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Biomedical subjects

M A Borger

Publications and source records attributed to M A Borger.

32 records · Page 2Linked to original sources
PubMed1999

Intraoperative myocardial protection: current trends and future perspectives.

BACKGROUND: The results of contemporary coronary artery bypass graft surgery (CABG) are excellent. However, recently changing trends in the population at risk have necessitated new measures to minimize perioperative morbidity and mortality. METHODS: We reviewed cardioplegic innovations developed, evaluated, and currently employed at the Toronto Hospital. In addition, we conducted an evaluation of novel cardioplegic formulations, with an eye towards future clinical applications. RESULTS: At the Toronto Hospital, we demonstrated that blood provided better protection than crystalloid cardioplegia. Subsequently, we found that a terminal infusion of warm blood cardioplegia repleted myocardial adenosine triphosphate (ATP) levels and improved postoperative ventricular function. Recently, we reported that tepid (29 degrees C) cardioplegia reduced lactate and acid production during cardioplegic arrest, and improved postoperative ventricular function. Combining antegrade and retrograde cardioplegic delivery reduced lactate production, preserved ATP stores, and improved metabolic recovery after cross-clamp release. Cardioplegic flows of at least 200 mL/min were required to washout detrimental metabolic end-products and improve ventricular function. To further optimize myocardial protection, attempts have been made to harness the beneficial effects of ischemic preconditioning using adenosine. Similarly, insulin cardioplegia has been employed in order to enhance ventricular performance by stimulating early postoperative aerobic metabolism. Finally L-arginine, a nitric oxide donor has been demonstrated to be beneficial in experimental studies and may represent a further option for the enhancement of intraoperative myocardial protection. CONCLUSIONS: Despite continued improvements in cardioplegic techniques, low output syndrome following high-risk CABG remains an ongoing concern. The development of novel additives with various protective properties may provide added protection, allowing for a reduction morbidity and mortality following CABG.

Acid-Base Equilibrium↗
PubMed1999

Decreased cerebral emboli during distal aortic arch cannulation: a randomized clinical trial.

BACKGROUND: Cerebral emboli occur during cardiopulmonary bypass and are a principal cause of postoperative neurologic dysfunction. We hypothesized that arterial cannulation of the distal aortic arch, with placement of the cannula tip beyond the left subclavian artery, will result in fewer cerebral microemboli than conventional cannulation of the ascending aorta. METHODS: Patients undergoing coronary bypass surgery with a single crossclamp technique were randomized to receive cannulation of the distal aortic arch (n = 17) or standard cannulation of the ascending aorta (control group, n = 17). Trendelenburg positioning was used whenever possible. Cerebral emboli were quantified by continuous transcranial Doppler monitoring of the middle cerebral artery. RESULTS: Baseline demographics were similar for the 2 groups of patients, including cardiopulmonary bypass and crossclamp times. Cerebral microemboli were detected during cardiopulmonary bypass in all patients, with a range of 17 to 627 emboli. The total number of detected emboli was lower in the arch cannulation group (152 +/- 33, mean +/- standard error of the mean) than in the conventional cannulation group (249 +/- 35, P =.04). Embolization rates were lower in distal arch patients than in control patients during cardiopulmonary bypass (2.0 +/- 0.3 vs 4.2 +/- 0.9 per minute, respectively, P =.03). Reduction in cerebral emboli by distal arch cannulation was most pronounced during perfusionist interventions. CONCLUSIONS: Cannulation of the distal aortic arch results in less cerebral microembolism than conventional cannulation of the ascending aorta. Provided it is performed safely, distal arch cannulation may be an important surgical option for patients with severe atherosclerosis of the ascending aorta.

Analysis of Variance↗
PubMed1999

A novel comparison of stentless versus stented valves in the small aortic root.

BACKGROUND: Previous studies have compared prosthetic valves on the basis of industry-labeled valve sizes. Unfortunately, the relationship between the labeled size and the true measured external or internal diameter differs between valve manufacturers. Therefore hemodynamic comparisons between prosthetic valves are inaccurate if based solely on industry-labeled valve sizes. METHODS: We have previously demonstrated that the internal diameter of a 21-mm Carpentier-Edwards pericardial stented valve is similar to that of a 25-mm Toronto stentless porcine valve. Therefore we chose to compare postoperative hemodynamics in patients who received 19-, 21-, or 23-mm Carpentier-Edwards pericardial stented valves (inner diameter 18-22 mm, n = 69) with those in patients who received 23- or 25-mm stentless porcine valves (internal diameter 19-21 mm, n = 41). RESULTS: Patients in the Carpentier-Edwards group were more likely to be elderly and more likely to require concomitant revascularization. Operative mortality was lower in the stentless porcine valve group (0% vs 9%, P =.06). Hospital stay and ventilation requirements were shorter in the stentless porcine valve group. Postoperative hemodynamics were similar in the two groups. CONCLUSIONS: These data provide evidence that stentless and stented valves have similar hemodynamic profiles in the small aortic root when matched on true measured internal diameters. The clinical benefit of the stentless porcine valve may be due to patient selection or the lack of a rigid stent in the small aortic root, but it is not due to hemodynamic superiority over stented aortic valves of similar sizes.

Aged↗
PubMed1999

Calcium channel blockers in myocardial and cerebral ischemia: a clinician's review from bench to bedside.

Calcium channel blockers constitute a very important group of drugs that are commonly used in the treatment of cardiovascular and cerebrovascular disorders. Current indications for these medications include hypertension, angina, supraventricular arrhythmias, and prevention of coronary and cerebral vasospasm. Although calcium channel blockers originally held great promise in the treatment of myocardial and cerebral ischemia, clinical results have been discouraging. An understanding of the basic physiological mechanisms of actions for these drugs is important for the practising clinician and may explain the disappointing results for the treatment of ischemia to date. This paper is a narrative review, from a clinician's viewpoint, of the structure and role of calcium channels in cardiac and cerebrovascular tissues, as well as a review of the in vitro and clinical results of calcium channel blockade in myocardial and cerebral ischemia.

Brain Ischemia↗
PubMed1998

Multiple arterial grafts. Radial versus right internal thoracic arteries.

BACKGROUND: Left internal thoracic artery (LITA) grafts to the left anterior descending coronary artery (LAD) during coronary bypass surgery (CABG) have greater patency rates than saphenous vein grafts and reduce long-term cardiac morbidity and mortality rates. The benefits of multiple versus single arterial grafts and the role of different arterial conduits with respect to short- and medium-term outcome remains controversial. The purpose of this study was to compare the perioperative and intermediate-term results of: (1) patients receiving 2 arterial grafts versus 1 arterial graft and (2) patients receiving a right internal thoracic artery (RITA) versus a radial artery (RA) as the second arterial graft. METHODS AND RESULTS: Retrospective analysis of prospectively gathered data on consecutive patients undergoing isolated CABG at our institution between 1989 and 1996 was conducted. The first section of the study compared outcomes for 1 arterial graft (LITA to LAD, n = 2333) versus 2 arterial grafts (LITA + RA or LITA + RITA, n = 378). The second section of the study compared outcomes for the RITA (n = 132) versus the RA (n = 171) as second arterial grafts since 1992, when the radial series was initiated. Part I: By multivariable stepwise logistic regression, the use of 1 arterial graft was associated with an increased incidence of perioperative cardiac morbidity and mortality (odds ratio 2.2, 95% confidence interval 1.4 to 3.3), with the use of our current patient selection criteria. Double-arterial graft patients had a nonsignificant trend toward increased intermediate-term actuarial survival (P = 0.12) and cardiac event-free survival (P = 0.09). Part II: Comparison of preoperative demographics revealed a higher incidence of diabetes (27% vs 11%, P < 0.001), peripheral vascular disease (16% vs 8%, P = 0.03), and elderly age (13% vs 2%, P = 0.001) in patients receiving an RA versus those receiving a RITA as the second arterial graft. Perioperative outcome analysis revealed a decreased intensive care unit stay in the RA versus RITA group (median 30.4 vs 36.2 hours, respectively, P = 0.005) but no significant difference in hospital length of stay. There was no significant difference in perioperative mortality or cardiac morbidity rates. RITA patients had a higher incidence of sternal wound infection (5.3% vs 0.6%, P = 0.01), however, and tended to have increased blood product transfusion rates (51% vs 40%, P = 0.06). CONCLUSIONS: The use of 2 arterial grafts is safe, with a reduction in perioperative cardiac morbidity or mortality rates compared with 1 arterial graft after adjustment for other risk variables. When comparing RITA to RA as second arterial grafts, patients receiving an RA have a lower incidence of sternal wound infection and decreased transfusion requirements, with no difference in perioperative or intermediate-term cardiac morbidity or mortality rates.

Aged↗
PubMed1998

Decreasing incidence of stroke during valvular surgery.

BACKGROUND: The predictors and causes of stroke after valvular surgery are incompletely defined. We examined the incidence, predictors, and mechanisms of stroke during valvular procedures over a 15-year time period. METHODS AND RESULTS: We retrospectively reviewed prospectively gathered data on 5954 consecutive patients undergoing valvular procedures at our institution from 1982 to 1996. Stroke was defined as persistent central nervous system deficit, usually with confirmatory CT imaging. Patients were divided into 3 groups according to date of operation: group 1, 1982 to 1986 (n = 1819); group 2, 1987 to 1991 (n = 2022); and group 3, 1992 to 1996 (n = 2113). Chart review was undertaken of all patients who developed stroke (n = 189). Stroke occurred in 3.8% of group 1 patients, 3.3% of group 2, and 2.6% of group 3 (P = 0.120). The decreasing incidence of stroke over time was confirmed by multivariable logistic regression analysis, in which earlier date of operation was an independent risk factor for stroke (P < 0.001). Predictors of stroke identified by multivariable logistic regression were (listed in decreasing order): (1) endocarditis (OR, 3.0; 95% CI, 1.8 to 5.0); (2) age > 74 years (OR, 2.3; 95% CI, 1.5 to 3.7); (3) earlier time period of operation (1982 to 1986: OR, 2.2; 95% CI, 1.5 to 3.2; 1987 to 1991: OR, 1.5; 95% CI, 1.0 to 2.2); (4) urgent timing (OR, 2.0; 95% CI, 1.4 to 2.8); (5) concomitant coronary bypass (OR, 2.0; 95% CI, 1.4 to 2.8); and (6) reoperation (OR, 1.7; 95% CI, 1.2 to 2.4). In more recent years of operation, we found an increasing prevalence of age > 74 years (7.4% in group 1, 9.5% in group 2, and 15.3% in group 3; P < 0.001), urgent timing (11%, 26%, and 34%, P < 0.001), and concomitant coronary bypass surgery (25%, 27%, and 33%; P < 0.001). CONCLUSIONS: The incidence of stroke during valvular surgery has decreased with time, despite an increased prevalence of risk factors. Predictors of stroke suggest 3 major causes (multivariable predictors in parentheses): atherosclerotic emboli (elderly age, concomitant coronary bypass), shock (urgent timing, reoperation), and septic emboli (endocarditis).

Aged↗
PubMed1998

Optimal myocardial preconditioning in a human model of ischemia and reperfusion.

BACKGROUND: Adenosine (ADE) may mediate the protective effects of preconditioning (PC). However, human data are lacking, and the optimal method of ADE administration and the mechanism of protection remain unresolved. METHODS AND RESULTS: We have developed a model of simulated "ischemia" (I) and "reperfusion" (R) in quiescent human ventricular cardiomyocytes. Cellular injury and metabolic parameters were assessed after various interventions: Cells were preconditioned with anoxia (PC0), hypoxia (PC16), anoxic supernatant (SUP0), or hypoxic supernatant (SUP16) with or without the ADE receptor antagonist (SPT) or ADE deaminase (ADA). ADE was applied before, during, or after I or continuously with and without SPT. Cells were treated with the PKC agonist PMA. PC cells were incubated with the protein kinase-C (PKC) antagonist Calphostin-C (Cal-C). PKC translocation and PKC activity were assessed. PC0 was most protective. Protection was transferable via SUP0, which produced the highest concentrations of ADE. Protection was lost with SPT or ADA. Intracellular ATP fell after PC and prolonged I and R. Exogenous ADE was most protective when administered before I at 50 mumol. ADE during I was partially protective. No additional protection was provided with continuous ADE treatment. ADE prevented ATP degradation but increased lactate immediately after its administration. SPT abolished the protective effects of ADE. PMA conferred protection, which was abolished with Cal-C. ADE stimulated PKC translocation and PKC activity in the absence of SPT. CONCLUSIONS: Maximal I confers maximal PC. The degree of I is reflected in supernatant ADE concentrations. The initial ATP fall with PC may account for a lack of ATP preservation after I and R. ADE reproduces the protective effects of PC, preserves ATP, and increases lactate production, perhaps by stimulating glycolysis. Clinical trials of ADE administered during cardiac surgery are necessary to further define its beneficial effects in humans.

Adenosine↗
PubMed1998

Deep sternal wound infection: risk factors and outcomes.

BACKGROUND: Deep sternal wound infection (DSWI) is a serious complication of cardiac operations performed by median sternotomy. We attempted to define the predictors of DSWI and to describe the outcomes of two treatment strategies used at our institution. METHODS: Retrospective review was performed using prospectively gathered data on 12,267 consecutive cardiac surgical patients from 1990 to 1995. Chart review was performed on all patients in whom DSWI developed, and follow-up was obtained on 100% of these patients. RESULTS: Deep sternal wound infections developed in 92 patients (incidence 0.75%). Multivariable predictors for development of DSWI in all patients were (odds ratios and 95% confidence intervals in parentheses) (1) diabetes mellitus (2.6; 1.7 to 4.0) and (2) male sex (2.2; 1.3 to 3.9). In patients receiving coronary artery bypass grafting alone, independent predictors were (1) bilateral internal thoracic artery grafts (3.2; 1.1 to 8.9), (2) diabetes (2.7; 1.6 to 4.3), and (3) male sex (1.8; 0.9 to 3.7). For all other patients, predictors were (1) age more than 74 years (3.3; 1.1 to 10.1), (2) male sex (3.0; 1.1 to 8.1), and (3) diabetes (2.3; 0.9 to 5.8). Bilateral internal thoracic artery grafts increased the risk of DSWI in all subgroups of coronary artery bypass graft patients, particularly in diabetics who had a 14.3% incidence of DSWI after bilateral internal thoracic artery grafting. Patients with DSWIs received either sternal debridement with primary closure (n=45) or sternectomy with flap reconstruction (n=46). The 6-month freedom from adverse event rate (ie, readmission, reoperation, or death) was 76% for both groups of patients. CONCLUSIONS: Male sex and diabetes are predictors of DSWI in all cardiac surgical patients. Bilateral internal thoracic artery grafting may be contraindicated in diabetic patients.

Age Factors↗
PubMed1998

Inaccurate and misleading valve sizing: a proposed standard for valve size nomenclature.

BACKGROUND: The sizes with which manufacturers label valves are nonuniform and haphazard. This has led to confusion and inappropriate comparisons of hemodynamics between valves with the same labeled size. Hemodynamic performance of valves is primarily determined by the internal diameter (ID) of their orifice. METHODS: The purpose of this study was to determine the ID and external diameter of aortic valves used at our institution and compare the measurements to manufacturers' labeled sizes. We also evaluated valve size (ID, manufacturers' labeled size) in 527 patients undergoing isolated aortic valve replacement between 1990 and 1996. RESULTS: We demonstrated that no two manufacturers' tissue or mechanical valves have the same ID or external diameter for a given labeled size. The labeled size of tissue valves was 1 to 4 mm larger than the measured ID. The labeled size of mechanical valves was 3 to 5 mm larger than the measured ID. The St. Jude HP mechanical valve has a greater ID than all other mechanical valves for each labeled size. Among 403 patients operated on for predominant aortic stenosis, those patients receiving the Toronto Stented Porcine Valve (n = 98) had a larger mean ID (22.3+/-1.9 mm) than 204 patients receiving stented tissue valves (ID = 20.9+/-1.9 mm) and the 101 patients receiving mechanical valves (ID = 19.3+/-1.9 mm, p < 0.0001). However, when the manufacturers' labeled size was used as a measure of the size, the results were greatly exaggerated in favor of the Toronto Stented Porcine Valve (ID = 26.3+/-1.9 mm) compared with stented tissue valves (ID = 23.1+/-2.1) or mechanical valves (ID = 23.6+/-1.9) (p < 0.0001). CONCLUSIONS: Manufacturers' labeling of valves is nonuniform and may lead to erroneous comparisons and conclusions of hemodynamic differences between valves. We therefore recommend a standardized nomenclature for the size of all valves based on the ID measurement.

Aortic Valve↗
PubMed1998

Optimal flow rates for integrated cardioplegia.

BACKGROUND: Antegrade cardioplegic delivery may be impaired by coronary occlusions, whereas retrograde delivery of cardioplegic solution may be inhomogeneous, leading to an accumulation of lactate and hydrogen ions, the products of anaerobic metabolism. Integrated cardioplegia using continuous retrograde cardioplegia and antegrade infusions into completed vein grafts washes out metabolites accumulated in regions inadequately perfused by retrograde cardioplegia alone. To determine the flow rates required to achieve the greatest washout, we compared a high flow rate (200 ml/min) to a low flow rate (100 ml/min). METHODS: Twenty patients scheduled for isolated coronary bypass surgery were prospectively randomized to compare two flow rates for integrated cardioplegic protection using tepid (29 degrees C) blood cardioplegia. Arterial and coronary sinus blood samples were collected to evaluate myocardial metabolism. After antegrade arrest, cardioplegic solution was delivered by coronary sinus perfusion and simultaneous infusions into each completed vein graft at either high or low flow. RESULTS: Increasing from low to high flow increased the washout of lactate and hydrogen ions during the aortic crossclamp period. Two hours after crossclamp removal, ventricular function was better in the high flow groups. CONCLUSIONS: Tepid retrograde cardioplegia resulted in an accumulation of toxic metabolites. The addition of antegrade vein graft infusions at a flow rate of 100 ml/min resulted in a washout of these metabolites. A flow rate of 200 ml/min further improved this washout and resulted in improved ventricular function. An integrated approach to myocardial protection using a flow rate of 200 ml/min may improve the results of coronary bypass surgery.

Blood↗
PubMed1997

Coronary artery bypass grafting in patients with non-dialysis-dependent renal insufficiency.

BACKGROUND: Preoperative renal failure increases the morbidity and mortality of coronary artery bypass graft (CABG) surgery. The results of CABG in patients with non-dialysis-dependent, mild renal insufficiency are unknown. METHODS: From a population of 2978 consecutive patients undergoing isolated CABG from 1990 to 1996, 38 patients with preoperative renal insufficiency (Renal group; serum creatinine >150 micromol/L) were identified and matched on six prognostic variables to a cohort of 152 control patients (Control group). Two patients with preoperative dialysis-dependent renal failure were excluded from analysis. RESULTS: Compared to the overall population, the Renal group were more likely to be over age 70, diabetic, hypertensive, and suffer from peripheral vascular disease and left ventricular dysfunction. Compared to the Control group, the Renal group were more likely to require perioperative blood transfusions (P<.001) and had a greater requirement for postoperative dialysis (P<.01). The Renal group had longer ventilation times, intensive care unit stay, and postoperative hospital stay. Mild renal insufficiency was found to be an independent predictor of postoperative low output syndrome (odds ratio=3.6). CONCLUSIONS: Mild renal insufficiency, even in the absence of dialysis, increases the risk of blood transfusion, low output syndrome and prolonged the length of intensive care unit and postoperative stay for patients undergoing CABG.

Aged↗
PubMed1997

Early experience with stentless versus stented valves.

BACKGROUND: The Toronto stentless porcine valve (SPV) was designed to improve hemodynamics after aortic valve replacement by maximizing available flow area in comparison to stented valves (STD). METHODS: To assess possible hemodynamic differences between STD and SPV, 59 patients undergoing isolated aortic valve replacement (+/-coronary artery bypass graft) were prospectively evaluated by preoperative and 3- to 6-month postoperative echocardiography. Among these, 23 patients received a STD, whereas 36 received the Toronto SPV. RESULTS: The mean size (mm) of SPV implanted was larger (SPV, 26.6+/-2.1; STD, 24.0+/-2.9; P=0.0002). Patients receiving STD valves were older and had a higher prevalence of coronary artery disease and congestive heart failure. There were no preoperative differences in left ventricular mass index (g/mo2), peak or mean pressure gradients (mmHg), effective orifice area (cm2), extent of fractional shortening (%), or velocity of circumferential shortening (cf/sec). ANOVA demonstrated a significant reduction in left ventricular mass index at 3 to 6 months (P=.0001) but no differences in left ventricular mass index regression between groups (STD, -28.8+/-37.5; SPV, -31.2+/-32.4; P=.36). Effective orafice area was increased postoperatively (P=.0001), particularly among SPV cases (STD, 1.5+/-0.4; SPV, 1.9+/-0.7; P=.01). Postoperative left ventricular mass index and mean pressure gradient were reduced (P=.0001) but did not differ between groups. Fractional shortening and velocity of circumferential shortening were greater in the SPV patients at 3 to 6 months after aortic valve replacement (P=.0004 and .0001, respectively), and an interactive effect was seen between time and prosthetic group (P=.0028 and .032, respectively). CONCLUSIONS: In a consecutive series of patients, we identified no hemodynamic differences between STD and SPV, although ventricular function improved after SPV. Because of the nonrandomized nature of the study, selection bias may have accounted for some of the observed results. A prospective, randomized trial is necessary to determine the hemodynamic advantages, if any, of the SPV valve.

Aged↗
PubMed1996

Cost-effective provision of cardiac services in a fixed-dollar environment.

In the Canadian single-payer system, all hospital payments, including payments for cardiac operations, are negotiated with the government annually. Each hospital is required to remain within 50 cases of its negotiated surgical target. Physicians are paid on a capitated basis and are subject to penalties if negotiated targets are exceeded. There is a computerized waiting list for cardiac operation, with patients classified by an urgency rating scale and objectives set for the maximum period for any given urgency category. Experience has shown that many patients are delayed in the queue, waiting longer than expected for surgical procedures. Waiting times are not influenced by age, sex, or reoperative status, but are influenced by factors such as the presence of multiple risk factors, the number of diseased vessels, stability or unstability of angina, left main coronary artery disease, and recent angioplasty. Waiting time has not been shown to affect operative mortality, the incidence of postoperative low-output syndrome, or length of hospital stay. Canada's 30-year experience with the provision of cardiac services under managed care may provide useful information to hospitals and physicians in the United States currently confronting capitation. The following overview focuses on two critical issues: negotiation of costs and management of patient waiting lists.

Canada↗