Invited commentary.
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Coronary Artery Bypass↗
Biomedical subjects
Brian F Buxton
Publications and source records attributed to Brian F Buxton.
Emergency coronary artery bypass grafting: a moving target.
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Coronary Artery Bypass↗
Proceedings of the Victorian Heart Centre.
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Angioplasty, Balloon, Coronary↗
CD34 Class III positive cells are present in atherosclerotic plaques of the rabbit model of atherosclerosis.
CD34 is a positive marker for haematopoietic stem cells and endothelial cells. Recent evidence suggests that haematopoietic progenitor cells are involved in atherogenesis. CD34-positive haematopoietic progenitor cells have never been described in rabbit atherosclerotic tissues. The aim of this study is to identify CD34-positive haematopoietic progenitor cells in rabbit atherosclerotic tissues, and to compare this with macrophage (RAM-11), alpha smooth muscle cell actin and fibroblast (prolyl-4-hydroxylase) immunoreactive cells. Sixteen Male New Zealand White rabbits were divided into two groups: Group 1, control diet (Con); group 2, 0.5% cholesterol diet, and killed after 12 weeks. Immunohistochemistry was used to detect CD34 haematopoietic progenitor cells. CD34-positive haematopoietic progenitor cells were identified both within and overlying atherosclerotic plaques. As well, these haematopoietic progenitor cells also stained for RAM-11, CD45, prolyl-4 hydroxylase and alpha smooth muscle cell actin. These findings suggest that in the rabbit model of atherosclerosis, the previously identified macrophages, smooth muscle cells and fibroblasts within and overlying atherosclerotic plaques might be of haematopoietic origin.
Animals↗
Immunolocalization of ACE2 and AT2 receptors in rabbit atherosclerotic plaques.
Evidence suggests that angiotensin type 2 receptor (AT2R) and angiotensin-converting enzyme 2 (ACE2) play a protective role in atherogenesis. These factors have not been identified in rabbit atherosclerotic plaques. Our goal was to localize ACE2 and AT2R in rabbit atherosclerotic tissues, and determine which cell types express these factors. New Zealand White rabbits were fed either a control diet or a 0.5% cholesterol diet (n=8/group) for 12 weeks. Paraffin-fixed thoracic aorta were serially sectioned and processed for immunohistochemistry using commercially available antibodies to ACE2, AT2R, RAM 11 (to identify macrophages), and alpha smooth muscle cell actin (alphaSMC) to identify smooth muscle cells and myofibroblasts. AT2R immunoreactivity, but not ACE2 immunoreactivity, was clearly present in endothelia overlying normal wall. However, both AT2R and ACE2 immunoreactivity were clearly present in endothelia overlying neo-intima formation and atherosclerotic plaques. Within plaques, both AT2R and ACE2 immunoreactivity were observed in macrophages and alphaSMC actin-positive cells. Examination of serial sections showed that the majority of cells were both ACE2- and AT2R-positive. Macrophages and alphaSMC actin-positive cells produce ACE2 and the AT2R in atherosclerotic plaques. Determining a role for these factors in the control of atherosclerosis will require additional studies.
Actins↗
The combination of high dietary methionine plus cholesterol induces myocardial fibrosis in rabbits.
UNLABELLED: Limited evidence suggests that myocardial fibrosis might be associated with dietary cardiovascular risk factors. OBJECTIVE: To investigate the effects of high dietary cholesterol, methionine (the precursor to homocysteine), and the combination of the two diets on myocardial fibrosis. METHODS: Rabbits were randomly allocated into four dietary groups for 12 weeks: control (Con), 1% methionine (Meth), 0.5% cholesterol (Chol) or 1% methionine plus 0.5% cholesterol (MethChol). RESULTS: Myocardial fibrosis was not significantly increased in Chol or Meth. However, interstitial fibrosis increased by 85% (p = 0.03) and perivascular fibrosis 28-fold (p < 0.01) in the MethChol group compared to Con. CONCLUSIONS: These results suggest that high levels of dietary cholesterol or methionine alone do not significantly increase myocardial collagen content. However, the combination of the two diets does cause myocardial fibrosis. Therefore, excessive cholesterol and methionine intake may be an important pathogenic factor in the development of myocardial fibrosis.
Animals↗
The immunoquantification of caveolin-1 and eNOS in human and rabbit diseased blood vessels.
In this study, caveolin-1 (cav-1), an inhibitor of endothelial nitric oxide synthase (eNOS), was semi-quantified in diseased human and rabbit blood vessels. New Zealand White rabbits were fed, for 12 weeks, a high methionine diet (to induce intimal hyperplasia), 0.5% cholesterol diet, a normal diet, or the combination of both experimental diets. Excess segments of human internal mammary arteries (IMA) and radial arteries (RA) were obtained from patients undergoing coronary artery bypass surgery. eNOS and cav-1 were localized throughout both human and rabbit vessels. In rabbit arteries, eNOS was significantly increased in the endothelium overlying intimal thickening and atherosclerotic plaques compared with the adjacent endothelium overlying normal media. Interestingly, the endothelial cav-1:eNOS ratio increased 5-fold only in endothelium overlying plaques but decreased in endothelium overlying vessels with neo-intimal thickening. In human tissue, there was no difference between RA and IMA eNOS immunoreactivity in endothelium, intima, or media; however, RA endothelial, intimal, and medial cav-1 immunoreactivity increased 4-fold (p<0.02), 8-fold (p<0.001), and 4-fold (p<0.004), respectively, compared with IMA. Furthermore, the cav-1:eNOS immunostaining ratio in the media correlated with intimal thickening (r2 = 0.5). Our results suggest a close relationship between increased cav-1 and diseased blood vessels.
Animals↗
Do angiographic results from symptom-directed studies reflect true graft patency?
BACKGROUND: Coronary artery graft patency results have been obtained from repeat angiograms in patients who presented with evidence of ischemia. The purpose of this study is to compare protocol-directed angiographic results from a randomized clinical trial with symptom-directed angiography in nontrial patients. METHODS: Repeat angiography after primary isolated coronary artery bypass grafting was performed in 337 of 2,259 patients between July 1996 and September 2004. Patients were divided into two groups: 596 graft angiograms in 192 trial patients were compared with 389 graft angiograms in 142 nontrial patients. The mean interval from surgery was 1,306 +/- 800 days versus 1,119 +/- 777 days, respectively. Grafting techniques were similar in both groups except that the right internal thoracic artery was used almost exclusively as a free graft in the trial patients. Angiographic outcomes were defined as patent (stenosis <80%) or failure (stenosis > or =80%, occlusion, or the string sign). Comparisons of trial versus nontrial grafts were made using a generalized linear mixed model. Five-year estimates of graft patency were made using survival analyses accounting for interval censoring. RESULTS: The odds ratio for graft failure for nontrial compared with trial patient grafts was 2.6 (95% confidence interval, 1.6 to 4.3; p < 0.001). Cumulative patency estimates for all grafts at 5 years were trial 91% versus nontrial 83%, p = 0.004. Five-year estimates for individual conduits were left internal thoracic artery, 99% versus 92%, p = 0.002; right internal thoracic artery, 86% versus 87%, p = 0.8; radial artery, 87% versus 86%, p = 0.6; and saphenous vein, 86% versus 56%, p = 0.003. CONCLUSIONS: Graft patency rates were superior in the trial compared with nontrial patients. Symptom-directed graft failure rates were approximately double those of trial patients.
Clinical Protocols↗
Has the in situ right internal thoracic artery been overlooked? An angiographic study of the radial artery, internal thoracic arteries and saphenous vein graft patencies in symptomatic patients.
OBJECTIVE: The right internal thoracic artery is being used infrequently despite favorable observational angiographic data. Conversely, the radial artery utilization has increased with only limited data available. The purpose of this paper is to re-evaluate the roles of the right internal thoracic artery and the radial artery grafts. METHODS: We reviewed all ischemia-directed coronary angiographic procedures from January 1996 to December 2003. A total of 219 patients had primary coronary artery bypass grafting with an internal thoracic artery and a radial artery as two of the bypass grafts. Six hundred and seventy-nine (679) graft angiograms (45 saphenous vein, 363 radial artery, 54 right internal thoracic artery and 217 left internal thoracic artery) were studied. The mean period from operation to re-angiogram was 1104+/-761 days. Angiographic outcomes were divided into groups as: (1) patent (<50% stenosis) or (2) failed (>or=50% stenosis, string sign or occluded). A generalized linear mixed model was used to analyze predictors of graft patency. Turnbull's estimates of cumulative patency were used to compare graft failure rates over time. RESULTS: A total of 632/679 (93%) grafts were patent and 47/679 (7%) grafts had failed. Empirical saphenous vein graft patency was 40/45 (89%), radial artery patency 329/363 (91%), right internal thoracic artery patency 51/54 (94%) and left internal thoracic artery patency 212/217 (98%). Pairwise comparisons of patency from the generalized linear mixed model were: LITA>RITA, OR=1.5 (P=0.5); LITA>RA, OR=5.7 (P<0.001); LITA>SV, OR=6.5 (P<0.001); RITA>RA, OR=3.9 (P=0.01); RITA>SV, OR=4.4 (P=0.01); RA>SV, OR=1.1 (P=0.7). Five-year patency estimates from the Turnbull's model were the left internal thoracic artery (95.9%), right internal thoracic artery (91.2%), the radial artery (90.6%) and the saphenous vein (81.8%). CONCLUSIONS: Consideration should be given to the routine use of both internal thoracic arteries for coronary artery bypass grafting. When additional grafts are required, there is no evidence to suggest that either the radial artery or saphenous vein is superior.
Aged↗
Factors influencing the mean postoperative gradients across stentless porcine valves.
BACKGROUND: To study the preoperative and intraoperative variables influencing the mean post-operative transvalvular gradient across stentless porcine valves. METHODS: From 1995 to 2002, 84 patients underwent stentless valve insertion. The mean age was 73 years, and 63% were male. The valve pathology was aortic stenosis (AS) in 79%, aortic regurgitation (AR) in 12%, and mixed in 9%. Valve sizes ranged from 21 to 29 with size 27 being most frequent. 54% of patients had concomitant procedures. Patients had at least yearly clinical and echocardiographic follow-up. RESULTS: There was no operative mortality. 9.5% of the patients had significant postoperative complications. The average echo interval was 18.6 months (range 1-88). The overall mean transvalvular gradient was 9.88+/-5.67 (SD) mmHg. Variables associated with significantly reduced gradients were: larger valve sizes (p=0.002), younger age (p=0.05), pre-op AR (p=0.008), and increasing post-operative interval (p=0.05). The mean gradients decreased by 0.28 mmHg for each post-operative year. The method of implantation did not significantly affect gradients (p=0.26). CONCLUSIONS: Excellent mean transvalvular gradients were achieved with stentless valves studied, with a low operative risk. The gradients did not appear to be related to intra-operative factors, suggesting that insertion techniques can be tailored to suit patient conditions and surgeon preferences.
Aged↗
Coronary artery bypass surgery in undiagnosed traumatic pericardial rupture--25 years later.
A 55-year-old man was electively admitted for coronary artery bypass surgery. His admission chest X-ray showed an abnormal cardiac silhouette with complete leftward displacement. He had a past history of blunt thoracic trauma due to a motor vehicle accident treated conservatively. We present our findings and surgical difficulty during an operation on a patient with a previously undiagnosed pericardial rupture. This is the first reported case of its kind in the cardiac surgical literature.
Accidents, Traffic↗
High dietary methionine plus cholesterol exacerbates atherosclerosis formation in the left main coronary artery of rabbits.
UNLABELLED: Although mild hyperhomocysteinemia is a risk factor for cardiovascular events and mortality, there is no evidence to suggest that mild hyperhomocysteinemia stimulates coronary artery atherosclerosis formation. OBJECTIVE: To compare the development of coronary artery atherosclerosis in rabbits following the induction of hyperhomocysteinemia and hypercholesterolemia through diet, and whether the combination of these risk factors exacerbated atherosclerosis formation. METHODS: New Zealand White rabbits were fed for 12 weeks either a control diet, a 1% methionine diet (Meth), a 0.5% cholesterol diet (Chol) or the combination of the two diets (MethChol). Using volumetric stereological techniques, we quantitated the volume of intima, media and lumen of the left main coronary artery (LMCA). RESULTS: Atherosclerosis was present in the Chol group, and increased in the MethChol group. There was no atherosclerosis in the control or Meth groups. CONCLUSIONS: These results underscore the difference in the atherogenicity of hypercholesterolemia alone and mild hyperhomocysteinemia alone. Thus, we suggest that isolated mild hyperhomocysteinemia is not a risk factor for the initiation of coronary artery atherosclerosis formation over a short period of time, but may act in conjunction with other risk factors to further increase plaque formation.
Animal Feed↗
Factors affecting patency of internal thoracic artery graft: clinical and angiographic study in 1434 symptomatic patients operated between 1982 and 2002.
OBJECTIVE: The purpose is to define factors influencing long-term patency of the internal thoracic artery (ITA) to optimize the operative strategy. METHODS: 1482 left internal thoracic artery (LITA) and 636 right internal thoracic artery (RITA) symptom-directed angiograms were studied in 1434 patients. Data were prospectively collected from patients who had primary coronary artery bypass surgery during the period 1982-2002. The mean age of patients was 59 years; 85% were male. The mean period from operation to re-angiogram was 80 months. LITA was grafted to left anterior descending coronary artery (LAD) in 82% of cases, RITA to right coronary artery (RCA) in 40% and circumflex artery in 35% of cases. Graft failure was defined as > or =80% stenosis. RESULTS: 96.3% of LITA and 88.1% of RITA grafts were patent. No patient variables were significantly associated with graft patency (age, gender, diabetes, hypertension, LVEF, NYHA, AMI). Target coronary artery was associated with patency of both LITA and RITA grafts with maximum patency when grafted to LAD (P = 0.02) RITA had the worst patency to RCA, patency for the left system was identical to LITA. Proximal anastomosis to aorta (free RITA) had significantly better patency when compared with in situ RITA to RCA system (P = 0.005) while similar patency when grafted to left system. ITA diameter and target artery diameter were not associated with graft patency. Recent operations had better RITA patency (P = 0.03). The interval from operation to angiogram was not associated with ITA patency (96% patency for LITA and 88% patency for RITA, remained stable when studied at <1, 1-4, 5-9, 10-14 and >15 years). CONCLUSIONS: Even in a patient cohort that had adverse symptoms, excellent LITA and RITA patency was achieved which almost remained constant through all time intervals studied.
Aged↗
Post-infarct left ventricular free wall rupture-not always a lethal complication of acute myocardial infarction.
Post-myocardial infarction cardiac rupture is an important complication and cause of death in the period following myocardial infarction. It is rarely diagnosed before death. However, early diagnosis is crucial as successful treatment is possible with surgery. A successful outcome is sometimes compromised by difficult anatomy or an extensive infarct. Presentation, diagnosis and treatment of cardiac rupture is reviewed in this article, and is illustrated by five cases of cardiac rupture.
Journal Article↗
Patency of the radial artery graft: angiographic study in 209 symptomatic patients operated between 1995 and 2002 and review of the current literature.
OBJECTIVES: The purpose of this study is to define the long-term patency of the radial artery (RA) graft and review the current literature. METHODS: Two hundred and eighty-six RA symptom-directed graft angiograms were studied in 209 patients. The preoperative patient characteristics and intraoperative variables were collected prospectively from patients who had primary coronary artery bypass grafting between 1995 and 2002. A total of 166 (79%) patients were male with a mean age of 65 years. The mean period from operation to re-angiogram was 35 months. Actuarial techniques are not valid in graft patency studies as the time when the graft occluded is not known. Therefore, RA patency was analyzed at four categorical time intervals. The RA was grafted to the left anterior descending artery (LAD) in six patients (2%), diagonal (DIAG) in 29 (10%), obtuse marginal (OM) in 166 (58%), right coronary artery (RCA) in 9 (3%) and posterior descending artery (PDA) in 76 (27%) cases. The graft failure was defined as >or=80% stenosis. RESULTS: A total of 259 (91%) grafts were patent and 26 (9%) had failed. Most grafts were widely patent or occluded. The LAD/DIAG patency was 30/35 (86%), OM patency 154/166 (93%) and RCA/PDA patency 79/84 (94%). The interval from surgery to angiogram did not affect the RA graft patency (86% at <1 year, 95% at 1-3 years, 89% at 4-5 years, 96% at >5 years). CONCLUSIONS: Even in a patient cohort with adverse symptoms, excellent RA patency was achieved that remained almost constant through all time intervals studied. Better selection, harvesting and preservation may further improve early patency.
Journal Article↗
Victorian heart centre proceedings 2003.
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Editorial↗
Clinical trials and graft patency data in coronary artery surgery--a 30-year perspective.
The treatment of coronary artery disease, initially by medical and surgical and subsequently using percutaneous interventions, has evolved rapidly over the last 50 years. Randomized controlled clinical trials and observational studies of large cohorts have been instrumental in the evolution of the current practice of coronary artery revascularisation. This paper traces some of the historic trials of medical versus surgical therapy, surgical versus percutaneous intervention and graft patency studies. Medical therapy and percutaneous intervention are now the primary therapeutic modalities. However, there was an early recurrence rate with percutaneous intervention which has decreased with the use of drug-eluting stents. Coronary artery bypass surgery remains a major option for treating advanced coronary artery disease. Furthermore, it remains the treatment of first choice in most patients with left main coronary artery disease and those with extensive three-vessel proximal coronary artery disease, especially when associated with poor left ventricular function. The choice of a coronary artery bypass conduit is of major importance in developing a single long-term strategy for the surgical treatment of coronary artery disease. Bilateral internal thoracic artery grafting is now accepted as the treatment of choice, although not universally practiced. The role of other arterial conduits is being defined.
Journal Article↗