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Ann Thorac Surg 1998;66:1640-1645
© 1998 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Columbia University College of Physicians & Surgeons, New York, New York, USA
b Division of and Cardiology, Columbia University College of Physicians & Surgeons, New York, New York, USA
Accepted for publication May 12, 1998.
Address reprint requests to Dr Umaña, c/o Mehmet Oz, MD, Milstein Hospital Building—Division of Cardiovascular Surgery, 177 Fort Washington Ave, 7GN Room # 7-435, New York, NY 10032
Abstract
Background. Current techniques of mitral valve repair rely on decreasing valve area to increase leaflet apposition, but fail to address subvalvular dysfunction. A novel repair has been introduced with partial left ventriculectomy, which apposes the anterior leaflet to a corresponding point on the posterior leaflet creating a double-orifice valve, with reported adequate control of mitral regurgitation.
Methods. We started to use the "bow-tie" repair as an adjunct to posterior ring annuloplasty in cases in which mitral regurgitation was not adequately controlled by decreasing mitral valve area (n = 6), or when placement of an annuloplasty ring was impractical (n = 4). Mean follow-up was 336 days (range, 82 to 551 days) with no postoperative deaths.
Results. Mitral regurgitation decreased from 3.6 ± 0.5 to 0.8 ± 0.4 (p < 0.0001), with a concomitant increase in ejection fraction from 33% ± 13% to 45% ± 11% (p = 0.0156) before hospital discharge. Mitral valve area, measured by pressure half-time, decreased from a mean of 2.5 ± 0.3 to 2.1 ± 0.3 cm2, with a mean transvalvular gradient of 4.5 ± 2.0 mm Hg. In patients whose mitral valve was repaired using the bow-tie alone, mitral regurgitation was reduced from 4+, to a trace to 1+. Postoperatively, mitral valve area increased from 1.9 to 2.5 cm2 during exercise, further supporting the concept that this technique preserves mitral valve annular function.
Conclusions. These observations suggest that the bow-tie repair may offer advantages over conventional techniques of mitral valve repair and should be considered as an adjunct, especially in patients with impaired left ventricular function.
Elucidation of the physiology of the subvalvular apparatus and its contribution to overall left ventricular function has led to a better understanding of the different mechanisms of mitral regurgitation (MR). This, in turn, has changed the surgical approach to MR, making replacement less acceptable and forcing a shift toward preferentially repairing the valve or preserving the subvalvular structures when replacement is unavoidable [1–3].
Ischemic MR (IMR) is the second most common cause of MR in the United States [4] after degenerative diseases, yet its pathophysiology remains unclear. Experimental as well as clinical studies suggest a combination of factors including annular dilatation and posterior papillary muscle fibrosis with scarring of the underlying ventricular wall [5–7]. The latter causes this segment of the ventricle to move paradoxically during systole, tethering the posterior leaflet and causing MR [8]. The pathophysiology of acute MR in ischemia seems to differ, as demonstrated recently by Llaneras and colleagues [7] and Gorman and associates [9] using rapid sonomicrometry array localization in a sheep model of IMR. Their data suggest that MR in this setting is caused by a number of alterations in the mitral annulus and subvalvular system, eg, asymmetrical dilatation of the annulus, failure of the posterior papillary muscle to contract, and dislocation of its tip towards the centroid of the annulus [9]. The combination of these alterations led to leaflet malcoaptation and MR.
Unclear understanding of the disease process complicates selection of the appropriate repair technique and explains reintervention rates as high as 50% by 7 years in this cohort of patients [10]. The operative approach to mitral valve repair (MVR) in these patients is further complicated by the usually small left atrium. Use of an annuloplasty ring as sole therapy in these patients can understandably lead to compromised results if revascularization does not additionally improve function of the subvalvular mechanism. The variability of the subvalvular apparatus depending on the degree of ischemia, both among patients and in the same patient, makes a simple technique to ensure leaflet coaptation an attractive possibility. This observation led at least one center to advocate edge-to-edge suturing of the anterior and posterior leaflets in selected cases. This "bow-tie"-shaped repair, performed in 35 cases, has reportedly led to uniform satisfactory reduction of MR with no reoperations and excellent functional status with a maximum follow-up period of 3 years [10].
With this background, we initiated a program using the bow-tie repair in selected cases in which conventional annuloplasty achieved only marginal reduction of MR and in which replacement of the valve would have high morbidity and mortality because of poor preoperative ventricular function. Our early experience is reported below.
Patients and methods
Patients
The charts of 10 patients (5 men and 5 women) undergoing MVR in conjunction with a central leaflet suture (bow-tie repair) were reviewed. Patients were operated on between August 1996 and November 1997. Mean age was 66 years (range, 44 to 77 years). The cause of MR was ischemic in all patients. Mitral regurgitation was attributed to ischemia if any of the following criteria proposed by Radford and coworkers [11] were met: (1) rupture of a papillary muscle chord or head (n = 2); (2) infarction of the papillary muscle in the absence of leaflet disease (n = 3); or (3) clear history of new onset or worsening of MR after documented myocardial infarction (n = 5).
The diagnosis of MR was established by echocardiography in all patients, and semiquantitatively graded as severe (4+), moderate–severe (3+), mild–moderate (2+), mild (1+), and trace. Left-sided cardiac catheterization confirmed the presence of MR in 8 patients and the presence of critical coronary artery disease invariably involving the circumflex or posterior descending artery territories in all patients. Preoperative diagnoses and hemodynamics obtained during catheterization are shown in Table 1.
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For the MVR we generally use a posterior approach through the interatrial groove to access the left atrium. After placing the aortic cross-clamp, a bulb syringe with cold saline is used to distend the left ventricle and confirm the mode of valve failure. A conventional repair using an annuloplasty ring is generally performed, and the valve is reinspected with saline injection. If the leaflet edges do not oppose each other in a concentric circle parallel to the annuloplasty ring and continued regurgitation is observed, then a bow-tie repair is initiated. If the repair is performed from the transventricular or transaortic exposure, a single figure-of-eight 4-0 Prolene suture (Ethicon, Somerville, NJ) is placed without screening leaflet coaptation. Using a 4-0 Prolene suture, the anterior leaflet is attached to a corresponding point on the posterior leaflet at the site of malapposition. The figure-of-eight suture is placed through each leaflet just as the edge turns down to attach to the primary chordae (Fig 1). This is usually the most cephalad site where the two leaflets would touch during systole and creates the largest area of coaptation possible.
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Five patients were operated on electively for worsening MR leading to intractable congestive heart failure or unstable angina. Five patients underwent emergent operation because of an acute worsening of MR secondary to ischemic papillary muscle rupture (n = 2), acute myocardial infarction with cardiogenic shock requiring intraaortic counterpulsation balloon, severe MR and malignant arrhythmias (n = 2), and severe MR with unstable angina and a left ventricular aneurysm (n = 1). Mean degree of preoperative MR by echocardiography was 3.6 ± 0.5, with mean ejection fraction of 33% ± 13%. Eight patients underwent preoperative cardiac catheterization. Mean pulmonary capillary wedge pressure was 25 ± 6 mm Hg, with mean atrial v wave of 37 ± 23 mm Hg; mean cardiac output as measured by thermodilution technique was 4.2 ± 0.2 L/min (Table 1). Concomitant procedures performed at the time of MVR included coronary artery bypass grafting in all patients. Six patients had a posterior ring annuloplasty as the primary procedure for treatment of MR (Table 2). Two patients required repair of ischemic ventricular septal defect and left ventricular aneurysm through ventriculotomies, which made insertion of an annuloplasty ring impractical. Their mitral valves were successfully repaired with a bow-tie alone. A third patient presented with acute MR secondary to rupture of the anterior head of the posterior papillary muscle. Repair was performed using pericardial pledgets to reattach the muscle head. Because of the lack of annular dilatation and persistence of MR, a bow-tie suture was placed without an annuloplasty ring. The last patient underwent a coronary artery bypass graft reoperation for recurrent unstable angina. At completion of the procedure the patient could not be weaned off CPB because of severe MR. Using a transatrial approach, a bow-tie repair was performed allowing the patient to come off CPB without complications. Control of MR assessed intraoperatively by direct cold saline injection and transesophageal echocardiography was satisfactory in all patients.
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Initial postoperative cardiac output obtained on arrival to intensive care was 4.3 L/min (range, 3.5 to 4.9 L/min). The last cardiac output for the same patients after discontinuation of pressor support and before extraction of the thermodilution catheter was 4.5 L/min (range, 4.0 to 4.7 L/min), with average pulmonary artery diastolic pressure of 18 mm Hg (range, 12 to 24 mm Hg). Six patients required pressor support postoperatively for an average of 71 hours (range, 20 to 170 hours). Average length of stay in intensive care was 4 days (range, 1 to 8 days). There were no perioperative deaths.
Postoperative control of MR was satisfactory in all cases, decreasing from 3.6 ± 0.5 to 0.8 ± 0.4 (p < 0.0001). Despite significant improvement in the degree of regurgitation, a significant increase in ejection fraction was observed, from 33% ± 13% to 45% ± 11% (p = 0.0156) (Fig 3). Mitral valve area, calculated by pressure half-time, decreased from 2.5 ± 0.6 cm2 preoperatively to 2.1 ± 0.3 cm2 postoperatively, with a mean gradient of 6.0 ± 2.0 mm Hg. The 4 patients in whom the bow-tie repair was used alone showed a decrease in MR from 3.5 ± 0.6 to 0.8 ± 0.5 (p = 0.0286), with mean CPB and cross-clamp times of 168 ± 37 minutes and 111 ± 18 minutes, respectively. Postoperative exercise echocardiogram, performed in one of these patients, revealed a mitral valve area of 1.9 cm2 that increased to 2.5 cm2 during exercise without evidence of transvalvular gradient. This was seen in contrast to the patients who received annuloplasty rings in conjunction with bow-tie repairs. Mitral valve areas in the latter were reduced when compared with preoperative echocardiograms, with significant impairment in posterior leaflet mobility secondary to fixation of the posterior annulus.
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Comment
Mitral valve replacement for IMR has the highest operative mortality and the poorest postoperative outcome of all valvular lesions [3, 4]. Multiple investigators have tried to identify markers of ventricular function that would be prognostic of outcome. One complicating factor in obtaining adequate repairs may be the intrinsic variations and limited understanding of the pathophysiology of the disease. In a series of experiments using a canine model, Sarris and associates [5] and Hansen and coworkers [12] have demonstrated the importance of the mitral subvalvular apparatus in overall ventricular performance. Mitral regurgitation leads to left ventricular volume overload, with a minimal pressure load on the myocardium because of excess volume being ejected into the low-pressure left atrium. As a consequence, peak- and end-systolic stress, indicators of afterload, are not significantly increased as demonstrated by Carabello [13] and Wisenbaugh and colleagues [14]. This type of overload leads to increased ventricular radius with little change in wall thickness, resulting in a chamber that is ill suited to cope with the increased afterload imposed on it after mitral repair or replacement [14–16]. Preservation of the subvalvular apparatus minimizes the decrease in ventricular ejection fraction usually seen after this operation. These observations have led to a preferentially reparative approach to the mitral valve, which decreases risk of thromboembolic complications and avoids the need for anticoagulation, thus making return to normal activity easier. We postulate that the bow-tie repair, as an adjunct to annuloplasty, provides an alternative to MVR if annuloplasty yields unsatisfactory results. When used alone, this technique has the potential of being time saving and easy to perform, and at the same time directly addressing the issue of subvalvular dysfunction in IMR.
Several advantages make this technique intrinsically appealing. The suture can be placed even if another repair has been attempted. The use of this simple adjunctive technique for repair of IMR can further reduce the need for MVR in this high-risk cohort. The procedure is quick to perform and can be implemented from a variety of different approaches including transaortic and transventricular exposures. More importantly, this technique addresses the experimentally demonstrated mechanism of MR during ischemia. As opposed to annuloplasty rings, which reduce the valve area and hopefully indirectly facilitate coaptation of dysfunctional leaflets, the bow-tie repair directly addresses the subvalvular mechanism of failure and forces coaptation of leaflets that no longer will naturally and efficiently move together during systole.
We have avoided the use of pledgets for two reasons. First, in the event of suture fracture, the resulting embolism would be considerably larger. Second, the pledget may provide a crowbar or plow effect into which blood can flow and torque apart the sutured repair.
An additional issue is the correct material for the suture. A body of literature documenting the ability of polytetrafluoroethylene to endothelialize exists; however, this material tends to slip easily. Polytetrafluoroethylene-coated Dacron (Deknatel DSP, Fall River, MA) should endothelialize as well and would tie easily without leaving rigid tips, which could perforate the leaflets. We have used 4-0 polypropylene, our traditional suture for MVR, and have had short-term success.
The repair has been used frequently in conjunction with left ventricular reduction operations without a significant incidence of early failure [17]. The report of transatrial bow-tie style repair available [10] reviews 35 cases performed during a 3-year period for both posterior (n = 13) and anterior (n = 22) prolapse. The authors report uniform success with no reoperations. No mortalities were reported. There is, nonetheless, no mention of postoperative functional status or follow-up echocardiograms.
Two major concerns are raised by this technique. The current report provides only an 11-month follow-up and therefore can only be considered a medium-term assessment. We cannot yet assess the durability of the repair, although we now have a 5-year follow-up on the Alfieri experience (personal communication) and the data are reassuring. Surgeons are understandably skeptical of the durability of a single-suture repair in an area of apparently high stress. However, there is likely less tension on the site of apposition, and consequently the suture, than is anticipated. The stresses on the closed mitral valve have been mathematically modeled and calculated by Arts and colleagues [18]. To apply this concept to the mechanics of the bow-tie repair, we make use of the fact that the mitral valve leaflets are composed of a "core" of collagenous tissue (the fibrosa layer) that radiates from the annulus toward the tips of the leaflets to coalesce into the chordae connecting to the papillary muscles [19]. Membrane tension is assumed to be directed along collagen fibers to the annulus, minimizing forces acting perpendicular to the membrane. To mathematically determine the forces acting on the tips of the leaflets, the latter have to be assumed to be symmetrical and semicircular in relation to horizontal plane y (Fig 4). In the plane of symmetry (y = 0), both leaflets touch each other at point Q. The force acting on the tips of the leaflets during systole is defined by the following equation:
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The bow-tie repair, when performed alone, preserves the sphincter mechanism of the mitral valve and the systolic performance of the base of the heart. As a consequence, the annulus dilates during diastole, increasing the valve area and avoiding functional mitral stenosis. This effect has been documented by our group [20] using a sheep model of chronic IMR previously described by Llaneras and coworkers [7]. Rapid sonomicrometry array localization at the time of repair confirms the normal motility of the annulus after bow-tie repair. Concomitantly, echocardiographic examination of the valve demonstrates a decreased MVA but no evidence of mitral stenosis even after pharmacologic simulation of strenuous exercise conditions. In sharp contrast, posterior annuloplasty decreases MR by stiffening and fixing the posterior annulus, thereby diminishing posterior leaflet excursion. We believe this effect to be detrimental to overall ventricular performance, because it diminishes the contribution of the base of the heart to systolic function. The use of flexible rings has failed to avoid this effect because of progressive calcification of the prosthesis [21].
In one of the patients without annuloplasty rings, the mitral valve area was shown to increase from 1.9 to 2.5 cm2 during exercise, confirming our experimental findings. Despite these potential advantages we continue to favor the inclusion of a posterior annuloplasty ring, because most studies have demonstrated its increased reliability and durability in MVRs. As our experience evolves we will begin to more frequently use the bow-tie repair alone.
In conclusion, we have had success using a novel technique to repair ischemic mitral valve disease that is easy to apply, reproducible, and can serve as a useful adjunct to ring annuloplasty in cases in which the latter gives an unsatisfactory result. This technique directly addresses the mechanism of MR in these patients and can easily be applied from a variety of surgical approaches. A non-CPB approach, including a transcatheter system, may succeed in placing this suture and may be able to provide adequate palliation for IMR in the future. We are currently developing such a system, which would likely use a clip or a ring rather than a suture to secure the leaflets in place.
References
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