Wednesday Afternoon, April 10, 1963

2:00 P.M. Scientific Session: THORACIC SURGERY FORUM

Emerald Room

37. Evaluation of Two Prostheses for Total Replacement of the Mitral Valve

F. S. Cross, (and by invitation) A. N. Gerein, and

R. D. Jones, Cleveland, Ohio

Although significant advances have been made in the clinical use of total valve prostheses, continued research is necessary to improve designs, materials, and techniques of insertion. Two types of mitral replacements have been developed and tested. The first is a modified Starr valve, constructed entirely of silicone rubber, incorporating what are felt to be important changes in the design of the attachment ring. The second, likewise constructed of silicone rubber, eliminates the necessity of a cage, and substitutes a lens-shaped body for the ball. This latter valve is more compact and it can be constructed with a larger orifice to afford better hemodynamic relationships. Both valves have been studied in a fatigue testing apparatus. They have been inserted in 65 dogs with the longest survival being eight months to date. In vivo studies include problems of insertion, patterns of fibrin formation, pressure relationships across the valves, and cineangiocardiograms. As a result of these studies clinical use of the ball valve is anticipated prior to the meeting.

38. Sutureless Mitral and Aortic Valve Prostheses

George J. Magovern, and Harry W. Cromie

(by invitation), Pittsburgh, Pa.

In order to simplify both the methods of insertion and fixation of prosthetic mitral and aortic valves and thereby lessen both the time of cardio-pulmonary bypass and the hazard of postoperative thrombus formation, two valves have been designed and clinically employed in the aortic and mitral positions which utilize a rapid mechanical nonsuture fixation which has not previously been described. These valves employ a cage-ball mechanism, but housed within their base are multiple curved pins which following insertion of the valve in the desired position, are simultaneously ejected through orifices in the lateral rim of the base of the valve, and engage the adjacent tissue for fixation, thus eliminating the prolonged period of time necessary for suturing the prosthesis in position. The valves have been used in the aortic position on three patients, and in the mitral position on one patient, with follow-up of four to nine months. In all patients the fixation has been satisfactory. The design and mechanism and the continued progress of the clinical application will be described. Coronary perfusion and/or hypothermia have not been necessary in the aortic replacement.

39. An Inverted Tricuspid Plastic Mitral Valve

Richard W. Ernst, and Harry D. Stokes

(both by invitation), Dallas, Texas

Sponsored by Donald L. Paulson

Adherence to flow principles with regard to turbulence and resistance led to the development o£ a tricuspid valve which functions conversely to presently available valves. Suspended on three pillars the leaflets move toward the center of the valve to open, and close by approximation to the valve's annulus. The dome of the valve is located in the center of the left atrium. No space is taken up in the left ventricle. The valve is molded in one piece including leaflets and annulus thus giving added strength. Tissue in growth is permitted by cementing porous material circumferentially to the annulus. In the pulse duplicator no gradient was obtained with a flow of eight liters per minute. In the dog a pressure of 8/2 mm Hg was obtained in the left atrium with a similar valve. This valve has the following advantages: (1) absence o£ turbulence; (2) absence of "dead" space, thus avoiding formation of thrombi; (3) no component of the valve occupies the left ventricular lumen and thus the ventricular myocardium cannot be damaged and the diastolic filling can be maximal; (4) the valve is molded in one piece, giving it added strength.

40. The Implantable Synchronous Pacer in the Treatment of Complete Heart Block

Sol Center, David Nathan, Chang-Yu Wu, and

Philip Samet (all by invitation), Miami, Fla.

Sponsored by Thomas H. Burford

An implantable synchronous pacer has been modeled to synchronize the activity of the atria and ventricles. Previous work in animals has proven the feasibility of long term pacing in the treatment of complete heart block. Synchronous pacers have been implanted in patients with Stokes-Adams disease. Physiologic studies were obtained before and after implantation to determine cardiac function under varying degrees of activity. In its simplest form, the atrial potential is picked up from the left atrium, relayed to the pacer, delayed and amplified, and then conducted to the electrode implanted on the left ventricle resulting in a ventricular contraction. With this pacer, naturally induced speeding or slowing of the atria will cause the ventricles to follow as the heart responds to body demands. The battery life of the unit is four or five years. Safeguards have been built into the unit to prevent ventricular rates above 115 and below 60. In the event of return to normal sinus rhythm the pacer follows but does not interfere with normal rhythm.

41. The Denbrillator and Cardiac Burns

Laurence M. Rivkin, San Francisco, Calif.

The deleterious effects of electrical cardiac defibrillation are primarily the result of burns. These burns are caused by heat developed as the resistance of the heart transforms electrical energy into heat. The heat produced by shocks from a defibrillator was measured after implanting micro-miniature thermocouples in the myocardium. Shocks were administered from an AC and a condenser discharge ("DC") defibrillator. The effect of increasing voltage and varying the duration (AC) or wave form (DC) was studied. In addition, hearts of varying mass were utilized. Approximately 800 determinations were made. In 20 dogs, shocks were applied to the exposed heart. The animals were sacrificed hours to days later and the myocardium examined for burns. This study suggests criteria for predicting the safety of a technic of internal cardiac defibrillation. This is particularly important in the use of the "DC" de-fibrillator where heat and burns are produced despite the small amount of power applied.

42. Hemodilution Studies in Extracorporeal Circulation Employing a Rotating-Disc Oxygenator

Donald R. Kahn, hugo F. Hidalgo, Georgine M. Steude

(all by invitation), and Herbert Sloan, Ann Arbor, Mich.

In order to evaluate hemodilution using a rotating-disc oxygenator with a 2000 ml. priming volume, the following concentrations were used: 1) all blood, 2) 25% Dextran-75% blood, 3) 50% Dextran-50% blood, 4) 75% Dextran-25% blood, 5) 100% Dextran, 6) 50% 5%G/water-50% blood, 7) 75% 5%G/water-25% blood, 8) 100% 5%G/water. Total cardiopulmonary bypass was instituted in dogs for one hour at 32 °C. hypothermia with flow rates between 50-85 cc/kg/minute, depending upon the amount of venous return. No extra blood was given during or after perfusion. Volume in extracorpor-eal circuit was unchanged. Studies were obtained before and one hour after perfusion. Selected dogs were studied at one week. During perfusion all dogs did well. Venous return was best, and, therefore, higher flow rates were maintained in the hemodilution experiments. 100% hemodilution dogs died in 24 hours. The remaining dogs stayed well after perfusion. Platelet decrease, plasma hemoglobin, PH, pCO₂, and pO₂ were the same for all groups. Total blood volume was greater after perfusion in the hemodilution group than in the all blood group, but the red cell volume was proportionally lower depending upon the degree of hemodilution. With hemodilution the usual unaccountable blood loss after perfusion was not present.

43. The Perfusion Hematocrit

Howard L. Gadboys (by invitation), and Robert S. Litwak,

New York, N.Y.

It has been demonstrated that hypovolemia involving both erythrocytes and plasma is seen frequently following extracorporeal circulation. The purpose of this communication is present data suggesting that immediate and late blood volume alterations are not clearly reflected in the postperfusion hemaocrits. Fifty-eight patients had pre- and postperfusion blood volume studies with Cr⁵¹ and RISA. Simultaneous hematocrits were done. The pump-oxygenator was primed with whole blood in 26 cases and 30% hemodilution was employed in 32. Ninety-nine determinations 4 and 18 hours postperfusion showed RCV fall averaging 22% from control whereas the hematocrit fell only 5%. Six observations on the second and third post-perfusion days revealed RCV and Hct drops of 32% and 22% from control respectively. Eight determinations on the fourth to thirteenth days demonstrated RCV to be only 9% less than control despite a 31% decline in Hct. Thirty-two patients perfused with hemodilution had 4 hour postperfusion RCV fall of 24% from control but simultaneous Hct fall of only 4%. The 26 non-diluted patients averaged 17% RCV decline while the hematocrit fell 3%. It is felt that these discrepancies relate to sequestrative changes of the homologous blood syndrome and that treatment of "postperfusion anemia" with blood may be unwarranted.

44. Coronary Artery Flow Patterns in the Intact Dog

Sanford A. Hepps (by invitation), Benson B. Roe, and

Burt Rutkin (by invitation), San Francisco, Calif.

A reliable, accurate electromagnetic flowmeter probe small enough to be implanted surgically on the anterior descending coronary artery has been developed to evaluate coronary artery flow patterns in the conscious, intact animal under various conditions of exercise, drug infusion and aortic valve incompetence. Undamped coronary artery pulse curves have been obtained with simultaneous ascending aortic flow curves and electrocardiograms. A satisfactory technique has been developed for obtaining frequent zero flow baseline and for obliterating EKG interference. Mean and cyclical coronary flow changes have been measured during treadmill exercise and after infusion with a variety of pressor agents and vasodilators. Alterations in the coronary flow curve in relation to ventricular systole are demonstrated in the presence of aortic valve incompetence. Studies to date include reliable data on eight animal preparations with consistent results showing significant differences in coronary flow with several drugs commonly used to augment the coronary circulation. Further studies are in progress and will be described.

45. Peripheral Vascular Responses During Hypothermia

Will C. Sealy, Alan Lesage (by invitation),

and W. Glenn Young, Jr Durham, N.C.

Alterations of the reaction of the peripheral vascular tree by hypothermia may significantly influence the development of temperature gradients and post-hypothermic metabolic acidosis. In 30 dogs cooled to as low as 7°C by a pump oxygenator, the following experiments were done: (1) Sympathetic stimulation by carotid occlusion and central vagal stimulation, (2) Peripheral vagal stimulation, (3) Injection of nor-epinepherine, (4) Injection of quinidine, (5) Studies of dilution curves. Sympathetic stimulation failed to increase the blood pressure at 18°C, though, as an indication of impulse transmission, cardiac effects of peripheral vagal stimulation continued until 10°C was reached. Norepinepherine caused an increase (110% to 180%) in blood pressure at 7°C. Quinidine not only reduced (50%) the blood pressure at 7°C, but blocked the action of nor-epinepherine. Mixing curves obtained at 7°C indicated paralysis of the peripheral vascular bed. During varying levels of hypothermia, the difference in the response of the peripheral vascular tree to stimulation and to nor-epinepherine suggests that this may be important in the development of areas of rapid and slow perfusion during induction and reversion of hypothermia. The possibility will be discussed of using these facts for instituting a more uniform perfusion during hypothermia.

46. The Importance of the Azygous Vein in Superior Cava Pulmonary Artery Anastomosis

W. Sterling Edwards, and L. M. Bargeron, Jr.

(by invitation), Birmingham, Ala.

In a series of 18 patients with tricuspid atresia treated with a superior cava right pulmonary artery shunt, there were three deaths in the first ten patients from cerebral edema. In all ten patients the azygous vein was ligated and the anastomosis made at its junction with the vena cava. In the next six patients the azygous was left open. The immediate postoperative course, especially in infants was significantly smoother, with no evidence of the "Superior Vena Caval Syndrome". One patient did not get the usual improvement in cyanosis, however, until the azygous was ligated at a second operation. This experience led to the development of a simple technique of encircling the azygous with a loose ligature which is brought out to a small subcutaneous button for azygous ligation 2-3 days postoperatively. This allows decompression of the superior cava through the azygous immediately after operation but permits azygous ligation a few days later to obtain full superior caval flow through the right lung.

47. Inflow Occlusion for Coronary Arteriography: Experimental Comparison with Other Methods

J. Y. Templeton III, R. R. Greening (by invitation),

C. Fineberc, (and by invitation) T. G. Peters,

J. R. Griffith, C. L. Reese, and D. L. Clark, Philadelphia, Pa.

Injection of radio-opaque material into the base of the aorta produces satisfactory opacification of the coronary arteries when cardiac output is temporarily diminished by acetyl choline cardiac arrest (Bjork) or by increasing endothoracic pressure (Nordenstrom). A third method, that of inflow occlusion by inflating the balloon of a specially devised catheter in the right atrium has been developed by us. In these experiments the three methods were used in varying sequence in each animal and the results compared. Arterial and venous pressures, electrocardiograms and electroencephalograms were recorded. Appropriate roentgenograms were made using the Franklin rapid film changer and cine radiographs were obtained using the Marconi Image Amplifier. Satisfactory visualization of the coronary arteries was obtained by all three methods. Inflow occlusion produced less disturbance of cardiac function, may be done under local anesthesia, may be readily repeated and is controllable so that cardiac output can be altered to the degree desired. Successful application of the method for coronary arteriography in patients with angina has begun and will be included in the report.

48. Autogenous Vein Aorto-Coronary Bypass: An Experimental Study

Lester R. Sauvage, Stephen J. Wood, and Kenneth M. Ever

(all by invitation), Seattle, Wash.

Sponsored by Robert E. Gross

We have thus far done 26 coronary bypass experiments in the dog. An autogenous external jugular vein graft is run from the upper thoracic aorta to the circumflex or the anterior descending coronary artery. The procedures are done using moderate hypothermia without extra-corporeal circulation. The technical difficulties have been appreciable, but less than anticipated. Six animals are living at this time, from 6 to 77 days since operation. In all of these survivors the graft has been anastomosed to the side of the distal circumflex coronary artery. In 5 of the 6 the circumflex coronary was ligated proximal to the anastomosis. In one the left main coronary was ligated. Four of these survivors had postoperative coronary anteriography at a mean period of 43 days after operation. All grafts were patent. None showed dilatation. Excellent filling of the coronary bed was apparent. Despite difficult problems, it is our belief that bypass surgery of the coronary arteries is a feasible undertaking with considerable clinical potential. Further experimental work should resolve many of the remaining difficulties. The technic of the procedure, postoperative coronary cineangiograms, autopsy specimens and additional studies will be presented.