The relationship between severity of calcific aortic stenosis and serum uric acid levels

Uric acid promotes aortic valve calcification via mediating valve interstitial cell osteogenic differentiation and endothelial dysfunction

Aortic valve calcification is a lethal valvular heart disease lacking effective drug therapy. However, whether uric acid is involved in the development of aortic valve calcification is unclear. Two-sample Mendelian randomization (MR) analyses confirmed the causal relationship between uric acid and valvular heart disease. Uric acid levels were assessed in aortic valve tissue from patients with/without aortic valve calcification. To investigate the impact of hyperuricemia on aortic valve calcification, apolipoprotein E knockout (ApoE-/-) mice fed a high-fat diet (HFD) were also given an adenine diet, with some receiving allopurinol in their drinking water. RNA sequencing was performed on valve interstitial cells (VICs) and endothelial cells (VECs) with/without uric acid. MR analysis has revealed a causal effect of uric acid levels on valvular heart disease. Furthermore, our clinical data indicate a positive correlation between elevated serum uric acid levels and aortic valve calcium score. Specifically, uric acid levels were upregulated in calcified valves. In ApoE-/- mice, an adenine-diet-induced hyperuricemia accelerated aortic valve calcification. RNA sequencing analysis demonstrated that uric acid-promoted osteogenic differentiation, primarily through the activation of hypoxia-inducible factor-1alpha (HIF-α). Additionally, uric acid impaired endothelial barrier function by activating HIF-α, resulting in increased macrophage infiltration in ApoE-/- mice. Inhibiting HIF-1α suppressed osteogenic differentiation and reduced endothelial injury both in vitro and in vivo in the presence of uric acid. This study reveals a new role of hyperuricemia in aortic valve calcification, suggesting uric acid-lowering drugs or HIF-1α inhibition as potential treatments for associated aortic valve calcification.

Epidemiological study of calcified aortic valve stenosis in a Chinese community population

BACKGROUND AND AIMS

Due to the ageing global population, calcified aortic valve disease is currently the most common cardiac valve disorder. This study aimed to investigate the prevalence and the risk factors for calcified aortic valve stenosis (CAVS), and develop a prediction model for predicting CAVS risk.

METHODS AND RESULTS

This study was derived from the cross-sectional baseline survey of the PRECISE study (NCT03178448). The demographic, clinical and laboratory information of each participant was obtained. Univariable and multivariable logistic regression models were used to determine CAVS risk factors. A prediction model for predicting CAVS risk based on risk factors was developed and the result was performed by nomogram. The discrimination of the prediction model was assessed by receiver operating characteristic curve analysis. The degree of fitting for the prediction model was assessed by calibration curve analysis. A total of 3067 participants (1427 men and 1640 women) were included. The prevalence of CAVS among those aged below 60 years old, 60-70 years old and over 70 years old was 4.1%, 10.3% and 21.9%, respectively. Multivariable regression analysis revealed that age (OR: 1.099; 95% CI: 1.076 to 1.123, p<0.001), pulse pressure (OR: 1.020; 95% CI: 1.009 to 1.031, p<0.001), uric acid (OR: 1.003; 95% CI: 1.001 to 1.004, p<0.001), glycosylated haemoglobin (HbA1c) (OR: 1.152; 95% CI: 1.028 to 1.292, p=0.015) and lipoprotein(a) (OR: 1.002; 95% CI: 1.001 to 1.002, p<0.001) were independent risk factors for CAVS. High-density lipoprotein cholesterol (HDL-C) was a protective factor for CAVS (OR: 0.539; 95% CI: 0.349 to 0.831, p=0.005). The prediction model including the above risk factors showed a risk prediction of CAVS with good discrimination. The area under the curve value was found to be 0.743 (95% CI: 0.711 to 0.775).

CONCLUSION

CAVS is currently prevalent in the elderly Chinese population. Age, pulse pressure, HbA1c, lower-level HDL-C, lipoprotein(a) and uric acid are the independent risk factors for CAVS.

The Impact of Monocyte to High-Density Lipoprotein Cholesterol Ratio on All-Cause and Cardiovascular Mortality in Patients with Transcatheter Aortic Valve Replacement

BACKGROUND

Inflammation plays a significant role in the pathogenesis of aortic stenosis. This study aimed to investigate the prognostic value of the monocyte-HDL cholesterol ratio (MHR), a new inflammatory marker, in severe aortic stenosis (AS) patients who underwent transcatheter aortic valve replacement (TAVR).

METHODS

A total of 125 patients with severe AS who underwent TAVR were assessed. Clinical, echocardiographic and laboratory data relevant to the research were retrospectively obtained from the patients' records. The MHR was determined by dividing the absolute monocyte count by the HDL-C value. The primary endpoints were overall and cardiovascular mortality.

RESULTS

During a median follow-up time of 39 months, primary endpoints were developed in 51 (40.8%) patients (overall mortality) and 21 (16.8%) patients (cardiovascular mortality). A receiver operating characteristic (ROC) analysis showed that by using a cut-off level of 16.16, the MHR predicted the all-cause mortality with a sensitivity of 50.9% and specificity of 89.1%. In predicting cardiovascular mortality, the MHR exhibited a sensitivity of 80.9% and specificity of 70.1% when a cut-off level of 13.56 was used. In the multivariate analysis, the MHR (p < 0.0001; 95% CI: 1.06-1.15) and atrial fibrillation (p = 0.018; 95% CI: 1.11-3.38) were found to be significant predictors of overall mortality.

CONCLUSIONS

This study showed a significant elevation in the MHR among patients who experienced all-cause and cardiovascular mortality and this ratio emerged as an independent predictor of all-cause death in patients with severe AS undergoing TAVR.

A retrospective observational study of serum uric acid and in-hospital mortality in acute type A aortic dissection

There is currently insufficient evidence of correlation between on-admission serum uric acid and in-hospital mortality of patients with acute type A aortic dissection. Thus, this study analysed the relation between serum uric acid and in-hospital deaths in patients with acute type A aortic dissection. A total of 1048 patients with acute type A aortic dissection participated in this study between January 2010 and December 2018. The independent variable was on-admission serum uric acid, whilst the dependent variable was in-hospital deaths. The covariates of the study included patient age, gender, body mass index, smoking status, hypertension, diabetes, Marfan syndrome, bicuspid aortic valve, chronic renal insufficiency, stroke, atherosclerosis, time to presentation, systolic blood pressure, diastolic blood pressure, aortic diameter, aortic regurgitation, abdominal vessel involvement, arch vessel involvement, ejection fraction value, laboratory parameters, symptom, coronary malperfusion, mesenteric malperfusion, cerebral malperfusion, hypotension/shock, cardiac tamponade and operation status. The mean age of the sample was 50.17 ± 11.47 years, with approximately 24.24% of the participants being female. After analysis, it was found that the admission serum uric acid of patients with acute type A aortic dissection was positively correlated with in-hospital death (OR = 1.04, 95% CI 1.02–1.06). Subsequently, a non-linear relationship was determined between admission serum uric acid (point 260 µmol/L) and in-hospital mortality for patients with acute type A aortic dissection. The effect sizes and confidence intervals of the right (serum uric acid > 260 µmol/L) and left (serum uric acid ≤ 260 µmol/L) aspects of the inflection point were 1.04 (1.02–1.05) and 1.00 (0.99–1.02), respectively. Furthermore, subgroup analysis indicated a stable relationship between serum uric acid and in-hospital mortality, whilst an insignificant difference was found for the interactions between different subgroups. Overall, a non-linear correlation was determined between admission serum uric acid and in-hospital mortality of patients with acute type A aortic dissection. When serum uric acid > 260 µmol/L, it showed a positive correlation with in-hospital mortality.

The mechanistic pathways of oxidative stress in aortic stenosis and clinical implications

Despite the elucidation of the pathways behind the development of aortic stenosis (AS), there remains no effective medical treatment to slow or reverse its progress. Instead, the gold standard of care in severe or symptomatic AS is replacement of the aortic valve. Oxidative stress is implicated, both directly as well as indirectly, in lipid infiltration, inflammation and fibro-calcification, all of which are key processes underlying the pathophysiology of degenerative AS. This culminates in the breakdown of the extracellular matrix, differentiation of the valvular interstitial cells into an osteogenic phenotype, and finally, calcium deposition as well as thickening of the aortic valve. Oxidative stress is thus a promising and potential therapeutic target for the treatment of AS. Several studies focusing on the mitigation of oxidative stress in the context of AS have shown some success in animal and in vitro models, however similar benefits have yet to be seen in clinical trials. Statin therapy, once thought to be the key to the treatment of AS, has yielded disappointing results, however newer lipid lowering therapies may hold some promise. Other potential therapies, such as manipulation of microRNAs, blockade of the renin-angiotensin-aldosterone system and the use of dipeptidylpeptidase-4 inhibitors will also be reviewed.

Cardiac structural and functional abnormalities in primary hyperparathyroidism

PURPOSE

Studies on cardiac structural and functional abnormalities in primary hyperparathyroidism (PHPT) have yielded conflicting and inconsistent results. In this prospective case-control study, we sought to compare cardiac structure and function in symptomatic PHPT patients and controls.

METHODS

One hundred consecutive symptomatic PHPT patients and 113 matched controls underwent echocardiographic evaluation by the same operator.

RESULTS

Left ventricular mass index (LVMI) was significantly higher in patients as compared to controls, (median of 90.95 g/m² vs 86.5 g/m², p = 0.041). Patients had significantly lower early trans-mitral diastolic flow (E velocity) as compared to controls (57.13 ± 14.88 vs 64.76 ± 15.45 cm/s, p < 0.001). Patients also had significantly lower early to late mitral annular velocity (E/A) as compared to controls (0.98 ± 0.37 vs 1.10 ± 0.34, p 0.013). Patients had higher frequency of aortic valve calcification (29% vs 2.65%, p < 0.001), mitral annular calcification (23% vs. 4.42%, p < 0.001), myocardial and septal calcifications (25% vs none, p < 0.001) as compared to controls. Serum PTH, calcium and uric acid significantly correlated with calcifications. Serum calcium showed a negative correlation with E/A ratio.

CONCLUSIONS

Symptomatic patients with PHPT have substantial cardiac structural and functional abnormalities. These abnormalities include elevated LVMI, diastolic dysfunction, and aortic valve, mitral annular, septal and myocardial calcifications. We strongly suggest and conclude that the evaluation of PHPT patients should not only include traditional end organs like bones and kidneys but also the cardiovascular system in the form of echocardiography to detect subclinical cardiac dysfunction so that the cardiovascular health of such patients can be optimized.

Gout and Progression of Aortic Stenosis

BACKGROUND

Patients with aortic stenosis are nearly twice as likely to have a diagnosis of gout compared with individuals without aortic valve disease.

METHODS

This retrospective study evaluated consecutive adults age ≥65 years with aortic stenosis between December 2012 and November 2016 who underwent at least 2 transthoracic echocardiograms (TTEs) separated by at least 1 year. Severe aortic stenosis was defined as any combination of an aortic valve peak velocity ≥4.0 m/sec, mean gradient ≥40 mm Hg, aortic valve area ≤1 cm2, or decrease in left ventricular ejection fraction as a result of aortic stenosis.

RESULTS

Of the 699 study patients, gout was present in 73 patients (10%) and not found in 626 patients (90%). Median follow-up was 903 days [552-1302] for patients with gout and 915 days [601-1303] for patients without gout (P = 0.60). The presence of severe aortic stenosis on follow-up transthoracic echocardiogram was more frequent in patients with gout compared to those without gout (74% vs 54%, P = 0.001; hazard ratio [HR] 1.45 [1.09-1.93]), even among the 502 patients without severe aortic stenosis at baseline (63% vs 39%, P = 0.003; hazard ratio 1.43 [1.07-1.91]). Gout remained associated with the development of severe aortic stenosis after multivariable adjustment (adjusted hazard ratio [aHR] 1.46 [1.03-2.08], P = 0.03). The annualized reduction in aortic valve area was numerically greater in the group with gout compared with the group without gout (-0.10 cm2/y [-0.18, -0.03] vs -0.08 cm2/y [-0.16, -0.01], P = 0.09); annualized change in peak velocity and mean gradient did not differ between groups.

CONCLUSIONS

Progression to severe aortic stenosis was more frequent in patients with gout compared with those without gout, supporting the hypothesis that gout is a risk factor for aortic stenosis.

Serum uric acid level is associated with the incidence of heterotopic ossification following elbow trauma surgery

BACKGROUND

Heterotopic ossification (HO) is a common complication after surgery for elbow trauma. Uric acid is the end product of purine metabolism and has several physiological and pathogenic roles. However, the relationship between HO and uric acid has not been explored. This retrospective study aimed to assess the relationship between HO and serum uric acid (SUA).

MATERIAL AND METHODS

We retrospectively reviewed data from 155 patients undergoing elbow trauma surgery in our hospital between January 2013 and December 2018. One hundred patients were included according to the inclusion criteria. They were divided into 2 groups according to the presence or absence of HO, and the SUA level was compared between groups using the independent samples t test. The optimal prognostic cutoff value was obtained using the maximum value of the Youden index.

RESULTS

The SUA level was significantly higher in the HO group than in the non-HO group (362.0 ± 87.4 μmol/L vs. 318.3 ± 87.0 μmol/L; P < .05). Using the maximum value of Youden index, 317.5 μmol/L was determined to be the optimal SUA cutoff value for the prediction of HO, with a sensitivity of 68.75% (95% confidence interval [CI], 54.67%-80.05%) and specificity of 55.77% (95% CI, 42.34%-68.40%).

CONCLUSIONS

Our study was the first to find that the high SUA level is a risk factor for HO of the elbow joint after trauma. Moreover, 317.5 μmol/L is the SUA threshold predicting the occurrence and development of HO of the elbow, with high sensitivity and specificity.

Periaortic adipose tissue volume is associated with sclerotic changes in the adjacent aortic valve

Aortic sclerosis is associated with increased cardiovascular mortality and morbidity. Numerous studies have shown that visceral adiposity is associated with development of atherosclerosis, especially in the adjacent vascular wall. Considering the similar pathophysiology of aortic sclerosis and atherosclerosis, it can be hypothesized that visceral adipose tissue adjacent to aortic valve may be associated with aortic sclerosis. In this study, we investigated the relationship between periaortic adipose tissue volume and sclerotic changes in the adjacent aortic valve. In this retrospective study, 80 patients with a concurrent MSCT and echocardiography in the last 6 months were enrolled. Echocardiographic examinations were retrospectively evaluated regarding the presence of aortic sclerosis. Periaortic adipose tissue volume was calculated on a computer assisted work station (Leonardo Workstation, Siemens, Erlangen, Germany) by an experienced radiologist. Patient group (61.63 ± 8.55 years and 50% male) and the control group (61.45 ± 5.68 years, 50% male) each consisted 40 participants. Patient group had significantly higher BUN (42.50 (15.00-211.00) vs. 34.00 (12.00-107.00) mg/dL, p = 0.003), uric acid (5.40 (3.40-14.70) vs. 4.30 (2.30-6.70) ng/mL, p = 0.005) and LDL-C levels (121.50 (60.00-215.00) vs. 86.50 (49.00-209.00) mg/dL, p = 0.001) when compared to control group. Patient group had also significantly higher periaortic adipose tissue volume (32.45 (11.70-51.23) vs. 16.00 (6.29-32.96) ml, p < 0.001). Multivariate regression analysis revealed that periaortic adipose tissue volume was independently associated with the presence of aortic sclerosis (OR 0.241, 95% CI 0.143-0.946, p = 0.001). In this study, we demonstrated for the first time that periaortic adipose tissue volume was independently associated with the presence of sclerotic changes in the adjacent aortic valve.

Impact of gout on in-hospital outcomes of acute coronary syndrome-related hospitalizations and revascularizations: Insights from the national inpatient sample

BACKGROUND

Previous studies have established a role of gout in predicting risk and prognosis of cardiovascular diseases. However, large-scale data on the impact of gout on inpatient outcomes of acute coronary syndrome (ACS)-related hospitalizations and post-revascularization is inadequate.

AIM

To evaluate the impact of gout on in-hospital outcomes of ACS hospitalizations, subsequent healthcare burden and predictors of post-revascularization inpatient mortality.

METHODS

We used the national inpatient sample (2010-2014) to identify the ACS and gout-related hospitalizations, relevant comorbidities, revascularization and post-revascularization outcomes using the ICD-9 CM codes. A multivariable analysis was performed to evaluate the predictors of post-revascularization in-hospital mortality.

RESULTS

We identified 3144744 ACS-related hospitalizations, of which 105198 (3.35%) also had gout. The ACS-gout cohort were more often older white males with a higher prevalence of comorbidities. Coronary artery bypass grafting was required more often in the ACS-gout cohort. Post-revascularization complications including cardiac (3.2% vs 2.9%), respiratory (3.5% vs 2.9%), and hemorrhage (3.1% vs 2.7%) were higher whereas all-cause mortality was lower (2.2% vs 3.0%) in the ACS-gout cohort (P < 0.001). An older age (OR 15.63, CI: 5.51-44.39), non-elective admissions (OR 2.00, CI: 1.44-2.79), lower household income (OR 1.44, CI: 1.17-1.78), and comorbid conditions predicted higher mortality in ACS-gout cohort undergoing revascularization (P < 0.001). Odds of post-revascularization in-hospital mortality were lower in Hispanics (OR 0.45, CI: 0.31-0.67) and Asians (OR 0.65, CI: 0.45-0.94) as compared to white (P < 0.001). However, post-operative complications significantly raised mortality odds. Mean length of stay, transfer to other facilities, and hospital charges were higher in the ACS-gout cohort.

CONCLUSION

Although gout was not independently associated with an increased risk of post-revascularization in-hospital mortality in ACS, it did increase post-revascularization complications.

Serum uric acid level predicts adverse outcomes after myocardial revascularization or cardiac valve surgery

Background

High levels of serum uric acid have been associated with adverse outcomes in cardiovascular diseases such as myocardial infarction and heart failure. The aim of the current study was to evaluate the prognostic role of serum uric acid levels in patients undergoing cardiac rehabilitation after myocardial revascularization and/or cardiac valve surgery.

Design

We performed an observational prospective cohort study.

Methods

The study included 1440 patients with available serum uric acid levels, prospectively followed for 50 ± 17 months. Mean age was 67 ± 11 years; 781 patients (54%) underwent myocardial revascularization, 474 (33%) cardiac valve surgery and 185 (13%) valve-plus-coronary artery by-pass graft surgery. The primary endpoints were overall and cardiovascular mortality while secondary end-points were combined major adverse cardiac and cerebrovascular events.

Results

Serum uric acid level mean values were 286 ± 95 µmol/l and elevated serum uric acid levels (≥360 µmol/l or 6 mg/dl) were found in 275 patients (19%). Overall mortality (hazard ratio = 2.1; 95% confidence interval: 1.5–3.0; p < 0.001), cardiovascular mortality (hazard ratio = 2.0; 95% confidence interval: 1.2–3.2; p = 0.004) and major adverse cardiac and cerebrovascular events rate (hazard ratio = 1.5; 95% confidence interval: 1.0–2.0; p = 0.019) were significantly higher in patients with elevated serum uric acid levels, even after adjustment for age, gender, arterial hypertension, diabetes, glomerular filtration rate, atrial fibrillation and medical therapy. Moreover, strong positive correlations between serum uric acid level and probability of overall mortality ( p < 0.001), cardiovascular mortality ( p < 0.001) and major adverse cardiac and cerebrovascular events ( p = 0.003) were found.

Conclusions

Serum uric acid levels predict mortality and adverse cardiovascular outcome in patients undergoing myocardial revascularization and/or cardiac valve surgery even after the adjustment for age, gender, arterial hypertension, diabetes, glomerular filtration rate and medical therapy.

Association Between Gout and Aortic Stenosis

BACKGROUND

An independent association between gout and coronary artery disease is well established. The relationship between gout and valvular heart disease, however, is unclear. The aim of this study was to assess the association between gout and aortic stenosis.

METHODS

We performed a retrospective case-control study. Aortic stenosis cases were identified through a review of outpatient transthoracic echocardiography (TTE) reports. Age-matched controls were randomly selected from patients who had undergone TTE and did not have aortic stenosis. Charts were reviewed to identify diagnoses of gout and the earliest dates of gout and aortic stenosis diagnosis.

RESULTS

Among 1085 patients who underwent TTE, 112 aortic stenosis cases were identified. Cases and nonaortic stenosis controls (n = 224) were similar in age and cardiovascular comorbidities. A history of gout was present in 21.4% (n = 24) of aortic stenosis subjects compared with 12.5% (n = 28) of controls (unadjusted odds ratio 1.90, 95% confidence interval 1.05-3.48, P = .038). Multivariate analysis retained significance only for gout (adjusted odds ratio 2.08, 95% confidence interval 1.00-4.32, P = .049). Among subjects with aortic stenosis and gout, gout diagnosis preceded aortic stenosis diagnosis by 5.8 ± 1.6 years. The age at onset of aortic stenosis was similar among patients with and without gout (78.7 ± 1.8 vs 75.8 ± 1.0 years old, P = .16).

CONCLUSIONS

Aortic stenosis patients had a markedly higher prevalence of precedent gout than age-matched controls. Whether gout is a marker of, or a risk factor for, the development of aortic stenosis remains uncertain. Studies investigating the potential role of gout in the pathophysiology of aortic stenosis are warranted and could have therapeutic implications.

Prevalence of birefringent crystals in cardiac and prostatic tissues, an observational study

INTRODUCTION

The prevalence of urate crystals in residual tissue samples from coronary arteries, aortic valves and prostate glands was assessed.

METHODS

Alcohol-fixed coronary arteries from 55 explanted hearts, alcohol-fixed aortic valves collected from 75 valve replacement surgeries and 40 frozen, unfixed prostate specimens resected during cancer surgery were examined for birefringent crystals with polarising microscopy.

RESULTS

In the 55 explanted hearts, 6 (10.9%) contained a coronary artery with birefringent crystals. One of the 75 aortic valves (1.4%) contained negatively and positively birefringent crystals. Nineteen of the 40 (47.5%) prostates contained birefringent crystals.

CONCLUSIONS

We found that a remarkable percentage of coronary arteries and prostate specimens contained birefringent crystals. Crystal presence is an obvious prerequisite for possible crystal induced-inflammation in these tissues, just as similar crystals elicit a gouty inflammatory cascade in synovial joints. Further studies are necessary to determine whether urate crystals may play this role in these tissues and, if so, to establish whether urate-lowering therapy may be beneficial in prostatitis and coronary disease.

Relationship of serum uric Acid level and angiographic severity of coronary artery disease in male patients with acute coronary syndrome

Background and objective: The association between serum uric acid and ischemic heart disease remains controversial and it has not yet been established as cardiovascular risk factor. Our objective was to study the association of serum uric acid level with angiographic severity of coronary artery disease in men with acute coronary syndrome (ACS).

Methods: This cross-sectional study was conducted on 100 consecutive male patients presenting with ACS at Punjab Institute of Cardiology. Hyperuricemia was defined as serum uric acid level > 6.5 mg/dl. Severity of ischemic heart disease was assessed on the basis of Gensini score, number of diseased vessels, critical lesions and total occlusions on coronary angiogram.

Results: Mean age of normouricemic group (n=59) was 52.62 ± 9.46 years and mean age of hyperuricemic group (n=41) was 50.52 ± 9.40 years (p=0.273). Mean uric acid level; normouricemic group (4.75 ± 1.05), hyperuricemic group (7.61 ± 1.24), p<0.001. Mean Gensini score; normouricemic group (22.15 ± 21.52), hyperuricemic group (35.69 ± 26.80). Mann Whitney U test was applied to compare the Gensini score of two groups and it showed statistically significant difference (p value <0.006). Critical lesions, total occlusions and multi-vessel disease were more frequent in hyperuricemic group but statistically significant difference was found only for total occlusions (p=0.013) and critical lesions (p=0.046).

Conclusions: Hyeruricemia is associated with higher Gensini score and more frequent total occlusions and critical lesions in men presenting with acute coronary syndrome.

Gastrointestinal complications after open heart surgery: incidence and determinants of risk factors

Acute mesenteric ischemia is a rare but serious complication of open heart surgery. Between January 2009 and January 2012, 1360 adult patients underwent open heart surgery with cardiopulmonary bypass at our institution; 29 patients presented gastrointestinal complications. Eight patients developed acute mesenteric ischemia and all of them died. Significant predictors of the complication were New York Heart Association functional class III/IV, history of extensive atherosclerosis and chronic renal failure, acute renal failure following surgery, low cardiac output, use of 2 or more vasoconstrictor drugs, prolonged mechanical ventilation, and multiorgan failure. Atherosclerosis is a multisystemic disease that affects several organs. Radiologic evaluation of mesenteric arterial system should be performed in high-risk patient populations. Perioperative percutaneous and open vascular procedures will reduce the risk of acute mesenteric ischemia that may develop after cardiac surgery and consequent morbidity and mortality rates.