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Eur J Cardiothorac Surg 2000;17:431-439
© 2000 Elsevier Science NL

Biological versus prosthetic ring in mitral-valve repair: enhancement of mitral annulus dynamics and left-ventricular function with pericardial annuloplasty at long term

^a II Cardiac Surgery Division, Civil Hospital, Piazzale Spedali Civili n° 1, 25125 Brescia, Italy
^b ‘Salvatore Maugeri’ Foundation IRCCS, Rehabilitation Institute, Division of Cardiology (Fondazione ‘S.Maugeri’ Istituto di Riabilitazione e Cura a Caratterere Scientifico IRCCS, Ospedale Richiedei), Gussago, Italy

Corresponding author. Tel.: +39-30-3995-638; fax: +39-30-3995-004
e-mail: roberto_lorusso{at}iol.it

	Abstract

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
Objective: The effects of different annuloplasty rings on mitral annulus dynamics and left-ventricular (LV) function after mitral-valve repair (MVR) are still controversial. This study sought to compare biological versus prosthetic rigid rings for annular remodelling in MVR at long term. Methods: Forty-four consecutive patients were retrospectively enrolled. All patients had isolated posterior-leaflet prolapse and underwent identical surgical mitral-valve reconstruction (quadrangular resection of the posterior leaflet associated with annuloplasty). Twenty-three patients underwent mitral annuloplasty with an autologous pericardial ring (group I), whereas 21 patients had MVR with a Carpentier–Edwards rigid ring (group II). No differences existed between the groups in terms of pre-operative patient profile. Post-operative LV systolic indices have been assessed by two-dimensional echocardiography at rest and during supine bicycle exercise. Mitral annular motion has been examined by means of the extent of mitral annulus systolic excursion (MASE), as measured in four longitudinal LV segments (anterior, inferior, septal and lateral). Mean and peak trans-mitral flow velocities (TMFV) have been also evaluated by continuous-wave Doppler. Results: The mean follow-up did not differ between the groups, those being 41±12 months in group I (range17–65 months) and 46±15 months in group II (range 23–83 months), respectively. Post-operative echocardiographic study did not show significant mitral regurgitation at rest or at peak exercise in any patient. ANOVA analysis for repeated measures showed a significant interaction in peak TMFV (F_(1,42)=5.23; P=0.03), and in left-ventricular ejection fraction (LVEF; F_(1,42)=7.61, P=0.01). The analysis of contrasts showed a significant increase in TMFV in both groups (group I from 1.22±0.22 to 1.79±0.32 m/s, t=-8.8, P<0.0001; and group II from 1.19±0.17 to 1.96±0.33 m/s, t=-12.8, P<0.0001). Recruitment of LVEF reserve during exercise was observed only in group I (from 59.5±6 to 65.8±6%, t=-3.95, P<0.005), whereas no substantial change occurred in LV performance in group II. A trend towards better MASE at all the studied longitudinal segments at rest and during exercise was observed in group I. No minor or major calcifications have been observed on pericardial rings. Conclusions: The autologous pericardium seems to be superior to rigid prosthetic rings for annuloplasty in MVR since it provides more favourable mitral annulus dynamics and preserves LV function during stress conditions. Effective and durable annular remodelling with the autologous pericardium is achieved up to 6 years from surgery, with no echocardiographic sign of degeneration in the long term. Further studies are required to compare biological versus flexible prosthetic rings in MVR.

Key Words: Mitral-valve repair • Pericardial annuloplasty • Mitral annulus dynamics

	1. Introduction

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
The mitral annulus provides an active contribution to the physiology of the valvular apparatus throughout the cardiac cycle [1,2]. Annular size and shape change continuously during diastole and systole, owing mainly to the contraction and relaxation of muscle bundles posteriorly surrounding the mural portion of the mitral annulus. There are evidences that annular dynamics may play an important role in the valvular/ventricular interaction with ultimate influence on left-ventricular (LV) function. The maintenance of such annular dynamics has therefore been advocated as an additional target of mitral-valve repair (MVR) techniques, leading to the introduction of several types of flexible annular prosthetic supports to overcome the potential induction of geometrical deformity and excessive fixation during annuloplasty procedures [3–10]. Comparative studies between rigid and flexible prosthetic rings, in terms of postoperative annular motion and LV function, have been performed in limited experimental and clinical settings [11–18]. In spite of controversial results, the use of flexible annuloplasty devices seems to be advisable due to the less restrictive effect on annular dynamics, better ventricular/valvular interaction, and preserved LV function [11,12,16–18]. The glutaraldehyde-treated autologous pericardium has been proposed as an additional option for the annuloplasty procedure [19]. Recent clinical series, which reported on the use of such a biological tissue for annular remodelling, have shown excellent results in terms of the long-term efficacy of MVR [20,21]. To our knowledge, however, there is no early or late comparative evaluation between prosthetic and pericardial rings in MVR. Our study was undertaken to specifically address this clinical issue in a selected group of surgical patients, submitted to postoperative echocardiographic assessment during basal and stress conditions, to analyze MVR effects in relation to the type of annuloplasty ring used.

	2. Methods

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
From February 1992 to March 1997, in a cohort of 250 patients who underwent MVR due to mitral-valve insufficiency secondary to isolated prolapse of the posterior leaflet, 44 consecutive patients were retrospectively selected for the present study. Inclusion criteria for the study enrolment consisted of: (1), presence of pure chronic (>1 year) mitral insufficiency; (2), presence of prolapse of the central scallop of the posterior mitral leaflet; (3), absence of calcified mitral annulus; (4), absence of rheumathic etiology; (5), absence of active endocarditis; (6), preserved left ventricular function; (7), absence of coronary artery disease or ischemic etiology of mitral-valve insufficiency; (8), preserved exercise capacity and respiratory function; and (9), no pre-operative arrhythmic disorders.

Preoperative mitral regurgitation was severe (++++) in all patients. The etiology of posterior mitral-leaflet prolapse was mixomatous degeneration in 40 patients, whereas healed bacterial endocarditis was present in two patients in group I and two patients in group II. Barlow disease was present in one patient in group I and two patients in group II.

All patients underwent identical surgical correction of the valvular insufficiency, consisting of quadrangular resection associated with the annuloplasty procedure. Twenty-three patients received an autologous pericardium ring (group I), whereas 21 patients had a Carpentier–Edwards classic prosthetic ring (group II). Preoperative patient data are listed in Table 1.

After MVR, the left ventricle was forcefully filled in with saline water to test the valve competence. Intraoperative transesophageal echocardiography was not performed routinely, but all patients were submitted to postoperative echocardiographic assessment before hospital discharge. All patients were treated with anticoagulant therapy for the first 3 months.

2.2. Echocardiographic study protocol
All patients underwent a bicycle ergometre stress test in the supine position, with a 25-W incremental step every 3 min, until 70% of the maximal age-predicted heart rate was reached. Real-time phased array echo-Doppler recordings were obtained at rest and during maximal exercise with a GE Vingmed CFM 750 CV (2.75- or 3.25-MHz transducer). The examinations were carried out by two experienced investigators. Digital images were stored on a magneto-optical disk for subsequent analysis. The LV diameters and volumes (area–length method) were determined from two-dimensional parasternal long-axis view and from apical four-chamber view, respectively. Calculations of LV fractional shortening and left-ventricular ejection fraction (LVEF) were then derived from the diameters and volumes, respectively. Continuous-wave Doppler was used to obtain trans-mitral flow velocity curves; both mean and peak velocities were considered. Assessment of longitudinal atrio-ventricular plane displacement, in order to elucidate regional mitral annulus systolic excursion (MASE) in relation to LV segmental mechanics, was determined with two-dimensionally-guided M-mode, from the apical four-chamber view for septal (S) and lateral (L) segments, and from the apical two-chamber view for inferior (I) and anterior (A) segments. Starting from Q wave on ECG tracing, maximal excursion of M-mode tracing during systole (Fig. 1) was considered. Measurements of all echo-Doppler examinations were performed in a single day, by only one investigator, blinded to the type of annuloplasty. The mean value of three measurements was considered for each variable.

View larger version (172K): [in this window] [in a new window]   Fig. 1. Two-dimensional-guided M-mode tracings from the apical four-chamber view are shown, documenting the excursion of septal (on the left) and lateral (on the right) mitral annular segments. Upper panels, positioning of M-mode cursor; mid panels, M-mode tracings at rest; lower panels, M-mode tracings at peak exercise. In the lower panels, the cyclic annulus excursion can be appraised to synchronized ECG tracing. MASE occurs during the corresponding Q–T interval, showing the points taken for measurements of MASE (arrow-heads).

The relationship between mean follow-up and echocardiographic variables was evaluated using the Pearson correlation. A P-value of <0.05 was considered to be of statistical significance.

	3. Results

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
There were neither hospital nor late deaths. Follow-up was similar in both groups, with a mean of 41±12 months in group I (range 17–65 months) and 46±15 months in group II (range 23–83 months). No patient experienced valve- or cardiac-related postoperative complications. Paroxysmal atrial flutter occurred in one patient in group II who required hospitalization, with recovery of sinus rhythm. No patient from either group required reoperation for recurrence of hemodynamically-significant mitral regurgitation during follow-up.

All patient data recorded during echocardiographic monitoring are shown in Table 2. Heart rate and blood pressure values were comparable between the two groups. Echocardiographic assessment at rest did not show any difference in terms of LV diameters, LV fractional shortening, LVEF, mean and peak trans-mitral flow velocities (TMFV). All patients had no (35 patients) or trivial (9 patients) mitral regurgitation at basal conditions.

Two patients in group II showed a slight pressure gradient at the LV outflow tract at peak exercise, but this did not reach clinical significance (pressure gradient <20 mmHg). No mitral regurgitation was elicited by the stress conditions in any patient.

During the stress test, a significant interaction was observed for LVEF and TMFV (F_(1,42)=7.61, P=0.01; and F_(1,42)=5.23, P=0.03, respectively). Detailed analysis of this interaction showed a significant increase of LVEF in group I, whereas no changes were detected in group II (from 59.5±6 to 65.8±6%, t=-3.95, P<0.005 in group I; and from 61.4±5 to 61.9±5%, t=-0.4, not significant (n.s.) in group II; Fig. 2).

View larger version (11K): [in this window] [in a new window]   Fig. 2. Changes in LVEF at rest and during exercise are shown. Gr 1, Autologous pericardial ring; Gr 2, rigid prosthetic ring. A significant interaction (P<0.01) between groups and phases (rest and exercise) is present. A significant difference between rest and exercise values is present in group 1. No difference was observed at rest between groups, whereas a significant increase of LVEF was found at peak exercise in group 1. Interaction *P<0.01.

View larger version (11K): [in this window] [in a new window]   Fig. 3. This figure shows peak trans-mitral flow velocity at rest and during exercise. A significant increase of peak velocity in group 2 during stress condition was detected. Gr 1, Pericardial annuloplasty; Gr 2, rigid prosthetic ring. Interaction *P<0.05.

Effective atrio-ventricular plane displacement was found at rest and during exercise in all the studied segments of both groups. Enhancement of MASE, however, was shown in all longitudinal planes of patients with pericardial annuloplasty, although not statistically different from patients in group II (Fig. 4).

View larger version (22K): [in this window] [in a new window]   Fig. 4. MASE in patients after MVR and annuloplasty procedure with (Gr 1), autologous pericardial ring; or (Gr 2) Carpentier–Edwards classic ring is shown. Enhancement of atrio/ventricular plane displacement in patients with pericardial annuloplasty is evidenced in all segments, although the differences were not statistically significant.

No sign of pericardial degeneration, either fibrous overgrowth or calcium depots, was observed in any of the patients in group I.

	4. Discussion

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
Prosthetic annuloplasty as part of the reconstructive procedure for correcting mitral-valve insufficiency has been introduced by Carpentier and associates [22]. The application of a rigid ring was originally intended to remodel annular deformity, secondary to chronic atrial and ventricular enlargement, to stabilize MVR by reducing the tension on reconstructed valvular portions, to enhance leaflet coaptation by reducing the mitral surface area and to prevent further annular dilatation. The mitral annulus is a dynamic structure, providing an active contribution to the mechanics of the mitral-valve apparatus, thanks to a sphincter-like action achieved by the contraction and relaxation of basoconstrictor muscles surrounding the annulus posteriorly. A possible disadvantage of the rigid fixation of the mitral annulus induced by prosthetic rings is the reduction of such a dynamic annular motion, which may affect transvalvular blood flow in the diastole, alter ventricular/valvular interaction and impair LV function [11,12,16]. Flexible prosthetic devices have been proposed to overcome these potential drawbacks [3–6]. In this light and based on the anatomic concept that the mural portion of the mitral annulus is the only segment prone to dilation, isolated posterior annuloplasty in MVR was independently introduced by Cooley and Bex [23,24]. Additional types of prosthetic supports to achieve selective annuloplasty have been subsequently proposed [7–10]. The use of foreign material, however, may predispose to valve-related postoperative complications. The autologous pericardium in MVR was introduced by Carpentier and associates [25], whereas the application of a pre-treated pericardial strip for posterior annular remodelling was first reported by Salati [19].

Despite the numerous options for annuloplasty procedures, information regarding the effects of such rings on postoperative annular motion and LV function is scarce. A comparative study regarding the effects of rigid and flexible prosthetic rings on annular dynamics and LV performance after MVR was first reported by David and collaborators [11]. This prospective study of 25 randomized patients undergoing MVR showed that flexible annuloplasty was beneficial, in terms of LV function, at short-term (2–3 months), whereas, in a more limited number of patients, this advantage was offset at later follow-up (2 years), suggesting that compensatory mechanisms of LV performance or impairment of ring flexibility may occur in the long term. Okada and co-workers addressed the same clinical issue in 26 non-randomized patients, submitted to mitral-valve reconstruction and annuloplasty with the Carpentier classic ring or Duran flexible ring [16]. By two-dimensional echocardiographic assessment, performed at basal and stress conditions at variable intervals from MVR, they showed a better trans-mitral blood flow in patients with flexible annuloplasty, and the disappearance of dynamic changes of the mitral surface area after rigid annuloplasty fixation. These findings are in accordance with the data obtained in pig hearts by van Rijk-Zwikker, who showed, in contrast to the rigid ring, that unrestrictive annular remodelling was achieved by flexible devices which ensured the maintenance of the physiological change of the mitral surface area [12]. The experimental work performed at the Stanford laboratory did not corroborate these conclusions, since no differences were shown in a canine model comparing rigid versus flexible rings with regard to regional or global LV mechanics [13,14]. Surprisingly, they also failed to demonstrate that the type of annuloplasty used may affect mitral annular dynamics, since the application of annular prosthetic rings abolished the cyclic annular changes regardless of the type of annular support used [15], suggesting that the main mechanism of effective annuloplasty in MVR is due to valve-orifice reduction. Dall'Agata recently reported on the intraoperative assessment of 12 patients undergoing Cosgrove-ring implantation along the mural annulus [17]. The three-dimensional echocardiographic reconstruction of the mitral valve showed preserved valvular mechanics early after the implantation of this flexible C-shape device, whereas no annular motion was observed throughout the cardiac cycle after complete annular fixation with a rigid ring.

These controversial premises led us to undertake a retrospective, non-randomized comparative study between the rigid prosthetic ring and the autologous glutaraldehyde-treated pericardium implanted during MVR in selected group of patients. The homogeneous population of our clinical investigation ensured a highly selective interpretation of the effects of the type of ring used for annular remodelling during mitral-valve reconstruction. The excellent long-term results in terms of morbidity and mortality observed in our series are not surprising due to the expected high benefit from MVR in this peculiar patient cohort (isolated prolapse of the posterior leaflet) [26], and from the favourable preoperative patient profile. Our clinical results are markedly in accordance with the hemodynamic changes documented in patients submitted to mitral annuloplasty using flexible prosthetic rings [11,16]. We demonstrated that rigid prosthetic support exerts a constraint effect on annular dynamics, particularly regarding diastolic motion. Pliable biological fixation of the mitral annulus in our patients appeared to favour diastolic blood flow across the mitral valve at peak exercise, suggesting enhanced annular motion and more effective valve-orifice area in the diastole under demanding mechanical conditions [27]. Annular downsizing with a rigid ring cannot be considered a potential explanation for our findings, since large rings were used in the majority of patients in our series (five patients with ring size n.32, seven with n.34 and seven with n.36), making this hypothesis extremely unlikely.

The consequences of the functional and anatomical rigidity of the mitral annulus on LV mechanics are still poorly defined. Our data showed that long-term enhanced LV function represents an actual advantage of the flexible annuloplasty concept, which was achieved in our series using biological material. Indeed, we demonstrated that LV function, although not different at rest in the two groups, maintained a significant functional reserve during exercise in patients with posterior flexible annuloplasty, whereas rigid annulus fixation hampered exercise-related increase in LVEF. This finding may be indirectly explained by the more restrictive trans-mitral blood flow during stress conditions in patients fitted with the rigid ring, as shown by the increase in TMFV and reduced LV end-diastolic volumes at peak exercise, although volume data did not reach statistical significance. These observations are in accordance with previous findings, which showed an absence of LV functional reserve, as measured by fractional shortening, during exercise in cases of MVR and annuloplasty achieved by rigid support, whereas MVR with flexible annuloplasty allowed a significant recruitment of LV contractility at peak exercise [16].

Another disadvantage of rigid rings in annular remodelling relates to the change of the physiological saddle shape of the mitral annulus, leading to a more planar configuration [17]. This effect has been claimed to represent a predisposing factor to the development of LV outflow tract obstruction by exacerbating mitral-leaflet systolic anterior movement, or by narrowing the intersection angle between the aortic and the mitral-valvular planes [28]. Direct visualization of mitral annular dynamics was not performed in our investigation, since preliminary reconstruction by two-dimensional echocardiography in some patients did not appear to provide reliable and easy reproducibility of this measurement, although this method was effectively used by other investigators [9,16,20]. Therefore, we could not elucidate this particular aspect of annular geometrical changes induced by the annuloplasty procedure. However, we can postulate that the lack of complete annular plication and the softness of the pericardial ring are favourable factors for the maintenance of the physiological, non-planar configuration of the mitral annulus, with obvious advantages in terms of anatomical and functional valvular–ventricular interaction.

The evaluation of blood-flow velocity across the mitral valve at rest and during exercise, in addition to the longitudinal assessment of atrio-ventricular plane displacement, provide useful clues for the evaluation of annular dynamics. Valve excursion (MASE), as assessed by long-axis echocardiographic view in four different longitudinal planes, was shown to provide effective analysis of the segmental reconstruction of annular/ventricular motion and global LV function [29]. Atrio-ventricular plane displacement showed a trend towards enhanced segmental annular motion in patients with the autologous pericardial ring; although, unquestionably, the rigid prosthetic ring did not substantially impair longitudinal valve excursion.

Concerns regarding potential calcium degeneration, leading to gradual rigidity of the pericardial ring in the long term has been raised by some investigators. Our study definitely excludes this hypothesis, as previously shown in large clinical series [20], since no evidence of tissue calcification could be demonstrated up to 6 years from surgery, concomitantly documenting preserved and effective pericardial flexibility at late follow-up.

Correct echocardiographic assessment of the effects of MVR, as shown in our study, cannot be irrespective of hemodynamic monitoring during stress conditions in order to accurately elucidate actual functional consequences to the repaired mitral valve. Echocardiographic studies during rest may not disclose subtle yet significant changes in the valvular/ventricular interaction, which may occur only during stressful hemodynamic conditions and ultimately affect global LV function. Three-dimensional reconstruction of the mitral valve as achieved by transesophageal echocardiography represents, although currently time-consuming, the gold standard for postoperative evaluation of functional or anatomical details of the valvular apparatus after MVR [17,18], provided that provocative studies (inotropic infusion) are concomitantly performed.

In conclusion, although we showed that the rigid ring provides effective long-term annular support in MVR and does not induce detrimental effects on LV mechanics at rest, posterior annular support with the autologous pericardium appears to be superior to rigid annular fixation. Indeed, the biological ring for selective annular plication favours annular dynamics and enhances postoperative diastolic and systolic LV function during stress conditions. The use of the autologous pericardium appeared to fulfil all the conventional criteria for successful and durable annuloplasty support after MVR. The apparent absence of any sign of tissue degeneration at long term makes the pre-treated autologous pericardial ring an attractive option for the annuloplasty procedure, and a step forward in the application of a totally ‘biological’ valve reconstruction in the treatment of mitral-valve insufficiency.

Further studies are required to compare flexible and C-shape prosthetic rings with the autologous pericardium in terms of long-term durability and function of MVR, and the related impact on postoperative LV function at rest and during stress conditions.

	Acknowledgments

 
The authors are grateful to Paola Valtulini for the kind and precious assistance during the study accomplishment. The authors are also indebted to Giacomo Corica for the imaging processing.

	Footnotes

 
Presented at the 13th Annual Meeting of the European Association for Cardio-thoracic Surgery, Glasgow, Scotland, UK, September 5–8, 1999.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 
Dr T. Orszulak (Rochester, MN, USA): The question I have is related to a study published by O'Dell, comparing commissural annuloplasty versus rigid ring versus flexible ring. In that study, it is very difficult to identify any differences. I think the bottom line is when or whether they have repeat regurgitation. What is your rate of reoperation in the patients that had the pericardial ring versus the rigid ring?

Dr Borghetti: In our experience, there were no reoperations in these patients because the use of strict inclusion criteria allowed us to obtain a very homogenous population with a predictable favourable outcome, so the results in terms of morbidity and mortality were excellent.

Dr A. Carpentier (Paris, France): I think there is a misunderstanding. There is no surprise at a rigid ring fixed at the annulus, but I think the misunderstanding stems from the fact that you make a confusion between the annular dynamics and the ventricular dynamics. If you assess the ventricular dynamics immediately below the annulus, there is no surprise that the rigid ring doesn't contract, there is nothing new about that; but as far as ventricular dynamics, the global dynamics, which have not been assessed here, it is very different, because this is not something we have seen. So that is my first comment that when you are talking about annular dynamics, you don't talk about ventricular dynamics. It remains to be seen whether it is adversary or beneficial to fix the annulus when the annulus is diseased.

The second point I would like to make is that it would have been fair to compare the Physio-ring with the pericardial support and not the old classic ring in order to convince us; however, it is always interesting to speculate and theorize, but again, I don't think that you should say that pericardial, I quote, support provides durable long-term results based on the rather mid-term results you have presented.

Dr Borghetti: As far as the annulus dynamics is concerned, the difference in terms of global LV function, as shown by lack of increment ejection fraction (EF) during the stress test, could be referred to a reduction in diastolic dynamics of the mitral annulus induced by the rigid ring. For the second consideration, my answer is that we didn't compare the Physio-ring with the pericardial ring because we didn't use it in our surgical experience in our centre. Lastly, the pericardial ring, in our series, showed to be at least as effective as the prosthetic ring in terms of postoperative durability in the long term.

	References

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion Appendix A. Conference... References

 

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