Biomedical subjects

G T Christakis

Publications and source records attributed to G T Christakis.

84 records · Page 5Linked to original sources

PubMed1986

Prevention of myocardial platelet deposition and thromboxane release with dipyridamole.

Although current methods of myocardial preservation for coronary bypass surgery provide excellent protection, perioperative ischemic injury persists. Platelet activation and myocardial deposition may contribute to perioperative ischemic injury and early postoperative graft occlusion. Dipyridamole may reduce platelet activation and myocardial deposition and reduce perioperative ischemic injury. A prospective randomized trial was instituted in 40 patients undergoing elective coronary bypass surgery to evaluate the effects of dipyridamole on myocardial platelet and leukocyte deposition and the cardiac release of thromboxane and prostacyclin. Twenty patients received intravenous dipyridamole (0.24 mg/kg/hr) beginning 20 hr before surgery and continuing for 24 hr after surgery. Autologous platelets, leukocytes, and erythrocytes were labeled with 111In, 99mTc, and 51Cr, respectively, and were infused before release of the cross-clamp. Myocardial biopsy samples were obtained 10, 20, and 30 min after aortic declamping and indicated that platelets and leukocytes were deposited in the myocardium during reperfusion. Dipyridamole reduced both platelet (with dipyridamole 1540 +/- 2100 cells/mg, no dipyridamole 14,500 +/- 33,000 cells/mg) and leukocyte deposition (with dipyridamole 16 +/- 32 cells/mg, no dipyridamole 63 +/- 110 cells/mg). Cardiac release of thromboxane B2 (the stable metabolite of thromboxane A2) occurred in the early postoperative period and was reduced by dipyridamole (with dipyridamole 0.039 +/- 0.16 mg/liter, no dipyridamole 0.27 +/- 0.18 micrograms/liter, p less than .05). Dipyridamole reduced cardiac platelet deposition and thromboxane release and may reduce perioperative ischemic injury and early graft occlusion.

Arteries↗

PubMed1985

Thromboembolism in patients with aortic porcine bioprostheses.

Thromboembolism was prospectively studied in 215 patients who survived aortic valve replacement with porcine bioprostheses. All patients were anticoagulated with warfarin sodium during the first 3 postoperative months. Thereafter, 80 patients received aspirin (325 or 650 mg per day) and 135 received no antiplatelet or anticoagulant drugs. The two groups of patients were similar. Thromboembolic complications were carefully searched for during the follow-up interviews. Patients were removed from the study after a thromboembolic event unless there was no change in their management. The follow-up ranged from 6 to 80 months (mean, 36 months). The linearized thromboembolic rate in patients on a regimen of aspirin was 1.3% per patient-year and in patients not taking aspirin, 5.2% per patient-year (p less than 0.02). Replacement of the ascending aorta and patch enlargement of the aortic annulus with a Teflon graft were identified as significant risk factors for thromboembolism in patients with aortic porcine bioprostheses. These findings indicate that patients with aortic porcine bioprostheses should receive aspirin, especially if they also had replacement of the ascending aorta or patch enlargement of the aortic annulus with a Teflon graft.

Adolescent↗

PubMed1985

A comparison of nitroglycerin and nitroprusside: I. Treatment of postoperative hypertension.

Nitroglycerin improves perfusion to ischemic myocardial regions and therefore has theoretical advantages over sodium nitroprusside to treat hypertension (mean arterial pressure [MAP] greater than 95 mm Hg) following coronary bypass operation. Thirty-three hypertensive patients were randomized to an initial infusion of either nitroglycerin or nitroprusside in a crossover trial designed to reduce MAP to 85 mm Hg. Thermodilution cardiac output measurements permitted calculation of left ventricular stroke work index (LVSWI), and nuclear ventriculograms permitted estimation of left ventricular ejection fraction, left ventricular end-diastolic volume index (LVEDVI), and left ventricular end-systolic volume index (LVESVI). Coronary sinus blood flow was measured by the continuous thermodilution technique, and arterial and coronary sinus lactate measurements permitted calculation of myocardial lactate flux (MVL). Both nitroglycerin and nitroprusside reduced MAP (-25 +/- 12 mm Hg and -20 +/- 10 mm Hg, respectively; not significant [NS]). Nitroglycerin reduced LVSWI more than did nitroprusside (-15 +/- 13 gm-m/m2 and -7 +/- 9 gm-m/m2, respectively; p less than 0.01). Both agents increased left ventricular ejection fraction (nitroglycerin, +8 +/- 8%, and nitroprusside, +10 +/- 7%; NS), and decreased LVEDVI (-20 +/- 22 ml/m2 and -11 +/- 17 ml/m2, respectively; NS) and LVESVI (-13 +/- 14 ml/m2 and -10 +/- 12 ml/m2, respectively; NS). Coronary sinus blood flow decreased with both drugs (NS), but MVL increased with nitroglycerin (+0.02 +/- 0.14 mmol/min) and decreased with nitroprusside (-0.02 +/- 0.02 mmol/min) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Output↗

PubMed1985

A comparison of nitroglycerin and nitroprusside: II. The effects of volume loading.

The treatment of postoperative hypertension with nitroglycerin or nitroprusside reduces cardiac filling, and volume loading is required to maintain hemodynamic and metabolic stability. Postoperative hypertension (mean arterial pressure greater than 95 mm Hg) developed in 33 patients who were randomized to an initial infusion of nitroglycerin or nitroprusside in a crossover trial. Volume loading (a rapid infusion of 250 to 500 ml of colloid to raise the left atrial pressure 2 to 4 mm Hg) was instituted prior to hypertension and again following the crossover trial during the infusion of nitroglycerin (11 patients) and nitroprusside (13 patients). Volume loading increased left ventricular end-diastolic volume index (LVEDVI) as documented by nuclear ventriculography, cardiac index (CI), and left ventricular stroke work index (LVSWI). Although CI was higher (p less than 0.01) with nitroprusside at any level of LVEDVI, myocardial performance (the relation between LVSWI and LVEDVI) was not different. Diastolic compliance (the relation between left atrial pressure and LVEDVI) was increased (p less than 0.01) with nitroglycerin. Myocardial metabolism was assessed by calculating myocardial lactate flux (MVL), the product of myocardial lactate extraction and coronary sinus blood flow by the thermodilution technique. Volume loading increased MVL during nitroglycerin therapy and decreased (p less than 0.01) MVL during nitroprusside therapy. Volume loading restored preload and increased CI with both nitroglycerin and nitroprusside. Only nitroglycerin improved myocardial lactate utilization. Nitroglycerin is the preferred vasodilator when ischemia is suspected after coronary bypass operations.

Cardiac Volume↗

PubMed1985

Hemodynamic and myocardial metabolic consequences of PEEP.

The cardiac effects of positive end expiratory pressure (PEEP) were examined in 50 patients six hours after elective coronary bypass surgery. Increasing the level of PEEP from 5 to 10 to 15 cm H2O decreased cardiac index (evaluated by thermodilution), stroke index and left ventricular end diastolic volume index without a change in left ventricular ejection fraction (evaluated by nuclear ventriculography). Right ventricular end diastolic volume index remained unchanged. Coronary sinus blood flow (measured by the continuous thermodilution technique) and myocardial oxygen and lactate consumption were unchanged with the application of 15 cm H2O PEEP. In 21 patients, volume loading (250 ml [mL] of plasma) was performed at 5 cm, and again at 15 cm H2O PEEP. Volume loading produced a similar increase in cardiac volumes and cardiac index at 5 and 15 cm H2O PEEP. Right and left ventricular performance and left ventricular systolic function were not altered by PEEP (by analyses of covariance). Coronary sinus blood flow and myocardial oxygen consumption increased with volume loading at 5 and 15 cm H2O of PEEP, but myocardial lactate utilization tended to increase at 5 cm, and decrease at 15 cm H2O PEEP (p = 0.08). Of the 33 patients who underwent complete hemodynamic and metabolic measurements, 16 increased cardiac lactate utilization at 15 cm H2O PEEP and 17 decreased cardiac lactate utilization at 15 cm H2O PEEP. PEEP decreased cardiac index, perhaps by reducing left but not right ventricular volumes. Volume loading during PEEP restored cardiac index and revealed no depression in myocardial performance or systolic function. With the application of PEEP, myocardial metabolism was maintained in half the patients, but ischemic metabolism was observed in the other half.

Blood Pressure↗

PubMed1985

Right ventricular dysfunction following cold potassium cardioplegia.

Right coronary artery stenoses limit cardioplegic delivery to the right ventricle and may contribute to postoperative right ventricular dysfunction. Right ventricular function was evaluated in 39 patients with right coronary artery stenoses following elective coronary bypass operations. Hemodynamic and nuclear ventriculographic measurements, made between 3 and 6 hours postoperatively, revealed a progressive increase in pulmonary arterial pressure, pulse rate, and right ventricular ejection fraction (p less than 0.05). Right ventricular end-diastolic volume index (calculated from the thermodilution stroke index divided by the nuclear ejection fraction) decreased, but right atrial pressure increased (suggesting a decrease in compliance). The response to the infusion of 2 units of plasma (volume loading) was evaluated 3 hours postoperatively (EARLY) and again 5 hours postoperatively (LATE) in 21 patients. Right ventricular performance (the relation between cardiac index or right ventricular stroke work index and right ventricular end-diastolic volume index) and right ventricular systolic function (the relation between systolic pulmonary arterial pressure and right ventricular end-systolic volume index) were depressed EARLY and improved LATE (p less than 0.01 in analysis of covariance). Left ventricular performance (the relation between cardiac index or left ventricular stroke work index and left ventricular end-diastolic volume index) and left ventricular systolic function (the relation between systolic blood pressure and left ventricular end-systolic volume index) were similar EARLY and LATE. Right ventricular diastolic function (the relation between right atrial pressure and right ventricular end-diastolic volume index) and left ventricular diastolic function (the relation between left atrial pressure and left ventricular end-diastolic volume index) were significantly greater LATE than EARLY. Right, but not left, ventricular performance and systolic function were transiently depressed, and right and left ventricular diastolic stiffness were transiently decreased in the EARLY postoperative period. In patients with right coronary artery stenoses, current methods of cardioplegia may inadequately protect the right ventricle, but further studies are required to establish the relation between intraoperative protection and postoperative function.

Blood Pressure↗

PubMed1985

Morbidity and mortality in mitral valve surgery.

To develop strategies for the management of high-risk patients, contemporary risk factors for operative mortality and postoperative ventricular dysfunction were identified in 214 patients undergoing mitral valve surgery in 1982 and 1983. Thirty-eight preoperative and perioperative variables were prospectively collected and analyzed by univariate and multivariate statistics. The overall mortality was 4.6% and the incidence of postoperative low-output syndrome (LOS) was 18.7%. Forty-seven patients with coronary artery disease (CAD) had a higher mortality and incidence of LOS (as evidenced by the need for inotropic drugs or counterpulsation to maintain blood pressure) (those with CAD 15% mortality, 40% LOS; those without CAD 2% mortality, 13% LOS; p less than .05). The presence of unstable angina and ischemic mitral regurgitation further increased the risk. Age was also a predictor of outcome. Patients who died or had LOS were older (those who died, 65 +/- 7 years, those with LOS, 58 +/- 11 years) than patients who survived and did not have postoperative dysfunction (those who survived, 53 +/- 11; those with no LOS, 53 +/- 11; p less than .01). Mitral regurgitation was associated with a higher (p less than .05) mortality and incidence of LOS (mortality 10.5%, LOS 36%; n = 76) than was mitral stenosis (mortality 0%, LOS 4%; n = 74) or mixed lesions (mortality 3%, LOS 15%; n = 64). In patients without CAD, mitral regurgitation remained a significant predictor of mortality and ventricular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

A clinical trial of blood and crystalloid cardioplegia.

Although experimental studies suggest that blood cardioplegia provides better protection than crystalloid cardioplegia, clinical studies have been inconclusive. Ninety patients undergoing coronary bypass grafting were randomized to receive either blood (n = 43) or crystalloid cardioplegia (n = 47). The incidence of perioperative myocardial infarction was lower with blood cardioplegia (blood, n = 0; crystalloid, n = 5; p = 0.06), and the maximum MB isoenzyme of creatine kinase was significantly less with blood cardioplegia (blood, 26.3 +/- 12.6 U/L; crystalloid, 35.6 +/- 17.0 U/L, mean +/- standard deviation; p less than 0.02.) Sixty patients (blood cardioplegia, n = 28; crystalloid cardioplegia, n = 32) had more sensitive measurements to assess the metabolic response to aortic occlusion and to compare the metabolic and functional recovery from the operation. Coronary sinus blood flow (by the continuous thermodilution technique) was significantly lower after cross-clamp removal with blood cardioplegia (blood, 160 +/- 100 ml/min; crystalloid, 220 +/- 120 ml/min; p less than 0.05), indicating less reactive hyperemia. The cardiac production of lactate was significantly less with blood cardioplegia during aortic occlusion (blood, -0.5 +/- 0.9 mmol/L; crystalloid, -0.9 +/- 0.9 mmol/L; p less than 0.05) and immediately after aortic declamping (blood, -0.2 +/- 0.4 mmol/L; crystalloid, -0.7 +/- 0.7 mmol/L; p less than 0.01). Thermodilution cardiac output measurements permitted calculation of the left ventricular stroke work index, and nuclear ventriculograms permitted calculation of the left ventricular end-diastolic volume index and end-systolic volume index. Myocardial performance, systolic elastance, and diastolic compliance were determined from volume loading studies (250 to 500 ml colloid) performed 2 to 4 hours postoperatively. Myocardial performance (the left ventricular stroke work index-left ventricular end-diastolic volume index relation) and systolic elastance (the systolic blood pressure-left ventricular end-systolic volume index relation) were significantly better with blood cardioplegia (p less than 0.01 by multivariate analysis); diastolic compliance (the left atrial pressure-left ventricular end-diastolic volume index relation) was similar. Blood cardioplegia reduced ischemic injury, decreased anaerobic metabolism during arrest, and permitted better functional recovery. Blood cardioplegia provides superior protection for elective coronary bypass grafting and may improve the clinical results in patients with unstable angina and in other high-risk patients.

Anti-Arrhythmia Agents↗

PubMed1983

A comparison of volume loading and atrial pacing following aortocoronary bypass.

Although cold potassium cardioplegia provides adequate myocardial protection, transient hemodynamic and metabolic instability occasionally occurs after uncomplicated coronary bypass surgery. Two methods to increase cardiac output were compared 2 to 6 hours postoperatively in 24 patients recovering from elective coronary bypass operation. Volume loading increased cardiac index (CI) from 2.1 +/- 0.5 to 2.7 +/- 0.6 L/min/m2 by increasing left atrial pressure (LAP) from 8.6 +/- 3.6 to 13.0 +/- 4.1 mm Hg. Atrial pacing at a rate of 112 +/- 8 beats per minute increased CI from 2.4 +/- 0.5 to 2.7 +/- 0.8 L/min/m2 without a change in LAP. Ejection fraction by nuclear angiography did not change, but the calculated left ventricular end-diastolic volume index (stroke index/ejection fraction) increased with volume loading and decreased with atrial pacing--a decrease in diastolic compliance. Myocardial oxygen extraction did not change, but myocardial lactate extraction increased with volume loading and decreased with atrial pacing. Coronary sinus blood flow was measured in 5 patients and increased with both methods studied. Volume loading demonstrated that myocardial performance was normal and myocardial metabolism increased commensurate with the increase in work. Atrial pacing increased CI but resulted in anaerobic metabolism and a decrease in diastolic compliance. Volume loading rather than atrial pacing will improve CI without producing ischemia in the early postoperative period.

Adult↗

PubMed1983

Optimal postoperative volume loading.

Intravenous infusions are required to maintain ventricular preload after uneventful coronary bypass operation. During the early postoperative period, when myocardial metabolic recovery is incomplete, volume loading is intended to stabilize ventricular function and metabolism and to prevent progressive ischemic injury. This study attempts to define the optimal preload for both metabolism and performance. Thirty-seven patients recovering from elective coronary bypass operations and cold potassium cardioplegia underwent volume loading with whole plasma. The initial response (VLA) from a low left atrial pressure (LAP = 7.3 +/- 3.3 mm Hg) was compared with the subsequent response (VLB) from a higher filling pressure (LAP = 10.9 +/- 2.7 mm Hg). Both VLA and VLB produced a similar increase in cardiac index, stroke work index, and end-diastolic volume index (EDVI), and a decrease in ejection fraction (measured by nuclear angiography). Myocardial lactate extraction increased with VLA, but myocardial lactate production resulted with VLB. A careful analysis of these volume loading studies suggested that myocardial performance and compliance were not altered in the early postoperative period. The decrease in ejection fraction with volume loading may have resulted from a combination of increased wall tension and decreased inotropic stimulation. After uneventful coronary bypass surgery, an LAP between 5 and 12 mm Hg corresponded to an EDVI between 30 and 80 ml/m2 and produced adequate cardiac index, stroke work index, and lactate extraction. A lower or higher preload did not improve function and resulted in abnormal metabolism.

Coronary Artery Bypass↗

PubMedDate not supplied

The current status of myocardial revascularization: changing trends and risk factor analysis.

From November 1989 to December 1994, we performed 2264 bypass procedures. Data were collected prospectively. The population was divided into three subgroups: group 1 = single internal mammary artery (IMA) +/- veins (n = 1584); group 2 = veins only (n = 503); and group 3 = two or more arterial conduits +/- veins (n = 177). Patients who received only saphenous vein conduits (group 2) were significantly older (66.7 +/- 8.9 years) than either group 1 (60.3 +/- 8.3 years) or group 3 (51.6 +/- 9.2 years). Furthermore, this cohort group had the highest percentage of females (28.6%), urgent cases (43.5%), preoperative myocardial infarction (MI) (18.5%), and redo surgery (5.4%). In contrast, patients who received two or more arterial conduits were 94.9% male, and had the lowest incidence of urgent cases (18.1%) and redo surgery (0.5%). Mortality was 1.4% in group 1 and 3.2% in group 2; there were no deaths in group 3. Furthermore, group 2 patients had the highest incidence of perioperative MI (6.6%), low output syndrome (22.1%), intra-aortic balloon pump (IABP) assist (6.2%), and stroke (2.7%). By multivariate logistic regression analysis (odds ratio in parentheses), redo surgery (7.92), preoperative IABP (5.53), poor LV function (4.01), renal impairment (3.94), and advanced age (2.12) were all predictors of operative mortality. When mortality and morbidity (death, infarction, low output syndrome, IABP assist) were combined, regression analysis revealed that in addition to the above variables, female gender and cold cardioplegia were also independent predictors of combined mortality and morbidity. Resource utilization was determined for the three patient groups. There was concern that the increased technical demands of multiple arterial grafting along with longer periods of aortic occlusion and pump times may lead to increased complications and prolonged hospital stay. However, we found that group 3 had the lowest ventilation time, intensive care unit stay, and hospital stay. The results no doubt were influenced by case selection. Whether or not this approach to revascularization will increase long-term survival and freedom from reoperation will require further study.

Aged↗

PubMedDate not supplied

Preferred method for insertion of the Toronto Stentless Porcine Valve.

The Toronto Stentless Porcine Valve has been extensively used for aortic valve replacement. A standardized, detailed description of a preferred operative technique has been absent from the literature. A method is described that stresses (a) proper position and orientation of the aortotomy, (b) debridement of the diseased native valve, (C) proper sizing of the aortic root and choice of prosthesis and (d) implantation of the valve. Using this technique, the prosthesis can be reproducibly implanted with relative ease, without valvular insufficiency or coronary obstruction.

Aortic Valve↗