SYSTOLIC ANTERIOR MOTION
MV repair can be accomplished in almost all cases of degenerative MV
insufficiency (Type 2 according to Carpentier classification). Different
techniques have been described and many surgeons documented excellent
long-term results with different reparative options. It is important,
however, not to face every operation in the same way. When considering,
for example, flail leaflet pathology, in young patients with redundant
myxomatous degenerative mitral leaflets the type of repair should not be
equal to elderly patients with fibro-elastic deficiency.
One of the reasons why these differences need to be considered is the
possible occurrence of systolic anterior motion (SAM). SAM is a
complication of MV repair in which an anterior dislocation of the
anterior mitral leaflet during systole occurs leading to the obstruction
of the left ventricular outflow tract (LVOT) and to mal-coaptation of
the leaflets with varying degree of eccentric mitral regurgitation
(directed towards the interatrial septum) [2]. The incidence of SAM
following mitral valve repair varies from 1 to 10% according to
different reports and definition used in the studies [3-4].
Avoiding SAM is one the goal of surgical repair of the MV. For this
purpose, linking echocardiographic information to type of repair is
essential. Preoperative trans-esophageal echocardiography (TEE) helps
predicting the risk of postoperative SAM. Besides the usual data
regarding the severity of regurgitation, the regurgitant jet origin and
direction, the presence of a flail leaflet, and the annular dimensions,
TEE must advice surgeons about the risk of SAM particularly when
abundant redundancy of the leaflets, hypertrophic interventricular
septum, and anterior dislocation of the coaptation line during systole
are observed. A distance between the coaptation point and the septum in
systole (C-Septum distance) inferior to 25 mm, that usually occurs when
the height of the posterior leaflet exceeds 25 mm (particularly in the
median scallop P2), has been associated with increased risk of SAM after
repair [5] (Figure 1). This is a situation typically seen either in
young patient with severe myxomatous disease, where the
anterior/posterior leaflet ratio is close to 1, or in elderly patients
with less abundant leaflet height but accentuated septum hypertrophy.
The combination of a smaller LV end-systolic volume, lower ratio of
anterior to posterior leaflets heights and presence of bileaflet
prolapse are associated with high risk of SAM after separation from
cardiopulmonary bypass (CPB) [4].
In these cumbersome anatomical circumstances, goal of the correction has
to create a coaptation line positioned posteriorly, towards the
posterior annulus, having the anterior leaflet as much as possible
extended in systole towards the posterior one. The height of the
posterior leaflet needs to be reduced and this can be accomplished by
resections of the prolapsing scallop (quadrangular, triangular or any
kind of resection) and, in case of >25 mm leaflet, by
detaching the remaining posterior scallops from the annulus according to
the sliding plasty technique described by Alain Carpentier [6]. When
the height of the posterior scallops is extreme (>30 mm) or
when there is discrepancy between the height of the remaining scallops
after resection and sliding, then shortening of the scallop can be
performed by gently removing 5-10 mm of tissue from the posterior part
of the scallop before suturing it back to the annulus. An alternative to
resections and sliding plasty is to fold the posterior leaflet towards
the posterior annulus with several stiches in order to reduce leaflet
length and mobility [7].
Lately, the “respect rather than resect” concept has been applied in
the treatment of the prolapsing posterior leaflet [8]. In this
technique artificial chords (i.e., Gore-Tex®) are positioned from the
papillary muscles to the free margin of the prolapsing leaflet. It is an
excellent alternative to the resection technique. Both repairs for
posterior mitral leaflet prolapse are associated with excellent results
and appear comparable in the early postoperative course [9].
However, in an anatomical situation at risk of developing SAM following
repair, the “loop technique” should be avoided because it would
facilitate anterior displacement of the coaptation line and resection
preferred instead.
Placing an annular ring is a key element for long-lasting mitral valve
repair. In fact, in Type II degenerative mitral regurgitation the valve
almost invariably takes a circumferential shape, and the ring serves to
restore normal intercommissural and septo-lateral diameter recreating
the normal elliptical shape. However, when the risk of SAM exists, the
choice of the ring is crucial. Placing a small complete ring
(<34 mm) in a large and redundant myxomatous valve may favor
anterior displacement of the coaptation line leading to SAM. If the
“loop technique” is preferred over resection of the prolapsing
posterior scallop, then a large rather than small ring should be
considered. The ring should have the only goal of recreating elliptical
shape rather than forcing coaptation and with this in mind an open ring
can also be used.
In most cases, SAM occurring in the operating room, observed when the
patient has been weaned from CPB, can be successfully treated by
increasing left ventricle filling volume with fluids, removing any
inotropic drug used to come off bypass and by reducing heart rate with
beta-blockers. Very seldom this strategy is insufficient, and decision
needs to be taken to correct the anomaly. In this situation the surgeon
faces difficult moments: the patient has already gone through a certain
amount of time on CPB and cardioplegic arrest, another mitral repair
attempt must be resolutive without the risk of another early failure and
a third pump run. In this scenario surgeons can correct the problem
using a larger ring, decreasing posterior leaflet height, or adding an
Alfieri stich [4,10].