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Use of indigenous pig pericardial valves for mitral valve replacement.
In recent years great advances have been made in the designing and application of prosthetic and biological tissue valves. Prosthetic valves have been accepted as the most common valves used for replacement of diseased valves. At present a large variety of these prosthetic valves are available in several shapes and designs[8] each claiming several advantages. But all of them have one common disadvantage that they need life long anti-coagulation. In India, as in several other Asian countries, the high cost of prosthetic valve and inability to maintain patients on long term anticoagulation poses a very great problem. Early results of frame mounted fascia lata were encouraging.[4], [5] However, in 1972 it became evident that autologous fascia lata valves were totally unacceptable in atrioventricular position.[9] We were encouraged by the successful reports of the use of dura mater valves by Zerbini[12] and the pericardial valve by Ionescu et al[7] and Tandon and Ionescu[11] prompted us to design pig pericardial valves locally in our laboratory. We are presenting here our early experience in 10 patients who have undergone mitral valve replacement using pig pericardial valves, mounted on a locally made valve frame.
Since August 1978, glutaraldehyde stabilised pericardial xenografts were used for mitral valve replacement. There were seven cases with single valve replacement. In two cases tricuspid annuloplasty was done in addition to mitral valve replacement. One patient underwent triple valve replacement with one of the biological valves that was an indigenous pig pericardial valve. There were 8 males and 2 females in the series. The age distribution in these patients is shown in [Table 1]. The type of pathology is shown in [Table 2]. The etiology was rheumatic in all cases. In 3 cases there were signs of active rheumatic carditis. All these patients were from low socio-economic status and poorly nourished. Procuring, mounting and preserving Pericardium was procured from the slaughter house within half an hour after death of the animal. Following collection a sterile procedure was observed during the entire process of preparation. Pericardial sheets of uniform thickness were selected and were carefully cleaned and trimmed. These sheets were washed with normal saline for five hours. This was an essential step to wash out the soluble proteins which are highly antigenic. Following this, quadrangular strips measuring 3.2 cms X 1.5 cms are cut. The clean pericardial strips are then stored in 0.5 per cent purified glutaraldehyde buffered to a pH of 7.4 with 0.0067 M phosphate buffer at 4° C for two weeks. The stent on which the valve is mounted is locally made. It consists of a stainless steel ring covered with a dacron cloth. The sewing rim is made of siliconized rubber covered with dacron cloth. The struts have two holes at their lower end. These holes are necessary to fix the pericardial strip at these points. Specially designed moulds are used to give an accurate tricuspid shape to the pericardial cylinder and to maintain that shape till mounting of the valve is complete [Fig. 1]. Suturing is done by using 3-0 merselene or 4-0 white merselene suture. The valve so made is treated with 2% purified glutaraldehyde solution for 48 hours before it is ready for valve replacement. Operative Technique In this series all valve replacements were performed by a median sternotomy and conventional cardiopulmonary bypass. The heart was arrested with cold cardioplegia injected in the ascending aorta. Its heat was furher cooled by topical hypothermia. 2-0 prolene continuous suture technique was used to replace the mitral valve. [Fig. 2].
Of the ten patients who underwent surgery, one died on the 4th postoperative day. This patient was an extremely sick boy, aged 11 years, with evidence of rheumatic carditis. The remaining nine patients are well and are regularly followed up at monthly intervals.
Pericardial xenograft is a relatively new bioprosthesis. Ionescu's data has already shown that this valve possesses the beneficial characteristics of tissue valve viz. a low rate of post-operative thromboembolism without the use of anticoagulation.[6], [7], [11] Other advantages are avoidance of catastrophic failure, sudden death and haemolysis in patients without a perivalvular leak. The follow up results of our patients are from 3 months to 1 year and our findings are consistent with those of Ionescu's data. The advantage of a very low embolic rate and the absence of valve thrombosis without long term anticoagulation becomes even more significant when considering both the psychological anxieties and the haemorrhagic risks associated with long term anti coagulant therapy.[1],[2],[3],[10] Improved exercise tolerance, reduction in heart size and symptom-free patients are obviously due to the excellent flow characteristics of this valve. The surface area of the pericardial xenograft available to the flow is significantly larger than those of the frame mounted aortic homografts and heterografts. This is because the aortic annulus which is mounted inside the stent reduces the inner diameter of the aortic homograft or heterograft. In this small series there was one hospital death. This mortality is comparable to the results reported by other workers using similar or other prosthetic valves.' The long term results of these indigenously made pig pericardial valves remain to be studied. However, the negligible cost and the absence of thromboembolism without anticoagulation are two main factors which necessitate further interest in these valves.
We are thankful to the Research Society of K.E.M. Hospital and Seth G.S. Medical College, Bombay, for financially supporting this research project and allowing its publication.
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