'Pseudo' coronary graft stenosis from radial artery spasm.
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Coronary Artery Bypass↗
Biomedical subjects
B Buxton
Publications and source records attributed to B Buxton.
Drug design by machine learning: support vector machines for pharmaceutical data analysis.
We show that the support vector machine (SVM) classification algorithm, a recent development from the machine learning community, proves its potential for structure-activity relationship analysis. In a benchmark test, the SVM is compared to several machine learning techniques currently used in the field. The classification task involves predicting the inhibition of dihydrofolate reductase by pyrimidines, using data obtained from the UCI machine learning repository. Three artificial neural networks, a radial basis function network, and a C5.0 decision tree are all outperformed by the SVM. The SVM is significantly better than all of these, bar a manually capacity-controlled neural network, which takes considerably longer to train.
Algorithms↗
Angina pectoris and coronary artery disease in severe isolated valvular aortic stenosis.
BACKGROUND: Angina pectoris has long been recognised as one of the principal symptoms of severe aortic valve stenosis (AS), even in patients without significant coronary artery disease (CAD). However, controversy exists concerning the prevalence of angina pectoris and associated CAD in such patients. OBJECTIVE: To determine the prevalence of CAD detectable by angiography and its relation to angina pectoris and coronary risk factors in patients with severe AS. PATIENTS AND METHODS: All patients with symptomatic AS who had undergone aortic valve replacement and preoperative cardiac catheterisation at the Austin and Repatriation Medical Centre between 1 January 1986 and 31 May 1996 were retrospectively analysed. Those patients with multiple valve disease, aortic regurgitation of grade 2 or more in severity, or who had had prior coronary artery or valve surgery were excluded from this analysis. RESULTS: A total of 328 consecutive patients with severe AS (242 men and 86 women; mean age 72 years, range 39-84 years) were studied. Significant CAD (reduction in luminal diameter > or = 50%) was found in 162 patients (49.4%). Typical angina was present in 74.7% of these 162 patients but it was also found in 44.6% of the 166 patients without obstructive CAD. Of the patients without angina (n = 133), 30.8% had significant CAD. By multivariate logistic regression, we have identified seven significant predictors for CAD among severe AS patients. Five factors increased risk. Expressed as odds ratio with 95% confidence interval, these included: (i) age in years (1.07; 1.04-1.11, P = 0.001); (ii) male gender (2.09; 1.14-3.80, P = 0.016); (iii) angina pectoris (3.19; 1.89-5.37, P < 0.001); (iv) history of myocardial infarction (2.87; 1.38-5.97, P = 0.005); and (v) peripheral vascular disease (2.28; 1.28-4.05, P = 0.005). Factors associated with decreased likelihood of CAD were serum high density lipoprotein (HDL) cholesterol (0.58; 0.34-0.71, P = 0.002) and peak systolic gradient across the aortic valve (0.97; 0.95-0.99, P = 0.0113). CONCLUSION: Coronary arteriography can probably be omitted for a patient with severe AS if that patient has no symptoms of angina and has no risk factors known to increase its incidence.
Journal Article↗
Data analysis for the National Cardiac Surgery Database.
The planned Australian National Cardiac Surgery Database is likely to have a number of positive outcomes, including increased patient satisfaction, improved quality assurance and increased economic efficiency. In relation to cardiac surgery, performance indicators associated with the commonly performed procedure of coronary artery bypass surgery will be used for peer review and to measure outcomes. Several different risk-adjusted models are available for analysing national databases. However, the potential weaknesses of database analysis are lack of both compliance and data validity. A number of other major issues, such as location of the data analysis centre, who will hold authority over data accuracy, and the security of and access to the Database, must also be considered when setting up the National Database. Overall, however, the benefits of a national database will be enormous. Cardiologists and cardiac surgeons will benefit from a disease-based registry with shared common definitions. In addition, the provision of such a database will represent a crucial step towards developing national strategies for treating heart disease.
Journal Article↗
Prevalence and prediction of calcification and plaques in radial artery grafts by ultrasound.
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Adult↗
[Early outcome with the Alfieri mitral valve repair].
OBJECTIVES: Mitral regurgitation in cases of prolapse of the anterior leaflet, posterior leaflet with calcified annulus, or prolapse of both leaflets is thought to be difficult to repair. The Alfieri repair has been developed to address these conditions. METHODS: Seven patients (four men and three women, mean age 71 +/- 9 years) underwent the Alfieri repair for mitral regurgitation at Austin and Repatriation Medical Centre between January 1999 and December 1999. The mechanism of mitral regurgitation was prolapse of the posterior leaflet with calcified annulus in one patient, prolapse of the anterior leaflet in two, and prolapse of both leaflets in four. Mitral regurgitation before operation was severe in all patients. The Cosgrove ring was used in all patients. Four patients underwent combined operation, coronary artery bypass surgery in three and tricuspid annuloplasty in one. RESULTS: There was no hospital death. Two patients had postoperative complications, transient ischemic attack in one patient and rapid atrial fibrillation in one. The mean hospital stay was 11.3 +/- 8.7 days. Mitral regurgitation after operation was mild in five patients and trivial in two. Mean pressure gradient of the transmitral valve was 4.0 +/- 1.4 mmHg. CONCLUSIONS: The Alfieri mitral valve repair is a simple and satisfactory technique to repair mitral regurgitation in selected patients. Long-term follow-up is required to evaluate the durability of this technique.
Aged↗
Comparative histopathology of radial artery versus internal thoracic artery and risk factors for development of intimal hyperplasia and atherosclerosis.
BACKGROUND: In this study, we examined the comparative histopathology, morphometry, and risk factors for the development of intimal hyperplasia and atherosclerosis in the radial artery (RA) and the internal thoracic artery (ITA). METHODS AND RESULTS: Paired specimens of RAs and ITAs, obtained from 150 patients who underwent CABG, were evaluated with histopathology; 110 pairs of arteries were suitable for morphometric analysis. The severity of disease was evaluated on the basis of percentage of luminal narrowing, intimal thickness index, and intima-to-media ratio. Risk factors were determined with stepwise linear regression. Intimal hyperplasia was seen in 141 RAs (94%) and 103 ITAs (69%) (P<0.001). Atherosclerosis was seen in 5% of RAs and 0.7% of ITAs (P=0.04). Medial calcification was found only in RAs (20 of 150, 13.3%) (P<0.001). Morphometric analysis showed that compared with ITAs, RAs had a significantly higher intimal area, medial area, percentage of luminal narrowing, intimal thickness index, and intima-to-media ratio (all P<0.001) Factors found to be significant (P<0.05) predictors of the 3 severity indices of intimal hyperplasia, including atherosclerosis, in RAs were peripheral vascular disease, smoking, age, and diabetes. Risk factors for intimal hyperplasia in ITAs were age and smoking. CONCLUSIONS: The RA is more likely to have atherosclerosis, intimal hyperplasia, and medial calcification than the ITA. Morphometric analysis indices showed marked differences between the RA and the ITA. Care should be taken when selecting the RA as a conduit in CABG, particularly in patients who are elderly, diabetic, smoke, or have peripheral vascular disease.
Adult↗
The aetiology and pathogenesis of cardiopulmonary bypass-associated metabolic acidosis using polygeline pump prime.
OBJECTIVE: The pathogenesis of the metabolic acidosis of cardiopulmonary bypass (CPB) is not fully understood. New quantitative methods of acid-base balance now make it possible to describe it more clearly. Accordingly, we studied acid-base changes during CPB with polygeline pump prime and defined and quantified the factors which contribute to metabolic acidosis. DESIGN: Prospective cohort study. SETTING: Tertiary institution. PARTICIPANTS: 10 cardiac bypass graft surgery patients. INTERVENTIONS: Sampling of arterial blood at four time intervals: post-induction, on CPB during cooling and rewarming, and at skin closure. Measurement of serum Na+, K+, Mg++, Ca++, Cl-, bicarbonate, and phosphate concentrations, arterial blood gases, and serum albumin, lactate, and pyruvate concentrations at each collection point. Analysis of findings according to quantitative physicochemical principles, including calculation of the strong ion difference apparent, the strong ion difference effective, and the strong ion gap (SIG). MEASUREMENTS AND MAIN RESULTS: All patients developed a mild metabolic acidosis. The median serum standard bicarbonate concentration decreased from 25.0 mEq/l post-induction to 22.3 mEq/l at cooling and 22.2 mEq/l at rewarming (p < 0.05). The standard base excess decreased from a median of 1.55 mEq/l prior to CPB, to -2.50 mEq/l at cooling, -1.65 mEq/l at rewarming and, -0.85 mEq/l at skin closure (p < 0.001). This mild metabolic acidosis occurred despite a decrease in the median serum lactate concentration from 3.20 mEq/l post-induction to 1.83, 1.80, and 1.58 mEq/l at the three other time points. The increase in the median serum chloride concentration from 104.9 mEq/l post induction to 111.0, 111.1, and 110.0 mEq/l at the subsequent time points (p < 0.0001) was the main cause of the acidosis. There was also a significant increase in the SIG of 3.8 mEq/l at cooling and rewarming (p < 0.0001), suggesting a role for other unmeasured anions (polygeline) in the genesis of this acidosis. CONCLUSIONS: Using quantitative biophysical methods, it can be demonstrated that, in patients receiving a pump prime rich in chloride and polygeline, the metabolic acidosis of CPB is mostly due to iatrogenic increases in serum chloride concentration and unmeasured strong anions (SIG). Its development is partially attenuated by iatrogenic hypoalbuminaemia. Changes in lactate concentrations did not play a role in the development of metabolic acidosis in our patients.
Acid-Base Equilibrium↗
Passive ventricular constraint amends the course of heart failure: a study in an ovine model of dilated cardiomyopathy.
OBJECTIVE: Dilated cardiomyopathy (DCM) is associated with a progressive deterioration in cardiac function. We hypothesised that some of the deleterious effects of DCM could be reduced by mechanically limiting the degree of cardiac dilatation. METHODS: A Transonic 20A cardiac output (CO) flow-probe was implanted in the pulmonary artery of 12 adult (52 +/- 4 kg) sheep. Early heart failure was created by rapid right ventricular (RV) pacing for 21 days at a rate which resulted in an initial 10% decrease in CO (to a maximum of 190 bpm). A custom polyester jacket (Acorn Cardiovascular, St Paul, MN) was then placed, via a partial lower sternotomy, on the ventricular epicardium of all sheep. Animals were randomised either to jacket retention (wrap) or removal (sham). Pacing was recommenced at a higher rate (that initiated a further 10% decrease in CO) for 28 days. Haemodynamic and echocardiographic parameters were determined at baseline, implant and at termination. RESULTS: At termination, the left ventricular fractional shortening was significantly higher (p = 0.03), the degree of mitral valve regurgitation lower (scaled 0-3) (p = 0.03) and the left ventricular long axis area smaller (p = 0.02) in the wrap animals compared with sham. CONCLUSIONS: In this model of heart failure, ventricular constraint with a polyester jacket diminished the deterioration in cardiac function associated with progressive dilated cardiomyopathy. These results suggest that maintainance of a more normal cardiac size and shape may be beneficial in patients with dilated cardiomyopathy.
Animals↗
Role of the splanchnic circulation in acid-base balance during cardiopulmonary bypass.
OBJECTIVE: The role of the splanchnic circulation in the development of the metabolic acidosis of cardiopulmonary bypass (CPB) is not fully understood. New quantitative methods of acid-base balance now offer the ability to define this phenomenon more accurately. Accordingly, we studied acid-base changes across the splanchnic circulation during CPB and defined and quantified the factors that contributed to acid-base balance. DESIGN: Prospective cohort study. SETTING: Tertiary institution. PATIENTS: Ten patients undergoing CPB for coronary artery bypass surgery. INTERVENTIONS: Sampling of arterial and hepatic venous blood at four time intervals: postinduction, on CPB during cooling and rewarming, and at skin closure. MEASUREMENTS: Measurement of serum Na+, K+, Mg++, Ca++, Cl-, HCO3-, and phosphate concentrations, arterial and hepatic venous blood gases and serum albumin, and lactate and pyruvate concentrations at each collection point. Analysis of findings according to quantitative physicochemical principles. MAIN RESULTS: All patients developed a mild metabolic acidosis with a decrease in median serum bicarbonate concentration from 24.97 mEq/L after induction to 22.29 mEq/L at cooling and 22.23 mEq/L at rewarming (p < .05). Before CPB, the pH decreased by 0.0275 (p < .05) across the splanchnic circulation, representing an increase of 2.26 nmol/L of hydrogen ions. Nevertheless, the splanchnic circulation induced a metabolic alkalosis, with a median transsplanchnic increase in the base excess of 1.50 mEq/L (p < .05). This change was largely due to a decrease in serum chloride and lactate concentration across the splanchnic circulation (p < .05). The acidifying effect of the splanchnic circulation was therefore the result of cell respiration with a median increase in carbon dioxide tension of 5.75 mm Hg (p < .05), causing the strong ion difference effective to increase by 1.94 mEq/L (p < .05). There were no other anions or acids added to the circulation by splanchnic organs (no change in strong ion gap). During and after CPB the splanchnic metabolic alkalinizing effect continued and the respiratory acidifying effect was reduced. This caused the splanchnic circulation to be pH neutral at these times. CONCLUSIONS: Using quantitative biophysical methods it can be demonstrated that the splanchnic circulation does not contribute to the metabolic acidosis of CPB, and that it continues to have a metabolic alkalinizing effect involving significant lactate extraction. However, its respiratory acidifying effect continues, although at a reduced rate.
Acid-Base Equilibrium↗
Effect of homocysteine and cholesterol in raising plasma homocysteine, cholesterol and triglyceride levels.
A high plasma homocysteine level is a newly regarded risk factor for coronary artery disease. We report a synergistic effect of homocysteine plus cholesterol feeding on further raising total plasma homocysteine, cholesterol and triglycerides levels than each agent alone, which further enhances the risk of coronary artery disease.
Animals↗
The road to complete arterial grafting for coronary artery disease.
In 1984, our department moved to the use of single, and subsequently, bilateral internal thoracic artery grafting which, when reviewed after 12 years, suggest the addition of a second internal thoracic artery is beneficial. The 10-year survival using all-cause mortality was 86.9% for bilateral internal thoracic artery grafting compared with 74.2% for the use of a single internal thoracic artery graft. The mortality rate ratio for single versus bilateral internal thoracic artery grafts was 1.4 (P=0.009). In 1995, we entered an era of total arterial grafting using combinations of radial and internal thoracic arteries. There have been no additional early complications in the first 2 years, furthermore the early results show that the postoperative creatinine kinase MB isoenzyme and the myocardial infarction rates were lower in patients receiving at least one radial artery graft compared with those not receiving a radial artery graft. Continued use of internal thoracic and radial arteries to achieve complete arterial revascularisation for patients with coronary artery disease appears justified.
Aged↗
Perindopril chronically inhibits angiotensin-converting enzyme in both the endothelium and adventitia of the internal mammary artery in patients with ischemic heart disease.
BACKGROUND: ACE inhibitors are widely used in treating hypertension and heart failure, but the sites and mechanisms of ACE inhibition in human blood vessels are not understood. The present study was undertaken to assess the sites and extent of in vivo inhibition of ACE by long-term perindopril treatment in different layers of the internal mammary artery in patients with ischemic heart disease. METHODS AND RESULTS: Sixteen patients with ischemic heart disease were treated either with perindopril (4 mg/d PO) for up to 36 days before surgery (n = 9) or without the inhibitor as control subjects (n = 7). The segments of the internal mammary artery were collected for measurement of vascular free and total ACE by quantitative in vitro autoradiography with 125I-351A binding. The patients treated with perindopril had lower plasma ACE (P < .001) and plasma angiotensin (Ang) II-to-Ang I ratio (P < .05). In the internal mammary artery, free ACE was similarly inhibited by perindopril in the endothelium (P < .05) and adventitia (P < .05), and the free ACE-to-total ACE ratio, an index of ACE inhibition, was markedly decreased by perindopril in parallel in the endothelium (P < .001) and adventitia (P < .001). Moreover, plasma ACE correlated highly with vascular ACE in the endothelium (r = .85, P < .001) or adventitia (r = .78, P < .001), and mean arterial pressure correlated significantly with free ACE in the endothelium (r = .52, P < .05) or adventitia (r = .53, P < .05) and with the plasma Ang II-to-Ang I ratio (r = .53, P < .05). Light microscopic autoradiographs of 125I-351A binding revealed a marked inhibition of ACE by perindopril in both layers of the vascular wall. CONCLUSIONS: The present demonstrates that long-term administration of perindopril potently inhibits both endothelial and adventitial ACE to a comparable degree in the human internal mammary artery. These results indicate that perindopril effectively penetrates the vascular wall to inhibit ACE in the adventitia, thus providing evidence that perindopril may be beneficial in inhibiting both circulating Ang II and its local formation in the vascular wall.
Aged↗
The 21st-century college student: implications for athletic training education programs.
OBJECTIVE: With the onset of the 21 st century and increasing student diversity, institutions of higher education must become more attuned to the challenges, concerns, and needs of students entering the professions of athletic training and sports medicine. This review discusses the characteristics of the 21st-century college student. DATA SOURCES: The sources for this information were courses of study in the authors' doctoral programs from 1980 to 1994. DATA SYNTHESIS: In the 21 st century, students of increasingly diverse ages, races, cultures, ethnicities, and classes will enter the professions of athletic training and sports medicine. Institutions of higher education that recognize the needs of their nontraditional students will be better able to serve these students. CONCLUSIONS/RECOMMENDATIONS: To effectively serve the 21st-century student, institutions of higher education must provide multicultural training, flexible schedules, accelerated programs, and learning experiences that are both practical and tangible.
Journal Article↗
The radial artery as a bypass graft.
The radial artery is being reintroduced into clinical practice to increase the number of arterial grafts for patients undergoing coronary artery bypass surgery. The radial artery is readily available from one or both forearms and removal is safe in patients who have a normal collateral circulation to the hand. Harvesting the radial artery with the adjacent veins using a minimal touch technique and vasodilators will prevent vasospasm and possibly early occlusion. A concern is that subclinical atheroma is present in many patients. The radial artery can be used as a single graft, anastomosed in a "Y" fashion with the internal mammary artery, or used as a sequential graft. The early mortality and complications are low. There are potential cost savings because the need for an incision in the leg is avoided, so that patients may be discharged early. The early results of radial artery grafting are encouraging. Further follow-up is required to determine the late patency and effects on survival of using the radial artery graft.
Aged↗
Concomitant coronary revascularization and resection of lung cancer.
As age and smoking are common risk factors, patients with lung cancer frequently have coexistent ischaemic heart disease. Ignoring the coronary disease results in an unacceptable operative mortality, whilst sequential coronary grafting and lung resection may prejudice the results of the resection. A series of 10 patients underwent combined coronary revascularization (average 2.9 grafts per patient) and lung resection for carcinoma (seven lobectomies, one bilobectomy, one sleeve lobectomy, and one pneumonectomy). The majority of patients had unstable angina, triple vessel or left main coronary artery stenosis and poorly staged tumours. There was no operative mortality and the average hospital stay was 20 days. Half the patients had significant peri-operative morbidity; seven are alive and well at between 12 and 38 months follow-up; but three have died of recurrent carcinoma (one with associated sepsis) at 3, 8, and 13 months. Combined coronary revascularization and lung resection can be safely performed in selected patients. The early morbidity is mainly related to the cardiac procedure and impaired respiratory function preoperatively, but the long-term results are dependent upon the control of the lung carcinoma.
Adenocarcinoma↗
Retrophrenic location of the internal mammary artery graft.
A technique of locating the internal mammary artery behind the phrenic nerve is described, which extends the application of internal mammary artery grafting to the lateral wall of the left ventricle. The technique also facilitates the performance of the posterolateral anastomosis between the internal mammary and circumflex coronary arteries.
Humans↗
Weak beta-adrenoceptor-mediated relaxation in the human internal mammary artery.
The function of beta-adrenoceptors in the human internal mammary artery was studied in vitro to predict the way in which the internal mammary artery graft would respond to beta-adrenergic agonists and antagonists given in the perioperative period. Ring segments of the distal internal mammary artery obtained from patients not receiving beta-blocker therapy were mounted in organ baths and isometric wall force was measured. For comparison, similar experiments were conducted on segments of canine coronary artery, a vessel known to have powerful beta-adrenoceptor function. All arteries were precontracted with potassium or the thromboxane mimetic agent, U46619, before isoproterenol cumulative concentration-relaxation curves were constructed. In the human internal mammary artery, the maximum relaxation induced by isoproterenol was only 14% of the potassium-induced contraction and 24% of the U46619-induced contraction. These responses were weak compared with 54% and 86% for beta-adrenoceptor relaxation measured in corresponding experiments in the canine coronary artery. In all experiments, propranolol antagonized the relaxation induced by isoproterenol. These studies suggested that the human internal mammary artery has only a small number of beta-adrenoceptors. We conclude that beta-adrenoceptors would contribute little to the reactivity of the human internal mammary artery graft to sympathomimetic drugs.
Animals↗