Imperial Ballroom

15. Fixation of the Homograft Aortic Valve by Interposed Metal Rings

Alexander S. Geha,* Jack L. Titus,* and Dwight C. McGoon

Rochester, Minn.

The homograft aortic valve is excellent in many ways as a replacemen for the diseased aortic valve, but has three chief limitations: 1) greater technical difficulty of insertion, 2) a high incidence of postoperative incompetence, and 3) the late result remains in doubt. This study is an evaluation of a method designed to overcome the first two of these limitations and to provide data relative to the third. The homograft aortic valve is attached preoperatively to a fine ring of metal shaped to the exact configuration o its basal rim. The ring is clothed in a closely fitting sleeve of porous Teflon cloth. This unit is attached to the basal rim of the excised cusp with ; single row of interrupted sutures which are placed prior to lowering the valve into position. The aortic root is thus obligated to conform to the dimensions of the homograft. No metal is exposed to the blood stream Homograft aortic valves of this type have been inserted in a series of calves allowing functional, gross and microscopic examinations of the valves a regular intervals up to five months postoperatively. Clinical application o this method appears to be warranted.

16. Heterotransplantation of the Aortic Valve in Calves

Peter E. Blundell,* and J. K. Macfarlane,* Montreal, Quebec

Sponsored by Henry J. Scot

Widespread acceptance of the aortic valve homograft has revived an interest in the use of biologic materials for replacement of the diseased aortic valve. Recently, preliminary studies of both experimental and clinical aortic valve heterografts have been reported. This paper presents the fat of 27 human aortic valves inserted in the subcoronary position of calves Three methods of valve preparation and storage were used; a) fresh ant sterile, b) treated with betapropiolactone and c) treated with betapropiolactone and freeze-dried. When death occurred all valves were examined photographed and submitted for microscopic study. Twenty-two calve survived more than two weeks and one animal still lives 52 weeks post operatively. The typical lesion noted was early fibrin deposition on the ventricular aspect of the valve. This progressed until leaflet mobility was impaired and the valvular apparatus became stenotic and calcified. N< difference was noted between different methods of valve preparation ant storage. Two animals surviving 3 weeks and 3 months had almost normal appearing valves. No infection was noted on any valve. The results of the gross and microscopic findings will be interpreted and compared with : similar series of 10 aortic valve homografts.

17. Biological Study of the Homologous Aortic Valve in Dogs

Hitoshi Mohri,* Dennis D. Reichenbach,* Robert W. Barnes,*

and K. Alvin Merendino, Seattle, Wash.

Clinical experience with homologous aortic valves has demonstrated prolonged function of transplants. We have demonstrated low antigenicity of the aortic valve. However, the ultimate fate of transplants is not well understood. Fate of orthotopically transplanted single homologous aortic leaflets has been studied in 35 dogs. Valves obtained from females were prepared as 1) fresh, 2) betapropiolactone-sterilized or 3) frozen leaflets, and transplanted into male recipients. Histology and viability of transplants were studied utilizing tissue culture methods and sex chromatin body analysis. No rejection of any transplanted leaflets has been demonstrated up to 11 weeks postoperatively. Fresh leaflets survived and even proliferated 8 weeks after transplantation. By contrast, no cell growth was shown in tissue culture of betapropiolactone-sterilized or frozen leaflets up to 11 weeks, suggesting such leaflets maintain function as dead tissue. However, possible early host substitution was implied by endothelialization at the base of one of the betapropiolactone-sterilized leaflets at 11 weeks postoperatively. Fate of the transplanted living tissue or substitutional process by host cells over longer periods following transplantation will be discussed.

18. Prevention of Thrombus on Rigid Prosthetic Cardiac Valves by an Autogenous Tissue Covering

Nina Braunwald, and Lawrence I. Bonchek,* Bethesda, Md.

Thromboembolism seldom occurs after the insertion of intracardiac fabric prostheses that permit tissue ingrowth. This experience suggested the evaluation of rigid prosthetic heart valves covered by host tissue. Specially modified ball or lens valves were inserted in 31 calves; all metal parts of the valves were covered with porous synthetic fabric. No anticoagulants were administered. In 16 animals, sacrificed one to 9/2 months postoperatively, no thrombus was found; the fabric-coated valve cages and orifices were symmetrically covered with thin, transparent layers of vascularized fibrous tissue. The movement of the ball or lens within the cage was unrestricted. Twelve animals are well, two to 10 months postoperatively, and two died with thrombosed valves two and four weeks postoperatively, before tissue ingrowth occurred. Of 20 control calves with standard prostheses, four died with thrombosed valves; 12 others had thrombus on the valve cages at the time of death or sacrifice. These findings demonstrate that thrombus formation on prosthetic heart valves of conventional design can be prevented by encouraging tissue encapsulation of all stationary foreign material. This can be accomplished by covering all metal parts of the valves with porous fabric that promotes autogenous tissue ingrowth.

19. The Production of Muscular Subaortic Stenosis in Dogs

Thomas H. Burford, Alex F. Hartmann, Jr.,* Thomas B. Ferguson,

and Raymond W. Ferrier,* St. Louis, Mo.

To gain etiologic and pathophysiologic information about this condition, the ascending aortas of 31 six-week-old puppies (5-7 pounds) were snugly banded with Dacron tape. When the animals reached adult size serial left heart catheterizations and angiocardiograms were performed. Satisfactory data were obtained on 8 animals 17 to 22 months after banding. The resting systolic gradient across the banded area averaged 34 mm Hg. There was no resting gradient across the left ventricular outflow tract in any of the animals. After 5 mgm/kilo of Isuprel intravenously the gradient across the banded area increased to 74 mm Hg., and 7 of the 8 dogs had an average LV outflow tract gradient of 20 mm Hg. The 8th dog developed a LV gradient of over 200 mm Hg. with Isuprel. Angiograms and later autopsy studies showed that the animals with the low LV gradient had chamber dilatation and moderate hypertrophy of the ventricular wall (6 mm), while the animal with the high LV gradient had no dilatation, but had marked hypertrophy of both the septum (15 mm) and free wall (10 mm). This study supports the view that the development of muscular subaortic stenosis may depend more on anatomic variations in the left ventricle than on pure functional stress.

20. Diaphragmatic Pacing in the Treatment of Hypoventilation Syndromes

Edward A. Stemmer,* Donald W. Crawford,* James P. Carey,*

and John E. Connolly, Los Angeles, Calif.

Although the availability of transistorized circuits has made prolonged cardiac pacing practical, this technic has not been widely applied to other organs. Our attempts to treat a patient with hypoventilation due to primary carbon dioxide insensitivity led us to investigate the possibility of using electrical stimuli to pace diaphragmatic contractions. The problem is more complex than cardiac pacing since constant stimulation of the diaphragm will interfere with swallowing and speaking. Moreover, the contour of the wave form, frequency of impulse and duration of impulse are also important if smooth, non-painful diaphragmatic motion is to be produced. The basic problems involved in diaphragmatic pacing were studied in ten dogs using a nerve stimulator. Transvenous placement of the electrodes was utilized to avoid the risks of thoracotomy. Respiratory rate and volume were measured with a pneumotachygraph. The effectiveness of ventilation was evaluated by means of serial blood gas analyses while diaphragmatic activity was monitored by cineradiography. After determining the electrical characteristics necessary to stimulate normal diaphragmatic contractions, a transistorized device was developed that was small enough to be implantable. The design of the instrument and the application of this technic in patients will be presented.

21. The Role of Functional Demand on Development of Pulmonary Lesion During Hemorrhagic Shock

Ben M. Willwerth,* Fred A. Crawford, Jr.,* Will C. Sealy, and

W. Glenn Young, Jr., Durham, N. G.

During hemorrhagic shock in the dog significant morphologic changes in the lung may develop. This could be the result of a circulating toxin liberated during shock, or from local changes that follow increased functional demand in a lung supplied with inadequate blood flow. To study this, one lung of 10 dogs was completely isolated from all of its vascular connections during a 2 hour period of severe hemorrhagic shock. The lung was reconnected after shock period. In a group of 10 dogs not in shock, one lung was occluded for 2 hours as in the experimental group. Nine of 10 lungs perfused during shock revealed severe morphologic changes but little immediate functional change, whereas none of the isolated lungs in the experimental or control group revealed either functional or morphologic alterations. The results of this study show that the lung forced to function during shock may show severe morphologic changes, whereas the lung in the same dog isolated from the circulation during shock will be spared. Local changes in the lung resulting from functional demand in face of low blood flow rather than a circulating toxin may be the cause of the morphologic changes in the lung in hemorrhagic shock.

22. A Study of the Acute and Chronic Respiratory Pathophysiology of Hemorrhagic Shock

J. N. Henry,* A. H. Mcardle,* H. J. Scott, and F. N. Gurd,*

Montreal, Quebec

Cardiac outputs, right and left atrial pressures, and pulmonary artery pressures were monitored by means of chronically implanted catheters in dogs subjected to 4 hours of hemorrhagic shock. The animals were resuscitated and a chronic shock preparation was obtained which allowed continued study for 18-72 hours. The expected sustained rise in pulmonary arterial pressure was accompanied by a fall in cardiac output to 23% of control value during the period of hypovolemia, and to 70-93% of control value during resuscitation. The left atrial pressure remained low during the time that the right atrial and pulmonary arterial pressures were elevated. This suggested a pulmonary etiology for the increased pulmonary arterial and right atrial pressures. The lungs showed a significant increase in water content when wet and dry weights were compared, while microscopic examination revealed congestive atelectasis, pulmonary edema, and intra-alveolar hemorrhage. Previous studies have demonstrated a significant decrease in the surface activity of the alveolar lining, and a defect in phospholipid metabolism during the period of resuscitation. These findings support the thesis that the elevated central venous pressure and the pulmonary lesions accompanying hemorrhagic shock can be due to intrinsic pulmonary pathology causing increased pulmonary resistance without left ventricular failure.

23. Pathogenesis of the Post-Cardiotomy Syndrome

Donald R. Kahn,* Paul Y. Ertel,* William H. Murphy,*

Marvin M. Kirsh,* Sathaporn Vathayanon,* Aaron M. Stern,*

and Herbert Sloan, Ann Arbor, Mich.

During the fall of 1965, 23 of 70 patients undergoing cardiac surgery developed the "post-cardiotomy syndrome." Symptoms, appearing in a few days after operation, were prolonged fever, pleuritic chest pain, tachycardia, extreme fatigue, hepatomegaly, and pericardial and pleural friction-rubs. Most patients showed characteristic mucosal lesions of the mouth or lip, which were small, white, painful areas of induration raised above the mucosal surface, and not ulcerated. Microscopic examination of the oral lesions disclosed patchy areas of edematous, degenerating epithelial cells containing deeply basophilic inclusion bodies. Symptoms subsided in two weeks only to reappear three to six weeks later. Some patients had no early symptoms. Laboratory studies showed the appearance of or a rising cold-agglutinin titer, atypical lymphocytes, and EKG findings. Specimens taken from the oral lesions and blood yielded agents with properties of viruses by tissue culture techniques. The agents isolated appear to be members of the para-influenza family. One patient had a similar agent found in the bone marrow taken at the time of operation. These studies suggest that pre-existing virus of the para-influenza family is activated by cardiac surgery to produce a clinical picture described as the "post-cardiotomy syndrome."

24. Hematologic Limitations of Prolonged Cardiopulmonary Bypass

Robert L. Reploole,* and Sherwin V. Kevy,* Boston, Mass.