Inhibition of human internal mammary artery contractions. An in vitro study of vasodilators.

The internal mammary artery is currently the preferred conduit for myocardial revascularization; however, perioperative vasospasm of the internal mammary artery may limit its use as a bypass graft. The ability of various vasodilators to inhibit internal mammary artery contraction was investigated with the use of discarded segments of human internal mammary artery not used in coronary artery bypass grafting. Ring segments of human internal mammary arteries were suspended on strain gauges in muscle baths containing 37 degrees C Krebs solution for measurement of isometric tension in vitro. Arterial contraction was stimulated by elevating the extracellular potassium concentration to 70 mmol/L or by exposure to a 10 mumol/L concentration of norepinephrine, and inhibition of contraction by vasodilators was measured. The order of potency to inhibit potassium-induced contraction was as follows: nifedipine > verapamil > nitroprusside > papaverine. At maximal effective doses, nifedipine, verapamil, and papaverine almost completely inhibited potassium-induced contraction, whereas nitroprusside inhibited contraction by only 55%. When norepinephrine was used to contract the arteries, a biphasic relaxation curve was seen with nifedipine, but not with other vasodilator drugs. The order of potency to inhibit norepinephrine-induced contraction was as follows: nifedipine > nitroprusside > verapamil > papaverine. Maximal inhibition of norepinephrine contraction by these vasodilators ranged from 68% to 95%. Nitroglycerin, isoproterenol, and adenosine produced little or no inhibition of internal mammary artery contraction caused by potassium or norepinephrine. Although nifedipine was the most potent vasodilator, papaverine produced the greatest maximal inhibition of both potassium- and norepinephrine-induced contraction of human internal mammary artery.

Emergency coronary artery bypass surgery for failed percutaneous coronary angioplasty. A 10-year experience.

Six hundred ninety-nine patients have required emergency coronary artery bypass after failed elective percutaneous coronary angioplasty during the decade September 1980 through December 1990. This represents 4% of 9860 patients having 12,146 elective percutaneous coronary angioplasty procedures during this interval. Emergency coronary artery bypass was required for acute refractory myocardial ischemia in 82%. Hospital mortality rate for all patients was 3.1%; 3.7% in patients with refractory myocardial ischemia but 0.8% in patients without refractory myocardial ischemia, p = 0.08. Postprocedural Q-wave myocardial infarctions were observed in 21% versus 2.4%, p less than 0.0001, and intra-aortic balloon pumping was required in 19% with versus 0.8% without refractory myocardial ischemia, p less than 0.0001. Multivessel disease, p = 0.004, age older than 65 years, p = 0.005, and refractory myocardial ischemia, p = 0.08, interacted to produce the highest risk of in-hospital death. Follow-up shows that there have been 28 additional late deaths, including 23 of cardiac causes for a 91% survival at 5 years. Freedom from both late death and Q-wave myocardial infarction at 5 years was 61%. In the group going to emergency coronary artery bypass with refractory myocardial ischemia, the late cardiac survival was 90%, and in those without ischemia, 92% at 5 years, p = not significant. The MI--free survival in the group with refractory ischemia, however, was 56% versus 83% in the group without ischemia, p less than 0.0001. Multivariate analysis showed the highest late event rates for patients with Q-wave myocardial infarction at the initial emergency coronary artery bypass, age older than 65 years, angina class III or IV, and prior coronary bypass surgery. In spite of a continuing high incidence of early acute myocardial infarction and an increasing operative mortality rate (7%) in the latest 3 years cohort of patients, excellent late survival and low subsequent cardiac event rates demonstrate the lasting effectiveness of prompt, successful emergency coronary bypass surgery for failed percutaneous coronary angioplasty.

Cardioplegia for transplantation: failure of extracellular solution compared with Stanford or UW solution.

Crystalloid cardioplegia with an extracellular fluid formulation is widely used for donor heart protection. A survey of 109 transplant programs yielded 62 replies with 42% of respondents using variations of extracellular solution and 45% using the dextrose and mannitol-based Stanford solution. These two commonly used clinical solutions and University of Wisconsin (UW) solution, which has had success in clinical hepatic and renal transplantation, were compared in a canine model of cardiac transplantation. After antegrade hypothermic cardioplegic arrest, the experimental hearts were excised and stored at 4 degrees C for 6 hours (n = 29). An oxygenated, blood-primed isolated heart preparation was used for reperfusion. After a rest of 45 minutes, cardiac output was increased against constant afterload until a left atrial pressure of 15 mm Hg was reached. The maximum cardiac performance measured by cardiac index, minute work, and stroke work was highly significantly better with Stanford or UW solution protection than with the extracellular solutions (p less than 0.0001). Assuming a cardiac index of 50 mL.kg-1.min-1 is necessary for successful separation from cardiopulmonary bypass, only 1 of 14 extracellular and 15 of 15 Stanford and UW animals would have survived (p less than 0.0001). This study strongly suggests that extracellular cardioplegia is inferior for cardiac transplantation and that programs using this solution should reevaluate their method of myocardial protection for donor hearts.

Cardiac missiles. A review of the literature and personal experience.

The management of retained missiles in the heart is still controversial. In an attempt to define the issue more clearly, the reported cases in the English literature from 1940 to 1988 (group 1) and our experience from 1968 to 1988 (group 2) were reviewed. In group 1 there were 222 missiles retained in the hearts of 201 patients. The retained missiles were 45 bullets in 45 patients, 109 shrapnel in 99 patients, 18 pellets in 7 patients, and 50 unidentified missiles in 50 patients. Thirteen of the missiles were completely embedded intramyocardial missiles, 122 were partially intramyocardial, 47 were free in a cardiac chamber, and 40 were intrapericardial. One hundred four of the missiles were removed and 118 were left in place. In group 2 there were 24 missiles, 18 bullets, 1 bullet fragment, and 5 pellets retained in the hearts of 24 patients. Ten missiles were removed, no attempt was made in 13 patients, and an unsuccessful attempt was made to remove one other. From group 1 patients, 6 died, 2 with intracavitary missiles, 3 patients with partially intramyocardial, and 1 patient with an intrapericardial missile, all of whom had either unsuccessful or no attempt to remove the missile. Twenty-seven patients had symptoms, all of whom, except two, had either unsuccessful or no attempt to remove the missile. All group 2 patients did well and had been free of symptoms related to the missiles. This review suggests that the management of missiles in the heart should be individualized according to the patient's clinical course, the site, shape, and size of the missile, and that in selected patients missiles in the heart are tolerated well.

Ten-year experience with the porcine bioprosthetic valve: interrelationship of valve survival and patient survival in 1,050 valve replacements.

The porcine bioprosthetic valve was used in 440 patients having isolated mitral valve replacement (MVR), 522 patients having isolated aortic valve replacement (AVR), and 88 patients having MVR + AVR between 1974 and 1981. Patients with associated surgical procedures were excluded. Mean follow-up was 8.3 years. At 10 years, there was no difference in patient survival between those having AVR and those having MVR. Reoperations were performed on 192 patients. Endocarditis was the reason for reoperation in 3.7% of patients who had MVR and 10.6% of those who had AVR. Structural valve degeneration was the reason for reoperation in 89.7% of MVR patients and 78.8% of AVR patients (p = 0.04). Hospital mortality among patients having valve reoperations was 4.7%. At 10 years, the freedom from valve reoperation for all causes and from structural valve degeneration was significantly better for the AVR group than the MVR group (74% +/- 3% versus 61% +/- 4%, p = 0.004; and 79% +/- 3% versus 63% +/- 4%, p = 0.0006, respectively). For patients in their 60s, the 10-year freedom from reoperation was 92% +/- 2% for AVR and 80% +/- 6% for MVR (p = not significant). At 10 years, freedom from cardiac-related death and valve reoperation was best for both MVR and AVR patients in their 60s. Patients 70 years old or older rarely had reoperation but died before valve failure occurred. The 10-year freedom from all major valve-related events (cardiac-related death, reoperation, thromboembolism, endocarditis, and anticoagulant-related bleeding) was practically the same for both MVR and AVR patients (48% +/- 3% versus 49% +/- 3%, respectively). The porcine bioprosthetic valve is the valve of choice only for patients 60 years old or older. Patients in their 70s have an extremely low rate of reoperation but a high rate of cardiac-related death and do not outlive the prostheses.

Preischemic perfusion of hypertrophied myocardium with perfluorocarbons.

The increased susceptibility of hypertrophied myocardium to ischemic injury is well known. Hypertrophied hearts possess lower preischemic high energy phosphate stores and develop ischemic contracture following a shorter ischemic interval than normal hearts. The purpose of this study was to determine the ability of preischemic, arrested perfusion of the hypertrophied rat heart with oxygenated, glucose-containing perfluorocarbon cardioplegia (FC-43) to restore myocardial ATP stores to normal and prolong the duration of global ischemia prior to contracture initiation. Hearts from normal (NL) rats and hypertrophied hearts from spontaneously hypertensive rats (SHR) were subjected to 2 or 15 min of preischemic, arrested perfusion with FC-43 utilizing a modified Langendorff preparation. ATP was determined via HPLC and time to initiation of ischemic contracture was measured. Two minutes of FC-43 perfusion restored ATP in the SHR group to normal levels (P = NS compared to normal controls) and prolonged the time to initiation of ischemic contracture by 107%. Perfluorocarbons, with their unique oxygen-carrying properties, may be an ideal vehicle for intervention designed to enhance the tolerance of hypertrophied hearts to ischemia.

Reperfusion of infarcting myocardium: benefit of surgical reperfusion in a chronic model.

Surgical reperfusion of experimental infarction leads to improved recovery of regional function compared with medical reperfusion, but sustained myocardial salvage has not been demonstrated. Twenty-two dogs were subjected to two hours of anterior descending occlusion and divided into three groups: group P (n = 7), no reperfusion; group M (n = 8), medical reperfusion; and group S (n = 7), controlled surgical reperfusion. Ischemia caused systolic bulging (-36% of control systolic shortening, p less than 0.01) and decreased regional work (9% of control pressure-length loop area, p less than 0.05). Thirty minutes after reperfusion group M had persistent systolic bulging (-9% of control systolic shortening) and decreased regional work (9% of control pressure-length loop area), whereas group S had +17% of control systolic shortening and 33% of control pressure-length loop area. After 1 week, regional function improved in all three groups (percent of control systolic shortening: group P, 26%; group M, 19%; group S, 52%), but systolic shortening was significantly better in group S (p less than 0.05 versus group M). Surgical reperfusion also resulted in one half of the eventual myocardial necrosis found in the other groups (group P, 45% of area at risk; group M, 38%; group S, 19%; p less than 0.05, group S versus group P or M). In this model, medical reperfusion offered no demonstrable benefit, whereas controlled surgical reperfusion led to a sustained (1 week) improvement in regional function and significant myocardial salvage.

Missiles in the heart.

The records of 24 patients who had a missile retained in the heart and who were treated at Grady Memorial Hospital from 1968 to 1987 were reviewed. In 22, the missile lodged in the heart after its direct injury and in the remaining 2, after the bullet injured a systemic vein. Immediately after the cardiac injury, 7 of the 22 patients were seen with cardiac tamponade (3 also had hemothorax), 11 were seen with hemothorax, 5 were asymptomatic, and 1 was in shock. Seven patients underwent emergency thoracotomy; the bullet was removed in 3, but in the remaining 4 patients, it was not located. In the other 17 patients and in the 4 in whom the bullet could not be found during emergency thoracotomy, the diagnosis was suspected from the chest roentgenograms and confirmed by cardiac fluoroscopy or angiocardiography. Eight patients with retained bullets underwent elective operation; the bullet was removed from 7 and in 1 it was left embedded in the right ventricular septum. All 10 patients who underwent excision of the missile recovered without complication except 1 in whom pericarditis developed, and all were followed for up to 17 years. All 14 patients with a retained missile in the heart had no cardiac symptoms referable to the bullet and were followed for up to 15 years. This experience suggests that the management of patients with a bullet of .38 caliber or smaller that is retained in the heart should be individualized according to the patient's clinical course and the site of the bullet and that in select patients, bullets left in the heart are tolerated well.

Intracavitary right heart cooling during coronary bypass surgery. A prospective randomized trial.

Augmented right heart cooling (RHC) with bicaval cannulation, pulmonary artery venting, and intracavitary cooling has been advocated for prevention of right ventricular failure and supraventricular tachyarrhythmias after open heart surgery. To evaluate RHC, 78 patients undergoing coronary bypass surgery were prospectively randomized to receive added RHC (n = 38) or standard protection with single atrial cannulation (SC) (n = 40). RHC and SC patients were similar regarding right coronary artery occlusion (n = 10 and 12, respectively), number of grafts performed (3.7 +/- 1.0 and 3.4 +/- 0.9), and cross-clamp time per graft (10.2 +/- 1.8 and 9.8 +/- 2.3 minutes). RHC led to significantly lower right atrial (11.6 degrees +/- 1.0 degree vs. 19.5 degrees +/- 3.3 degrees C) and right ventricular (7.2 degrees +/- 1.9 degrees vs. 12.2 degrees +/- 1.9 degrees C) temperatures. There was no detectable deterioration in right heart function or left heart function in either group after cardiopulmonary bypass. Bypass time was longer in RHC patients (86.7 +/- 17.9 vs. 76.0 +/- 18.2 minutes, p less than 0.05). Technical problems related to multiple cannulation occurred in four RHC patients. After cross-clamp removal, creatine kinase-MB levels were significantly higher with RHC at 2 hours (14.2 +/- 7.6 vs. 6.4 +/- 4.6 IU/l, p less than 0.001), 12 hours (19.1 +/- 19.5 vs. 8.6 +/- 10.3 IU/l, p less than 0.005), and 24 hours (14.1 +/- 19.6 vs. 7.1 +/- 9.2 IU/l, p less than 0.05). Mortality and morbidity were similar in the two groups. In particular, supraventricular tachyarrythmias occurred in 11 (28.9%) RHC and 10 (25%) SC patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictors of mortality, complications, and length of stay in aortic valve replacement for aortic stenosis.

The introduction of aortic balloon valvuloplasty has prompted review of established techniques to treat aortic valve disease. To this end, the surgical results were reviewed for 1,148 patients undergoing aortic valve replacement, with and without associated coronary artery bypass grafting, for aortic stenosis between January 1, 1975 and September 1, 1987. The overall death rate was 4.6%. The neurological event rate (stroke or reversible ischemic event) was 4.2%, the myocardial infarction rate was 3.5%, and 30.7% had a hospital stay in excess of 10 days. Mortality for isolated elective aortic valve replacement rose from 2.5% for patients under age 70 to 7.3% for those over age 70. Mortality for elective aortic valve replacement plus coronary bypass was 3.8% for patients under age 70 and 11.6% for patients over age 70. The neurological event rate rose from 3.0% to 8.4% and the prolonged length of stay from 28% to 42%. By stepwise logistic regression analysis, the predictors of in-hospital mortality were age and emergent surgery. Age was the only multivariate predictor of neurological events. The year of surgery and emergent status were the multivariate predictors of prolonged length of hospital stay. Aortic valve replacement for aortic stenosis is a well-established technique with low neurological event rates and mortality, which may be predicted in advance. Newer techniques must be considered in light of data such as these.

Hemangioma of the right ventricle causing outflow tract obstruction.

A 3 1/2-year-old child had a murmur of pulmonary stenosis. Echocardiography and cardiac catheterization revealed a pulmonary infundibular obstruction. Magnetic resonance imaging of the heart demonstrated a mass in the interventricular septum. The mass was successfully resected and a pathologic diagnosis of capillary hemangioma was made. Only two previous cases of hemangioma causing right ventricular outflow obstruction have been reported; both of these cases involved adults. This case represents the first report of a hemangioma causing right ventricular outflow tract obstruction in a child. An exploratory operation with resection is the treatment of choice.

Treatment of moderate mitral regurgitation and coronary disease by coronary bypass alone.

We have favored treatment of moderate mitral regurgitation and coronary disease with coronary bypass alone because of the high operative mortality of combined mitral valve replacement and coronary bypass. Between 1977 and 1983, coronary bypass alone was performed on 58 patients (mean age 63 +/- 8 years). Preoperatively, 90% had Canadian Cardiovascular Society class III or IV angina, and 10% had class III or IV congestive heart failure. In 72% mitral regurgitation had been caused by coronary disease. Hospital mortality was 3.4% (2/58). At follow-up (100% complete, mean 4.3 years) 66% of survivors were functional classes I and II (compared with 7% preoperatively, p less than 0.0001). Of those patients who worked preoperatively, 84% returned to work. There were no reoperations. The 5-year survival was 77%. In the same period combined mitral valve replacement and coronary bypass was required in 20 unmatched patients with moderate mitral regurgitation and coronary disease. Indications for valve replacement included congestive heart failure (10 cases), high left atrial pressure (three cases), and mitral stenosis (four cases). In these patients with more advanced symptoms the hospital mortality was 25%, and the 5-year survival was 31%. Treatment of moderate mitral regurgitation and coronary disease by coronary bypass alone achieved excellent hospital survival and long-term functional stability without a subsequent valve operation.

Vasodilator drug effects on internal mammary artery and saphenous vein grafts.

The internal mammary artery is a dynamic conduit used for myocardial revascularization in which potential exists for spasm as well as for vasodilation. This study investigated vasodilator drug effects on the mammary artery using nitroprusside and nitroglycerin in vitro to measure the inhibition of contraction of human internal mammary artery and in vivo to examine blood flow through a canine mammary artery. In the in vitro study, ring segments of human internal mammary arteries were suspended on strain gauges in muscle baths containing 37 degrees C Krebs solution for measurement of isometric tension in vitro. Arterial contraction was stimulated with 70 mM potassium and 10 microM norepinephrine, and inhibition of contraction by vasodilators was measured. Nitroprusside was more potent and effective than was nitroglycerin in inhibiting potassium and norepinephrine contraction. The in vivo study utilized a canine (n = 8) right heart bypass preparation that allowed precise control of cardiac output, blood pressure and heart rate, which were maintained constant. The internal mammary artery graft and the saphenous vein graft perfused the same coronary artery bed. Electromagnetic flow probes measured graft flow (with the other graft occluded) before and after 15 min of drug infusion (1 microgram/kg per min). Nitroglycerin significantly increased mammary artery flow 36 +/- 13%, whereas nitroprusside significantly decreased it 12 +/- 2%. Saphenous vein grafts responded differently; graft blood flow decreased with nitroglycerin and increased with nitroprusside. Thus, although nitroprusside was more effective than nitroglycerin in inhibiting mammary artery contraction in vitro, it decreased internal mammary artery graft flow measured in vivo. Nitroglycerin had the opposite effect, increasing mammary graft flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Trends in invasive treatment of single-vessel and double-vessel coronary disease.

We examined our practice of invasive therapy for one- and two-vessel coronary disease to assess the impact of the randomized trials of coronary surgery and the current use of angioplasty. We first reviewed our results with coronary artery bypass graft in equivalent patients in the Coronary Artery Surgery Study with one- and two-vessel disease between 1976 and 1981. Among 1376 patients, hospital mortality was 0.07%, and 5-year survival was 95.2% +/- 0.8%. To define trends in invasive therapy, which have since occurred, we compared 100 patients with one- and two-vessel disease in each of three groups: 1979 coronary artery bypass graft, 1984 coronary artery bypass graft, and 1984 percutaneous transluminal coronary angioplasty. Preoperative characteristics in the average 1979 and 1984 patients were similar; however, in 1984, patients who had a coronary artery bypass graft were older than patients who had percutaneous transluminal coronary angioplasty (61.5 versus 56.7 years, p less than 0.01), they required more heart medications (2.1 versus 1.5, p less than 0.01), had more previous infarctions (0.8 versus 0.5, p less than 0.01), and more patients had an ejection fraction of less than 50% (34% versus 7%, p less than 0.01). Patients who had angioplasty had a shorter postoperative stay (median number of days 7, 7, 2, p less than 0.01). Freedom from major complications was similar among the groups (91%, 87%, 85%). Unstable symptoms were the most frequent indication for invasive therapy (approximately 80%), whereas long-term symptoms, those considered in the randomized trials, occurred in relatively few patients. The number of patients without at least one definite indication for invasive therapy was 13%, 3%, and 11%, p less than 0.05, suggesting that the indications for the 1984 coronary artery bypass graft group have become more restrictive since the 1979 coronary artery bypass graft group. Indications for the 1984 percutaneous transluminal coronary angioplasty group remained less restrictive, being similar to those for the 1979 coronary artery bypass graft group. A continuing trend toward the use of percutaneous transluminal coronary angioplasty was evident, as 56% of the 1979 coronary artery bypass graft group of patients and 32% of the 1984 coronary bypass group of patients would be offered percutaneous transluminal coronary angioplasty rather than coronary artery bypass graft on the basis of 1986 percutaneous transluminal coronary angioplasty criteria. The p values were obtained with analysis of variance or chi 2 test.

Emergency coronary bypass for cardiogenic shock.

Emergency coronary bypass for cardiogenic shock has been associated with a high operative mortality. From January 1983 through March 1986, 69 patients at Crawford W. Long Hospital underwent emergency coronary artery bypass. Seventeen of 69 were in shock, 15 with hypotension requiring treatment (intra-aortic balloon pump in 10; catecholamines in six). The other two patients had a low cardiac index and a pulmonary capillary wedge pressure greater than 25 mm Hg. Of these patients, nine presented with acute infarction, four with failed angioplasty, and four with uncontrollable angina. Four patients required cardiopulmonary resuscitation. After operation, 94% of the patients required catecholamine support and 71% were treated with an intra-aortic balloon pump. There were two hospital deaths (12%). The median postoperative stay for survivors was 9 days. Major complications occurred in 47%. Follow-up (100%, mean 20.5 months) revealed no late deaths, a 3 year survival of 88 +/- 8%, and a functional class of I in six patients, II in seven patients, and III in two patients. The nine patients who were working before operation all returned to work. Of the 52 emergency coronary bypass patients without shock, one patient died in the hospital (2%), 52% required catecholamines (p less than .05 vs shock group by chi-square analysis), and 12% required an intra-aortic balloon pump after operation (p less than .05 vs shock group by chi-square analysis). Median stay was 8 days. Complications occurred in 13% (p less than .05 vs shock group by chi-square analysis). Three year survival was 91 +/- 4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Limited resection of bronchogenic carcinoma in the patient with marked impairment of pulmonary function.

Surgical resection is the treatment of choice for non-small cell bronchogenic carcinoma, and it is the only method providing prolonged arrest and chance for cure. From 1974 through 1984, 32 patients with marked impairment of pulmonary function had a limited resection for carcinoma of the lung. Marked impairment is defined as a maximum breathing capacity less than 35 to 40% of predicted, forced expiratory volume in one second less than or equal to 1 liter, and forced expiratory flow (FEV25-75) of less than or equal to 0.6 liter. Limited resection is defined as an operation that is less than a lobectomy, generally a wide wedge or segmental resection. The pathological stage of disease was Stage I in 31 patients and Stage II in 1 patient. Ten patients were treated by segmental resection and 22 by wide wedge resection. Two-year and three-year survival is 84 and 78%, respectively, and 10 patients (31%) have survived for five years. Recurrent disease developed in 8 patients, 5 of whom died. Recurrence was highest when the lesion crossed an intersegmental plane. In 1978, postoperative radiation therapy was added to the treatment of all patients whose lesion crossed an intersegmental plane. Since then, 18 patients have undergone wedge resection and postoperative irradiation with only 2 local recurrences at two years.

A valveless counterpulsation left ventricular assist pump in the descending aorta: hemodynamic benefit with a reduced risk of cerebral emboli.

Because of valve malfunction and cerebral embolism reported with use of the total artificial heart, the descending aorta was reexamined as a site for a valveless counterpulsation left ventricular assist pump. The pump was introduced into the thoracic aorta at the level of the eight thoracic vertebra in 11 canine right-heart bypass preparations. Heart rate (110 beats per minute), stroke volume (20 ml), and mean arterial pressure (80 or 100 mm Hg) were precisely controlled. The pump ejection volume was adjusted to equal 1 time or 2 times the stroke volume of the dog. A 20-ml ejection led to an 11% reduction in left atrial pressure, an 11% reduction in peak left ventricular pressure, and a 20% reduction in tension time index (all, p less than .05 at a mean arterial pressure of 80 mm Hg). Systolic shortening (ultrasonic crystals) increased by 5% (p less than .05 at a mean arterial pressure of 80 mm Hg). A 40-ml pump ejection led to an 11% reduction in mean left atrial pressure, a 17% reduction in peak left ventricular pressure, and a 21% reduction in tension time index (all, p less than .05 at a mean arterial pressure of 80 mm Hg). The systolic shortening increased by 15% (p less than .05). To assess the relative risk of cerebral embolism, albumin spheres (40 to 60 micrograms) labeled with technetium-99 were injected into the pump chamber in 5 dogs (40-ml ejection, 2.1 +/- 0.1 times the dog's stroke volume).(ABSTRACT TRUNCATED AT 250 WORDS)