Heart valve replacement

The basic principles of the technique and tactics of implantation of framed bioprostheses are similar to those when using mechanical valves. Unlike mechanical and framed biological prostheses, frameless biovalves (xenografts, allografts, etc.) are not rigid, deformation-resistant structures, and therefore such a replacement of the heart valve can be accompanied by a change in both geometric and functional characteristics. To what extent and how does the function of frameless biovalves change as a result of implantation? What factors should be taken into account before and during the implantation of frameless heart valve substitutes in order to maximally preserve their original functional characteristics? Which heart valve replacement provides the best functional result? A number of experimental and clinical studies have attempted to obtain answers to these and other questions.

Comparison of the hydrodynamic characteristics of the Medtronic Freestyle prosthesis implanted in an elastic silicone "aorta" showed that the pressure gradient and regurgitant volume on the prosthesis depend largely on the size of the prosthesis and, to a lesser extent, on the implantation technique. The maximum leaflet opening areas measured during prosthesis visualization on the bench were larger when simulating prosthesis placement using the "full root" method.

In subsequent works by other authors, the experimental model for assessing the effect of the size and implantation technique of frameless bioprostheses on their functional characteristics in vitro was improved. For this purpose, the frameless bioprostheses under study were implanted into native porcine aortic roots, and then also into porcine aortic roots stabilized with glutaraldehyde. According to the authors, this simulated implantation into “young” and “old” human aortic roots.

In these studies, heart valve replacement was accompanied by a significant decrease in the extensibility of native "young" aortic acceptor roots, into which frameless Toronto SPV prostheses were implanted. Hydrodynamic parameters were better, and flexion deformations of open leaflets were smaller when implanting a Toronto SPV prosthesis with an outer diameter 1 mm smaller than the inner diameter of the acceptor root. According to the authors, moderately reduced disproportion of xenograft implantation can increase their wear resistance, depending on leaflet deformation and flexion stresses. The hydrodynamic efficiency of "young" composite aortic roots was significantly and reliably higher than that of "old" ones. Subcoronary heart valve replacement of both stabilized and native aortic roots led to deterioration of their original functional characteristics.

The study conducted a comparative analysis of the functional results of experimental implantations of xenografts into allogeneic aortic roots on non-embalmed cadavers of young and elderly individuals, followed by an assessment of the anatomical and functional characteristics of the removed composite aortic roots in bench studies.

A comparative analysis of the functional results of two groups of composite aortic roots showed that the best biomechanical and hydrodynamic characteristics were obtained using such a technique as subcoronary heart valve replacement with excision of all three xenograft sinuses. When preserving the non-coronary sinus of the xenograft, a paraprosthetic "hematoma" was often formed, significantly distorting the geometry of the composite aortic root and negatively affecting its flow characteristics and the biomechanics of the cusps. In clinical practice, such formation of paraprosthetic hematomas in the area of the preserved non-coronary sinus of the xenograft often leads to a high systolic pressure gradient in the postoperative period, gradually regressing as the hematoma resolves. With significant sizes of the hematoma and its further organization, high residual pressure gradients may persist or it may become infected with the formation of a paraprosthetic abscess.

The study also showed that the main factors influencing the functional outcome of such a procedure as heart valve replacement with the developed xenograft model are the acceptor root extensibility, adequate selection of the xenograft size and its position relative to the fibrous ring of the acceptor root. In particular, aortic root replacement does not affect the initial functional characteristics of the developed xenograft model. Supraannular subcoronary heart valve replacement, in contrast to aortic root replacement, leads to the formation of moderate circumferential precommissural deformations of the xenograft cusps, and also provides it with better flow characteristics, compared to implantation in the intraannular position.

The choice of surgical technique in case of using a frameless bioprosthesis in the aortic position is determined, first of all, by its design. A number of bioprostheses (AB-Composite-Kemerovo, AB-Mono-Kemerovo, Cryolife-O'Brien, Toronto SPV, Sonn Pencarbon, Shelhigh Standard and Shelhigh SuperStentless, etc.) are implanted only in the subcoronary position. Prostheses made in the form of a solid xenogenic aortic root (Medtronic Freestyle, PnmaTM Edwards) can be implanted in the subcoronary position with excision of two or three sinuses, as well as in the form of "root insertion" (root-inclusion) with partial excision of the coronary sinuses of the xenograft. Finally, these prostheses can be implanted using the "full-root" technique. Most surgeons prefer to use the subcoronary implantation technique when using solid xenografts.

In aortic prosthetics using the subcoronary implantation technique, transverse (2/3 of the perimeter of the ascending aorta slightly above the sinotubular junction) or oblique, less often complete transverse or semi-vertical aortotomy is performed. After careful excision of the aortic valve cusps and maximum removal of calcifications, anatomical changes and geometry of the aortic root, features of the location of the coronary artery orifices are visually assessed.

The choice of the frameless bioprosthesis size remains debatable. Usually, a bioprosthesis with a diameter 1-3 mm larger than the maximum caliber, which is freely passed through the patient's aortic ring, is selected. Sometimes, a prosthesis with a diameter equal to the diameter of the aortic ring or the diameter of the sinotubular junction is selected; in some cases, the root is reconstructed. In case of a low position of the right coronary artery orifice, subcoronary heart valve replacement is used with a bioprosthesis rotation, placing its right sinus into the patient's non-coronary sinus, or aortic root replacement is performed. At the first stage of implantation of frameless bioprostheses in the supraannular subcoronary position, a proximal row of interrupted sutures (3-0 ticron, 2-0 or 3-0 etibond, 4-0 prolene at the discretion of the surgeon) is applied to the fibrous ring in the plane of the ventriculoaortic junction, passing, in fact, through the base of the fibrous ring. At the second stage, the bioprostheses, washed from the preservative and produced in the form of a whole aortic root, are prepared for implantation by excising two or three xenograft sinuses. Some authors do not recommend excising the sinuses at this stage so as not to disrupt the spatial orientation of the commissure columns at the following stages of implantation. Frameless bioprostheses, produced with excised sinuses, are not subjected to this procedure. At the third stage, the threads of the proximal row of interrupted sutures are passed through the base of the xenograft, being careful not to damage the cusps with the needle. At the fourth stage, the xenograft is placed in the patient's aortic root, and the threads are tied and cut. For the correct orientation of the commissures, provisional U-shaped supporting sutures are applied 3-5 mm above the xenograft commissures, passing them through the patient's aortic wall to the outside. The fifth stage of the operation can be performed differently, depending on the bioprosthesis model used. If a bioprosthesis model without sinuses is used or they were excised at the second stage of implantation, then they are “adjusted” to the mouths of the patient’s coronary arteries. In this case, it is recommended to maintain the original spatial orientation of the commissures and cusps.

Only after performing the suture orientation of the commissures, the excess tissue of the xenograft aorta is excised. At the sixth stage of implantation, a distal continuous twisted sealing suture (4-0 or 3-0 Prolene) is applied. The thread is passed through the excised edge of the xenograft sinus and the wall of the root-acceptor sinus below the orifice of the coronary arteries. The distal suture is applied starting at the deepest proximal point of the excised xenograft sinus and ending at the apex of the adjacent commissures (sometimes it is recommended to start the distal suture in the opposite direction - from the apex of the intercoronary commissure). The ends of adjacent threads are brought out to the outer surface of the aorta and tied together. In some cases, before tying the distal suture threads, fibrin glue is introduced into the paraprosthetic space between the non-coronary sinuses to avoid the formation of a paraprosthetic hematoma. It can form due to a discrepancy in the sizes of the non-coronary sinuses of the bioprosthesis and the patient, and can also become infected with the formation of a paraprosthetic abscess. The last stage of the operation is to close the aortotomy incision with a continuous suture (4-0 prolene). In some patients, aortic plastic surgery is performed with native autopericardium or xenopericardium. The Cryolite-O'Brien bioprosthesis is fixed with a single-row (4-0 prolene) continuous suture in the supraannular position.

In some cases, the root-inclusion implantation technique is used for dilatation of the sinotubular junction and annuloaortic ectasia. This technique involves incomplete excision of the coronary sinuses and preservation of the sinotubular junction of the xenograft in order to ensure its original spatial configuration. The proximal row of nodal sutures is applied according to the standard scheme. The orifices of the patient's coronary arteries are implanted into the adapted openings of the coronary sinuses of the xenograft. The upper edge of the xenograft and the edge of the aorta-tomal incision are sutured with a continuous polypropylene suture with simultaneous closure of the aorta.

Heart valve replacement using the "full root" technique is performed much less frequently (4-15%) than heart valve replacement in the subcoronary position. First, a complete transverse aortotomy is performed slightly above the sinotubular junction. Then, the orifices of both coronary arteries of the patient are excised together with the preceding part of the sinuses, and then the affected cusps of the aortic valve are removed. The proximal anastomosis is applied using 28-35 interrupted sutures (3-0), which are tied on a strip of Teflon or native autopericardium 1 mm wide in order to seal the sutures. The orifices of the coronary arteries of the bioprosthesis are excised. The orifice of the left coronary artery is reimplanted with a continuous wrapping suture (5-0 Prolene) into the corresponding sinus of the bioprosthesis. A distal anastomosis is performed between the xenograft and the patient's ascending aorta using a continuous suture (4-0 Prolene) of the end-to-end type. At the final stage, the orifice of the right coronary artery is reimplanted.

It should be noted that technical errors or inaccuracies in the implantation of frameless bioprostheses can lead to their distortion, loss of mobility of one or more cusps and, as a result, to the early development of structural degeneration and calcification. During implantation, it is necessary to constantly irrigate the bioprosthesis with a physiological solution to prevent drying out and damage to the tissue of the cusps.

Replacement of the heart valve with frameless bioprostheses in the aortic position is performed in patients with hemodynamically significant defects, mainly over 40 years old, or in younger patients with intolerance to anticoagulants. Replacement of the heart valve with xenografts is performed mainly in patients aged 60-70 years and older. This type of bioprosthesis is the valve of choice for elderly patients and those with a narrow aortic root (less than 21 mm) or with a low left ventricular ejection fraction, since the absence of a frame in the patient's narrow aortic root provides a high hemodynamic effect. Severe calcification of the sinuses of Valsalva, aneurysm of the root and/or ascending aorta, abnormalities in the location of the coronary artery orifices (close location of the coronary artery orifices to the fibrous ring of the valve or their location opposite each other in a bicuspid valve), the presence of non-removable calcifications of the fibrous ring, significant dilation of the sinotubular junction are considered contraindications to the implantation of frameless bioprostheses in the subcoronary position. The way out of this situation is replacement of the heart valve with a xenograft using the aortic root prosthesis technique.

Normally, in young healthy people, the sinotubular junction diameter is always smaller than the fibrous ring diameter. However, in patients with aortic valve defects, especially with aortic stenosis, the sinotubular junction diameter often exceeds the fibrous ring diameter. In this case, the bioprosthesis size is selected based on the diameter of its sinotubular junction and is implanted using the "root insertion" or root prosthetics technique, or subcoronary heart valve replacement with sinotubular junction reconstruction is performed.

In case of aortic root aneurysm, isolated valve replacement is performed or in combination with replacement of the ascending aorta, or a valve-containing conduit is implanted.

Without highlighting absolute contraindications to the use of frameless bioprostheses, some authors recommend refraining from their use in cases of active infective endocarditis. Other authors have widely used Medtronic Freestyle, Toronto SPV bioprostheses in active infective endocarditis.

Some surgeons recommend implanting xenografts in a subcoronary position only in uncomplicated forms, when the infectious process is limited to the aortic valve cusps, since infection of the synthetic lining of the bioprosthesis is possible.

According to some authors, frameless bioprostheses sheathed with stabilized pericardium have greater resistance to infection. For example, Shelhigh xenografts were used mainly in emergency cases when the required homograft size was not available. The frequency of reinfection of Shelhigh frameless bioprostheses and homografts (4%) in patients of both groups was the same.

Usually, in the postoperative period, patients with a frameless bioprosthesis are prescribed warfarin (INR = 2-2.5) for 1.5-3 months. However, with the accumulation of experience, many surgeons prescribe warfarin to patients with atrial fibrillation and a high risk of thromboembolic complications. Some authors prescribe only aspirin to those patients who additionally underwent aortocoronary bypass.

Aortic valve replacement with a pulmonary autograft using the DN Ross method (1967) is performed in patients with infective endocarditis of the aortic valve, and in cases of congenital aortic valve defects - mainly in newborns and infants. There are several modifications of the Ross operation - aortic root replacement, cylindrical technique, Ross-Konn operation, etc. The Ross II operation, in which a pulmonary autograft is implanted in the mitral position, is also described. In case of using the aortic root replacement technique, an incision of the ascending aorta is made using a transverse approach and a revision of the aortic valve. The pulmonary artery trunk is incised transversely and below the level of origin of the right pulmonary artery. The pulmonary artery root is excised carefully so as not to damage the first septal branch of the left coronary artery. Both coronary arteries are cut off together with areas of surrounding tissue of the sinuses of Valsalva. The aortic root is excised at the level of the aortic ring along the lower edge of the walls of the aortic sinuses. The pulmonary artery trunk together with the valve is sutured to the base of the aortic root, and the coronary artery orifices are reimplanted into the autograft. The pulmonary artery allograft is sutured to the opening of the right ventricular outlet and to the distal part of the pulmonary trunk.

Frameless biological (allo- and xenogenic) atrioventricular heart valve substitutes have been developed and have been introduced into clinical practice to a limited extent for the purpose of almost complete anatomical and functional replacement of natural valves in cases where valve-preserving surgery is impossible. Replacement of the heart valve with these atrioventricular valve substitutes ensures their high throughput and good locking function while maintaining the annulopapillary continuity of the ventricles, which ensures a high functional result.

Mitral valve replacement with a homograft was one of the first operations in the development of cardiac valve surgery. Experimental studies in the early 1960s on animal models had encouraging results demonstrating rapid integration of the homograft, with the cusps and chords remaining intact 1 year after implantation. However, the first attempts to replace the mitral valve with a mitral homograft in a clinical situation were associated with the development of early valve dysfunction due to a misunderstanding of the function of the valve apparatus and the difficulty of fixing the papillary muscles. Progress made over the past 20 years in the evaluation of the mitral valve by echocardiography has significantly increased the knowledge base of valvular pathophysiology. Experience gained in reconstructive surgery of the mitral valve has allowed surgeons to master the operative technique on the subvalvular apparatus.

The essence of the operation of implantation of a frameless atrioventricular valve substitute is reduced to suturing the tops of the papillary muscles of the allo- or xenograft to the papillary muscles of the patient, and then fixing the fibrous ring of the graft to the fibrous ring of the recipient. The operation consists of several stages. After excision of the pathologically altered valve of the patient, the anatomy of his papillary muscles is assessed, the atrioventricular opening and the distance between the fibrous triangles are measured with a caliber. Then the size of the graft is selected, focusing on the measurements taken, and the implant on the holder is placed in the ventricular cavity, trying it on relative to the papillary muscles, the fibrous ring of the patient and for matching the sizes between the fibrous triangles. The level of suturing on the papillary muscles is calculated. The tops of the implant are fixed to the papillary muscles with U-shaped sutures on pads passed through the bases of the papillary muscles.

After tying the U-shaped sutures, the second (upper) row of sutures is performed with continuous or single sutures. First, sutures are provisionally placed in the area of the fibrous triangles through the marked areas of the fibrous ring of the graft. After restoration of cardiac activity, intraoperative transesophageal echocardiographic assessment of the closure function of the graft is mandatory.

Replacement of the heart valve with cryopreserved mitral homografts according to Acar et al. (1996). The mitral apparatus complex is excised in patients who have undergone heart transplantation at the sites of attachment of the papillary muscles to the walls of the ventricle and the myocardium surrounding the fibrous ring of the mitral valve. This manipulation is performed in an operating room. Cryopreservation is carried out for 18 hours, during which the homografts are kept in a tissue bank. A 5% preservative solution of dimethyl sulfoxide without the addition of antibiotics is used. Preservation is carried out with a gradual decrease in temperature to -150°C. The morphological characteristics of the papillary muscles and the distribution of the chords are recorded for each homograft and entered into an identification card. The recorded valve characteristics are the height and area of the anterior mitral leaflet measured with an annuloplasty obturator, and the distance between the apex of the papillary muscle and the fibrous ring of the mitral valve. Papillary muscles are classified according to their morphological features and are divided into 4 types. Myocardial protection is achieved by cold cardioplegia through the aortic root. Access to the left atrium is achieved by a classic parallel incision through the interatrial groove. The mitral valve is then examined to assess the pathological process and make a final decision on the type of surgical intervention. In the presence of an isolated lesion affecting less than half of the valve (calcification or valve abscess), only a part of the homograft is implanted, provided that the remaining part of the valve was normal. On the other hand, in the presence of extensive lesions involving the entire valve in the pathological process, complete mitral valve replacement with a homograft is performed. When implanting a mitral homograft, the pathologically altered valve tissue is first excised along with the corresponding chords, the integrity of the papillary muscles is carefully preserved. They are mobilized by separating the muscle layers attached to the left ventricular wall. Replacement of the homograft heart valve begins with fixation of the papillary muscles. The exposure of the recipient papillary muscle is clearly visible by traction on the stay suture. Each papillary muscle of the homograft is fixed to the incision between the native papillary muscle and the left ventricular wall. The head of the homograft papillary muscle, which supports the commissure, is used as a control point and is placed on the corresponding section of the native papillary muscle. This section is easily determined, since the commissural chords invariably originate from the apex of the papillary muscle. Typically, the homograft papillary muscle is sutured side-to-side to the recipient papillary muscle to position it at a lower level. A double row of mattress sutures, protected by multiple interrupted sutures, is used to suture the papillary muscles.The Carpentier annuloplasty ring is sutured to the recipient annulus fibrosus. The size of the annuloplasty ring is selected based on the size of the anterior homograft leaflet measured with the obturator. The homograft leaflet tissue is then sutured to the Carpentier ring using 5-0 prolene-polypropylene sutures. The various parts of the valve are sutured in the following order: posteromedial commissure, anterior leaflet, anterolateral commissure, posterior leaflet. Particular attention is paid to the location of the commissures. In the areas of the anterior leaflet and commissures, the sutures are placed without tension. In cases of excess or insufficient homograft leaflet tissue in relation to the annuloplasty ring, the suture line is adjusted to achieve balance during suturing of the posterior mitral leaflet. After the implantation of the homograft, the result is assessed by infusing a physiological solution under pressure into the ventricle (hydraulic test). Acar et al. (1996) performed a series of implantations of cryopreserved mitral homografts in 43 patients for acquired mitral valve pathology using the described technique with satisfactory long-term results (after 14 months).

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Heart Valve Replacement: Immediate and Long-Term Results

In-hospital or immediate 30-day mortality after isolated mitral or aortic valve replacement surgery, including combined coronary artery bypass grafting (CABG), was 10-20% 15-20 years ago. In recent years, perioperative mortality has significantly decreased to 3-8% and is due to the presence of severe chronic cardiac and pulmonary failure, severe chronic lung diseases, multiple organ failure, diabetes, and the development of various complications in the postoperative period: bleeding, acute purulent infection, myocardial infarction, acute cerebrovascular accident, etc. The decrease in mortality in the last decade is due to improved surgical valve implantation techniques, improved artificial blood circulation techniques, myocardial protection through the introduction of antegrade and retrograde blood cardioplegia, anesthetic and resuscitation support, and the use of more advanced models of artificial heart valves and bioprostheses. Hospital mortality remains higher in emergency and urgent surgeries performed for vital indications, in reoperations (repeated operations) and combined surgical interventions. It is noted that the majority of complications and fatal outcomes occur in the first 3-5 years after surgery, after which survival rates stabilize.

The criterion of functional efficiency of the implanted valve in maintaining homeostasis stability is the actuarial survival rate of patients - the absence of mortality from valve-dependent complications. In 90% of patients who have undergone mitral or aortic valve replacement, the signs of chronic heart failure are significantly eliminated or reduced, due to which they move to functional class I-II (according to the NYHA classification). Only a small group of patients remains in FC III or IV, which is usually associated with low myocardial contractility before surgery, high initial pulmonary hypertension and concomitant pathology. Survival and quality of life indicators are better in patients with artificial heart valves in the aortic position than in the mitral position. However, survival may undergo significant deterioration with an increase in the pressure gradient on the artificial valve, an increase in chronic heart failure and the duration of the postoperative observation period.

The hemodynamic parameters of the artificial heart valve have a significant impact on the state of homeostasis in the body, survival and quality of life of patients after surgery. As can be seen from Table 6.2, all artificial heart valves provide resistance to blood flow, especially under load: ball valves have a greater pressure drop than rotary disc valves, and bicuspid valves have the lowest resistance. In clinical practice, a detailed study of the hemodynamic characteristics of artificial heart valves is difficult. Therefore, the efficiency of the valves is judged by the peak and average pressure drop on the valve, detected both at rest and under load by transthoracic and transesophageal Doppler echocardiography (TEE), the values of which have a good correlation with the data obtained during catheterization of the heart cavities.

Pressure and/or volume overload caused by aortic valve pathology leads to increased pressure in the left ventricular cavity and its compensatory hypertrophy. Severe aortic insufficiency causes left ventricular volume overload with an increase in its end-diastolic volume and the development of eccentric left ventricular myocardial hypertrophy. In severe aortic stenosis, concentric left ventricular myocardial hypertrophy occurs without an increase in end-diastolic volume until the late stage of the process, thus increasing the ratio of the wall thickness to the ventricular cavity radius. Both pathological processes lead to an increase in the left ventricular myocardial mass. The positive effect after aortic valve replacement is a decrease in the volume and pressure overload of the left ventricle, which contributes to remodeling and regression of its mass in the near and long-term follow-up.

Although the clinical and prognostic significance of decreased left ventricular myocardial mass has not yet been fully elucidated, this concept is widely used as

A measure of the effectiveness of aortic valve replacement. It can be assumed that the degree of reduction in the left ventricular myocardial mass should be associated with the clinical outcome of the operation, which, especially in young patients, is of fundamental importance for their physical adaptation and subsequent employment in professions associated with physical stress.

Studies conducted in patients after aortic valve replacement have shown that the risk of developing cardiac complications was significantly lower in those patients who achieved a reduction in the left ventricular myocardial mass. In this case, when replacing the heart valve with optimally sized prostheses for isolated aortic stenosis, the left ventricular mass was significantly reduced and in some patients reached normal values already within the first 18 months. Regression of the ventricular mass continues for up to 5 years after surgery. A situation where inadequate hemodynamic characteristics of the prosthesis do not lead to a significant reduction in the left ventricular myocardial mass, which determines an unsatisfactory result of the operation, is considered by some authors as a prosthesis-patient mismatch.

Decreased patient survival in the late postoperative period, in addition to risk factors, is also associated with the negative aspects of ball artificial heart valves: large dimensions and weight, increased pressure gradient, inertia of the locking element, leading to a decrease in stroke volume and an increase in thrombus formation. However, according to some authors, the use of ball artificial heart valves is justified in the mitral position with large left ventricular volumes, severe calcification, or in the aortic position - with an aortic root diameter of >30 mm, due to their durability, mechanical reliability, satisfactory hemodynamic qualities for more than 30 years of operation in the body. Therefore, it is too early to write off ball artificial heart valves from cardiac surgery practice.

With the rotary-disc artificial heart valves Lix-2 and Emix (Mix), Bjork-Shiley, Sorm, Omniscience, Omnicarbon, Ullehei-Kaster, Medtromc-Hall in the aortic position by the 5-25th year, the actuarial survival rate of patients is slightly higher than with ball valves, and ranges from 89% to 44%, and in the mitral position - from 87% to 42%. Rotary-disc artificial heart valves, especially Medtromc-Hall, which has the largest opening angle and competes in hemodynamic efficiency with bicuspid mechanical heart valves, are distinguished by well-known advantages over ball valves in terms of better hemocompatibility, reduced thrombosis of artificial heart valves and thromboembolic complications, lower blood flow energy losses and resistance, fast response, small size and weight, and better blood flow structure.

Replacement of the heart valve with rotary-disc valves, compared to ball valves, significantly improves the morphofunctional parameters of the heart. Their hemodynamic advantage has a favorable effect on the course of the immediate and remote postoperative period, especially in patients with atrial fibrillation, and acute heart failure and "low cardiac output syndrome" become two times less frequent than with ball valves.

A noticeable hemodynamic advantage was noted in patients with implantation of bicuspid artificial heart valves Medinge-2; Carbonix-1; St. Jude Medical; Carbomedics; Sonn Bicarbon; ATS both in the mitral and aortic positions relative to rotary-disc and, especially, ball valves in terms of pressure gradient on the valve, effective valve area, valve performance, reduction in the volumes of the heart chambers, myocardial mass, as well as actuarial indicators of survival and stability of good results from 93% to 52% by 5-15 years in the mitral position and from 96% to 61% in the aortic position.

The joint STS/AATS document of the American Thoracic Society defines specific non-fatal valve-related complications of non-infectious and infectious origin that lead to decreased actuarial survival rates, quality of life, and increased disability. Non-infectious valve-related complications include structural valve dysfunction - any changes in the function of the implanted valve due to its wear, breakage, jamming of the leaflets, or rupture of the suture line, leading to stenosis or regurgitation. Non-structural valve dysfunction includes any dysfunction of the valve that is not related to its breakage: discrepancy between the size of the valve and surrounding structures, paravalvular fistula leading to stenosis or regurgitation.

Actuarial and linear rates of structural dysfunction of mechanical valves are 90-95% and 0-0.3% of patient-years, respectively. Long-term follow-up of patients with ball mechanical valves MKCh, AKCh, Starr-Edwards, as well as rotary-disc mechanical valves Lix-2, Mix, Emix, Medtronic-Hall and bicuspid mechanical valves Medinzh-2, Carbonix-1, St Jude Medical, Carbomedics and others have shown that these valves are extremely resistant to structural failure. A number of mechanical prostheses that are not currently used, such as Bjork-Shiley Convexo-Concave, had a fragile stroke limiter and were excluded from clinical practice. In contrast to mechanical valves, structural degeneration of bioprostheses, on the contrary, is the most common non-fatal valve-dependent complication. Thus, long-term observation of currently used second-generation frame bioprostheses, including the porcine Medtronic Hankock II and the pericardial Carpenter-Edwards, showed that in the aortic position, structural degeneration does not develop in more than 90% of bioprostheses within 12 years, while in the mitral position it occurs much earlier due to more pronounced systolic loads on the prosthesis leaflets.

The development of prosthetic endocarditis or massive calcification of the fibrous ring, as well as technical errors during valve implantation, can contribute to the formation of a paravalvular fistula in the early or late stages after surgery.

Hemodynamically significant paravalvular fistulas typically cause refractory hemolytic anemia, in contrast to the clinically insignificant degree of chronic intravascular hemolysis that occurs after implantation of virtually all mechanical valves, especially ball and swing-disc valves.

Technical errors in the form of too large gaps between the sutures contribute to the formation of areas of hypostasis without tight contact with the fibrous ring of the valve, which over time leads to the formation of a fistula. If the paravalvular fistula is hemodynamically significant and causes hemolysis, accompanied by anemia and requiring blood transfusions, then the fistula is sutured or the valve is re-prosthetized.

As a result of improvements in surgical techniques, the incidence of paravalvular fistulas has recently decreased and is, according to linear indicators, from 0% to 1.5% of patient-years for both mechanical valves and bioprostheses. Some authors have noted an increase in paravalvular fistulas after implantation of mechanical bicuspid valves, compared with bioprostheses, believing that this is due to the use of an eversion suture and a narrower sewing cuff.

Despite the improvement of surgical techniques, postoperative care and antibiotic prophylaxis, prosthetic endocarditis remains one of the unsolved problems of cardiac surgery and occurs in up to 3% of complications after heart valve replacement. Despite the fact that the materials from which mechanical artificial heart valves are made have thromboresistant properties, the source of infection can be the sutures that fix the prosthesis to the

Cardiac tissues where nonbacterial thrombotic endocardial thromboembolism is formed

Damage that can become infected during transient bacteremia. When the prosthesis is damaged in the aortic position, its failure most often occurs (67%), and when the mitral valve prosthesis is damaged, its obstruction (71%). Abscesses of the fibrous ring occur in 55% of cases of prosthetic endocarditis. Infective endocarditis of bioprosthetic valves causes not only destruction of the valve cusps, but also abscesses of the sewing ring, which develop more often during the first year after surgery than at a later date - 27%)

Depending on the development period, prosthetic endocarditis is usually divided into early (within 60 days after surgery) and late (more than 60 days). Early prosthetic endocarditis occurs in 35-37% of cases and is usually a consequence of bacterial seeding of the valve either during implantation intraoperatively or hematogenously in the postoperative period from the wound or venous catheter during intravenous infusions. The most common bacteria in this period are epidermal and golden staphylococcus (28.1-33% and 17-18.8% of cases, respectively), enterococcus - 6.3%, green streptococcus - 3.1%, gram-negative bacteria and fungal flora. Cases of infective endocarditis of viral etiology have been described, despite the fact that in most cases late prosthetic endocarditis (incidence 60-63%) is associated with non-cardiac septicemia.

According to D. Horstkotte et al. (1995), most often late prosthetic endocarditis occurs as a complication after dental procedures (20.3%), urological procedures and urosepsis (13.9%), intensive care using permanent venous catheters (7.4%), pneumonia and bronchitis (6.5%), manipulation of the respiratory tract (5.6%), fibroscopic examination of the digestive tract (4.6%), trauma, wound infection (4.6%), abdominal surgery (3.7%), childbirth (0.9%). In some cases, it can be caused by nosocomial infection with low-virulence pathogens oral epidermal staphylococcus.

Actuarial and linear rates of incidence of prosthetic endocarditis in the aortic position are 97-85% and 0.6-0.9% patient-years, respectively, slightly higher in the aortic position than in the mitral position. Five-year freedom from bioprosthetic endocarditis, according to most large studies, is more than 97%. The risk of developing prosthetic endocarditis for mechanical valves is slightly higher than for bioprostheses.

Prosthetic endocarditis of frameless bioprostheses and allografts is less common, so these valves may be more useful in replacing a mechanical prosthesis during reoperation for prosthetic endocarditis. Intravenous antibacterial therapy is prescribed under the control of blood culture sensitivity and should be started as soon as possible. Experience shows that when infected with low-virulence microorganisms (usually streptococci), most patients with prosthetic endocarditis can be cured conservatively. However, this therapy, especially when it comes to infection with highly virulent flora (staphylococci, fungal infection), should be supplemented by the introduction of antiseptics, and correction of the immune status of the body. Prosthetic endocarditis often requires urgent, and sometimes urgent surgery.

The most dangerous complication in the long-term observation period in patients who have undergone reimplantation of an artificial heart valve is its reinfection. The probability of reinfection of the prosthesis after repeated surgery depends on the reactivity of the body and the surgeon's ability to completely eliminate all foci of infection during the primary operation. The results of treatment of prosthetic endocarditis need to be improved. The incidence of paravalvular infections in patients with prosthetic endocarditis can reach 40%. Mortality in early prosthetic endocarditis is 30-80%, and in late - 20-40%.

Valve-dependent complications also include chronic intravascular hemolysis caused by direct mechanical damage to blood cells by a functioning artificial heart valve, distorted blood flow structure when flowing around the valve, turbulence, rupture currents, rarefactions, increased physical activity, any chronic infection, pannus proliferation, structural degeneration of bioprostheses, thrombosis of the artificial heart valve, disruption of the tissue coating and endothelial lining of the artificial valve saddle, renal and hepatic insufficiency, etc. In such situations, the process of homeostasis changes takes the form of a negative spiral course with rapid development of irreversible changes leading to the development of chronic disseminated intravascular coagulation syndrome and multiple organ failure, which are the cause of thrombotic complications. The development of chronic intravascular hemolysis is also influenced by autoimmune mechanisms, excessive occurrence of active oxygen species and activation of lipid peroxidation during hypoxia. Hemoglobin and iron ions released during chronic intravascular hemolysis are themselves powerful activators of lipid peroxidation. The level of chronic intravascular hemolysis does not change depending on the period of implantation of the artificial heart valve with its satisfactory function; atrial fibrillation and the degree of chronic heart failure do not affect the level of chronic intravascular hemolysis. When using normally functioning modern mechanical or frame biological prostheses, hemolysis is rare. Chronic intravascular hemolysis in patients with mechanical artificial heart valves occurs with a frequency of 99.7-99.8% and 0.06-0.52% of patient-years, according to actuarial and linear indicators, respectively. Such a significant spread in the frequency of chronic intravascular hemolysis does not allow an objective assessment of the advantages of a particular design of an artificial heart valve or bioprosthesis. In addition, there are currently no unified accurate biochemical tests for assessing the severity of hemolysis.

Chronic intravascular hemolysis, even at a clinically insignificant level, leads to disruption of blood rheology, progressive hemolytic anemia, disruption of hemostasis and thrombus formation due to the release of thromboplastin-like material from destroyed erythrocytes, liver pigment function, renal hemosiderosis, renal failure, iron deficiency anemia, and contributes to the development of septic endocarditis.

Treatment of chronic intravascular hemolysis in patients with artificial heart valves is carried out individually depending on its degree, development dynamics and the cause. In case of decompensated chronic intravascular hemolysis, limitation of physical activity, maintenance of erythropoiesis and replenishment of iron losses (iron preparations, folic acid, etc.) are indicated; tocopherol is prescribed to stabilize erythrocyte membranes, steroid hormones are prescribed in patients with positive autoimmune tests, in case of severe anemia - erythropoietin blood transfusions under the control of hemoglobin, haptoglobin, lactate dehydrogenase indices.

Thromboembolism and valve thrombosis are the most common valve-related complications of the postoperative period in patients with mechanical and biological mitral valve prostheses, leading to deterioration in quality of life and disability. They most often occur in patients with mechanical valves. More than 50% of patients after mitral valve replacement with chronic atrial fibrillation and other risk factors (low ejection fraction, history of thromboembolic complications, large left atrium, thrombus in its cavity, etc.) are susceptible to thromboembolic complications, despite adequate anticoagulant therapy, as well as an increased likelihood of mechanical valve thrombosis in cases of changes in the anticoagulant therapy protocol. Thromboembolism is relatively rare in patients after mitral valve replacement with a small left atrium volume, sinus rhythm and normal cardiac output. In addition, patients with older types of prosthetic valves receiving more intensive anticoagulant therapy may develop severe hypocoagulable bleeding.

Among the numerous etiologic risk factors for thrombotic complications, the following are the main ones: inadequacy of anticoagulant therapy, activity of the rheumatic process and infective endocarditis, especially prosthetic endocarditis with large vegetations; slowing and stasis of blood flow associated with low minute volume of blood circulation, hypovolemia, atrial fibrillation, and impaired myocardial contractility. Consumption coagulopathy and disseminated intravascular coagulation syndrome, pulmonary hypertension can lead to an increase in fibrinogen, imbalance of thromboxane and prostacyclin, endothelin-1, and contribute to endothelial dysfunction and thrombus formation. In addition, paravalvular fistulas and regurgitation on the artificial heart valve lead to further distortion of the blood flow structure with the development of increased separation flows, shear stresses, turbulence, cavitation, causing endothelial dysfunction, chronic intravascular hemolysis and thrombus formation.

A rare and extremely dangerous complication is thrombosis of the valve prosthesis, the risk of which does not exceed 0.2% of patient-years, it is more common in patients with mechanical valves. The frequency of actuarial and linear indicators of thrombosis of mechanical artificial heart valves varies from 97% to 100% and from 0% to 1.1% of patient-years, and in the mitral position these indicators are higher than in the aortic position. Such a significant spread in the indicators of thrombosis of artificial heart valves and thromboembolic complications can be explained by different initial risk factors and the level of anticoagulant therapy in patients. According to the summary data of a multicenter randomized study of foreign cardiac surgery centers, all cases of thrombosis of Carbomedics artificial valves were registered in patients with violation of the anticoagulant therapy regimen below the recommended level for INR (2.5-3.5) and prothrombin time (1.5), in some patients anticoagulant therapy was interrupted. In this regard, the actuarial indicator of valve thrombosis in patients with Carbomedics artificial heart valves was 97% by the 5th year, the linear indicator was 0.64% of patient-years in the mitral position, and in the aortic position - thrombosis of artificial heart valves was not observed. In 4000 implantations of Lix-2 and Emix artificial heart valves, thrombosis was 1%.