Stanton P. Nolan

Elevated Intra-abdominal Pressure and Renal Function

The effect of increased intra-abdominal pressure on cardiac output and renal function was investigated using anesthetized dogs into whom inflatable intraperitoneal bags were placed. Hemodynamic and renal function measurements were made at intra-abdominal pressures of 0, 20, and 40 mmHg. Renal blood flow and glomerular filtration rate decreased to less than 25% of normal when the intra-abdominal pressure was elevated to 20 mmHg. At 40 mmHg intra-abdominal pressure, three dogs became anuric, and the renal blood flow and glomerular filtration rate of the remaining dogs was 7% of normal, while cardiac output was reduced to 37% of normal. Expansion of the blood volume using Dextran-40 easily corrected the deficit in cardiac output, but renal blood flow and glomerular filtration rate remained less than 25% of normal. Renal vascular resistance increased 555% when the intra-abdominal pressure was elevated from 0 to 20 mmHg, an increase fifteen-fold that of systemic vascular resistance. This suggests that the impairment in renal function produced by increased intra-abdominal pressure is a local phenomenon caused by direct renal compression and is not related to cardiac output.

Assessment of preoperative left ventricular function in patients with mitral regurgitation: value of the end-systolic wall stress-end-systolic volume ratio.

Twenty-one patients with symptomatic, chronic, severe mitral regurgitation (MR) but without other valvular heart disease or coronary disease were evaluated to determine which hemodynamic and angiographic factors might be prognostic of surgical outcome. Sixteen patients were in New York Heart Association functional classes I or II postoperatively and formed group A. One patient remained in class III postoperatively and four patients died perioperatively; they constitute group B. End-diastolic volume index (EDVI) was less for group A than for group B, 119 ± 25 ml/m2 vs 170 ± 28 ml/m2 (p < 0.001). End-systolic volume index (ESVI) was also lower in group A, 39 ± 19 ml/m2 vs 72 ± 32 ml/m2 for group B (p < 0.01).The ratio of end-systolic wall stress to end-systolic volume index (ESWS/ESVI) was examined in normal persons and in groups A and B. This ratio was significantly lower in both groups than in normal persons, indicating relatively greater end-systolic volume at a given wall stress, suggesting left ventricular dysfunction. The ESWS/ESVI ratio in group B, 2.2 ± 0.2, was significantly less than in group A, 3.3 ± 0.4 (p < 0.001). The variables of age, pulmonary capillary wedge pressure, EDVI, ESVI, ejection fraction and the ESWS/ESVI ratio were subjected to stepwise discriminant multivariate analysis to determine if any were independent predictors of outcome. The only independent predictor determined by this method was the ESWS/ESVI ratio (p < 0.001). We conclude that the ESWS/ESVI ratio may be helpful in evaluating left ventricular function and operative risk in patients with chronic, symptomatic MR.

Coronary revascularization rather than cardiac transplantation for chronic ischemic cardiomyopathy.

Patients with very poor ventricular function have been thought to be highly vulnerable to elective myocardial revascularization. Ischemic cardiomyopathy is now the major indication for cardiac transplantation. The 2-year survival of medically treated patients with ejection fractions less than 20%, but who are not sufficiently symptomatic for cardiac transplantation, is less than 25%. At our institution we have taken an aggressive approach by using myocardial revascularization for chronic ischemic cardiomyopathy. Between 1983 and 1988, 39 patients with preoperative ejection fractions less than 20% underwent coronary artery bypass. Patients were excluded if they had valvular heart disease other than mild to moderate mitral regurgitation, required resection of a left ventricular aneurysm, or required emergency operation for acute coronary occlusion. Mean age was 63.3 years (range, 43 to 80 years) and 31 were men. Mean preoperative ejection fraction was 18.3% (range, 10% to 20%) and the mean preoperative left ventricular end diastolic pressure was 22 mm Hg (range, 8 mm Hg to 38 mm Hg). There was one operative death (2.6%). Mean follow-up was 21 months (range, 3 to 60 months) with eight late deaths (a total mortality rate of 21%). Seven deaths were due to arrhythmias. Three patients continued to have severe heart failure, one of whom underwent successful cardiac transplantation. By life table analysis, there was a 3-year survival rate of 83%. With the present shortage of cardiac transplant donors, myocardial revascularization for ischemic cardiomyopathy is a reasonably effective means for preserving residual ventricular function.

The management of anticoagulation during noncardiac operations in patients with prosthetic heart valves

Based on previous thromboembolic complications associated with the interruption of anticoagulation during subsequent noncardiac operations in patients with nonbiological mitral prostheses, a protocol was developed for this high risk group. We report the successful management of 26 such operations in which anticoagulation was interrupted for 12 hours and then rapidly restored by means of heparin in the postoperative period. Since an earlier study suggested no adverse effect from the interruption of chronic anticoagulants for three to five days among patients with isolated aortic valve prostheses, simple interruption was again employed during 16 subsequent noncardiac operative procedures in this group with no complications. There were three episodes of hemorrhage observed in patients receiving therapeutic doses of heparin postoperatively, but only one required blood replacement.

Stress Sharing Between the Sinus and Leaflets of Canine Aortic Valve

A knowledge of the behavior of the aortic valve sinuses is necessary to the understanding of stress sharing between the sinuses and the leaflets. Radiopaque markers were placed on the sinuses and the leaflets of dogs during cardiopulmonary bypass, and the movement of the markers was studied using fluoroscopy. The center of the sinus moved radially during each cardiac cycle, but in an inconsistent manner. The sinus was under a dual influence: the passive influence of aortic pressure and the active influence of myocardial contraction. The longitudinal curvature of the sinus showed no dimensional change, whereas the radius of the circumferential curvature decreased by 15.7% from systole to diastole. In diastole, the stress in the sinus was 6.1 g/mm2 and was 24.3 g/mm2 circumferentially and 12.1 g/mm2 radially in the leaflet. Histologically, the main stress-bearing component of the leaflet was made up of thick, dense, collagenous fibers oriented circumferentially. These fibers curved into the sinus wall instead of inserting straight into the aortic wall, thereby suggesting that the high stress in the leaflet is shared with the sinus and that continuity of the circumferential stress exists between the leaflet and the sinus. The leaflet does not pull inwardly on the aortic wall. In diastole, the sinus adapts to the new stress conditions in the leaflet by reducing its radius of circumferential curvature. This stress sharing is important for the longevity of the aortic valve.

Living with prosthetic heart valves. Subsequent noncardiac operations and the risk of thromboembolism or hemorrhage.

A total of 111 survivors of prosthetic valve insertion were followed an average of 4 years to assess the risk of thromboembolism or hemorrhage. Non-cloth-covered ball and/or disc valve prostheses were used, and all patients received long-term anticoagulant therapy. During the follow-up period the patients with mitral or combined valve replacement suffered four times more thromboembolic episodes and had a poorer survival rate than the patients with isolated aortic valve replacement. The management of anticoagulation and the complications resulting from 44 subsequent noncardiac operations were analyzed. Anticoagulation was discontinued before 25 noncardiac operations in patients with isolated aortic valve prostheses and there were no perioperative thromboemboli. Ten operations were performed on patients with mitral or combined valve prostheses with cessation of anticoagulation prior to surgery and there were two deaths due to perioperative thromboemboli. Unanticipated hemorrhage was encountered in four of nine patients in whom anticoagulation was maintained during surgery. Cessation of anticoagulation for 3 to 5 days appears safe in patients with aortic prostheses who require subsequent noncardiac operations. The incidence of thromboembolism in patients after mitral or combined valve replacement is high and constitutes a major risk whether or not a subsequent operation is required.

Four years' experience with fibrin sealant in thoracic and cardiovascular surgery

A single-donor fibrin sealant system was used in 689 thoracic and cardiovascular surgical procedures over the 4-year period between April 1, 1985, and March 31, 1989. An excellent overall success rate (646/689, 94% effective) was achieved with specific applications, including reduction of leakage of air (29/33, 88% effective), blood (595/634, 94% effective), and fluid (14/14, 100% effective), as well as positioning of anatomical structures such as coronary bypass grafts (8/8, 100% effective). Application methods included use of spray bottles (477/497, 96% effective), syringes (165/186, 89% effective), and a Silastic cannula through the flexible fiber-optic bronchoscope (4/6, 67% effective). The system was used in a wide variety of cardiac, pulmonary, esophageal, and vascular procedures to seal staple lines, suture lines, anastomoses, conduits, fistulas, and raw surfaces. No complications with this single-donor system secondary to blood-borne disease have been documented. Overall infection occurred at a nominal rate (16/689, 2%). Thus, fibrin sealant has been a useful tool to control the leakage of air, blood, and fluid during a wide variety of thoracic and cardiovascular procedures and may be of benefit to other surgeons.

Inhibition of atherosclerosis associated with reduction of arterial intramural stress in rabbits.

Atherosclerotic lesions commonly develop at arterial branch sites, which are also the sites of high arterial Intramural stress produced by Intralumlnal pressure. We Investigated the effect of reduced Intramural stress on the development of atherosclerotic lesions. We exposed the origin of the left renal artery In five rabbits and the aortic bifurcation in another five, lowered the mean arterial pressure to 35 to 45 mm Hg, and poured a dental acrylic liquid around the branch to form a rigid cast When the rabbits recovered and the arterial pressure Increased to normal, the casts prevented the arteries from expanding, thereby maintaining a low Intramural stress. These rabbits plus two unoperated, two sham-operated, two with silicons rubber casts placed at similar pressures, and four with casts placed at 95 mm Hg pressure were given a 2% cholesterol-enriched diet for 7 to 11 weeks, and then their arteries were examined. In all rabbits, atherosclerotic lesions developed at the origins of the Intercostal, cellac, superior mesenterlc, and both renal arteries, and at the aortic bifurcation, with these notable exceptions: no lesions developed at the origins of casted renal arteries or at the casted aortic bifurcations when the cast was placed at a low pressure. Measurements of the diameter and thickness of the aorta In the left renal branch and aortic bifurcation areas, with and without the casts, indicated that there was no significant narrowing of the aortic lumen or thinning of the aorta due to the cast In conclusion, the Inhibition of the development of atherosclerotic lesions appears to be associated with the reduction of arterial Intramural stress.

Anterolateral thoracotomy as an alternative to repeat median sternotomy for replacement of the mitral valve

Median sternotomy is the most common approach for repeat cardiac surgery despite the potential complications of cardiac injury. Right anterolateral thoracotomy has been recommended as an alternative for patients undergoing mitral valve replacement, but data supporting one approach over the other do not exist. To compare these procedures, the records of 43 patients who had had a previous median sternotomy and who underwent mitral valve replacement were reviewed. No statistically significant differences between patients undergoing repeat median sternotomy (33 patients) and those undergoing right anterolateral thoracotomy (10 patients) were demonstrable when compared for age, gender, New York Heart Association Functional Class, other diseased valves, urgency of operation, indication for operation, type of valve removed, type of valve implanted, length of postoperative hospitalization, length of operation, days of ventilatory support, length of intensive care unit stay, and survival (90% for thoracotomy group; 76% for median sternotomy group; p, NS). Significant differences between the two groups, favoring right anterolateral thoracotomy, were apparent when comparisons were made for length of perfusion (means, 94.8 min, thoracotomy group; 121.4 min, sternotomy group; p = .03), incidence of reexploration (0%, thoracotomy group; 13%, sternotomy group; p = .001), and blood transfusion (means, 5.3 units, thoracotomy group; 11.4 units, sternotomy group; p = .003). Right anterolateral thoracotomy is an effective alternative to repeat median sternotomy for replacement of the mitral valve in patients who have had a previous median sternotomy.

Stresses of Natural versus Prosthetic Aortic Valve Leaflets in Vivo

During normal function of the aortic valve, the aortic leaflets undergo not only cyclic loading and unloading but also cyclic reversal of their curvature. The stresses induced in the leaflet due to these variations have been computed using a new concept based on the structure of the leaflet. Membrane stresses have been related to the pressure difference across the leaflet and bending stresses to the leaflet curvature. Total stresses were obtained by adding the two stresses. Total stresses in bioprosthetic and synthetic leaflets also were computed using the same approach. In systole, the natural leaflet is subjected to much lower total stress than a bioprosthetic or a synthetic leaflet. The natural leaflet is not subjected to compressive stresses during the cardiac cycle, whereas bioprosthetic and synthetic leaflets must sustain compressive stresses during systole. The differences in stress patterns of these leaflets indicate that there is a difference in their longevity.