Biomedical subjects
Publications and source records attributed to D G Mulder.
Operative mortality associated with complete atrioventricular canals has decreased from 75 per cent to as low as 10 per cent. The present report reviews the UCLA Hospital experience with the six children who underwent repair of this defect in the past two years. Emphasis is placed on preoperative assessment, operative technics, and postoperative management.
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New and innovative developments in cardiothoracic surgery include the pulmonary effects of certain inotropic drugs, the role of patent ductus closure in neonatal respiratory distress syndrome, the use of immunostimulating agents as adjuvants in the treatment of cancer of the lung, ingenious operative procedures to correct transposition of the great vessels and aortic stenosis, and improved methods to protect and assist the heart during cardiac operations.
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Using visual inspection of phasic flow patterns and understanding their physical determinants, intraoperative decisions regarding flow distribution, function of revascularized myocardium, and collateral communications can be made. Mean flow measurements cannot provide this information. Systolic compressive forces across most of the normally contracting left ventricle limit systolic myocardial perfusion. Consequently, normal flow through the left anterior descending, left circumflex, and dominant right coronary artery (supplying the inferior left ventricle) is predominantly diastolic (greater than 60%) and remains so during reactive hyperemia. Representative examples from 100 consecutive revascularizations are presented showing that when more than 40% of flow is systolic in the right coronary artery, high mean flows (greater than 100 ml/min) may go predominantly to the right rather than the left ventricle; in the case of the left coronary artery, high mean flow may supply myocardium undergoing infarction or replaced by scar rather than normally contracting muscle. When more than 60% of flow is diastolic without reactive hyperemia, borderline mean flow (40 to 60 ml/min) may indicate lack of distal ischemia rather than fixed distal resistance.
Accurate continuous measurement of arterial blood pressure, especially during and following operation, is indispensable for optimal management of the seriously ill newborn or infant. Conventional indirect techniques (flush technique, auscultation, Doppler monitoring device) for assessing the circulatory status in this age group are not reliable, and a direct method would be preferable. Arterial cannulation in such patients has been discouraged by the technical problems related to former techniques.
The results following aortic valve replacement (AVR) were compared in 40 patients in whom the myocardium was protected by topical hypothermic arrest or continuous coronary perfusion with sustained electrical fibrillation (Group A) and 40 similar patients in whom the hearts were also continuously perfused but were kept in the beating state (Group B). The operative mortality was not greatly different between the two groups, being 10 and 5%, respectively. The postperfusion cardiac performance was strikingly different, however. Seventeen patients (43%) in Group A required inotropic support, while this was necessary in only 1 patient (3%) in Group B. In this instance, recurrent ventricular fibrillation persisted despite attempts at reversion. These data show that the myocardium is preserved best during AVR when continuous coronary perfusion is used and the heart is maintained in the beating state.
It is recognized that postoperative mortality, infarction and the need for inotropic support are increased following myocardial revascularization in highrisk patients. Operations were carried out in 57 such patients in whom one or more of the following factors were present: ventricular dysfunction-ejection fraction less than 0.4 (17), unstable (8) or preinfarction angina (29), evolving infarction (8), recent infarction (less than two weeks before) (5) and refractory ventricular tachyarrhythmia (4). Combined risk factors were present in nine patients. The following principles were utilized to minimize ischemic injury: (1) avoidance of prebypass hypertension and hypotension, (2) avoidance of extreme hemodilution, (3) avoidance of ventricular fibrillation, (4) maintenance of beating empty heart, when possible, (5) the limiting of ischemic periods to less than 12 minutes (hypothermia 32 degrees C) and (6) repaying myocardial oxygen debt with total (vented) bypass, when necessary. The following results were obtained: inotropic support was required in five patients (9 percent), "new" postoperative infarction occurred in five patients (9 percent) and one patient died (2 percent). These results are comparable to those reported in good-risk patients, and indicate that optimal myocardial protection will allow safe revascularization in a high-risk patient.
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Despite experimental evidence that myocardial depression resulting from rapid transfusion of ACD blood (citrate binds ionic calcium) is avoidable by simultaneous calcium administration, most hypovolemic patients receive calcium either after transfusion or not at all. Similar iatrogenic hypocalcemic myocardial depression occurs in normovolemic patients with known myocardial damage who are dialyzed for acute uremia when ACD blood prime is used at high initial flow rates (350 c.c. per minute) and when dialysis is performed against low calcium dialysate (2.5 mEq. per liter or less). This study tests the hypotheses that (1) rapid transfusion of as little as one unit of CPD blood causes a significant reduction in ionized calcium, (2) the depressive effect of CPD blood is significant and similar to that of ACD blood, (3) rapid blood transfusion (ACD or CPD) is safe if calcium is given simultaneously, (4) addition of calcium to the extracorporeal heparinized blood prime used in dialysis prevents initial depression, and (5) hemodynamic instability during dialysis is prevented when the dialysate is normocalcemic. From the results of our study, we made the following conclusions: (1) Ionized calcium is reduced significantly by rapid transfusion of CPD blood; (2) acute myocardial depression noted with CPD blood is similar to that previously observed with ACD blood and is prevented during transfusion of either type of blood by simultaneous calcium administration; and (3) hemodialysis in patients who have had cardiac surgery is safe if calcium is added to blood prime and dialysate is made normocalcemic.
Postoperative mortality, infarction, and need for inotropic support are reportedly increased following myocardial revascularization in "high-risk" patients. We believe these complications result from inadequate protection of the compromised myocardium and should not occur with greater frequency in "high-risk" than "Low-risk" patients if the heart is optimally protected during the entire course of the operative procedure. Results following revascularization in 50 consecutive "low-risk" and 50 consecutive "high-risk" patients were analyzed. One or more of the followin factors were present in the "high-risk" group: ventricular dysfunction--ejection fraction less than 0.4, preinfarction angina, evolving infarction, recent infarction (less than 2 weeks), and refractory ventricular tachyarrhythmia. The following principles were used in all patients to minimize ischemic injury: 1) avoidance of pre-bypass hypo- or hypertension, 2) limitation of ischemic arrest to less than 12 minutes, 3) avoidance of ventricular fibrillation, and 4) prolongation of total bypass as necessary to repay the myocardial oxygen debt. Postoperative inotropic support was required in 10% of "high" and 10% of "low-risk" patients, new postoperative infarction developed in 10% of "high" vs. 10% "low-risk" patients; death occurred in 2% of "high" vs. 4% "low-risk" patients. These results are comparable and indicate that optimum myocardial protection allows safe revascularization in the "high-risk" patient.
In 20 years, 19 patients with myasthenia gravis and invasive thymoma have been seen by the Neurology Service at the UCLA Center for Health Sciences. This represents 4 percent of 493 myasthenia gravis patients seen during the same time and 37 percent of myasthenic patients with thymomas. Eight are still alive and 11 have died. Fifteen patients had the onset of myasthenic symptoms before discovery of the thymoma, while only four patients had chest symptoms and/or radiographic evidence of an anterior mediastinal mass prior to the onset of weakness. Radical excision of the tumor, if possible, and the remaining thymus, high dosage alternate day prednisone, and radiation therapy, if indicated, seem the treatments of choice. Recurrences of tumor nodules may necessitate further local radiation or the use of cytotoxic agents.
Our experimental studies since 1972 show that the heart is preserved best during cardiopulmonary bypass when it is in the beating, nonworking state. Results after mitral valve replacement (MVR) from 1968 to 1974 using various techniques of cardiac preservation were compared. In group I were 47 patients (1968 to 1972) in which either profound, topical hypothermia with prolonged ischemic arrest (19) or ventricular fibrillation with continuous coronary perfusion (28) was used. In group II there were 22 patients (1972 to 1974) in whom the heart was in a beating, nonworking state between brief periods of ischemic arrest. In group I 55% (25/47) required inotropic support postoperatively, and 17% (8/47) died. In group II 5% (1/22) required inotropic support postoperatively, and this patient died (5% mortality). Extended periods of ischemic arrest were necessary because of intraoperative complications in this patient. These data show that depressed postoperative myocardial performance occurs rarely when the heart is preserved in the beating, nonworking state during MVR and ventricular fibrillation and prolonged topical hypothermic anoxic arrest are avoided.
Depressed postoperative myocardial performance (low output syndrome) requiring inotropic drugs or balloon counterpulsation is due to subendocardial ischemic damage. Before July, 1972, we needed inotropic drugs in 30 to 52 per cent of 189 patients undergoing coronary revascularization or aortic or mitral valve replacement in whom we used ischemic arrest, profound topical hypothermia, and ventricular fibrillation. The mortality rate ranged from 10 to 17 per cent. Our experimental studies show that morbidity and death in such cases are caused by ischemic injury to the heart resulting from inadequate myocardial protection during bypass. Based on these experimental studies, we have, since July, 1972, employed the following principles clinically: (1) Maintain beating empty heart whenever possible; (2) maintain adequate coronary perfusion pressure (less than 80 mm. Hg); (3) avoid extreme hemodilution; (4) avoid ventricular fibrillation; (5) avoid prolonged hypothermic arrest, limiting ischemic periods to less than 15 minutes; (6) repay myocardial ischemic oxygen debt with total (vented) bypass; and (7) optimize DPTI/TTI (supply/demand ratio) pre- and postoperatively. These principles were followed in 189 consecutive operations, and postoperative inotropic drugs were needed in only 12. The principles were violated in 4 of the 12 patients (6 per cent), and 5 others had identifiable causes of myocardial depression; low output syndrome was unexplained in only 3 patients (1.7 per cent).
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