particular, will increase in parallel. More and more, clinicians are seeing patients with symptomatic severe AS who are very advanced in age and have severe comorbidities or significant frailty, making operative intervention either impossible or of very high risk in the eyes of the cardiac surgeon. For this reason, the need of new diagnostic and prognostic methods, together with the urgent need of new drugs for therapy, has increased making a correct diagnosis in the early stages of the disease thereby reducing the cost burden to society. Several lines of evidence have demonstrated that degenerative AS is an active process in which inflammation plays a key role. As such, preventative approaches similar to those used in coronary artery disease (CAD) may be also applicable to AS (2, 3, 4, 5, 6). However, recent studies reported no reduction in later states of AS disease using statins, which significantly benefit patients with atherosclerosis (7, 8). Hence, further research is required to elucidate the pathogenic mechanism of this prevalent disease and to identify the similarities and differences in relation to atherosclerosis.Proteomics has emerged as a particularly suitable platform for the nonbiased analysis of proteins involved in the pathogenesis of various diseases, such as AS (9, 10). This type of approach provided the basis for the development of biomarkers to detect patients at risk of developing degenerative AS. Plasma and serum have been the main source used in proteomic studies to identify candidate protein biomarkers, followed by tissue and cell samples. However, the use of plasma and serum is hampered by their complex nature and by the large dynamic range of protein concentrations, which may favor the detection of abundant proteins at the expense of those present at lower concentrations (11, 12). As such, the aortic valve secretome has emerged as an attractive target to further understand the AS pathogenic process. Tissue secretomes provide a more accurate model of the in vivo situation and, by minimizing serum contaminants, they facilitate the detection of low abundance proteins secreted into the blood (13).In the present study, aortic valves from AS patients and nonaffected control subjects were cultured and the secretome analyzed by nLC-MS/MS. The addition of labeled amino acids to the culture media enabled the origin of the secreted proteins to be validated (truly secreted versus serum contaminants) and provided with information related to the dynamics of their synthesis and release from tissue.     

Inside human aortic stenosis: a proteomic analysis of plasma

Valvular aortic stenosis (AS) produces a slowly progressive obstruction in left ventricular outflow track. For this reason, aortic valve replacement is warranted when the valvular stenosis is hemodinamically significant, becoming the most common worldwide cause of aortic valve surgery. Recent epidemiologic studies have revealed an association between degenerative AS and cardiovascular risk factors for atherosclerosis, althought reducing the exposure to such factors and statin therapies both fail to delay or reverse the pathology. Hence, a deeper understanding of the pathophysiology of this disease is required to identify appropriate preventive measures. A proteomic analysis of plasma will permit to know and identify the changes in protein expression induced by AS in this tissue. Using two-dimensional difference gel electrophoresis (2D-DIGE) followed by mass spectrometry (MS), we compared the crude (not pre-fractioned) and pre-fractioned plasma from AS patients and control subjects. We sought to identify plasma proteins whose expression is modified in AS. In addition we investigated if crude plasma presented some alterations in the more abundant proteins since to date, has never been studied before. We also further investigated the link between this disease and atherosclerosis with a view to identifying new potential markers and therapeutic targets.     

Aortic valve stenosis: an active atheroinflammatory process

PURPOSE OF REVIEW: To summarize the current understanding of the pathobiology of aortic valve stenosis and portray the major advances in this field. RECENT FINDINGS: Stenotic aortic valves are characterized by atherosclerosis-like lesions, consisting of activated inflammatory cells, including T lymphocytes, macrophages, and mast cells, and of lipid deposits, calcific nodules, and bone tissue. Active mediators of calcification and cells with osteoblast-like activity are present in diseased valves. Extracellular matrix remodeling, including collagen synthesis and elastin degradation by matrix metalloproteinases and cathepsins, contributes to leaflet stiffening. In experimental animals, hypercholesterolemia induces calcification and bone formation in aortic valves, which can be inhibited by statin treatment. The potential of statins to retard progression of aortic valve stenosis has also been recognized in clinical studies; however, further prospective trials are needed. Angiotensin II-forming enzymes are upregulated in stenotic valves. Angiotensin II may participate in profibrotic progression of aortic valve stenosis and may serve as a possible therapeutic target. SUMMARY: Recent findings regarding the interaction of inflammatory cells, lipids, mediators of calcification, and renin-angiotensin system in stenotic valves support the current opinion of aortic valve stenosis being an actively regulated disease, potentially amenable to targeted molecular therapy. Evidence from prospective clinical studies is eagerly awaited.     

Actinobacillus actinomycetemcomitans endocarditis.

Two patients had infective endocarditis due to Actinobacillus actinomycetemcomitans. One, a 52-year-old woman with a prosthetic aortic valve, was successfully treated with carbenicillin and gentamicin. The other, a 47-year old man with calcific aortic valve disease, required emergency valvectomy and prosthetic valve replacement and responded to a combination of penicillin and gentamicin.     

Cytomegalovirus Seropositivity Is Associated with Increased Arterial Stiffness in Patients with Chronic Kidney Disease

Background

Patients with chronic kidney disease have an increased cardiovascular risk that is not fully explained by traditional risk factors but appears to be related to increased arterial stiffness. Cytomegalovirus (CMV) infection is associated with increased cardiovascular risk although the mechanisms for this are unknown. We examined whether CMV seropositivity was associated with increased arterial stiffness in patients with chronic kidney disease.

Methodology and Principal Findings

In 215 non-diabetic patients with chronic kidney disease, CMV seropositivity was determined using an anti-CMV IgG ELISA. Pulse wave velocity was measured and aortic distensibility assessed in the ascending, proximal descending and distal descending thoracic aorta. Patients seropositive for CMV had a higher pulse wave velocity and lower aortic distensibility at all 3 levels. These differences (except for ascending aortic distensibility) persisted in a subcohort matched for age, gender and renal function, and when the whole cohort was divided into quartiles of age. In multivariable analyses, CMV seropositivity was an independent determinant of pulse wave velocity and proximal and distal descending aortic distensibility.

Conclusions

In patients with chronic kidney disease, CMV seropositivity is associated with increased arterial stiffness and decreased distensibility of the proximal descending and distal aorta. These findings suggest that further research is required to examine CMV as a possible cause of arterial disease and increased cardiovascular risk in patients with CKD and may be relevant more widely for CMV seropositive patients with normal renal function.     

Aortic stenosis is associated with elevated plasma levels of asymmetric dimethylarginine (ADMA).

OBJECTIVES: We tested the hypothesis that the presence of aortic stenosis (AS) is associated with elevation of plasma levels of asymmetric dimethylarginine (ADMA), a physiological inhibitor of nitric oxide synthase, a mediator and marker of endothelial dysfunction and an indicator of incremental cardiovascular risk. BACKGROUND: The presence of aortic sclerosis (ASC), the precursor of AS is independently associated both with endothelial dysfunction, and with incremental coronary event risk. It remains uncertain whether elevations of ADMA levels might mediate endothelial dysfunction in these conditions. METHODS: Forty two consecutive patients referred for echocardiography for evaluation of AS, who had calculated aortic valve areas of <1.4 cm(2) (AS group) were evaluated together with 42 consecutive age-matched referred patients (non-AS group). Plasma ADMA levels were measured by high-performance liquid chromatography (HPLC). Determinants of elevation of plasma ADMA levels were identified via stepwise multiple linear regression analysis. RESULTS: Plasma ADMA levels were not statistically different between the AS and non-AS group (median 0.59 vs 0.54 micromol/L, p=0.13, Mann-Whitney test) on univariate analysis. However, in backward stepwise multiple linear regression, the presence of AS was a significant predictor of elevated ADMA levels (p=0.04, 95% CI=0.001, 0.072). In addition, elevated plasma ADMA levels were also associated with history of atrial fibrillation (p=0.009, 95% CI=0.015, 0.100), and negatively associated with creatinine clearance (p=0.01, 95% CI=-0.002, 0.000), and the use of statin therapy (p=0.01, 95% CI=-0.081, -0.011). CONCLUSIONS: AS is independently associated with elevation of ADMA levels, beyond that implied by "conventional" risk factors for endothelial dysfunction. The clinical status of AS as an incremental marker of cardiovascular risk may reflect ADMA-mediated endothelial dysfunction.     

Polymorphism in exon 6 of the human NT5E gene is associated with aortic valve calcification

ABSTRACT

NT5E encodes ecto-5′-nucleotidase (e5NT, CD73) which hydrolyses extracellular AMP to adenosine. Adenosine has been shown to play a protective role against aortic valve calcification (AVC). We identified two nonsynonymous missense single nucleotide polymorphisms (c.1126A > G, p.T376A and c.1136T > C, p.M379T) in exon 6 of the human NT5E gene. Since both substitutions might affect e5NT activity and consequently alter extracellular adenosine levels, we evaluated the association between NT5E alleles and calcific aortic valve disease in 119 patients (95 patients with AVC and 24 controls). In AVC patients, the frequency of the G allele at c.1126 and the frequency of the GG genotype as well as the frequency of the C allele at c.1136, and the frequencies of CC and TC genotypes tended to be higher as compared to controls. The allele and genotype frequencies in AVC patients and controls were also compared to those calculated from the 1000 Genomes Project data for control individuals of European ancestry (n = 503). We found that the frequency of the C allele at c.1136 is significantly higher in patients with AVC than in the European controls (0.111 vs. 0.054, P = 0.0052). Moreover, e5NT activity in aortic valves showed a trend toward lower levels in AVC patients with CC and TC genotypes than in those with the TT genotype. Our findings indicate that the genetic polymorphism of NT5E may contribute to the pathogenesis of calcific aortic valve disease and that the C allele of SNP c.1136 is associated with an increased risk of AVC.