Fig. 1.1
Panel (a): anatomical pitfalls during mitral valve surgery. Panel (b): section of the mitral valve complex, focusing on the structures which constitute the leaflet, the annulus, and the ventricular muscle
Fig. 1.2
Aortic sinuses, coronary arteries, and the location of the His bundle in respect to the sinuses
1.3 Importance of Degeneration or Inflammatory Processes on Stability of Tissues
Unless it is injured, the normal endothelium is resistant to infection by most bacteria and to thrombus formation. Except for those patients in whom the PVLs are caused by technical errors, the other cases are due to an endothelial injury (e.g., at the site of impact of high-velocity jets or on the low-pressure side of a cardiac structural lesion) which causes abnormal flow and allows either direct infection by microorganisms or the development of an uninfected platelet-fibrin thrombus. This thrombus subsequently serves as a site of bacterial attachment during transient bacteremia and will impair tissue stability. The cardiac lesions most commonly associated to this pathological process are mitral regurgitation, aortic stenosis and regurgitation, ventricular septal defects, and complex congenital heart disease. Also, these non-bacterial thrombi can arise as a result of a hypercoagulable state (marantic endocarditis—uninfected vegetations seen in patients with malignancy and chronic diseases) and to bland vegetations complicating autoimmune syndromes, in particular systemic lupus erythematosus and the antiphospholipid antibody syndrome. From a pathological standpoint, those organisms that will cause prostheses detachments due to infections generally reach the bloodstream from mucosal surfaces, the skin, or sites of focal infection. Except for more virulent bacteria (e.g., S. aureus) that can adhere directly to intact endothelium or exposed subendothelial tissue, microorganisms in the blood adhere to thrombi and induce a procoagulant state at the site. Although the relationship is not absolute, the causative microorganism is primarily responsible for the temporal course of endocarditis and, thereafter, for injuries between the sewing ring of the prosthesis, the sutures, and the native annulus. Hemolytic streptococci, S. aureus, and pneumococci typically result in an acute course, although S. aureus occasionally causes subacute disease. Endocarditis caused by Staphylococcus lugdunensis (a coagulase-negative species) or by enterococci may present acutely. Subacute endocarditis is typically caused by viridans streptococci, enterococci, coagulase-negative staphylococci, and the HACEK group (Haemophilus species, Aggregatibacter species, Cardiobacterium hominis, Eikenella corrodens, and Kingella species) [8].
1.3.1 Surgically Implanted Heart Valves (Types of Prostheses, Different Valve Implantation Positions, Suture Techniques, etc.)
Occurrence of PVL is related to the surgical technique and to endocarditis, usually affecting the sewing ring or the interface of the prosthetic valve and the annulus (often a site of clot formation; Fig. 1.3). It can result in a true detachment of the valve if the lesion is wide. More dramatically, progression of uncontrolled infection may lead to perivalvular abscess formation. Occurrence of PVL is related to the surgical technique and to inflammation/endocarditis. With careful annular decalcification and closely placed sutures (pledgeted), these events can be minimized. Above in the text the main techniques used for surgical replacement will be illustrated.
Aortic Valve Replacement
During the operation the leaflets of the aortic valve are excised to the level of the annulus, and the annulus is thoroughly debrided of any calcium. Extensive decalcification is of paramount importance, and this maneuver will minimize the risk of PVL and dehiscence, particularly in those patients implanting prostheses with thinner sewing rings (Fig. 1.4). More, it will allow for better seating of the valve prosthesis. In most cases, to replace the aortic valve, the annulus is encircled by three 2-0 prolene sutures. Alternatively, multiple single-braided 2-0 sutures may be placed, extending from the aortic to the ventricular surface (everting). Importantly, there could be an anatomic predisposition to periprosthetic leak in the area of the annulus extending from the right and non-coronary commissure, one-third the distance along the right coronary cusp, and two-thirds the distance to the non-coronary cusp, due to intrinsic weakness in this area of the annulus [9]. The current range of aortic PVL is less than 1% per patient-year, with early postoperative occurrence predominating.
Mitral Valve Replacement
Analyzing the surgical techniques adoptable during the first operation, suturing techniques vary according to the type of mitral prosthesis implanted. The strongest type of suturing technique to the mitral annulus is the one which places the sutures from the ventricle to the atrium (noneverting or subannular) [10]. To ensure adequate function of bileaflet valves, everting sutures (atrium to ventricle to sewing ring) could also be adopted. This technique pushes the prosthetic valve out into the center of the orifice and minimizes any tissue interference of the prosthetic valve leaflets. This is important when the subvalvular apparatus is preserved. Teflon pledgeted sutures, particularly with the thin sewing rings of the currently bileaflet mechanical valves, are advised. Alternatively, a running prolene suture for implantation of mitral valves is the other technique of choice. Although this technique makes a very clean suture line with minimal knots, it has an increased risk of valve dehiscence if an infection occurs [11]. Because of improved surgical techniques and the use of Teflon pledgets, the incidence of PVLs has fallen from below 1.5% per patient-year, without any differences for both mechanical and biologic prostheses [3, 12]. Historically, PVL was slightly more common with the bileaflet valve than with the porcine valve because of the need for the everting suture technique and less bulky sewing ring [13, 14].
Fig. 1.3
Multiple echocardiographic windows illustrating a perivalvular jet causing severe mitral regurgitation
Fig. 1.4
Wide variation between mechanical and tissue prostheses when the sewing cuff is considered
1.3.1.1 Factors Influencing Valve Detachment (Creation of Paravalvular Leaks)
The incidence of PVL for both mechanical and biologic valves is about 0–1.5% per patient-year. The PVLs are the result of an incomplete seal between the sewing ring and annulus. This may arise from abnormal pressure or traction forces on the prosthesis occurring after surgery [9, 15]. Several factors are known to increase the risk of PVL formation [16, 17]. They include annular calcification, infection, suturing technique, as well as the size and shape of prosthetic implant. The early occurrence of PVLs is usually associated with the technical aspects of the surgical implant. Late PVLs are commonly a consequence of suture dehiscence caused by endocarditis or the gradual disruption of incompletely debrided annular calcifications. The regurgitant flow across the perivalvular area frequently leads to hemolysis and, as discussed previously, through denuding of the endocardium to PVE. The number of cases of PVE is on the rise as the number of patients with prosthetic heart valves continues to increase, with an incidence of early PVE around 1% and an incidence of late PVE (after 1 month from operation) slightly inferior, 0.5–1% per year [18]. The risk of PVE appears to be greatest at approximately 5 weeks following valve implantation and thereafter declines [19]. According to the literature, the type of prosthesis (mechanical versus bioprosthetic) does not influence the risk of PVE. Early PVE is usually the result of intraoperative infection (common portals of entry for bacteria causing PVE are intravascular catheters and skin infection). Nosocomial infections contribute to late PVE, particularly in patients with medical comorbidities that require frequent hospital admission or instrumentation (e.g., hemodialysis patients) or immunosuppression (e.g., organ transplantation) [8].
Because of the highly invasive nature of PVE, around 40% of affected patients merit surgical treatment. In the case of perivalvular infections, a complication which occurs in 45–60% of prosthetic valve infections is suggested by persistent unexplained fever during appropriate therapy. Extension can occur from any valve but is most common with aortic valve infection. TEE with color Doppler is the test of choice to detect perivalvular abscesses (sensitivity more than 85%). Although occasional perivalvular infections are cured medically, surgery is warranted when fever persists, fistulae develop, prostheses are dehisced and unstable, and invasive infection relapses after appropriate treatment.
1.3.1.2 Surgical Treatment of Paravalvular Leaks (Techniques, Efficacy of Surgical Treatment, Clinical Trials, Registries)
Although for redo surgery median sternotomy remains the approach of choice, the right anterolateral thoracotomy approach could be an alternative in selected patients (e.g., patent bypass grafts on the left system). It is a safe alternative for mitral valve replacement, because it provides excellent exposure of the mitral valve with minimal need for dissection within the pericardium.
When evaluating patients with a PVL, an assessment of valve function is mandatory. If the valve itself is competent, direct repair of the leak avoids the hazards of valve replacement. While pledgeted suturing may be attempted for smaller leaks, fibrotic tethering of surrounding tissue and the size of the defect may require a bovine or autologous pericardial patch. In cases of significant dehiscence or associated valvular dysfunction, removal of the valve is necessary. However, in this situation, valve replacement is prone to leak recurrence because the annulus is partially intact, often calcified, and otherwise less than ideal for suture placement. In this context, accidental injury of the circumflex artery could happen (Fig. 1.5). A bovine pericardial skirt can be fashioned and sewn to the sewing ring of the valve. Annular sutures then are placed in a typical fashion through the sewing ring, and the valve is seated.
Reconstruction of the Mitral Annulus
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