Eur J Cardiothorac Surg 2006;30:887-891
© 2006 Elsevier Science NL
Mitral valve periprosthetic leakage: anatomical observations in 135 patients from a multicentre study
Giuseppe De Ciccoa,*,
Claudio Russob,
Antonella Moreob,
Cesare Beghic,
Carlo Fuccia,
Piersilvio Geromettad,
Roberto Lorussoa
a Cardiac Surgery Unit, Civic Hospital, Brescia, Italy
b Department of Cardiovascular Surgery, De Gasperis Centre, Niguarda Ca’ Granda Hospital, Milan, Italy
c Department of Cardiac Surgery, University of Parma, Parma, Italy
d Department of Cardiac Surgery, Humanitas Gavazzeni Clinic, Bergamo, Italy
Received 19 May 2006;
received in revised form 8 September 2006;
accepted 18 September 2006.
* Corresponding author. Address: U.O. di Cardiochirurgia, Spedali Civili di Brescia, Piazzale Spedali Civili, 1-25125 Brescia, Italy. Tel.: +39 030 3995636; fax: +39 030 3995004. (Email: giudeci{at}libero.it).
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Abstract
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Objective: Prosthetic valve dysfunction after mitral valve replacement (MVR) may be caused by several factors, which often lead to repeated surgery. One of the most frequent determinants of reoperation is periprosthetic leakage (PPL). A few published reports have analysed PPL incidence and postoperative results after MVR, but no specific attention has been paid towards the potential relation between anatomical factors and PPL occurrence, particularly not bacterial-related. The aim of this study was to evaluate the location of PPL after MVR through a multicentre retrospective study. Methods: Between January 1985 and November 2005, 135 patients underwent reoperation at four institutions because of PPL after MVR and met the study inclusion criteria. The mitral valve annulus (MVA) was analysed in a clockwise format, indicating 12 o’clock as the mid-point of anterior annulus as viewed from the atrium. Results: Overall hospital mortality was 3.7% (five patients). Repair of PPL was carried out in 83 cases whereas prosthetic valve replacement was necessary in 52 cases. The total number of sectors involved in PPL was 244. PPL occurred more frequently between hour 5 and hour 6, and hour 10 and hour 11, with the risk of leakage being, 2.8 and 2.0 times higher, respectively, than in any other portion of the MVA. Conclusions: Our study suggests that PPL occurs more frequently at antero-lateral and postero-medial segments of MVA. This finding might be linked to unusual anatomical and functional factors of the MVA and may call for adjunctive care to these sectors of MVA when performing suture placement during MVR.
Key Words: Mitral periprosthetic leakage • Mitral annulus • Prosthetic valve
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1. Introduction
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Mitral valve replacement (MVR) is a routine procedure in cardiac surgery with low mortality rate and considerable benefits in terms of postoperative quality of life and survival [1]. Indeed, recent advances in material and design have led to more hemodynamically efficient and durable artificial heart valves. However, the postoperative outcome after prosthetic valve implantation is not yet completely free of complications. Artificial valve dysfunction may occur postoperatively and be caused by a variety of factors often requiring surgical reintervention. One of the most frequent causes of reoperation in this setting is periprosthetic leakage (PPL). PPL occurs in up to 12.5% of patients submitted to MVR [1]. Some factors predisposing to PPL have been identified [2], but their influence on morphology and location of PPL has been poorly investigated [3]. The interaction between valve prosthesis and the mitral-ventricular apparatus or other peculiar cardiac factors, for instance, might also intervene and ultimately affect hemodynamic prosthesis efficiency, induce undue mechanical stresses on the artificial valve ring and, hence, influence long-term valve performance and durability. To our knowledge, only a few papers have analysed PPL incidence and pattern profiles, and very little attention has been paid to the potential relation between anatomical factors and PPL occurrence. Our retrospective multicentre study, therefore, attempted to evaluate anatomical characteristics of PPL following MVR.
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2. Methods
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Between January 1985 and November 2005, at four institutions, 5832 patients had undergone non-reconstructive mitral surgery. The median age of these patients was 63.4 ± 10.6 years and 4753 (81.5%) were males. In 3837 cases the mitral valve was replaced with mechanical protheses (65.8%) and 1995 bioprostheses (34.2%). Reoperation for PPL was performed in 559 patients (9.5%). The basis for diagnosing PPL was transthoracic echocardiography (TTE) until 1995. After 1996 transesophageal echocardiography (TEE) became the most important diagnostic tool for the assessment of PPL and was instituted intraoperatively, whereas TTE was only carried out before hospital discharge. Exclusion criteria for study enrolment were the diagnosis of an active or previous endocarditis on native aortic valve or valve prosthesis, Marfan syndrome, previous MVR for dilated cardiomyopathy or ischemic insufficiency. The diagnosis of endocarditis was determined by the presence of fever, positive blood cultures, vegetation observed upon trans-thoracic echocardiography and intraoperative inspection, or at pathology assessment. Of these 559 patients 135 (2.3%) met the inclusion criteria of the study. The mean time elapsed from surgery to redo operation was 67 ± 12 months (range 7 days to 12 years) and median of 67.4 months, interquartile range 18.5. Of these 135 patients 108 (80%) were originally operated in our centres. The demographic and preoperative data of the enrolled patients are shown in Table 1
, whereas data regarding the demographic-preoperative and the exclusion criteria for the study of the remaining 424 patients are listed in Tables 2 and 3
, respectively.
2.1 Surgical technique, intra- and postoperative assessment
In all patients, the previous valve prosthesis replacement had been carried out using horizontal mattress sutures of 2/0 Ethibond buttressed with Teflon felt pledgets. Cardiopulmonary bypass was instituted at mild hypothermia (range 22–32 °C). The approach to the re-replacement or repair of the PPL was trans-septal in 24 cases and conventional in the other 111 cases. PPL repairs (prosthesis refixation) came to a total of 83; mitral valve re-replacement consisted of implantation of 44 mechanical prostheses and eight tissue valves. The concomitant procedures included tricuspid valve repair in 11 cases, and tricuspid valve replacement in 4. Concomitant aortic valve replacement was performed in four cases, repair of aortic PPL and coronary aortic by-pass grafting in two.
In five patients, during the period before the advent of intraoperative TEE, postoperative TTE showed PPL a few days after MVR: in three cases the defect was minor, whereas in two cases it was immediately corrected. No further patients had any evidence of PPL (minor or more severe) either intraoperatively or postoperatively after surgery, although the absence of TEE in the patient series between 1985 and 1995 cannot definitely exclude PPL, which was non-detectable at TTE before hospital discharge.
In terms of anatomical or surgical information at the time of previous MVR, that is the presence of annular calcification and/or preservation of the mitral valvular apparatus, 46 patients (34%) had an operative report describing the presence of marked mitral annular calcification, and 26 cases (19%) had preservation of the posterior leaflet, respectively.
2.2 Anatomical–surgical study and data analysis
The anatomical–surgical study was performed analyzing the mitral annulus in a clock-wise format from a surgeon's view, indicating the location of the leakage with the corresponding hour. Twelve o’clock was assigned as the mid-point of the anterior annulus and 6 as the mid-point of the posterior annulus, as viewed from the atrium. Hour 2 was assigned to the postero-medial commissure, hour 10 was assigned to the antero-lateral commissure. This representation of the mitral annulus was adopted from our previously described model of aortic valve PPL localization [4], as shown in Fig. 1
.
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Fig. 1. Partition of mitral annulus adopting a clock format representing the virtual relationship between native mitral annulus and implanted prosthesis. AML: anterior mitral leaflet; PML: posterior mitral leaflet.
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Institutional approval of the study was obtained, and each patient within the study gave informed consent for personal data processing and use.
Statistical analysis was performed using the SAS statistical package (Version 9.1). Odds ratios with 95% of confidence intervals were calculated for the occurrence of PPL. In all analyses, p
< 0.05 was considered statistically significant.
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3. Results
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Overall surgical mortality was 3.7% (five patients), and all deaths occurred perioperatively (low cardiac output syndrome in four cases, atrio-ventricular groove rupture in one case). Postoperative complications are listed in Table 4
.
As far as the location of PPL is concerned, there were 244 sectors involved in the 135 patients analysed. This number comes from the fact that the majority of the studied patients had a PPL involving more than 1 sector (which corresponds to a 1-h length in the clockwise representation of the mitral annulus). As far as the theoretical occurrence is concerned, we considered that if PPL had come about by chance, PPLs would have been ubiquitously and rather homogeneously distributed along the 12 h sectors of the MVA, that is 100% divided by 12, with a rate of 8.3% of PPL for each sector. Therefore, the relationship between the theoretical number of PPL and the number of PPL occurrence in a determined sector or sectors was the basis for the calculation of Odds ratio.
The MVA non-contiguos sectors with the highest incidence of PPL were detected between hour 5 and hour 6, and hour 10 and hour 11, corresponding to the postero-medial and antero-lateral sectors, respectively. Table 5
illustrates this data and the other sectors with Odds ratio > 1.
Preservation of the posterior mitral leaflet was neither systematically carried out in MVR, particularly in the first phase of the study, nor homogenously performed in all centres.
Finally, no difference or relation was observed between PPL occurrence and type of artificial valve implanted at previous surgery among the four different institutions (Table 6
).
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Table 6. Comparison among the four institutions of the Odds ratio (95% CI) of the two highest sectors of incidence of periprosthetic leakage for each type of prosthetic valve
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4. Discussion
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PPL is a frequent cause of reoperation after MVR occurring between 1.2 and 12.5% of MVR procedures [2,3]. Conservative procedure, that is repair of PPL with preservation of the original prosthesis, is usually possible in the majority of the cases, as shown in our experience also. Prosthetic valve endocarditis, dilated cardiomyopathy, and ischemic mitral regurgitation are all factors claimed to predispose or to contribute directly to PPL occurrence [5–7]. Furthermore, suture material and other prosthesis implantation-related factors have been shown to be implicated in the development of PLL [8,9]. Besides bacterial, or procedural-related mechanisms, the relationship predisposing to PPL between the anatomy and dynamics of the MVA and prosthetic valve have been poorly investigated [10–12]. In fact, from a histological standpoint the collagen fibre distribution in the MVA (and related leaflets) is not homogeneous, either quantitatively or qualitatively [13,14]. From atrium to ventricle, the mitral annulus and leaflets are composed of three layers: atrialis/spongiosa, fibrosa and ventricularis, respectively. The fibrosa is the central core of the mitral valve tissue and is known to be less represented in the posterior sector of the annulus [13]. Furthermore, a well-formed chord-like fibrous annulus is not present all around the MVA, particularly along the posterior sector of MVA, as shown by Angelini and colleagues [14]. These anatomical factors indicate that the posterior annulus may potentially constitute a ‘locus minoris resistentiae’ to mechanical stresses applied along unusual annular sites, for instance by a rigid prosthesic ring, and therefore, predispose to PPL occurrence. Could anatomical factors alone justify this postoperative complication? Our data indeed showed that PPL occurred more frequently not only in limited zones of the posterior annulus, but also in unusual portions of the anterior one. Thus, these observations might call for adjunctive explanations or mechanisms responsible for PPL and, most likely, not entirely linked to the structural features of the MVA and the apparatus. The MVA is not a monoplanar, static structure and has peculiar mechanical characteristics, which have been shown to play a critical role in the global valve function and efficiency. The dynamic properties of the MVA have been recently highlighted by Komoda and colleagues who analysed and showed the three-dimensional movements of MVA during systole by means of magnetic resonance reconstruction [15]. These MVA dynamics could be explained by the interaction between the contractile vectors of the ventricular fibers (particularly the torsion of the base) and the fibrotic structures of the left cardiac valves. Lunkenheimer and colleagues have recently analysed the architecture of the ventricular mass and its functional implication by means of magnetic resonance [16]. They found the amount of mural thickening to be the greatest in the posterior and superior/anterior ventricular walls, close to the MVA location at the cardiac base, and that the ventricular myocardium shows a twisting motion of the basal portion and apex mainly due to helical anatomic distribution of the myocardial muscular fibres. This concept was recently confirmed and revised by Torrent-Guasp and colleagues [17]. The twisting contraction of the left ventricle in combination with the sphincter and tilting mechanics of MVA might variably interact and ultimately influence the impact of the mechanical stresses along the MVA and related artificial valve ring. But, how a prosthetic ring could modify the dynamics of the MVA predisposing to PLL? Komoda has shown that, following MVR with a rigid prosthetic ring, the MVA obviously becomes rigid and exhibits an anti-physiological tilting of the anterior portion of the MVA towards the left ventricular base during the systole, whereas the posterior portion exhibits a normal angle movement (Fig. 2A and B) [18]. Moreover, the MVA with a rigid prosthetic ring exhibits no contraction and shows an unnatural invasion of the left ventricular outflow tract during the systole (Fig. 2A and B) [18]. Therefore, these altered dynamics of MVA may increase the mechanical stress not only at the postero-medial annular segment, but also at the antero-lateral one, transforming these sectors into points of higher stress and ultimately predisposing to PPL development in these areas, as shown in Fig. 2B.
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Fig. 2. Different tilting movement (arrow) of the mitral valve annulus (MVA) with native valve (A) and with prosthetic ring (B). Presence of contraction of the MVA with native valve (a) and absence of contraction with prosthetic ring displacing into the left ventricular outflow tract (b). In this displacement the highest sectors of incidence of periprosthetic leakage (grey parts) correspond to the inge-points (*) of the prosthetic ring movement. Modified from F. Torrent-Guasp [17] and T. Komoda [18]. S: systole (dot line), D: diastole (full line), av: aortic valve, LF: left ventricle, LVOT: left ventricular outflow tract.
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Finally, we cannot underestimate that PPL could also be due to technical or surgeon-related causes (limited vision of the trigone sites, particularly of the antero-lateral one, right versus left handedness of the surgeons) as shown in a few studies [8,9]. However, the observation of similar PPL rates and locations in four different centres, as shown in Table 6, limit the importance of these technically related predisposing factors in our study, making structural and functional factors after MVR more likely to contribute to the development of PPL.
Limitations of this study: Endocarditis-related PPL was an exclusion criterion for this study, but undiagnosed infective etiology of analysed PPL cannot be definitely excluded, although no conventional parameter related to prosthetic valve endocarditis was found in this study population. The lack of detailed information concerning the presence of minor annular calcification at the time of previous MVR might have affected data analysis and interpretation, representing a confounding factor for an appropriate evaluation of potential cause–event relationship. Additional limitation of our analysis was also related to the retention of the mitral leaflet. It was not systematically pursued through the years in this multicentre experience, and not evenly distributed in this study population. Due to the small sample size, no analysis has been carried out in this respect and further studies are warranted to elucidate a potential relationship between mitral leaflet maintenance and PPL development.
In conclusion, PPL represents a non-rare complication in the setting of ordinary MVR. Apart from well-known factors predisposing to PPL after MVR, our study indicates that such a complication develops more frequently in determined segments of the MVA. Anatomical factors, together with anti-physiological dynamics of MVA after MVR, may interact and contribute to the occurrence of PPL at the postero-medial and antero-lateral sectors of MVA. Although this study has insufficient information, to our knowledge, no paper with this analysis has been previously published. Further studies concerning the changes of anatomical and functional MVA characteristics induced by prosthetic valve implantation or the potential influence of the type of surgical technique (leaflet retention) on such a complication are warranted in the hope of shedding additional light on the understanding of the occurrence and location around MVA of the PPL.
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Acknowledgments
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The authors express their gratitude to the Heart Synergy Group and ‘Associazione Cuore e Ricerca’ for the valuable support. We would like also to express our gratitude to Dr Marcello Maggio for the statistical elaboration.
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Abstract
1. Introduction
