Systolic Anterior Motion of the Mitral Valve after Mitral Valve Repair

Abstract

Factors predisposing patients to systolic anterior motion of the mitral valve (SAM) with left ventricular outflow tract (LVOT) obstruction after mitral valve repair are the presence of a myxomatous mitral valve with redundant leaflets, a nondilated hyperdynamic left ventricle, and a short distance between the mitral valve coaptation point and the ventricular septum after repair.

From December 1999 through March 2000, we used our surgical method in 6 patients with severely myxomatous regurgitant mitral valves who were at risk of developing SAM. Leaflets were markedly redundant in all 6. Left ventricular function was hyperdynamic in 4 patients and normal in 2. Triangular or quadrangular resection of the midportion of the posterior leaflet and posterior band annuloplasty were performed. To prevent SAM and LVOT obstruction, extra, posteriorly directed, mid-posterior-leaflet secondary chordae tendineae, which would otherwise have been resected, were transferred to the underside of the middle of the mid-anterior leaflet with a small piece of associated valve as an anchoring pledget. This kept the redundant anterior leaflet edge, which extended below the coaptation point, away from the LVOT.

No post-repair SAM or LVOT obstruction was observed on intraoperative or discharge echocardiography. All patients had no or trivial residual mitral regurgitation.

We conclude that extra chordae tendineae, when available, can be used in mitral valve repair to tether the redundant anterior leaflet and thus prevent it from flipping into the LVOT. This will theoretically prevent SAM and LVOT obstruction in patients with risk factors for SAM.

There is an increased risk for the development of systolic anterior motion of the mitral valve (SAM) after repair of a regurgitant, myxomatous valve with excessive anterior leaflet tissue and preserved left ventricular function. Left ventricular outflow tract (LVOT) obstruction due to SAM occurs in 4% to 5% of patients after mitral valve repair.¹ Factors predisposing patients to the development of SAM are repair of a regurgitant myxomatous mitral valve with excess leaflet tissue, hyperdynamic left ventricular function and near-normal size, and a short distance from the coaptation point of the mitral valve to the septum.^1–4 From December 1999 through March 2000, we used our technique of tethering the midsegment of the anterior leaflet (A2) to prevent the leaflet from flipping into the LVOT in 6 patients who had a high propensity for developing SAM. In these patients, LVOT obstruction did not occur.

All 6 patients underwent standard posterior leaflet midsegment (P2) resection, repair, and posterior annuloplasty of the mitral valve for severe mitral regurgitation. All had redundant myxomatous mitral valve anterior and posterior leaflets. Four patients had a hyperdynamic left ventricle (ejection fraction [EF] range, 0.60–0.75) with some left ventricular hypertrophy. The remaining 2 had an EF of 0.50. Left ventricular end-systolic size was nearly normal in 3 patients (≤34 mm) and mildly-to-moderately dilated in the other 3 (39, 44, and 48 mm). The LVOT diameter was 2.3 ± 0.25 mm.

Surgical Technique

Cardiopulmonary bypass was established, the aorta cross-clamped, and antegrade cold blood cardioplegia administered. The mitral valve was exposed through a standard Waterston groove incision. A triangular or quadrangular resection of the P2 section of the prolapsing posterior leaflet was performed (Fig. 1A). We transposed an intact secondary chorda tendinea from the resected portion of the posterior leaflet to the center of the undersurface of the anterior leaflet in a position between the anterior leaflet's primary and secondary chordae tendineae. The purpose was to prevent the redundant anterior leaflet from entering the LVOT. A small pledget-sized isle of the resected posterior leaflet with a primary or secondary chorda tendinea was transferred with the attached chorda tendinea. To affix the isle of the posterior leaflet to the undersurface of the anterior leaflet, we used a polypropylene suture (Prolene 4-0, Ethicon, Inc.; Somerville, NJ), which was passed through the anterior leaflet and tied over a small Teflon pledget (Ethicon). The position chosen for attachment on the undersurface of A2 was adjusted to account for the length of the transposed chorda tendinea. Only normal chordae were transposed. This technique places the most posteriorly directed chordae tendineae more anteriorly, thus tethering the redundant anterior leaflet more posteriorly (Fig. 1B). A posterior band annuloplasty was performed from trigone to trigone to downsize the dilated posterior annulus. A 63-mm-long flexible annuloplasty band (Medtronic, Inc.; Minneapolis, Minn) was used in all cases to reduce the annular circumference of the mitral valve to 10 cm. Intraoperative transesophageal echocardiography and predismissal transthoracic echocardiography showed no or trivial mitral regurgitation, no SAM, and a diastolic mitral valve gradient of 2 to 6 mmHg. The LVOT diameters were identical to the preoperative measurements. The redundant anterior leaflet extending below the coaptation point was observed to be tethered in a position that was parallel to the LVOT.

Fig. 1 A) A cross-sectional illustration after P2 resection and annuloplasty shows a redundant anterior leaflet extending beyond the point of coaptation. This redundant leaflet is partially obstructing the left ventricular outflow tract. B) The redundant anterior leaflet is tethered posteriorly by transposition of a posteriorly directed chorda tendinea to an intermediate position on the ventricular side of the anterior leaflet between the primary and secondary chordae tendineae of the A2 segment.

Discussion

We recommend the above-described technique as a possible adjunct during standard posterior leaflet repair in patients at risk for SAM, if extra secondary chordae tendineae are present in the leaflet portion that is to be resected. Appropriate patients have a billowing, redundant, and myxomatous anterior leaflet, and the left ventricle is of near-normal size and may be hyperdynamic. Such patients are at significant risk for post-cardiopulmonary bypass SAM.^1–4 Mihaileanu and colleagues⁵ reported that LVOT obstruction due to SAM occurred in 14% of patients with these predisposing factors.

Systolic anterior motion after mitral valve repair can often be managed with β-blockade and volume loading. However, the condition fails to resolve in some patients, who ultimately are better served with valve replacement. Jebara and coworkers¹ described sliding posterior-leaflet valvuloplasty, which is a technique used to move the coaptation point to a more posterior location, thus keeping the anterior leaflet redundancy from obstructing the LVOT.¹ Although effective, the technique adds a degree of complexity to a standard posterior leaflet repair. Ascertaining that the posterior annuloplasty band is of sufficient size or reducing the size of the anterior leaflet by triangular resection or plication are other ways to avoid pushing too much anterior leaflet into the LVOT after repair. The edge-to-edge repair of sewing A2 to P2, creating a double-orifice mitral valve, can also be used; however, this technique substantially alters the mitral valve anatomy.

Our technique allows tethering of a redundant anterior leaflet with extra chordae tendineae from the anticipated resected segment of the posterior leaflet by implanting them into an intermediate position on the A2 segment of the anterior leaflet. Many patients who require posterior leaflet mitral valve repair do not have extra chordae tendineae. When these chordae tendineae are present, however, the technique is technically easy, rapid, and effective in appropriate patients. Immediate and early follow-up echocardiography shows the avoidance of SAM, no interference with the primary repair, and no evidence of mitral valve stenosis. Although one cannot be sure that our 6 patients would have developed SAM, the redundant anterior leaflet tissue below the coaptation point did appear tethered and remained in a plane parallel to the LVOT postoperatively. In no case was the anterior leaflet tethered into the orifice of the mitral valve. We offer this as a simple approach to decrease the risk in patients with factors predisposing them to systolic anterior motion after mitral valve repair.