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Successful prolonged heparinless venoarterial bypass in sheep
Successful prolonged heparinless venoarterial bypass in sheep In order to investigate the safety of prolonged heparinless venoarterial bypass (HL-VAB), we subjected 18 sheep to prolonged HL-VAB for up to 6 days. Three animals died of granulomatous lung abscess and one died from intra-abdominal abscess. One animal died of generalized thromboembolism secondary to mechanical damage of the nonthrombogenic coating occurring at the time of cannulation. HL-VAB was successfully carried out in 13 sheep. Although clots were found at all tubing connections where blood turbulence occurred, only the previously mentioned animal showed evidence of thromboembolism. Damage to the nonthrombogenic tubing exposed to the roller pump head was seen in all animals, and its severity appeared to be related to the duration of bypass. Scanning electron microscopic examination revealed scattered platelet aggregates on the nonthrombogenic coated surfaces without clinical evidence of embolization. Hematocrit values, leukocyte counts, platelet counts, prothrombin time (PT), activated partial thromboplastin time (PTT), thrombin time (TT), plasma fibrinogen levels, and factor V and VIII levels remained unchanged, whereas free plasma hemoglobin levels rose slightly during 6 days of HL-VAB. HL-VAB for up to 6 days appears to have little adverse effect on blood cells and blood coagulation factors. For current clinical use, the nonthrombogenic coated tubing circuit should be changed every 48 hours because of time-related trauma to the coated tubing from the roller pump.
Akio Wakabayashi, M . D . , Dr. Med. Sci., Yoshimasa Nakamura, M.D., Telford Woolley, M.D., Chi-Chu Chen, Ph.D., Paul J. Mullin, B.A., and John E. Connolly, M.D., Irvine, Calif.
X \ . e c e n t l y we 1 , 2 reported a simplified technique of heparinless femorofemoral venoarterial bypass without oxygenation (HL-VAB) for the mechanical assistance of the failing heart. In studies on experimental animals we showed that (1) the need for systemic heparinization could be eliminated by the use of a tubing circuit coated with nonthrombogenic polyurethane-polyvinyl-graphite (PPG), (2) arterial oxygen saturation of the proximal aorta could be maintained within normal ranges by mechanical hyperventilation during bypass if the bypass did not exceed one third of the cardiac output, and (3) hypotension could be reversed promptly by venoarterial bypass. In our 1 , 2 experiments, all dogs suffering from acute cardiogenic shock recovered within 90 minutes after institution of HL-VAB support. From the Department of Surgery, University of California at Irvine, Irvine, Calif. 92664. This work was supported by U.S. Public Health Service Grant HL 13704-02. Read at the First Annual Meeting of The Samson Thoracic Surgical Society, Santa Barbara, Calif., May 28-30, 1975. Address reprintrequeststo Dr. Wakabayashi. 648
We 3 subsequently applied HL-VAB without oxygenation in the treatment of 6 patients affected with inadequate cardiac output either after open-heart surgery or after myocardial infarction. In those patients in whom HL-VAB was used in the treatment of postoperative cardiogenic shock, the duration of the mechanical assistance was short, as in our cardiogenic shock animal experiments. In one patient in cardiogenic shock secondary to acute myocardial infarction, however, HL-VAB was employed for 40 hours to reverse the shock. Thus it was apparent that some patients in cardiogenic shock from myocardial infarction may require mechanical circulatory support for many days. Therefore, the present study was undertaken to investigate the safety of HL-VAB for periods up to 6 days. The study was particularly directed to the effect of such bypass on the blood, the coagulation mechanism, and the coated tubing. Sheep were selected for these experiments because they are known to have extremely low fibrinolysin activity4 compared to man, and thus they appear to be the ideal animal for experimental evaluation of clot formation in extracorporeal circulatory devices.
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Fig. 1. Diagram of bypass circuit. The direction of bloodflowsis indicated by the arrows. Cross-sectional views demonstrate diagrammatically the areas of clot formation (shaded areas). Note that the clots are seen at locations of maximum turbulence. Transectional view shows concentric clot formation just outside the roller housing. Methods Eighteen adult sheep, weighing 50 to 110 kilograms, were used in this study. The HL-VAB circuit employed consisted of % inch polyvinyl tubing connected to poly vinyl arterial (18 Fr.) and venous cannulas (20 Fr.) with attached side arms for removal of air bubbles. A 32 inch section of Vi inch polyvinyl tubing was interspersed into the circuit of % inch polyvinyl tubing and used in the roller pump head. The edges of the % inch tubing which were glued into the Vi inch tubing were sharply cut in a conical shape to decrease turbulence of blood flow. All of the cannulas and tubing as well as polycarbonate connectors were coated with PPG5 and gas sterilized. Each animal was placed in the left lateral decubitus position on an animal operating table especially designed for roentgenologic studies. With the use of sterile conditions and local anesthesia, an external jugular vein and a common carotid artery were exposed and cannulated. The venous cannula was positioned in the superior vena cava and the arterial cannula was advanced deeply into the aortic arch in order to obtain good blood mixing. These cannula positions were checked by fluoroscopy. The skin was closed around the cannulas and the animal was placed in a restricting cage in which it could freely stand or crouch but could not turn around. It had free access to water and food. The cannulas were then connected to the nonfhrombogenic tubing, and air bubbles were removed via the side arms. HL-VAB was started slowly. If there was no sign of cerebral hypoxia, flows were set arbitrarily
between 350 and 1,200 ml. per minute (average 700 ml per minute) and HL-VAB was continued for 24 to 144 hours. The only medication employed was cephaloridine (Loridine*) given twice daily (1 Gm. intramuscularly) throughout the experiments. Upon completion of HL-VAB, the cannulas were removed and the animals were treated as survivors. All animals were electively put to death one week to 4 months after the completion of HL-VAB for pathological studies. Upon completion of bypass, the tubing and cannulas were inspected for clot formation and damage to the PPG coating by the roller pump. Representative portions of tubing were subjected to scanning electron microscopic examination. Unused portions of PPGcoated tubing from the same batch of coated tubing served as controls. Blood samples were obtained by direct venipuncture of the contralateral external jugular vein with plastic syringes and were immediately divided into three separate test tubes as follows. The first tube contained ethylene-diamine tetra-acetate and was used for the determination of hematocrit, white blood cell counts, and platelet counts. The second tube contained 3.13 per cent sodium citrate in a 9:1 ratio and was used to determine prothrombin time (PT), thrombin time (TT), activated partial thromboplastin time (PTT), factors V and VIII, and free plasma hemoglobin. Epsilon aminocaproic acid was added to the third tube, which also contained sodium citrate. *Courtesy of Eli Lilly & Co., Indianapolis, Ind. 46206.
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Fig. 2A. Scanning electron microscopic view of the control PPG surface. The PPG surface appears to be covered by a thin layer of serum proteins. The marking represents 1 ju,. (x 11,000.) This solution was used to determine plasma fibrinogen levels. Blood sampling was done immediately after the external jugular vein was exposed (base line), at 2, 24, 48, 72, and 144 hours on HL-VAB, and then 24 hours after HL-VAB was discontinued. Hematocrit was determined by a standard technique via capillary hematocrit centrifuge tubes. White blood cell determinations were performed by direct counting under a microscope with the aid of Neubauer counting chamber. Platelets were counted directly under a phase-contrast microscope.6 All blood counts were obtained in duplicate and, if there was a difference greater than 10 per cent, the counts were repeated. The average of two values was used as the final determination. Platelet function was assessed by the adenosine diphosphate (ADP) aggregation test7 and the platelet factor 3 availability test by means of Russell viper venom (Stypven) clotting time.8 The degree of platelet aggregation was examined under a microscope and graded from 1+ and 4 + . Free plasma hemoglobin
levels were determined by a modified benzidine method.9 Coagulation screening tests, PTT,10 PT,11 and TT12 were determined by standard techniques with commercially available agents.* Factor V was assayed by determining PT with factor V-deficient plasma which was made from sheep plasma by destroying factor V with heat. Commercially available factor VHI-deficient plasma substrate* was used in factor VIII assay.13 These values were checked against prebypass sheep plasma and expressed in percentage of base-line values. The significance of the differences was tested via the t test at a confidence level of 95 per cent. Results Thirteen of 18 sheep experiments were technically successful. Successful bypass times were 24 hours in 4 animals, 72 hours in 3 animals, and 144 hours in 6 *Hyland Labs, Costa Mesa, Calif.
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Fig. 2B. Scanning electron microscopic view of the PPG surface after 6 days of heparinless venoarterial bypass. The PPG surface appears to be covered by a thin layer of serum proteins. The marking represents 1 fi. (xl 1,000.) animals. The postoperative courses of these animals were uneventful, and they were electively put to death for pathological examination one week to 4 months later. One animal died after 72 hours on HL-VAB of disseminated thromboembolism resulting in gangrene of the small bowel. Clots were found to have been initiated by damaged PPG coating secondary to forceful insertion of an excessively large connector into the tubing. Three sheep died of caseous granulomatous lung abscess, and one died of ileus secondary to caseous granulomatous intraperitoneal abscess. All of the coated tubing circuits showed some clot formation at junctions and just outside the roller pump housings (Fig. 1). The amount of clots and plateletfibrin deposits appeared to correlate with the duration of extracorporeal circulation without heparin. The portion of tubing which was squeezed continually by the roller pump showed linear cracks on the PPG coating along the superior and inferior rims. After 6
days of bypass the damage to the PPG coating by the rollers was very severe, with uniform thinning of the coating. Scanning electron microscope examination of the PPG coating of the cannulas and tubing that did not come in contact with the pump head showed that the areas free of thrombi appeared normal and that the small whitish patches seen on the PPG surface were platelet aggregates (Fig. 2). Hematocrit values dropped slightly within 2 hours of HL-VAB but remained unchanged thereafter (Fig. 3). The base-line values for white blood cell count and platelet count were somewhat higher than reported normal values in sheep14 (Fig. 3). No statistically significant changes were noted in white blood cell count and platelet count during 144 hours of HL-VAB. Coagulation screening tests (Fig. 4) and plasma fibrinogen levels (Fig. 5) remained unchanged during 144 hours of HL-VAB. The ability of platelets to
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Fig. 2C. Patchy areas noted on gross inspection are shown to be platelet aggregates andfibrinsheets which are firmly adherent to the PPG surface. The marking represents 1 fi. (Original magnification x5,000.) aggregate in response to ADP slightly diminished from 4+ to 3+ in half of the animals but did not change in the other half. Platelet factor 3 availability expressed in terms of the Stypven clotting time remained unchanged (Fig. 5). Free plasma hemoglobin levels increased slightly during prolonged HL-VAB (Fig. 5). Factors V and VIII also did not change significantly during prolonged bypass (Fig. 6). Discussion Since the animals had free access to water and food, intravenous fluids were not administered. During the first 6 to 10 hours of bypass, all animals were closely observed. If the extracorporeal tubing did not kink during this period of close observation, it was felt safe to leave the animals unattended at night. Because caseous granulomatous disease is endemic in sheep, it was impossible to screen animals with this
disease before the experiments. Thus significant numbers of the animals in the present series died of this disease. There was some correlation between the degree of damage to the PPG coating and the pump flow rates. In general, the more severe damage was seen with higher flow rates. However, this correlation was not proportional. Damage to the PPG coating by the roller head did, however, proportionally worsen as the pumping time was extended. The fact that the portions of the cannulas extending into the carotid and jugular vessels became slightly stiff indicated that water was being absorbed by the poly vinyl material. A similar but lesser stiffening was also noted in the extracorporeal tubing outside the body. The nonthrombogenic property of PPG coating has been proved in our laboratory2,5 as well as by others.15 In earlier preliminary studies, two pairs of dogs were
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Fig. 3. Graph to show changes in hematocrit (Hct), white blood cell counts (WBC), and platelet counts (PLT) during and after prolonged heparinless venoarterial bypass (HL-VAB). No statistically significant changes are noted. (The mean values are shown with standard deviations. The number of the samples is shown inside parentheses.) I50-,
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Fig. 4. Graph to show changes in partial thromboplastin time (PTT), prothrombin time (PT), and thrombin time (TT) during and after prolonged heparinless venoarterial bypass (HB-VAB). No statistically significant changes are noted. placed on HL-VAB for 40 minutes and 2 hours, one group with PPG-coated circuits and the other with noncoated circuits. No clots were noted in the coated tubing circuits. In contrast, noncoated tubing circuits showed significant clot formation at 40 minutes and were completely thrombosed at 2 hours. Autopsies of the animals with clotted tubing showed disseminated thromboembolism. Thus control studies employing noncoated tubing circuits were not deemed necessary in the present study.
The sites of clot formation shown in Fig. 1 coincided with the areas where turbulence was expected. Such clot formation does not appear to be preventable by systemic heparinization. Bartlett and associates16 reported that white thrombi were formed at connectors and inlet and outlet headers after 24 to 48 hours of membrane oxygenator bypass in sheep that were administered continuous systemic heparinization. Pierce and associates17 reported clot formation inside a segmented polyurethane bladder blood pump which
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Fig. 6. Graph to show changes in factors V and VIII during and after prolonged heparinless venoarterial bypass (HL-VAB). No statistically significant changes are noted. was used in calves for several months with continuous systemic anticoagulation. Bernstein and Murphy18 noted massive clot formation around a nonthrombogenic intra-aortic balloon cannula in calves if the balloon was not pulsated. However, they reported that even a very slow pulsation (6 per minute) of the balloon completely prevented clot formation. Blatt and associates,19 in contrast, reported that systemic anticoagulation and continuous pulsation of an intraaortic balloon failed to prevent clot formation and that the majority of calves developed kidney infarction after one week of intra-aortic balloon counterpulsation. In our experiments, only one of 18 animals had throm-
boembolism, a fact indicating that clots formed at the sites of turbulence were not dislodged during continuous bypass. The one animal that had multiple fatal emboli was also the one in which the PPG coating was severely traumatized during forceful connection of tubing. Recently, Lagergren's group20 demonstrated that platelet adhesion to plastic surfaces was not prevented by systemic heparinization but was significantly reduced by coating the plastic surface with heparin-surfactant complex. Whether such a heparinized surface can reduce or eliminate clot formation at the site of turbulence appears to require further investigation.
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The immediate initial drop in hematocrit value was of interest. Since the priming volume of the HL-VAB was only 250 ml. and blood loss during surgery was negligible, this drop could not be explained by artificial hemodilution or blood loss. It is speculated that sheep may have a unique capability to mobilize water into the circulation in response to stress. After an initial drop, the hematocrit determinations remained unchanged throughout all experiments. Continuous roller pumping is known to be associated with high hemolysis. In our present study, free plasma hemoglobin levels, however, were only slightly elevated. This was probably related to the relatively low flow rates employed in our experiments. Signori and associates21 noted prolonged PT, accelerated PPT, and unchanged TT in patients undergoing open-heart surgery with a bubble oxygenator. Gralnick and Fischer,22 however, reported that PTT did not change in their patients subjected to extracorporeal circulation with a bubble oxygenator. Fong and colleagues23 observed that PT, PTT, and TT remained unchanged during prolonged membrane oxygenator bypass in sheep but that fibrinogen, factor V, and factor VIII decreased significantly at the beginning of bypass, gradually returning toward base-line levels. In contrast, Gralnick and Fischer22 reported that fibrinogen and factor VIII were not altered but that factor V decreased during open-heart surgery with bubble oxygenators. Bartlett and associates16 reported that no significant changes were observed in any of the previously mentioned coagulation studies during prolonged venoarterial bypass with a microporous membrane oxygenator and systemic heparinization. Whereas the previously mentioned studies were performed by means of extracorporeal circulation with systemic heparinization, Engleman and associates24 reported a unique study in which pulsatile left heart bypass without heparin was performed in dogs for 24 hours. They stated that PTT was markedly prolonged but TT and PT remained unchanged. In our present study, none of these determinations was significantly altered by HL-VAB. Many investigators have noted that platelets decrease almost immediately after initiation of conventional cardiopulmonary bypass.25, 26 This fall in platelets is usually more marked with a bubble than with a membrane oxygenator.23, 27 In our present study, however, total platelets did not change significantly even though many platelets were found adherent to the PPG surfaces. Fong and associates23 observed that the administration of heparin decreased ADP platelet aggregation and platelet factor 3 availability in intact
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sheep but that neutralization of heparin by polybrene in vitro restored platelet function to approximately 50 per cent of normal values. In our present study, platelet function was not affected significantly during HLVAB, perhaps because heparin was not employed. In conclusion, prolonged HL-VAB of up to 6 days appears to have little adverse effect on blood cells and blood coagulation factors. Further studies are required to augment the abrasion resistance of vinyl tubing coated with PPG against continuous prolonged roller pumping. For current clinical use of HL-VAB, coated vinyl tubing with PPG should be replaced every 48 hours.
REFERENCES 1 Wakabayashi, A., Nakamura, Y., Murphy, K. J., et al.: Controlled Venoarterial Bypass Without Oxygenation in the Treatment of Cardiogenic Shock, Trans. Am. Soc. Artif. Intern. Organs 19: 511, 1973. 2 Wakabayashi, A., Nakamura, Y., Murphy, K. J., et al.: Heparinless venoarterial Bypass: Its Application in the Treatment of Experimental Cardiogenic Shock, Arch. Surg. 108: 497, 1974. 3 Wakabayashi, A., Connolly, J. E., Stemmer, E. A., and Nakamura, Y.: Clinical Experience With Heparinless Venoarterial Bypass Without Oxygenation for the Treatment of Acute Cardiogenic Shock, J. THORAC. CARDIOVASC. SURG. 68: 687,
1974.
4 Gajewski, J., and Povar, M. L.: Blood Coagulation Values of Sheep, Am. J. Vet. Res. 32: 405, 1971. 5 Wakabayashi, A., Yim, D., Dietrick, W., et al.: Left Ventricular Bypass: A New Nonthrombogenic Device With Homograft Aortic Valves, Am. J. Cardiol. 25: 450, 1970. 6 Brecher, G., Schneiderman, M., and Cronkite, E. P.: The Reproducibility and Constancy of the Platelet Count, Am. J. Clin. Pathol. 23: 15, 1953. 7 Mitchell, J. R. A., and Sharp, A. A.: Platelet Clumping in Vitro, Br. J. Haematol. 10: 78, 1964. 8 Hardisty, R. M., and Hutton, R. A.: Platelet Aggregation and the Availability of Platelet Factor 3, Br. J. Haematol. 12: 764, 1966. 9 Crosby, W. H., and Furth, F. W.: A Modification of the Benzidine Method for Measurement of Hemoglobin in Plasma and Urine, Blood 11: 380, 1956. 10 Proctor, R. R., and Rappaport, S. I.: The Partial Thromboplastin Time With Kaolin: A Simple Screening Test for First Stage Plasma Clotting Factor Deficiencies, Am. J. Clin. Pathol. 36: 212, 1961. 11 Quick, A. J., Stanley-Brown, M., and Bancroft, F. W.: A Study of the Coagulation Defect in Hemophilia and in Jaundice, Am. J. Med. Sci. 190: 501, 1935. 12 Rappaport, S. J., and Ames, S. B.: Clotting Factor Assays on Plasma From Patients Receiving Intramuscular
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or Subcutaneous Heparin, Am. J. Med. Sci. 234: 678, 1975. Hardisty, R. M., and MacPherson, J. C : A One-Stage Factor VIII (Antihemophiliac Globulin) Assay and Its Use on Venous and Capillary Plasma, Throm. Diath. Haemorrh. 7: 215, 1962. Veterinary Clinical Pathology, Doxey, D. L., editor: Baltimore, 1971, The Williams & Wilkins Company, pp. 194-195. Gott, V. L., and Furuse, A.: The Current Status of in Vivo Screening of Synthetic Implant Materials for Blood Compatibility, J.A.A.M.I. 7: 121, 1973. Bartlett, R. H., Fong, S. W., Woldanski, C , et al.: Hematologic Responses to Prolonged Extracorporeal Circulation (ECC) With Microporous Membrane Devices, Trans. Am. Soc. Artif. Intern. Organs 21: 250, 1975. Pierce, W. S., Brighton, J. A., O'Vannon, W., et al.: Complete Left Ventricular Bypass With a Paracorporeal Pump: Design and Evaluation, Ann. Surg. 180: 418, 1974. Bernstein, E. F., and Murphy, A. E., Jr.: The Importance of Pulsation in Preventing Thrombosis From Intra-aortic Balloons: A Note of Caution, J. THORAC. CARDIOVASC. SURG. 62: 950,
1971.
19 Blatt, S. J., Schneider, M. D., Kayne, M. P., et al.: Hematologic, Biological and Pathological Effects of Intra-aortic Balloon Counterpulsation in the Calf, Surg. Gynecol. Obstet. 137: 238, 1973. 20 Langergren, H., Olsson, P., and Swedenborg, J.: Inhibited Platelet Adhesion: A Non-thrombogenic Characteristic of a Heparin-coated Surface, Surgery 75: 643, 1974. 21 Signori, E. E., Penner, J. A., and Kahn, D. R.: Coagulation Defects and Bleeding in Open-Heart Surgery, Ann. Thorac. Surg. 8: 521, 1969. 22 Gralnick, H. R., and Fischer, R. D.: The Hemostatic Response to Open-Heart Operations, J. THORAC. CARDIOVASC. SURG. 61: 909,
1971.
23 Fong, S. W., Burns, N. E., Woldanski, W. C , et al.: Changes in Coagulation and Platelet Function During Prolonged Extracorporeal Circulation (ECC) in Sheep and Man, Trans. Am. Soc. Artif. Intern. Organs 20: 239, 1974. 24 Engelman, R. M., Nyilas, E., Lackner, H., and Godwin, S. J.: Left Heart Bypass Without Anticoagulation, J. THORAC. CARDIOVASC. SURG. 62: 851,
1971.
25 Kendall, A. G., and Lowenstein, L.: Alterations in Blood Coagulation and Hemostasis During Extracorporeal Circulation, Canad. Med. Assoc. J. 87: 786, 1962. 26 Marquiss, O. M. P. J. E., and Breckenridge, R. T.: A Study of Platelet Counts During Cardiopulmonary Bypass, Transfusion 12: 119, 1972. 27 Kvarstein, B., Cappelen, C , and Osterud, A.: Blood Platelets and Leucocytes During Cardiopulmonary Bypass, Scand. J. Thorac. Cardiovasc. Surg. 8: 142, 1974.
Discussion DR. J. D O N A L D H I L L San Francisco, Calif.
I would like to congratulate the authors. I along with a number of other people have followed the work of Drs. Wakabayashi and Connolly for several years in their research and successes in producing antithrombogenic surfaces. Dr. Wakabayashi has shown fairly clearly in sheep that he can pump through an extracorporeal circuit for a number of days without encountering serious problems with the equipment or producing gross defects in the coagulation system. I would like to ask some specific questions regarding this system. First, Dr. Wakabayashi noted that protein or the byproducts of protein which may develop on the surfaces occurred at areas of turbulence, and he showed a scanning electron microscopic slide of that phenomena. I wonder whether, over a large surface area of nonturbulent blood flow, scanning electron microscopy would show the surface on the whole to be clean. This is particularly fearful, because if emboli do come off from a wide surface area, the numerical accumulation effect will be damaging to the organism. Second, does the pump tubing develop cracks in the nonthrombogenic material at the flexing surfaces? Dr. Wakabayashi recommends it be changed every 2 days. Is there thrombosed blood in these cracks? Third, Dr. Wakabayashi, why did you specifically wait 2 weeks to 4 months to do the autopsies to look for embolic material? Did you particularly study the brain? Fourth, do you have a problem in the quality control? Will you be able to produce this tubing and these circuits in large numbers and always know that they will give you relatively good results if they are used in large numbers of people? Last, I was a bit concerned about what the real underlying purpose of this paper was since you already knew you could use the system successfully in man for up to 80 hours. With the exception of organ histology, what specific information could be gained from sheep and not from man with this apparently safe system? I would be interested to know what the coagulation kinetics in the human were. Was there any clinical evidence of emboli? Once again, I would like to congratulate you for this work. I know I have asked a lot of questions and some of them are not simple. However, if, in fact, this material is really good, there are many opportunities to use it in a variety of places in cardiac surgery, and there are many people awaiting such a system. D R . W. G E R A L D
RAINER
Denver, Colo.
I enjoyed Dr. Wakabayashi's paper very much. We have viewed his work with respect for a long time. In the choice of materials and surfaces for prolonged bypass for support, there still remains an unsettled issue of whether the surface should be smooth or whether it should attract and produce an organized, firmly attached pseudointima.
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We have implanted left ventricular assist devices subdiaphragmatically, connecting the left ventricular apex to the infrarenal abdominal aorta in 8 calves undergoing continuous pumping of a greater flow than Dr. Wakabayashi reported. Our flows have been 2 to 6 L. per minute, either asynchronous or else synchronized with the animal's electrocardiogram. These experiments have lasted from 14 hours to 14 days. The blood-pump interface in our system has been Dacron fiber flocked, the fibers measuring 25 by 250 /u and numbering about 45,000 per square inch. This has been used intentionally to cause a pseudointima to be attached to the inner surface. Further observations in these animals have been carried out for up to 4 months after removal of the pumping device. Investigation for excessive blood trauma has shown little deleterious effect on the formed elements of blood or coagulation mechanisms, similar to the findings Dr. Wakabayashi has reported. Early fibrin deposition in these areas of Dacron fiber flocking has shown a very loosely attached pseudointima. Although on gross inspection it appears to be smooth, microscopic examination would lead us to believe that this pseudointima may embolize if enough force is present to shear it from its loose attachment. The later fibrin is attached more slowly and much more compactly. Dr. Wakabayashi, you have shown us the gross fibrin that has appeared from your experiment, but what does this look like microscopically? Are you able to look microscopically at a cross section to determine how firmly or how loosely attached this intima is to the tubing? DR. I V A N A. MAY Oakland, Calif.
Roger Ecker and I have used Dr. Wakabayashi's heparinless venoarterial bypass (HL-VAB) for the support of 2 patients in cardiogenic shock. In both we could not pass an intra-aortic balloon in either femoral artery because of arteriosclerosis. We found it necessary to bypass up to 2,000 c.c. per minute for adequate support. The first patient was supported for 16 hours. By that time the urine contained hemolyzed blood. The serum hemoglobin level was 153. We were able to discontinue HL-VAB and he recovered. A second patient whom we could not wean from cardiopulmonary bypass was supported by HL-VAB. After 20 hours the serum hemoglobin level was 151. We could not discontinue HL-VAB without a precipitous drop in blood pressure. He soon developed disseminated intravascular coagulopathy and died 24 hours later. In both of these patients the tubing showed areas where the PPG black coating was worn off within the roller pump. This has not occurred in the four instances in which we have used this tubing for short bypass times during resection of aneurysms of the descending thoracic aorta. Traumatic damage to the PPG tube coating is apparently related to time and velocity and results in progressive blood damage.
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Our experience with intra-aortic balloon counterpulsation (IABC) in 53 patients has been without evidence of blood damage. Thirty-one patients admitted to the medical service were treated by IABC: Eight patients were electively supported by IABC before, during, and after surgery. These were patients with unstable angina, severe main left coronary lesions, and/or were poor-risk patients. All survived. Two patients in shock because of acute myocardial infarcts were supported by IABC, catheterized, and treated by resection of the infarct. One of them survived. Four patients were in shock because of acute infarction with ventricular septal defects. They were supported by IABC throughout diagnostic studies and surgical repair, and 3 of them survived. Ten patients in cardiogenic shock were supported for varying lengths of time but were not operated upon. Some improved and IABC was stopped. Others were studied but not believed to be surgical candidates. There was one survivor. We currently treat patients in cardiogenic shock by intensive medical therapy using a Swan-Ganz catheter to determine fluid load required. If they do not respond, IABC is begun followed by cardiac catheterization. The decision regarding surgery depends upon the clinical course and the possibility that various surgical procedures might help. Our experience with IABC in postoperative patients comprises a group of 22. In 15 the balloon was inserted during the operation because of failure to wean from bypass. In 7 others, the balloon was inserted in the intensive care unit because of postoperative arrhythmias or instability. Of this group there were 13 survivors. Because of our success with IABC, we prefer this modality. When a patient cannot be weaned from cardiopulmonary bypass we put the balloon in a femoral artery or, if that cannot be done, in the ascending aorta. In the nonsurgical patient with cardiogenic shock in whom a balloon cannot be placed through either femoral artery, we will probably use HL-VAB again. However, we will be very careful about the rate and duration, since damage to the PPG coating is related to these two factors. D R . W A K A B A Y A S H I (Closing) I would like to thank all the discussers. First I shall answer Dr. Hill's questions. After 6 days of continuous HL-VAB, the PPG surface was grossly smooth and clean. The scanning electron microscope showed the surface to be free of platelet aggregates with possibly some minimal protein coverage. In answer to the second question, some cracking of the PPG coating was noted at the points of flexion of the tubing inside the pumping heads. Longitudinal linear cracks of the PPG coating were always noted along the superior and inferior rims of the tubing which was housed inside the roller head. Currently, we are continuing our studies to improve the mechanical strength of nonthrombogenic coating in order to prevent mechanical damage by the roller pump. We waited several weeks before sacrificing our animals so that we could observe them for any sequelae. The 5 animals which died of complications, such as lung abscess, were
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autopsied immediately after death. Thus we were able to examine also for immediate changes after prolonged bypass. None of these animals showed evidence of thromboemboli. In answer to the fourth question regarding the quality control of the PPG coating, we checked the uniformity of the PPG coating by transillumination, which discloses very small defects in coating. Dr. Hill also inquired why we did these animal experiments after having employed HL-VAB for many weeks in patients. Actually, our longest bypass period in man has been 42 hours. The degree of mechanical damage to the PPG coating in this case was similar to that described in this paper. In reply to Dr. Rainer's question, we have used a pulsatile heparinless left heart bypass system in the past for thoracic aneurysmectomy. The pulsatile pump had a Dacron velour lining and two porcine aortic valves. This pulsatile left heart bypass without heparin was employed in 16 patients undergoing thoracic aneurysmectomy, and the results were gratifying. The only problem with this pulsatile pump was that it was expensive to produce commercially. Therefore, we started using the much simpler system described today. However, I believe that pulsatile pumping has a place in
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extremely long bypass because of its superior mechanical durability. In a recent article (Ann. Surg. 180: 418, 1974), Pierce and associates reported an experimental study which is similar to Dr. Rainer's technique. They placed calves on pulsatile left heart bypass with continuous anticoagulation for up to 8 months. They also noted fibrin clots at the areas of turbulence or stagnation. Regarding Dr. May's 2 patients, one success in 2 patients with cardiogenic shock is significant, I believe, if the condition of the patients is taken into account. As in any technique of assisted circulation, HL-VAB is not applicable to all patients. HL-VAB cannot be used in a patient who requires bypass of more than one third of the cardiac output. Usually the flow rate in our patients has been around 1,500 ml. per minute. Occasionally we have had to increase the flow rate up to 2,500 ml. per minute, as in Dr. May's case, but the duration of such high flows was brief if the bypass was successful. The hemolysis that Dr. May mentioned may be related to high flow rates and poor renal function. In our experience, hemolysis has been subclinical, if present at all, unless the patient has renal failure.
Akio Wakabayashi, M . D . , Dr. Med. Sci., Yoshimasa Nakamura, M.D., Telford Woolley, M.D., Chi-Chu Chen, Ph.D., Paul J. Mullin, B.A., and John E. Connolly, M.D., Irvine, Calif.
X \ . e c e n t l y we 1 , 2 reported a simplified technique of heparinless femorofemoral venoarterial bypass without oxygenation (HL-VAB) for the mechanical assistance of the failing heart. In studies on experimental animals we showed that (1) the need for systemic heparinization could be eliminated by the use of a tubing circuit coated with nonthrombogenic polyurethane-polyvinyl-graphite (PPG), (2) arterial oxygen saturation of the proximal aorta could be maintained within normal ranges by mechanical hyperventilation during bypass if the bypass did not exceed one third of the cardiac output, and (3) hypotension could be reversed promptly by venoarterial bypass. In our 1 , 2 experiments, all dogs suffering from acute cardiogenic shock recovered within 90 minutes after institution of HL-VAB support. From the Department of Surgery, University of California at Irvine, Irvine, Calif. 92664. This work was supported by U.S. Public Health Service Grant HL 13704-02. Read at the First Annual Meeting of The Samson Thoracic Surgical Society, Santa Barbara, Calif., May 28-30, 1975. Address reprintrequeststo Dr. Wakabayashi. 648
We 3 subsequently applied HL-VAB without oxygenation in the treatment of 6 patients affected with inadequate cardiac output either after open-heart surgery or after myocardial infarction. In those patients in whom HL-VAB was used in the treatment of postoperative cardiogenic shock, the duration of the mechanical assistance was short, as in our cardiogenic shock animal experiments. In one patient in cardiogenic shock secondary to acute myocardial infarction, however, HL-VAB was employed for 40 hours to reverse the shock. Thus it was apparent that some patients in cardiogenic shock from myocardial infarction may require mechanical circulatory support for many days. Therefore, the present study was undertaken to investigate the safety of HL-VAB for periods up to 6 days. The study was particularly directed to the effect of such bypass on the blood, the coagulation mechanism, and the coated tubing. Sheep were selected for these experiments because they are known to have extremely low fibrinolysin activity4 compared to man, and thus they appear to be the ideal animal for experimental evaluation of clot formation in extracorporeal circulatory devices.
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Fig. 1. Diagram of bypass circuit. The direction of bloodflowsis indicated by the arrows. Cross-sectional views demonstrate diagrammatically the areas of clot formation (shaded areas). Note that the clots are seen at locations of maximum turbulence. Transectional view shows concentric clot formation just outside the roller housing. Methods Eighteen adult sheep, weighing 50 to 110 kilograms, were used in this study. The HL-VAB circuit employed consisted of % inch polyvinyl tubing connected to poly vinyl arterial (18 Fr.) and venous cannulas (20 Fr.) with attached side arms for removal of air bubbles. A 32 inch section of Vi inch polyvinyl tubing was interspersed into the circuit of % inch polyvinyl tubing and used in the roller pump head. The edges of the % inch tubing which were glued into the Vi inch tubing were sharply cut in a conical shape to decrease turbulence of blood flow. All of the cannulas and tubing as well as polycarbonate connectors were coated with PPG5 and gas sterilized. Each animal was placed in the left lateral decubitus position on an animal operating table especially designed for roentgenologic studies. With the use of sterile conditions and local anesthesia, an external jugular vein and a common carotid artery were exposed and cannulated. The venous cannula was positioned in the superior vena cava and the arterial cannula was advanced deeply into the aortic arch in order to obtain good blood mixing. These cannula positions were checked by fluoroscopy. The skin was closed around the cannulas and the animal was placed in a restricting cage in which it could freely stand or crouch but could not turn around. It had free access to water and food. The cannulas were then connected to the nonfhrombogenic tubing, and air bubbles were removed via the side arms. HL-VAB was started slowly. If there was no sign of cerebral hypoxia, flows were set arbitrarily
between 350 and 1,200 ml. per minute (average 700 ml per minute) and HL-VAB was continued for 24 to 144 hours. The only medication employed was cephaloridine (Loridine*) given twice daily (1 Gm. intramuscularly) throughout the experiments. Upon completion of HL-VAB, the cannulas were removed and the animals were treated as survivors. All animals were electively put to death one week to 4 months after the completion of HL-VAB for pathological studies. Upon completion of bypass, the tubing and cannulas were inspected for clot formation and damage to the PPG coating by the roller pump. Representative portions of tubing were subjected to scanning electron microscopic examination. Unused portions of PPGcoated tubing from the same batch of coated tubing served as controls. Blood samples were obtained by direct venipuncture of the contralateral external jugular vein with plastic syringes and were immediately divided into three separate test tubes as follows. The first tube contained ethylene-diamine tetra-acetate and was used for the determination of hematocrit, white blood cell counts, and platelet counts. The second tube contained 3.13 per cent sodium citrate in a 9:1 ratio and was used to determine prothrombin time (PT), thrombin time (TT), activated partial thromboplastin time (PTT), factors V and VIII, and free plasma hemoglobin. Epsilon aminocaproic acid was added to the third tube, which also contained sodium citrate. *Courtesy of Eli Lilly & Co., Indianapolis, Ind. 46206.
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Fig. 2A. Scanning electron microscopic view of the control PPG surface. The PPG surface appears to be covered by a thin layer of serum proteins. The marking represents 1 ju,. (x 11,000.) This solution was used to determine plasma fibrinogen levels. Blood sampling was done immediately after the external jugular vein was exposed (base line), at 2, 24, 48, 72, and 144 hours on HL-VAB, and then 24 hours after HL-VAB was discontinued. Hematocrit was determined by a standard technique via capillary hematocrit centrifuge tubes. White blood cell determinations were performed by direct counting under a microscope with the aid of Neubauer counting chamber. Platelets were counted directly under a phase-contrast microscope.6 All blood counts were obtained in duplicate and, if there was a difference greater than 10 per cent, the counts were repeated. The average of two values was used as the final determination. Platelet function was assessed by the adenosine diphosphate (ADP) aggregation test7 and the platelet factor 3 availability test by means of Russell viper venom (Stypven) clotting time.8 The degree of platelet aggregation was examined under a microscope and graded from 1+ and 4 + . Free plasma hemoglobin
levels were determined by a modified benzidine method.9 Coagulation screening tests, PTT,10 PT,11 and TT12 were determined by standard techniques with commercially available agents.* Factor V was assayed by determining PT with factor V-deficient plasma which was made from sheep plasma by destroying factor V with heat. Commercially available factor VHI-deficient plasma substrate* was used in factor VIII assay.13 These values were checked against prebypass sheep plasma and expressed in percentage of base-line values. The significance of the differences was tested via the t test at a confidence level of 95 per cent. Results Thirteen of 18 sheep experiments were technically successful. Successful bypass times were 24 hours in 4 animals, 72 hours in 3 animals, and 144 hours in 6 *Hyland Labs, Costa Mesa, Calif.
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Fig. 2B. Scanning electron microscopic view of the PPG surface after 6 days of heparinless venoarterial bypass. The PPG surface appears to be covered by a thin layer of serum proteins. The marking represents 1 fi. (xl 1,000.) animals. The postoperative courses of these animals were uneventful, and they were electively put to death for pathological examination one week to 4 months later. One animal died after 72 hours on HL-VAB of disseminated thromboembolism resulting in gangrene of the small bowel. Clots were found to have been initiated by damaged PPG coating secondary to forceful insertion of an excessively large connector into the tubing. Three sheep died of caseous granulomatous lung abscess, and one died of ileus secondary to caseous granulomatous intraperitoneal abscess. All of the coated tubing circuits showed some clot formation at junctions and just outside the roller pump housings (Fig. 1). The amount of clots and plateletfibrin deposits appeared to correlate with the duration of extracorporeal circulation without heparin. The portion of tubing which was squeezed continually by the roller pump showed linear cracks on the PPG coating along the superior and inferior rims. After 6
days of bypass the damage to the PPG coating by the rollers was very severe, with uniform thinning of the coating. Scanning electron microscope examination of the PPG coating of the cannulas and tubing that did not come in contact with the pump head showed that the areas free of thrombi appeared normal and that the small whitish patches seen on the PPG surface were platelet aggregates (Fig. 2). Hematocrit values dropped slightly within 2 hours of HL-VAB but remained unchanged thereafter (Fig. 3). The base-line values for white blood cell count and platelet count were somewhat higher than reported normal values in sheep14 (Fig. 3). No statistically significant changes were noted in white blood cell count and platelet count during 144 hours of HL-VAB. Coagulation screening tests (Fig. 4) and plasma fibrinogen levels (Fig. 5) remained unchanged during 144 hours of HL-VAB. The ability of platelets to
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Fig. 2C. Patchy areas noted on gross inspection are shown to be platelet aggregates andfibrinsheets which are firmly adherent to the PPG surface. The marking represents 1 fi. (Original magnification x5,000.) aggregate in response to ADP slightly diminished from 4+ to 3+ in half of the animals but did not change in the other half. Platelet factor 3 availability expressed in terms of the Stypven clotting time remained unchanged (Fig. 5). Free plasma hemoglobin levels increased slightly during prolonged HL-VAB (Fig. 5). Factors V and VIII also did not change significantly during prolonged bypass (Fig. 6). Discussion Since the animals had free access to water and food, intravenous fluids were not administered. During the first 6 to 10 hours of bypass, all animals were closely observed. If the extracorporeal tubing did not kink during this period of close observation, it was felt safe to leave the animals unattended at night. Because caseous granulomatous disease is endemic in sheep, it was impossible to screen animals with this
disease before the experiments. Thus significant numbers of the animals in the present series died of this disease. There was some correlation between the degree of damage to the PPG coating and the pump flow rates. In general, the more severe damage was seen with higher flow rates. However, this correlation was not proportional. Damage to the PPG coating by the roller head did, however, proportionally worsen as the pumping time was extended. The fact that the portions of the cannulas extending into the carotid and jugular vessels became slightly stiff indicated that water was being absorbed by the poly vinyl material. A similar but lesser stiffening was also noted in the extracorporeal tubing outside the body. The nonthrombogenic property of PPG coating has been proved in our laboratory2,5 as well as by others.15 In earlier preliminary studies, two pairs of dogs were
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£■ 48
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Fig. 3. Graph to show changes in hematocrit (Hct), white blood cell counts (WBC), and platelet counts (PLT) during and after prolonged heparinless venoarterial bypass (HL-VAB). No statistically significant changes are noted. (The mean values are shown with standard deviations. The number of the samples is shown inside parentheses.) I50-,
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Fig. 4. Graph to show changes in partial thromboplastin time (PTT), prothrombin time (PT), and thrombin time (TT) during and after prolonged heparinless venoarterial bypass (HB-VAB). No statistically significant changes are noted. placed on HL-VAB for 40 minutes and 2 hours, one group with PPG-coated circuits and the other with noncoated circuits. No clots were noted in the coated tubing circuits. In contrast, noncoated tubing circuits showed significant clot formation at 40 minutes and were completely thrombosed at 2 hours. Autopsies of the animals with clotted tubing showed disseminated thromboembolism. Thus control studies employing noncoated tubing circuits were not deemed necessary in the present study.
The sites of clot formation shown in Fig. 1 coincided with the areas where turbulence was expected. Such clot formation does not appear to be preventable by systemic heparinization. Bartlett and associates16 reported that white thrombi were formed at connectors and inlet and outlet headers after 24 to 48 hours of membrane oxygenator bypass in sheep that were administered continuous systemic heparinization. Pierce and associates17 reported clot formation inside a segmented polyurethane bladder blood pump which
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Fig. 5. Graph to show changes in fibrinogen, free plasma hemoglobin (Hgb) levels, and platelet factor 3 availability during and after prolonged heparinless venoarterial bypass (HL-VAB). No statistically significant changes are noted. Factor 3Z 150
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Fig. 6. Graph to show changes in factors V and VIII during and after prolonged heparinless venoarterial bypass (HL-VAB). No statistically significant changes are noted. was used in calves for several months with continuous systemic anticoagulation. Bernstein and Murphy18 noted massive clot formation around a nonthrombogenic intra-aortic balloon cannula in calves if the balloon was not pulsated. However, they reported that even a very slow pulsation (6 per minute) of the balloon completely prevented clot formation. Blatt and associates,19 in contrast, reported that systemic anticoagulation and continuous pulsation of an intraaortic balloon failed to prevent clot formation and that the majority of calves developed kidney infarction after one week of intra-aortic balloon counterpulsation. In our experiments, only one of 18 animals had throm-
boembolism, a fact indicating that clots formed at the sites of turbulence were not dislodged during continuous bypass. The one animal that had multiple fatal emboli was also the one in which the PPG coating was severely traumatized during forceful connection of tubing. Recently, Lagergren's group20 demonstrated that platelet adhesion to plastic surfaces was not prevented by systemic heparinization but was significantly reduced by coating the plastic surface with heparin-surfactant complex. Whether such a heparinized surface can reduce or eliminate clot formation at the site of turbulence appears to require further investigation.
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The immediate initial drop in hematocrit value was of interest. Since the priming volume of the HL-VAB was only 250 ml. and blood loss during surgery was negligible, this drop could not be explained by artificial hemodilution or blood loss. It is speculated that sheep may have a unique capability to mobilize water into the circulation in response to stress. After an initial drop, the hematocrit determinations remained unchanged throughout all experiments. Continuous roller pumping is known to be associated with high hemolysis. In our present study, free plasma hemoglobin levels, however, were only slightly elevated. This was probably related to the relatively low flow rates employed in our experiments. Signori and associates21 noted prolonged PT, accelerated PPT, and unchanged TT in patients undergoing open-heart surgery with a bubble oxygenator. Gralnick and Fischer,22 however, reported that PTT did not change in their patients subjected to extracorporeal circulation with a bubble oxygenator. Fong and colleagues23 observed that PT, PTT, and TT remained unchanged during prolonged membrane oxygenator bypass in sheep but that fibrinogen, factor V, and factor VIII decreased significantly at the beginning of bypass, gradually returning toward base-line levels. In contrast, Gralnick and Fischer22 reported that fibrinogen and factor VIII were not altered but that factor V decreased during open-heart surgery with bubble oxygenators. Bartlett and associates16 reported that no significant changes were observed in any of the previously mentioned coagulation studies during prolonged venoarterial bypass with a microporous membrane oxygenator and systemic heparinization. Whereas the previously mentioned studies were performed by means of extracorporeal circulation with systemic heparinization, Engleman and associates24 reported a unique study in which pulsatile left heart bypass without heparin was performed in dogs for 24 hours. They stated that PTT was markedly prolonged but TT and PT remained unchanged. In our present study, none of these determinations was significantly altered by HL-VAB. Many investigators have noted that platelets decrease almost immediately after initiation of conventional cardiopulmonary bypass.25, 26 This fall in platelets is usually more marked with a bubble than with a membrane oxygenator.23, 27 In our present study, however, total platelets did not change significantly even though many platelets were found adherent to the PPG surfaces. Fong and associates23 observed that the administration of heparin decreased ADP platelet aggregation and platelet factor 3 availability in intact
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sheep but that neutralization of heparin by polybrene in vitro restored platelet function to approximately 50 per cent of normal values. In our present study, platelet function was not affected significantly during HLVAB, perhaps because heparin was not employed. In conclusion, prolonged HL-VAB of up to 6 days appears to have little adverse effect on blood cells and blood coagulation factors. Further studies are required to augment the abrasion resistance of vinyl tubing coated with PPG against continuous prolonged roller pumping. For current clinical use of HL-VAB, coated vinyl tubing with PPG should be replaced every 48 hours.
REFERENCES 1 Wakabayashi, A., Nakamura, Y., Murphy, K. J., et al.: Controlled Venoarterial Bypass Without Oxygenation in the Treatment of Cardiogenic Shock, Trans. Am. Soc. Artif. Intern. Organs 19: 511, 1973. 2 Wakabayashi, A., Nakamura, Y., Murphy, K. J., et al.: Heparinless venoarterial Bypass: Its Application in the Treatment of Experimental Cardiogenic Shock, Arch. Surg. 108: 497, 1974. 3 Wakabayashi, A., Connolly, J. E., Stemmer, E. A., and Nakamura, Y.: Clinical Experience With Heparinless Venoarterial Bypass Without Oxygenation for the Treatment of Acute Cardiogenic Shock, J. THORAC. CARDIOVASC. SURG. 68: 687,
1974.
4 Gajewski, J., and Povar, M. L.: Blood Coagulation Values of Sheep, Am. J. Vet. Res. 32: 405, 1971. 5 Wakabayashi, A., Yim, D., Dietrick, W., et al.: Left Ventricular Bypass: A New Nonthrombogenic Device With Homograft Aortic Valves, Am. J. Cardiol. 25: 450, 1970. 6 Brecher, G., Schneiderman, M., and Cronkite, E. P.: The Reproducibility and Constancy of the Platelet Count, Am. J. Clin. Pathol. 23: 15, 1953. 7 Mitchell, J. R. A., and Sharp, A. A.: Platelet Clumping in Vitro, Br. J. Haematol. 10: 78, 1964. 8 Hardisty, R. M., and Hutton, R. A.: Platelet Aggregation and the Availability of Platelet Factor 3, Br. J. Haematol. 12: 764, 1966. 9 Crosby, W. H., and Furth, F. W.: A Modification of the Benzidine Method for Measurement of Hemoglobin in Plasma and Urine, Blood 11: 380, 1956. 10 Proctor, R. R., and Rappaport, S. I.: The Partial Thromboplastin Time With Kaolin: A Simple Screening Test for First Stage Plasma Clotting Factor Deficiencies, Am. J. Clin. Pathol. 36: 212, 1961. 11 Quick, A. J., Stanley-Brown, M., and Bancroft, F. W.: A Study of the Coagulation Defect in Hemophilia and in Jaundice, Am. J. Med. Sci. 190: 501, 1935. 12 Rappaport, S. J., and Ames, S. B.: Clotting Factor Assays on Plasma From Patients Receiving Intramuscular
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or Subcutaneous Heparin, Am. J. Med. Sci. 234: 678, 1975. Hardisty, R. M., and MacPherson, J. C : A One-Stage Factor VIII (Antihemophiliac Globulin) Assay and Its Use on Venous and Capillary Plasma, Throm. Diath. Haemorrh. 7: 215, 1962. Veterinary Clinical Pathology, Doxey, D. L., editor: Baltimore, 1971, The Williams & Wilkins Company, pp. 194-195. Gott, V. L., and Furuse, A.: The Current Status of in Vivo Screening of Synthetic Implant Materials for Blood Compatibility, J.A.A.M.I. 7: 121, 1973. Bartlett, R. H., Fong, S. W., Woldanski, C , et al.: Hematologic Responses to Prolonged Extracorporeal Circulation (ECC) With Microporous Membrane Devices, Trans. Am. Soc. Artif. Intern. Organs 21: 250, 1975. Pierce, W. S., Brighton, J. A., O'Vannon, W., et al.: Complete Left Ventricular Bypass With a Paracorporeal Pump: Design and Evaluation, Ann. Surg. 180: 418, 1974. Bernstein, E. F., and Murphy, A. E., Jr.: The Importance of Pulsation in Preventing Thrombosis From Intra-aortic Balloons: A Note of Caution, J. THORAC. CARDIOVASC. SURG. 62: 950,
1971.
19 Blatt, S. J., Schneider, M. D., Kayne, M. P., et al.: Hematologic, Biological and Pathological Effects of Intra-aortic Balloon Counterpulsation in the Calf, Surg. Gynecol. Obstet. 137: 238, 1973. 20 Langergren, H., Olsson, P., and Swedenborg, J.: Inhibited Platelet Adhesion: A Non-thrombogenic Characteristic of a Heparin-coated Surface, Surgery 75: 643, 1974. 21 Signori, E. E., Penner, J. A., and Kahn, D. R.: Coagulation Defects and Bleeding in Open-Heart Surgery, Ann. Thorac. Surg. 8: 521, 1969. 22 Gralnick, H. R., and Fischer, R. D.: The Hemostatic Response to Open-Heart Operations, J. THORAC. CARDIOVASC. SURG. 61: 909,
1971.
23 Fong, S. W., Burns, N. E., Woldanski, W. C , et al.: Changes in Coagulation and Platelet Function During Prolonged Extracorporeal Circulation (ECC) in Sheep and Man, Trans. Am. Soc. Artif. Intern. Organs 20: 239, 1974. 24 Engelman, R. M., Nyilas, E., Lackner, H., and Godwin, S. J.: Left Heart Bypass Without Anticoagulation, J. THORAC. CARDIOVASC. SURG. 62: 851,
1971.
25 Kendall, A. G., and Lowenstein, L.: Alterations in Blood Coagulation and Hemostasis During Extracorporeal Circulation, Canad. Med. Assoc. J. 87: 786, 1962. 26 Marquiss, O. M. P. J. E., and Breckenridge, R. T.: A Study of Platelet Counts During Cardiopulmonary Bypass, Transfusion 12: 119, 1972. 27 Kvarstein, B., Cappelen, C , and Osterud, A.: Blood Platelets and Leucocytes During Cardiopulmonary Bypass, Scand. J. Thorac. Cardiovasc. Surg. 8: 142, 1974.
Discussion DR. J. D O N A L D H I L L San Francisco, Calif.
I would like to congratulate the authors. I along with a number of other people have followed the work of Drs. Wakabayashi and Connolly for several years in their research and successes in producing antithrombogenic surfaces. Dr. Wakabayashi has shown fairly clearly in sheep that he can pump through an extracorporeal circuit for a number of days without encountering serious problems with the equipment or producing gross defects in the coagulation system. I would like to ask some specific questions regarding this system. First, Dr. Wakabayashi noted that protein or the byproducts of protein which may develop on the surfaces occurred at areas of turbulence, and he showed a scanning electron microscopic slide of that phenomena. I wonder whether, over a large surface area of nonturbulent blood flow, scanning electron microscopy would show the surface on the whole to be clean. This is particularly fearful, because if emboli do come off from a wide surface area, the numerical accumulation effect will be damaging to the organism. Second, does the pump tubing develop cracks in the nonthrombogenic material at the flexing surfaces? Dr. Wakabayashi recommends it be changed every 2 days. Is there thrombosed blood in these cracks? Third, Dr. Wakabayashi, why did you specifically wait 2 weeks to 4 months to do the autopsies to look for embolic material? Did you particularly study the brain? Fourth, do you have a problem in the quality control? Will you be able to produce this tubing and these circuits in large numbers and always know that they will give you relatively good results if they are used in large numbers of people? Last, I was a bit concerned about what the real underlying purpose of this paper was since you already knew you could use the system successfully in man for up to 80 hours. With the exception of organ histology, what specific information could be gained from sheep and not from man with this apparently safe system? I would be interested to know what the coagulation kinetics in the human were. Was there any clinical evidence of emboli? Once again, I would like to congratulate you for this work. I know I have asked a lot of questions and some of them are not simple. However, if, in fact, this material is really good, there are many opportunities to use it in a variety of places in cardiac surgery, and there are many people awaiting such a system. D R . W. G E R A L D
RAINER
Denver, Colo.
I enjoyed Dr. Wakabayashi's paper very much. We have viewed his work with respect for a long time. In the choice of materials and surfaces for prolonged bypass for support, there still remains an unsettled issue of whether the surface should be smooth or whether it should attract and produce an organized, firmly attached pseudointima.
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We have implanted left ventricular assist devices subdiaphragmatically, connecting the left ventricular apex to the infrarenal abdominal aorta in 8 calves undergoing continuous pumping of a greater flow than Dr. Wakabayashi reported. Our flows have been 2 to 6 L. per minute, either asynchronous or else synchronized with the animal's electrocardiogram. These experiments have lasted from 14 hours to 14 days. The blood-pump interface in our system has been Dacron fiber flocked, the fibers measuring 25 by 250 /u and numbering about 45,000 per square inch. This has been used intentionally to cause a pseudointima to be attached to the inner surface. Further observations in these animals have been carried out for up to 4 months after removal of the pumping device. Investigation for excessive blood trauma has shown little deleterious effect on the formed elements of blood or coagulation mechanisms, similar to the findings Dr. Wakabayashi has reported. Early fibrin deposition in these areas of Dacron fiber flocking has shown a very loosely attached pseudointima. Although on gross inspection it appears to be smooth, microscopic examination would lead us to believe that this pseudointima may embolize if enough force is present to shear it from its loose attachment. The later fibrin is attached more slowly and much more compactly. Dr. Wakabayashi, you have shown us the gross fibrin that has appeared from your experiment, but what does this look like microscopically? Are you able to look microscopically at a cross section to determine how firmly or how loosely attached this intima is to the tubing? DR. I V A N A. MAY Oakland, Calif.
Roger Ecker and I have used Dr. Wakabayashi's heparinless venoarterial bypass (HL-VAB) for the support of 2 patients in cardiogenic shock. In both we could not pass an intra-aortic balloon in either femoral artery because of arteriosclerosis. We found it necessary to bypass up to 2,000 c.c. per minute for adequate support. The first patient was supported for 16 hours. By that time the urine contained hemolyzed blood. The serum hemoglobin level was 153. We were able to discontinue HL-VAB and he recovered. A second patient whom we could not wean from cardiopulmonary bypass was supported by HL-VAB. After 20 hours the serum hemoglobin level was 151. We could not discontinue HL-VAB without a precipitous drop in blood pressure. He soon developed disseminated intravascular coagulopathy and died 24 hours later. In both of these patients the tubing showed areas where the PPG black coating was worn off within the roller pump. This has not occurred in the four instances in which we have used this tubing for short bypass times during resection of aneurysms of the descending thoracic aorta. Traumatic damage to the PPG tube coating is apparently related to time and velocity and results in progressive blood damage.
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Our experience with intra-aortic balloon counterpulsation (IABC) in 53 patients has been without evidence of blood damage. Thirty-one patients admitted to the medical service were treated by IABC: Eight patients were electively supported by IABC before, during, and after surgery. These were patients with unstable angina, severe main left coronary lesions, and/or were poor-risk patients. All survived. Two patients in shock because of acute myocardial infarcts were supported by IABC, catheterized, and treated by resection of the infarct. One of them survived. Four patients were in shock because of acute infarction with ventricular septal defects. They were supported by IABC throughout diagnostic studies and surgical repair, and 3 of them survived. Ten patients in cardiogenic shock were supported for varying lengths of time but were not operated upon. Some improved and IABC was stopped. Others were studied but not believed to be surgical candidates. There was one survivor. We currently treat patients in cardiogenic shock by intensive medical therapy using a Swan-Ganz catheter to determine fluid load required. If they do not respond, IABC is begun followed by cardiac catheterization. The decision regarding surgery depends upon the clinical course and the possibility that various surgical procedures might help. Our experience with IABC in postoperative patients comprises a group of 22. In 15 the balloon was inserted during the operation because of failure to wean from bypass. In 7 others, the balloon was inserted in the intensive care unit because of postoperative arrhythmias or instability. Of this group there were 13 survivors. Because of our success with IABC, we prefer this modality. When a patient cannot be weaned from cardiopulmonary bypass we put the balloon in a femoral artery or, if that cannot be done, in the ascending aorta. In the nonsurgical patient with cardiogenic shock in whom a balloon cannot be placed through either femoral artery, we will probably use HL-VAB again. However, we will be very careful about the rate and duration, since damage to the PPG coating is related to these two factors. D R . W A K A B A Y A S H I (Closing) I would like to thank all the discussers. First I shall answer Dr. Hill's questions. After 6 days of continuous HL-VAB, the PPG surface was grossly smooth and clean. The scanning electron microscope showed the surface to be free of platelet aggregates with possibly some minimal protein coverage. In answer to the second question, some cracking of the PPG coating was noted at the points of flexion of the tubing inside the pumping heads. Longitudinal linear cracks of the PPG coating were always noted along the superior and inferior rims of the tubing which was housed inside the roller head. Currently, we are continuing our studies to improve the mechanical strength of nonthrombogenic coating in order to prevent mechanical damage by the roller pump. We waited several weeks before sacrificing our animals so that we could observe them for any sequelae. The 5 animals which died of complications, such as lung abscess, were
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autopsied immediately after death. Thus we were able to examine also for immediate changes after prolonged bypass. None of these animals showed evidence of thromboemboli. In answer to the fourth question regarding the quality control of the PPG coating, we checked the uniformity of the PPG coating by transillumination, which discloses very small defects in coating. Dr. Hill also inquired why we did these animal experiments after having employed HL-VAB for many weeks in patients. Actually, our longest bypass period in man has been 42 hours. The degree of mechanical damage to the PPG coating in this case was similar to that described in this paper. In reply to Dr. Rainer's question, we have used a pulsatile heparinless left heart bypass system in the past for thoracic aneurysmectomy. The pulsatile pump had a Dacron velour lining and two porcine aortic valves. This pulsatile left heart bypass without heparin was employed in 16 patients undergoing thoracic aneurysmectomy, and the results were gratifying. The only problem with this pulsatile pump was that it was expensive to produce commercially. Therefore, we started using the much simpler system described today. However, I believe that pulsatile pumping has a place in
The Journal of Thoracic and Cardiovascular Surgery
extremely long bypass because of its superior mechanical durability. In a recent article (Ann. Surg. 180: 418, 1974), Pierce and associates reported an experimental study which is similar to Dr. Rainer's technique. They placed calves on pulsatile left heart bypass with continuous anticoagulation for up to 8 months. They also noted fibrin clots at the areas of turbulence or stagnation. Regarding Dr. May's 2 patients, one success in 2 patients with cardiogenic shock is significant, I believe, if the condition of the patients is taken into account. As in any technique of assisted circulation, HL-VAB is not applicable to all patients. HL-VAB cannot be used in a patient who requires bypass of more than one third of the cardiac output. Usually the flow rate in our patients has been around 1,500 ml. per minute. Occasionally we have had to increase the flow rate up to 2,500 ml. per minute, as in Dr. May's case, but the duration of such high flows was brief if the bypass was successful. The hemolysis that Dr. May mentioned may be related to high flow rates and poor renal function. In our experience, hemolysis has been subclinical, if present at all, unless the patient has renal failure.