Ann Thorac Surg 2004;77:518-522
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
Semirigid partial annuloplasty band allows dynamic mitral annular motion and minimizes valvular gradients: an echocardiographic study
Ram Sharony, MDa,
Paul C. Saunders, MDa,
Ambika Nayar, MDa,
Eileen McAleer, MDa,
Aubrey C. Galloway, MDa,
Julie Delianides, MAa,
Charles F. Schwartz, MDa,
Robert M. Applebaum, MDa,
Itzhak Kronzon, MDa,
Stephen B. Colvin, MDa,
Eugene A. Grossi, MDa*
a Division of Cardiothoracic Surgery, Department of Surgery, New York University School of Medicine, New York, New York, USA
Accepted for publication April 9, 2003.
* Address reprint requests to Dr Grossi, NYU Medical Center, Suite 9-V, 530 First Ave, New York, NY 10016, USA.
e-mail: grossi{at}cv.med.nyu.edu
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Abstract
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BACKGROUND: Traditional mitral annuloplasty devices include both rigid rings, which restrict annular motion, and soft rings and bands, which can locally deform. Conflicting data exist regarding their impact on annular dynamics. We studied mitral annuloplasty with a semirigid partial band and with a nearly complete rigid ring.
METHODS: Intraoperative three-dimensional transesophageal echocardiograms (n = 14) and predischarge transthoracic echocardiograms were retrospectively analyzed in patients undergoing mitral valve repair for degenerative disease with either a rigid ring (n = 77) or a semirigid partial band (n = 38). Each transesophageal echocardiogram was analyzed with TomTec three-dimensional software to produce cardiac cycle frame planimetry and to measure device geometry. Actual device sizes provided reference dimensions. Blinded analysis of Doppler data from transthoracic echocardiograms was performed.
RESULTS: Validation of the quantitative transesophageal echocardiogram methodology revealed a 1.3% ± 0.3% (mean ± standard error of the mean) underestimation of actual linear dimension. With the semirigid partial band, systolic valve orifice area and intertrigonal distance decreased from 6.14 ± 0.37 to 5.55 ± 0.24 cm2 (-9.6%; p = 0.01) and from 2.69 ± 0.08 to 2.55 ± 0.13 cm (-5.2%; p = 0.03), respectively. Systolic anterior-posterior distance decreased from 2.1 ± 0.10 to 1.95 ± 0.06 cm (-7.1%; p = 0.01) compared with diastole. In contrast, rigid ring orifice area was unchanged (4.12 ± 0.15 to 4.10 ± 0.16 cm2; -0.5%; p = 0.48) during the cardiac cycle. Transthoracic echocardiography revealed significantly lower mitral inflow gradients with semirigid partial band (mean gradients compared with rigid ring, 4.0 ± 0.3 versus 5.0 ± 0.3 mm Hg; p = 0.02; peak gradients, 8.9 ± 0.5 versus 11.1 ± 0.5 mm Hg; p = 0.01).
CONCLUSIONS: Three-dimensional transesophageal echocardiographic measurements of annular dynamics are valid and reliable when discrete annuloplasty devices are present. In contrast to the rigid ring, the semirigid partial band permits more physiologic geometric changes and is associated with lower postoperative mitral valve gradients.
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Introduction
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| Drs Colvin, Grossi, and Galloway disclose that they have a financial relationship with Medtronic.
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Mitral valve reconstruction corrects valvular pathology while it preserves left ventricular function, eliminates prosthetic valve complications, and avoids the added morbidity associated with anticoagulation [1, 2]. Mitral valve reconstruction generally requires annuloplasty for optimal results [3]. It has been documented that mitral repair without the use of an annuloplasty device contributes to the incidence of late failure, although which type of device to use remains controversial [4–6]. Traditional mitral annuloplasty may use more rigid devices, which may maintain fixed annular geometry and restrict annular motion, or softer devices, which have no shape memory.
The mitral annulus is a dynamic structure that undergoes alterations in size and shape throughout the cardiac cycle [7]. Contradictory reports exist regarding annular dynamics after complete and partial annuloplasty [8–11]. The discordance among experimental and human studies may arise from analytic differences and lack of echocardiographic markers or ‘fiduciaries’ on the annular structures [11]. Inasmuch as use of a flexible ring has been shown to preserve left ventricular function better than a rigid ring during rest and effort, it has been suggested that annular motion has an impact on left ventricular function [12, 13].
We hypothesized that three-dimensional transesophageal echocardiography (TEE) in conjunction with annuloplasty devices possessing discrete markings would permit reliable fiduciary identification and measurement of mitral annular mechanics. Additionally, we hypothesized that annuloplasty with a semirigid partial band (SRB) would allow annular motion and produce less transvalvular gradient when compared with annuloplasty with a nearly complete rigid ring (RR). We validated this echocardiographic technique and used this methodology to compare the annular dynamics of an SRB with an RR. Postoperative mitral valvular hemodynamics were compared with standard transthoracic echocardiography (TTE).
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Material and methods
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From January 2000 through December 2001, patients who underwent mitral valve reconstruction for degenerative disease and who had postoperative TTE studies were identified. One hundred thirty-two patients had implantation of either an RR (Carpentier-Edwards Classic Mitral Annuloplasty, Edwards Lifesciences, Irvine, CA; n = 77) or an SRB (FutureBand, Medtronic, Minneapolis, MN; n = 38). The SRB is a planar, kidney-shaped band containing an elastic MP-35N alloy stiffener wire, overmolded with silicone, and covered with an ironed polyester cloth (Fig 1).
The ratio of the transverse to anterior-posterior (AP) internal diameters is approximately 1.75, providing an aggressive remodeling. The wire core forms eyelets at the trigones to enhance fixation. The semirigid wire core design of the device permits intertrigonal movement while maintaining a remodeled AP diameter. When held in one's hand, light pressure can diminish the intertrigonal distance; one cannot stretch the device along the AP axis. Choice of annuloplasty device was dictated by surgeon preference and by availability of device. These patients were retrospectively analyzed in a blind fashion using the predischarge resting TTE. Additionally, intraoperative TEE of 14 patients was further analyzed with three-dimensional reconstruction.
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Fig 1. Engineering drawing of semirigid band (A) demonstrating internal wire stiffener and device photograph (B).
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Three-dimensional echocardiographic data acquisition
Intraoperative TEE was performed using a 5-MHz multiplane transesophageal transducer with a Hewlett-Packard Sonos 1000 or 5500 system (Andover, MA). After weaning from cardiopulmonary bypass, TEE examination was performed to assess the mitral valve anatomy, valve area, gradients, and presence of insufficiency; the three-dimensional dataset was also acquired [14]. These ultrasonographic images were electrocardiogram gated and acquired while the TEE transducer was rotated thru a 180-degree arc; the respiratory cycle was interrupted during the acquisition. Offline, the data were reduced to a three-dimensional dataset of an averaged cardiac cycle (TomTec GmbH, Munich, Germany). This dataset could be viewed from any user-chosen plane at any time during the cardiac cycle. For the current study, a short-axis view of the mitral valve region was reconstructed as previously described [15]. A horizontal cross-section of the annuloplasty device was obtained by rotating the cut plane around the axes of the three-dimensional coordinate system (Fig 2).
This cut plane was reacquired for each frame of the cardiac cycle (typically 12 to 18 frames per cardiac cycle, depending on heart rate). Finally, the annuloplasty device was displayed in its horizontal cross-section as viewed from an atrial perspective. End-systolic and end-diastolic images were defined as the frame just before opening of the mitral valve leaflets and the frame just before closure of the mitral valve leaflets, respectively [10].
Data analysis
The following planimetry measurements of mitral apparatus images were taken using the TomTec software: orifice area (tracing the border of the device orifice), AP distance (between anterior and posterior annuloplasty device border), and in the SRB group, the intertrigonal distance (between the trigonal tips of the device). Additionally, the linear length of the annuloplasty device was measured and compared with the manufacturer's data to validate our methodology. Postoperative TTE studies were performed in the standard manner and included parasternal long-axis and short-axis views, apical four-chamber and two-chamber views, and subcostal views. Blinded analysis of Doppler data from TTE was performed.
Statistics
All the clinical data were prospectively collected by trained nurse clinicians and analyzed using SPSS statistical software (ver. 11.0; SPSS Inc, Chicago, IL) using multivariable analysis of variance with the covariate of annuloplasty device size. Patient demographic and operative data were summarized as mean ± standard deviation, median, or prevalence, as appropriate. A p value of 0.05 or less was considered to be significant.
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Results
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Trigonal markers on the SRB were clearly demonstrated. To validate the accuracy of measurement using TEE and TomTec software, measurements obtained along the entire length of the band were compared with the manufacturer's data. Analysis of the observed data (Fig 3) revealed close correlation between actual and expected measurements (r = 0.97; p < 0.0001), with an average underestimation of 1.3% ± 0.3% (mean ± standard error of the mean). This was calculated to validate our methodology. The three-dimensional TEE revealed that semirigid annuloplasty resulted in a decrease in both the orifice area during systole by 9.6% (p = 0.01) and intertrigonal distance by 5.2% (p = 0.03) as compared with diastole (Table 1).
End-systolic AP distance decreased by 7.1% (p = 0.01) compared with end-diastole. In RR annuloplasty, by contrast, orifice area was unchanged (0.5%, not significant) during the cardiac cycle.
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Fig 3. Regression analysis between echocardiographic image measurements and manufacturer's data. Analysis of the observed data revealed close correlation between actual and expected measurements (r = 0.97; p < 0.0001).
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Table 1. Intraoperative Transesophageal Echocardiography Systolic and Diastolic Measurements of the Annuloplasty Devicea
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Postoperative TTE revealed (Table 2)
that mean and peak mitral valve gradients were significantly lower with SRB annuloplasty when compared with RR both overall and on a size-to-size basis. Annuloplasty device size was equally distributed between the two groups and did not affect gradient (F ratio = 0.07; p = 0.42) Postoperatively, 98% of patients in the RR group and 95% of patients in the SRB group were found to have either no or trace mitral insufficiency (not significant).
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Comment
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This study shows that three-dimensional TEE measurements of annular dynamics are valid and reliable when discrete annuloplasty devices are present. The trigonal markers on the SRB allow for echocardiographic identification and permit us to demonstrate physiologic geometric changes during the cardiac cycle. Validation of our technique demonstrated accuracy of 1.3%, as compared with a 10% variance previously reported with this technique when used on annuloplasty devices without discrete fiduciary markers [10]. As reported previously, the mitral orifice area normally expands during diastole, facilitating ventricular filling, and contracts during systole, permitting better leaflet coaptation [16, 17]. However, the mitral annulus has a nonplanar configuration; the geometry of its anterior segment contributes to the saddle shape. As the SRB has no echocardiographic fiduciaries present on the anterior annulus, we are unable to track the anterior horn of this saddle. Hence, our study of SRB annuloplasty measures device orifice only and may underestimate total annular changes with respect to the entirety of the anterior portion.
Controversy exists regarding annular dynamics observed in patients using echocardiographic techniques and those observed in animal experiments by cinefluoroscopy with implanted markers [9, 11, 18, 19]. It has been suggested that the absence of markers on the annulus may limit the accuracy of TEE [11]. In the current study, we clearly identified the trigonal edges of the SRB as well as its perimeter and could, therefore, track changes in annular motion accurately.
The significant reduction in orifice area we observed during systole is comparable to that reported with a flexible ring [10] and emphasizes that annular dynamics can be preserved after annuloplasty. In this study, flexible band annuloplasty maintains the systolic sphincter mechanism of the mitral orifice. This may explain the lower transvalvular peak gradient during diastole that was observed in the SRB group compared with the RR group. Postannuloplasty transvalvular gradients were comparable to those reported by Carpentier and colleagues [20]. A similar reduction in transmitral peak flow velocities was achieved when autologous pericardium annuloplasty was compared with rigid prosthetic ring annuloplasty [13].
The current study also shows that SRB annuloplasty results in a significant reduction in end-systolic AP distance. This change in AP distance is of major importance in leaflet coaptation and prevents mitral insufficiency [20] while allowing a larger orifice area during diastole. Anterior-posterior distance reduction has particular significance in ischemic mitral regurgitation and is the basic principle of the proposed septal-lateral annular cinching procedure for correction of ischemic mitral insufficiency [21].
Some controversy has arisen after the recent publication by Hueb and associates [22] demonstrating significant pathologic changes in the fibrous annulus in ischemic and idiopathic dilated cardiomyopathy. Although the anatomic data in their study demonstrate pathologic increases in both the anterior leaflet insertion and intertrigonal distances, it is not necessary to equate these changes with the need to fixate the anterior border of the annulus [23]. We would strongly advocate that appropriate valve reconstruction can be performed with a trigone-to-trigone annuloplasty with a device that aggressively elevates (remodels) the posterior annulus resulting in improved depth of leaflet coaptation. With the current device, the annuloplasty band is anchored to the trigones, effectively limiting the AP diameter, while still permitting normal dynamic changes along the base of the anterior mitral annulus. We believe that the current annuloplasty device functions quite well for these patient subsets; however, further study is necessary to validate this strategy.
Three-dimensional TEE measurements of annular dynamics are valid and reliable when discrete annuloplasty devices are present, and the trigonal markers on the SRB allow for reproducible identification by means of three-dimensional TEE. Although the SRB remodels AP diameter, it does not abolish annular motion. In contrast to the RR, the SRB is associated with lower postoperative mitral valve gradients.
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Abstract
Introduction
