First clinical experience with a new all-pyrolytic carbon bileaflet heart valve prosthesis

J THoRAc CARDIOVASC SURG 79:632-636, 1980

First clinical experience with a new all-pyrolytic carbon bileaflet heart valve prosthesis The specific characteristics of the SJM prosthesis are based on a new design in which there are two centrally hinged leaflets. Preclinical in vitro studies showed a favorable hemodynamic profile, causing minimal disturbance of the central flow. Therefore, starting in February, 1978, our department undertook a large-scale clinical trial of the SJM valvular prosthesis: 51 valves have been implanted in 46 patients ranging in age from 13 to 73 years. Thirty-four patients received one valve, 17 in the aortic and 17 in the mitral position. Three patients had a double- and one a triple-valve replacement. Seven patients also required coronary bypass procedures and one needed an aortic arch resection in combination with aortic valve replacement (AVR). The perioperative mortality rate (30 days) was 6%; according to postmortem results, in no case was death related to a mechanical malfunction of the valve. So far no postoperative complications have been observed in a total observation period of 303 patient-months. All patients had anticoagulation treatment with warfarin (Coumadin) except for one patient, who required AVR while on chronic dialysis. A comparative evaluation of multiple hemolytic parameters so far has not revealed any case of significant hemolysis. Fourteen patients (eight AVR and six MVR) were recatheterized postoperatively: The patients with MVR did not have a gradient across the valve at rest but the patients with AVR had a gradient of 8 ± 2 mm Hg. During isoproterenol infusion at a heart rate of 120 beats/min cardiac output increased by 42% ± 6%. This hemodnamic alteration produced a gradient of 11 ± 2 mm Hg across the mitral valve and 44 ± 8 mm Hg across the aortic valve. These results were compared to data obtained on the Bjork-Shiley prosthesis under identical conditions (p < 0.005). These preliminary data appear promising. They conform well with in vitro results and preclinical trials.

F. W. Hehrlein, M.D.,* M. Gottwik, M.D.,** G. Fraedrich, M.D.,* and J. Mulch, M.D.,* Giessen and Bad Nauhein, West Germany

NicOlOff and Passes developed the St. Jude Medical (SJM) valvular prosthesis (St. Jude Medical, Inc., St. Paul, Minn.) in 1972 in search of a mechanical valve that by its design would allow for the least possible disturbance of the central flow profile across the artificial valve. The in vitro hemodynamic data and experimental work in animals compared this valve very favorably with other models and made an initial clinical trial appealing to cardiac surgeons trying to improve Received for publication March 19, 1979. Accepted for publication May 24, 1979. Address for reprints: F. W. Hehrlein, M.D., Department of Surgery, Cardiovascular Surgical Division, Justus-Liebig-University, Giessen, West Germany. *Department of Surgery, Cardiovascular Surgical Division, JustusLiebig-University, Giessen, West Germany. **Kerckhoff-Klinik and Max-Planck-Institute for Clinical and Physiological Research, Bad Nauheim, West Germany.

632

postoperative hemodynamic conditions in patients in need of valvular replacement. 1-3 Therefore, starting in February, 1978, we initiated a clinical trial with the SJM valvular prosthesis. Material, patient population, and methods Valvular specifications. Fig. 1 shows the SJM aortic valve compared with the Bjork-Shiley prosthesis. The novelty of this design consists of the two centrally hinged valvular leaflets, equal in size and with a semi-circular surface. The valve has a very low profile and an excellent ratio of aortic cross-sectional area to valvular orifice. The valve is made entirely of a biologically inert Pyrolite carbon material; this includes the moving parts, which also have been designed according to an entirely new concept and so far have shown only minimal wear in accelerated "long-term" in vitro use.v 3

0022-5223/80/040632+05$00.50/0 © 1980 The C. V. Mosby Co.

Volume 79

Bileaflet hea rt valve prosthesis

Number 4

633

April. 1980

Fig. 1. SJMprosthesis (left) and Bjork-Shiley valve (right). demonstrating the different concepts of both valves. Patient population and methods of implantation. Since February, 1978, 51 SJM valvular prostheses have been implanted in 46 patients rang ing from 13 to 73 years of age ; 28 were male and 18 female (28 in the aortic , 22 in the mitral , and one in the tricuspid position). Thirty-four patients received one valve and four patients underwent a multiple valve replacement. Seven patients, in addition to valve replacement , had coronary bypass procedures, includ ing three single , three double , and one triple bypass . One patient needed an aortic arch resection in combin ation with aortic valve replacement (AVR). The technique used for implantation was the right lateral approach for the mitral valve replacement (MVR) in 17 cases, and the rnidsternal approach for AVR and comb ined procedures in 29 cases. The aortic prostheses ranged from 23 to 29 mm, the 25 and 26 mm sizes being the most frequent. The mitral prostheses were either 27 or 29 mm. Postoperative evaluation Parameters to detect hemolysis. With respect to the mechanically induced valvular hemolysis , we measured 10 parameters: hemoglobin , hematocrit, red blood cell morphology, reticulocyte count, direct bilirubin , indirect bilirubin, haptoglobin , lactic dehydrogenase (LDH), serum iron , and iron-binding capacity . Postoperative hemodynamic measurements. These measurements were obtained in 14 patient s, eight of whom had undergone AVR with the SJM prosthesis and six of whom had undergone M VR: All patients were recatheterized 3 months postoperatively. Simultaneous pressure measurements were obtained in the left ventricle and in the ascending aorta to observe pressure gradients across the aortic valvular prosthesis . To evaluate the function of the valve in the mitral position, simultaneous end-diastolic pressures were obtained in

the pulmonary capillary wedge position and the left ventricle. Identical measurements were repeated under stress consisting of an infusion of isoproterenol (0.03 JLg/kg/min) until a heart rate of 120 ± 5 cpm was reached . Cardiac output was measured simultaneously (thermodilution method). Results The operative results in 43 patients were excellent; All patients were improved at least by one class according to the New York Heart Association classification-all having been classified as beyond Class II at the time of the operation. There was no operative death but the perioperative 30 day mortality rate was 6% in these unselected consecutive patients . Two patients with end-stage mitral valve disease died on postoperative days 1 and 7 in pump failure . One patient died in renal failure 18 days following an emergency AVR because of an acute bacterial valvular endocarditis. A postmortem examination was performed in each case and revealed intact valvular function . There were no thrombosed valves and no acute paravalvular leaks. In the meantime a total of 303 patient-months' postoperative observation have passed without identification of mechanical valvular dysfunction or systemic embolization . All patients except one have received anticoagulation with warfarin (Coumadin) according to their individual prothrombin time and their condition has been stabilized at a value of twice the control time. One patient who receives chronic hemodialysis because of end-stage chronic glomerulonephritis was not given anticoagulation and so far has had no complications . Evaluation of mechanical hemolysis. Three months after operation, haptoglobin , red blood cell morphology, and lactic dehydrogenase (LDH) appear to be reliable parameters; the others still may be fluctuating

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Hehrlein et al.

Table I. Postoperative hemodynamic evaluation of SJM valvular prosthesis" Position

PG(mmHg)

CO (L/min)

Aortic: R Iso

8 8

75 ± 7 122 ± 5

8 ± 2 44 ± 9

5.6 ± 1.3 8.2 ± 2.1

6 6

73 ± 6 120 ± 3

O±O II ± 2

4.8 ± I.I 6.5 ± 1.2

Mitral: R Iso

R. Rest. Iso, Isoproterenol (0.03 mg/kg/min) infusion. HR. Heart rate. PG. Pressure gradient. CO. Cardiac output. All changes significant at p < 0.05.

secondary to the surgical and perioperative interventions. Compared to preoperative measurements LDH was elevated significantly, whereas red cell morphology and haptoglobin values were within normal limits, which lead us to conclude that major hemolysis has not occurred in our patient population so far. 4 Postoperative hemodynamic evaluation. Table I shows preliminary results of the postoperative hemodynamic evaluation of the SJM valvular prosthesis in the aortic and mitral position. There was no difference in the results related to the size of the prosthesis. Eight patients with AVR had a small gradient of 8 ± 2 mm Hg across the aortic valve at rest at a cardiac output of 5.6 ± 1.3 Llmin. The increase of the cardiac output by 48% at a physiological heart rate of 122 ± 5 cpm produced a significant gradient of 44 mm Hg across the valve. After MVR a gradient at rest was not measured across the artificial valve. During infusion of isoproterenol, however, a significant gradient of 11.2 ± 2 mrn Hg was produced, together with a 39% increase of the cardiac output. All changes produced by the intervention were significant when compared to the results at rest. These results correspond well with the predictions of the performance of this valvular prosthesis which were made on the basis of extensive in vitro testing.

Discussion After a quarter of a century of experimentation and clinical trials with mechanical heart valves we are at a point where the ball valve of the Starr-Edwards type still remains as the "gold standard," at least with respect to the total number of implants and the number of patient-years of successful use. 5 - 9 The continuing development of new valves confronted surgeons and their patients with a choice among "lesser evils," since the valves to be implanted still remained far from an ideal alternative to a natural valve.P- 10-14 Yet the develop-

ment of surgical skill and the ingenuity in the design and manufacturing of artificial valves over the years has led us to a stage where, with correct surgical indications, the prognosis for life expectancy and quality of life after valve replacement in the aortic and mitral positions is far superior to the natural course of valvular disease. 7, 15-19 At the same time, a continuously reduced surgical risk induced the medical community to be progressively more generous in its indications for valve replacement. 15, 17. 20 The cardiac surgeon finds himself, therefore, handicapped by still suboptimal prosthetic valves while confronted with an everincreasing need for valvular replacement. The specifications of an ideal valve are easily summarized: The material must be biologically inert so as to prevent autoimmune response which would cause rejection of the foreign body. It should function permanently, without wearing out during an expected lifetime, and it should not produce any resistance or obstruction against the natural flow of blood. In this context it should not have any noxious action on the corpuscular components of the blood and should prevent thrombus formation on the valvular surfaces. During the last decade the bioprosthesis was presented as an answer to most of these questions. However, after extensive trials and long-term clinical evaluation, it leaves the surgical community divided into three groups: One uses it under certain conditions, one does not use it at all, and one uses it despite its inadequacies. 10-13, 21-24 This is because a biological degradation of the graft occurs despite the much improved preservation by glutaraldehyde treatment. 14 Thus after years of wide experience with many different types of valvular prostheses, we are still in need of future improvement. However, in view of the relative success so far, any new valve should be received with due skepticism. We propose that any new model ought to fulfill two postulates: First, the concept ought to be entirely new and promise physical qualities different from those of previous models; second, based on in vitro testing and animal experiments, it should promise to be better than-or at least as good as-the models in use. With the SJM valvular prosthesis we feel that the postulate of an entirely new concept has been fulfilled to a large degree and the postulate of extensive preclinical trials in comparison to the conventional models has been complied with. Pyrolytic carbon in other valves': 25 has proved to be a very resistant, biologically inert material of high endurance and resistance to wear. The entire prosthesis is manufactured of this material; thus interfaces of different materials are

Volume 79 Number 4 April. 1980

avoided as is the inherent danger of delamination and the interposition of material of higher thrombogenicity. The simplicity of the design is ingeneous: In the open position the structures opposing the blood flow are similar to the structures that would remain from a baIl valve, after the baIl has been taken out of the cage. The impedance has to be much less than that caused by a ball, a disc, or even a tilting disc, all of which force the bloodstream to deviate lateraIly to the periphery and to areas of increased friction. How much the central flow of the SJM prosthesis is disturbed in vivo will have to be examined by flow studies in the ascending aorta. In vitro studies have shown very little disturbance. Minimal turbulence at the central flow by two open leaflets has to be weighed against the gain of mechanical strength which is provided by the broad base for the two leaflets to pivot around, which is close to the diameter of the circular surface. This design provides additional stability for the moving parts at no extra expense in structure. With the two-leaflet design in mind, two considerations offer themselves: First, obviously, the doubling of mechanical parts bears an increased risk of mechanical failure; second, if mechanical failure occurs, one leaflet may continue to operate, and aIlows time for the patient to receive emergency surgical care. This argument remains valid in the case of obstruction and insufficiency and may represent a unique advantage in contradistinction to single obturator valves. A low roentgenographic visibility of the valve is caused by the low profile of its structures and the poor radiopacity of Pyrolite carbon. This is disturbing to the clinician who is responsible for the postoperative foIlow-up. However, echo studies of our group have shown that identification of the valvular structures and their function is relatively easy to perform. 26 The postoperative parameters of hemolysis have been compared to our experience with the Bjork-Shiley valve, of which our team is foIlowing more than 1,000 implants. The LDH was elevated postoperatively in both models-less in the SJM series, although not statisticaIly significant at the present number of evaluations. Previous investigations of valvular prostheses have shown that little or no gradient across artificial valves at rest may be accompanied by a disproportionate gradient across the valve during stress. This phenomenon can be attributed to the relative diminution of the valve area which is caused by the rigid valvular circumference and its suture ring. The obstructing valvular structures located within the valve area play an additional role, which may be predominant, depending on the design of the valve. To further evaluate this

Bileaflet heart valve prosthesis

635

aspect of the valvular prosthesis, we decided to examine our patients at rest and to submit them to stress subsequently. We preferred isoproterenol to pacing and to the bicycle ergometer because it aIlows for a standardization of heart rate nearly as weIl as pacing but with the benefit of greater inotropism and a higher cardiac output. At the same time, the patient is less uncomfortable and the test becomes independent of patient cooperation. Our results have shown that a considerable increase of cardiac output can be achieved with this method under physiological increases of the heart rate. A considerable gradient was found under stress; however, this was within the limits of our expectations according to in vitro results and also according to previous comparative studies with tilting disc valves.f" The factor of valvular size with respect to its hemodynamic impedance at this point cannot yet be evaluated from our results, since so far only two medium sizes in the mitral and aortic positions have been evaluated. The thrombogenetic activity of the valve to date can be considered very low, which should be expected, since all patients have received anticoagulation. At this early stage of this first clinical trial of the SJM valvular prosthesis, and short of long-term foIlow-up studies, we have reason for an optimistic view. The SJM prosthesis may represent a viable alternative to some of the existing mechanical valvular prostheses.

2 3

4 5

6 7

REFERENCES Bjork VO, Olin C: A hydrodynamic comparison between the Bjork-Shiley tilting disc valve and the Lillehei-Kaster pivoting disc valve. Scand J Thorac Cardiovasc Surg 7:107, 1973 Emery R, PalmquistW, Arom K, Mettler E, Nicoloff D: A new cardiac prosthesis. All pyrolytic carbon bileaflet central flow valve. Circulation 58:Suppl 2:83, 1978 Steinmetz GP, Max KJ, Mueller V, Anderson HN, Merendino KA: An improved acceleratedfatigue machine and pulse simulator for testing and developing prosthetic cardiac valves. J THORAC CARDIOVASC SURG 47:186, 1964 Jaeger M, Sadeghi H, Rivier J-L: Comparative study of hemolysis induced by four different models of artificial aortic valves. Ann Cardiol Angeiol 24:401, 1975 Barnhorst DA, Oxman HA, Connolly DC, Pluth JR, Danielson GK, Wallace RB, McGoon DC: Long term follow-up of isolated replacement of the aortic or mitral valve with the Starr-Edwards prosthesis. Am J Cardiol 35:228, 1975 Hehrlein FW, Mulch J, Scheid HH: 25 Jahre Herzklappenchirurgie-Erstrebtes und Erreichtes. Med Welt 28:999, 1977 Rothlin ME, Krayenbiihl HP, Messmer BJ, Senning A:

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Langzeitverlauf nach Aorten- und Mitralklappenersatz. Herz 2:268, 1977 8 Starr A, Herr RH, Wood IA: Mitral replacement. Review of six years' experience. I THORAC CARDIOVASC SURG 54:333, 1967 9 Starr A, Grunkemeier G, Lambert L, Okies IE, Thomas D: Mitral valve replacement. A ten-year follow-up of non-cloth-covered vs. cloth-covered cagedball prosthesis. Circulation 54 Suppl 3:47, 1976 10 Carpentier A, Deloche A, Reiland 1, Fabiani IN, Forman I, Camilleri IP, Soyer R, Dubost C, MaIm IR: Six-year follow-up of glutaraldehyde-preserved heterografts. 1 THORAC CARDIOVASC SURG 68:771, 1974 11 Hehrlein FW: Konservierungsprobleme homologer und heterologer Aortenklappentransplantate. Thoraxchirurgie 19:394, 1971 12 Holper K, Struck E, Laas 1: Herzklappenersatz durch biologische Prothesen. Herz 2 :252, 1977 13 Ionescu MI, Tandon AP: Long term clinical and haemodynamic evaluation of the Ionescu-Shiley pericardial xenograft heart valve. Thoraxchirurgie 26:250, 1978 14 Sebening F, Struck E, Meisner H, Schmidt-Habelmann P: Herzklappenersatz mit Glutaraldehyd fixierten Bioprothesen. Z Kardiol 65:Suppl 3:63, 1976 15 Barnhorst DA, Guilani ER, Pluth IR, Danielson GK, Wallace RB, McGoon DC: Open-heart surgery in patients more than 65 years old. Ann Thorac Surg 18:971, 1973 16 Kalmar P, Rodewald G, Voss H, Westermann K-W, Wilde P: Spatresultate nach Mitralklappenersatz durch Bjork-Shiley-Prothesen. Herz 2:314, 1977 17 ScheId HH, Hehrlein FW, Schlepper M, Langebartels F, Mulch I: Heart valve replacement in patients more than 60 years old (abstr). Eur Soc Cardiovasc Surg (Tel Aviv) 1:45, 1979 18 Smith 1M, Lindsay WG, Lillehei RC, Nicoloff DM: Cardiac surgery in geriatric patients. Surgery 80:443, 1976 19 Walter P, Schwarz F, ScheId HH, Hehrlein FW: Experience with the Bjork-Shiley tilting disc valve prosthesis in 833 patients. 1 THORAC CARDIOVASC SURG (in press) 20 Hilgenberg F, Tillessen B: Klinischer Beitrag zum Herzklappenersatz im Kindesalter. Herz 2:335, 1977 21 Hehrlein FW: Eine Halterung fiir Aortenklappentransplantate zum homologen und heterologen Ersatz der Mitralis. Langenbecks Arch Chir 324: 154, 1969

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22 Hehrlein FW, Haas H: Biochemische Veranderungen an heterologen Aortenklappentransplantaten nach Anwendung verschiedener Sterilisationsverfahren. Langenbecks Arch Chir 325: 1183, 1969 23 Kutsche L, Oyer P, Shumway N, Baum D: An important complication of Hancock mitral valve replacement in children. Circulation 58:Suppl 2:149, 1978 24 Nitter-Hauge S, Enge I, Hall KV: The Hall-Kaster valve in aortic position. Primary results including hemodynamic studies. Circulation 58:Suppl 2:83, 1978 25 Bjork VO, Henze A, Holmgren A: Central haemodynamics at rest and during exercise before and after aortic valve replacement with the Bjork-Shiley tilting disc valve in patients with isolated aortic stenosis. Scand 1 Thorac Cardiovasc Surg 7: 111, 1973 26 Thormann I, Gottwik M, Hehrlein FW, Schlepper M: Stressbedingte hamodynarnische Anderungen bei aortal implantierten Bjork-Shiley und SIM-Herzklappenprothesen. Z Kardiol 68:248, 1979 27 Bjork VO, Henze A, Jereb M: Aortogrpahic follow-up in patients with the Bjork-Shiley aortic disc valve prosthesis. Scand I Thorac Cardiovasc Surg 7: I, 1973 28 Gams E, Meisner H, Mayr N: Reoperationen nach Herzklappenersatz. Herz 2:351, 1977 29 Harken DE, Soroff HS, Taylor WI, Lefemine AA, Gupta SK, Lunzer S: Partial and complete prosthesis in aortic insufficiency. I THORAC CARDIOVASC SUR~ 40:744, 1960 30 Hufnagel CA, Harvey WP, Rabil PI, McDermott T: Surgical correction of aortic insufficiency. Surgery 35:673, 1954 31 Kalmar P, Manske 1, Tilsner V, Akrami R: Das Verhalten der LDH und ihrer Isoenzyme nach Herzoperationen. Thoraxchirurgie 26:306, 1978 32 ScheId HH, Langebartels F, Mulch 1, Hehrlein FW: Langzeitergebnisse der Chirurgie erworbener Herzfehler. Medizin21:2376,1977 33 Scheid HH, Schlepper M, Fraedrich G, Hehrlein FW: Indication for reoperations on patients with heart valve disease. Doc Med Oberval Tome I, 395, 1978 34 Struck E, Meisner H, Schmidt-Habelmann P, Sebening F: Dreijahrige Erfahrungen mit biologischen Herzklappenprothesen. Thoraxchirurgie 26: 245, 1978