Mitral Valve Redacernent with the Modified Univekity of Cape Town (UCT) Prosthesis: Clinical and Hernodynamic Results

Transcription

1 Mitral Valve Redacernent with the Modified Univekity of Cape Town (UCT) Prosthesis: Clinical and Hernodynamic Results F. Henry Ellis, Jr., M.D., Ph.D., Robert W. Healy, M.D., and Sidney Alexander, M.D. ABSTRACT Mitral valve replacement with the modified University of Cape Town prosthesis was performed in 42 patients. In 35 the procedure was an isolated one, and the hospital mortality was 6%. The late survival rate was 6O%, half of the late deaths being the result of thromboembolism or complications of anticoagulant therapy. The incidence of hemolysis was low, and hemodynamic results demonstrated improvement in cardiac index and lowering of pulmonary artery pressure, pulmonary artery wedge pressure, pulmonary arteriolar resistance, and transvalvular mean gradients. However, the calculated prosthetic valve orifice area was lower than the measured area. Because of complications of thromboembolism, the high incidence of late deaths, and high transvalvular gradients, this prosthetic valve is no longer used in patients requiring mitral valve replacement. The choice of an appropriate replacement device for the mitral valve remains controversial, as evidenced by the wide variety of prostheses available. While reduction in hospital mortality after prosthetic replacement of the mitral valve has been gratifying in recent years, the high rate of late deaths in many reports has been attributed to a variety of causes, some of which were probably related to the valve. Discouraged by these late failures, one of us (F. H. E.) some years ago sought to explore the possibility of an alter- From the Department of Surgery, Section of Thoracic and Cardiovascular Surgery, and the Department of Internal Medicine, Section of Cardiovascular Disease, Lahey Clinic Foundation and New England Deaconess Hospital, Boston, MA. Supported in part by the United States Catheter and Instrument Corporation (USCI), a Division of C. R. Bard, Inc, BOX 566, Billerica, MA. The help of Elton Watkins, Jr., M.D., in assisting with the statistical analysis is gratefully acknowledged. Accepted for publication Apr 23, Address reprint requests to Dr. Ellis, Lahey Clinic Foundation, 605 Commonwealth Ave, Boston, MA native replacement device. Selection of xnother device was made at a time when late results were complicated by thromboembolism after use of the then-availatde ball valves [2, 91, high transvalvular gradier.ts across disc valves [6, Ill, excessive hemolysis with one of the disc valves [7, 141, and excessive tissue growth on the sti-uts of the original cloth-covered Starr-Edwards valve, interfering with free excursion of the ball [I., 101. The University of Cape Town Valve Among the experimental prosthetic clevices studied in the laboratories of the Mayo Clinic in the late 1950s wa; a disc valve resembling a collar button [5]. Although all the early studies failed because of valve occlusion caused by thrombosis, the collar-button concept remained an appealing one and 1 nfluenced us to conduct a clin i- cal trial of the modified University of Cape 'Town (UCT) valve, wh Ich incorporates design characteristics similar to those of the collar-button valve. Prosthetic devices for replacement of both aortic and mitral valves were developed at the University of Cape Town in the 1960s. Although early reports [121 of the results of replacement with the mitral,xosthesis were discouraging, the unit was later modified in an effort to ininimize its hazards. The valve we used consisis of a stainless-steel crossbar with a central ring that controls excursion of an unbalanced polypropylene poppet (Fig 1). The eccentrically placed stem permits the disc to tilt when fully open, providing more central flow than is possible with most disc lxostheses. Because this disc offers freedom of travel, the hazards of wear associated with fixed tilting-disc valves, are avoided. In vitro flow studies comparing this design with a number of others revealed lower transvalvular gradients and high flow rates with the UCT valve [15]. Furthermore, the low inertia 26

2 27 Ellis, Healy, and Alexander: Mitral Valve Replacement with Modified UCT Prosthesis of the UCT valve allows it to maintain a low transvalvular gradient at high flows, even at rates as high as 150 per minute [4]. Fig I. Modified University of Cape Town valve manufactured by Lancer Specialties, Lawrence, MA. Fig 2. Technique Of inserting University Of Cape Town valve. (A, B) Excision of valve. (C) Placement of mattress sutures. (D) Insertion of continuous suture. Clinical Material and Technique From 1971 to 1974, the UCT valve was used to replace the mitral valve in 42 patients; 15 patients were in New York Heart Association Functional Class IV, 25 were in Class 111, and 2 were in Class 11. Of these patients, 6 had had previous operations on the mitral valve and 32 were experiencing atrial fibrillation at the time of operation. Patients ranged in age from 42 to 72 years, averaging 60.8 years. Conventional methods of cardiopulmonary bypass with a Harvey oxygenator employing moderate hypothermia and hemodilution permitted exposure of the mitral valve through a sternum-splitting incision (Fig 2A, B). The sewing ring of the UCT prosthesis facilitates its in-

3 28 The Annals of Thoracic Surgery Vol 23 No 1 January 197;' sertion using four mattress sutures for initial placement (Fig 2C). The final fixation was completed by a continuous suture of heavy Polydek (Fig ZD), thus reducing bypass time. The mitral valve was replaced in 35 patients. The other 7 had mitral valve replacement as part of a multivalve procedure, 3 with aortic valve replacement, 2 with tricuspid valve repair, and 2 with tricuspid valve replacement. All patients were given long-term anticoagulant therapy. Results Of the 35 patients who had isolated mitral valve replacement, 2 died within 30 days of operation, 1 from a myocardial infarction and the other with progressively lowered cardiac output. In retrospect, the aortic valve should probably have been replaced concomitantly in the latter patient, as postmortem examination revealed more narrowing than had been suggested by analysis of the data recorded at preoperative catheterization. One patient who underwent aortic and mitral valve replacement died suddenly on the fifth postoperative day, presumably from an arrhythmia (postmortem examination was not performed). Another patient who had replacement of the mitral and tricuspid valves died 2 days after operation from low cardiac output. Of the 12 late deaths in patients who underwent isolated mitral valve replacement, 5 were considered the result of cardiac failure. A paravalvular leak was present in 1 patient who refused reoperation, and a saddle embolus occurred and was associated with cardiac failure and death in another. Hemorrhagic complications of anticoagulant therapy were responsible for 4 deaths. Two patients died suddenly, presumably due to an arrhythmia since postmortem examination failed to reveal any other obvious cause. The final patient who died had complications of prosthetic valve endocarditis. Therefore, at the time of completion of the follow-up study, only 60% of the original group remained alive. When computed on an actuarial basis (Fig 3), these survival rates are similar to results recently reported from the Mayo Clinic using the Smeloff-Cutter valve [9] and the non-clothcovered Starr-Edwards ball valve [2]. An analysis was made of the symptomatic re- ' MONTHS Fig3. Actuarial su~~vival curve for all patients undergoing isolated mitral valve replacement with the University of Cape Town valve. sults in all long-term survivors who unclerwent isolated mitral valve replacement, as well as those who also E ad tricuspid annuloplasty. Thus 22 patients were available for study; Figure 4 illustrates their preoperative and postoperative NYHA Functiorial Classification. With 1 Iexception, all patients showed improvement by at least one functional class, the majority being in Class 1 after operation. The exception was the single patient in the group who had evidence of valve malfunctj on. Increasing symptciins of dyspnea and cardiac failure developed 1% years after operation. Ultimately the patient underwent reoperation at another hospital, at which time a tear in the sewing ring was found to have caused partial occlusion of the valve orifice. The patient has done well since replacement of the defective device, and the deficiency in the valve has been corrected by the manufacturer. Fig4. Preoperative irnd postoperative functional classificution (NYH,4) of 22 patients undergoing mitral valve replaceinent with a University of Cape Town valve. I II III m PREOP FQSTOP

4 29 Ellis, Healy, and Alexander: Mitral Valve Replacement with Modified UCT Prosthesis 'Thro m boem bol ism Of the 35 patients who initially survived either isolated mitral valve replacement or replacement combined with tricuspid annuloplasty, 7 (20%) experienced thromboembolic complications. One patient died from cardiac failure at 6 months, having experienced right hemiplegia before dismissal from the hospital. Late deaths occurred in 2 patients in whom saddle emboli had developed. One of these patients died of cardiac failure and the other of an arrhythmia after surviving embolectomy. The other 4 patients who experienced arterial emboli are among the long-term survivors; 2 remain partially incapacitated by hemiplegia, while the other 2 have no residual effects from their arterial emboli. Hemolysis Studies No clinical evidence of red cell destruction by the prosthetic device was recorded. However, 21 patients who underwent isolated mitral valve replacement had hemolysis studies (Table 1). Evidence of red cell damage was minimal, and urinalysis revealed positive findings of hemosiderin in only 2 patients. Hemody namics Preoperative and postoperative hemodynamic studies were performed in 15 patients. The early postoperative studies were conducted approximately 2 weeks after operation, and the late studies were performed 6 to 12 months after the procedure. The data are summarized in Table 2 and are presented in more detail in Figure 5. All of the late results showed a statistically significant improvement compared with the preoperative values, and in contrast to experience with other replacement devices [61, pulmonary arteriolar resistance was lower at the time of late study than early after operation. However, lack of correlation between the calculated area of the Table 1. Mitral Valve Replacement with UCT Prosthesis: Hemolysis Studies in 21 Patients Determination Normal Value Surgical Group Mean (range) Hemoglobin (gml100 ml) ( ) Hematocrit (%) ( ) Reticulocyte count (YO) ( ) Serum haptoglobin (mgldl) (25-64) Lactic dehydrogenase (units) ( ) Urine hemosiderin Negative Positive (2 of 21) UCT = University of Cape Town. Table 2. Mitral Valve Replacement with UCT Prosthesis: Hernodynamic Results in 15 Patients Results Early Late Preoperative Postoperative Postoperative Determination (+ SD) (+ SD) (+ SD) Pulmonary artery pressure, mean 41.8 k k k 7.3 (mm Hg) Pulmonary artery wedge pressure, 24.2? k 7.8 mean (mm Hg) Pulmonary arteriolar resistance 352 k k (dynes ~eclcm-~) Cardiac index (Umirdm') 2.4 k k k 0.9 Mean diastolic gradient (mm Hg) 17.7 k & k 2.5

5 ..., 30 The Annals of Thoracic Surgery Vol 23 No 1 January 1977 mm I Ha --- I5Ol. ;y I.. 0' I PREOP EARLY POSTOP LATE POSTOP A D. I * I 0 E PREOP EARLY POSTOP LATE POSTOP looti : \/.. o I 0 1 ' PREOP EARLf POSTOP LATE POSTOP +I #2 VALVKSIZE #3 B I LlminlM' Fig5. Preoperative rind postoperative hemodynaniic data in 2 5 patients undergoing mitral valve replacenzent with Uaiversity of Cape Town prosthesis. (A) Systolic pulmonary artery pressurc (B) Pulmonary artery wedge pressure. (0 Cardiac 1. index. (D) Transvaliulargradient. (E) Compariso v of actual orifice area of the prosthesis used with tht. : area calculated from postoperative hemodynamic data. The spurious13 large calculated area in 1 patient with a No. 2 valve distorts the mean valuefor. this prosthesis. 0 PREOP EARLY POSTOP LATE POSTOP C

6 31 Ellis, Healy, and Alexander: Mitral Valve Replacement with Modified UCT Prosthesis valve orifice and the actual area of the orifice was disappointing and was even more marked when exercise values were analyzed. Comment The hospital mortality rate for isolated mitral valve replacement with the UCT valve is low and is comparable to rates reported for other devices. Only 1 known valve failure occurred in the patients reported, and, fortunately, that patient survived reoperation. However, late results are disappointing; only 60% of the patients undergoing mitral valve replacement, including those having tricuspid annuloplasty, were alive when follow-up was completed. Although this survival figure is not significantly different from reported results after use of disc or ball valves, it is not comparable to current rates reported for the modified cloth-covered Starr-Edwards ball valve [3] and for the glutaraldehyde-preserved porcine xenograft 18,131. Furthermore, the incidence of thromboembolism is excessive and requires long-term anticoagulation therapy that has led to a number of fatal complications in patients in this series who might otherwise have survived and done well. Postoperative hemodynamic studies have failed to support the encouraging prospects engendered by in vitro studies. The calculated area of the effective valve orifice was usually considerably less than the measured valve orifice area, resulting in transvalvular gradients in excess of acceptable standards. As a result, we have discontinued use of the UCT valve and, for the past few years, have employed the glutaraldehydepreserved porcine xenograft for mitral valve replacement with gratifying results. References 1. Allen WB, Karp RB, Kouchoukos NT: Mitral valve replacement: Starr-Edwards cloth-covered composite-seat prosthesis. Arch Surg 109:642, Barnhorst D, Oxman HA, Connolly DC, et al: Ten-year isolated replacement of the mitral valve with the Starr-Edwards prosthesis: an 11-year review. J Thorac Cardiovasc Surg 71:230, Bonchek LI, Anderson RE', Starr A: Mitral valve replacement with cloth covered composite-seat prostheses: the case for early operation. J Thorac Cardiovasc Surg 67:93, Cook W, Yellin E, Frater RWM: Hernodynamic function of the University of Cape Town (UCT) mitral valve. Circulation 42:Suppl 3:145, Ellis FH Jr, Bulbulian AH: Prosthetic replacement of the mitral valve: I. Preliminary experimental observations. Proc Staff Meet Mayo Clin 33:532, Hawe A, Frye R, Ellis FH Jr: Late hemodynamic studies after mitral valve surgery. J Thorac Cardiovasc Surg 65:351, Henderson BJ, Mitha AS, le Roux BT, et al: Haemolysis related to mitral valve replacement with the Beall valve prosthesis. Thorax 28:488, McIntosh CL, Michaelis LL, Morrow AG, et al: Atrioventricular valve replacement with the Hancock porcine xenograft: a five year clinical experience. Surgery 78:768, Oxman HA, Connolly DC, Ellis FH Jr: Mitral valve replacement with the Smeloff-Cutter prosthesis: experience with 154 patients and comparison with results of replacement with a Starr-Edwards prosthesis. J Thorac Cardiovasc Surg 69:247, Pietras RJ, Long DM, Rosen KM: Late postoperative clinical and hemodynamic assessment of the early cloth-covered Starr-Edwards mitral valve prosthesis. J Thorac Cardiovasc Surg 67:450, Reid JA, Stevens TW, Sigwart U: Hemodynamic evaluation of the Beall mitral valve prosthesis. Circulation 45:Suppl 1:1, Schrire V, Barnard CN: Immediate and long-term results of mitral valve replacement with University of Cape Town mitral valve prosthesis. Br Heart J 32:245, Stinson EB, Griepp RB, Shumway NE: Clinical experience with a porcine aortic valve xenograft for mitral valve replacement. Ann Thorac Surg 18:391, Williams JC, Vernon CR, Daicoff GR, et al: Hemolysis following mitral valve replacement with the Beall valve prosthesis. J Thorac Cardiovasc Surg 61:393, Wright JTM, Temple LJ: Relationship between the physical size, incompetence, and stenosis of prosthetic mitral valves. Thorax 27:287, 1972