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Surgery of the Mitral Valve
Degenerative and myxomatous changes are the most common cause of mitral valve disease in North America
and Western Europe today. These changes affect the leaflets and subvalvular apparatus, leading to mitral
regurgitation. As the population ages, surgeons are seeing more patients with mitral insufficiency secondary to
calcific mitral valve diseases.
Rheumatic fever continues to be the major cause of acquired valve disease worldwide. Rheumatic fever results
in pancarditis, but the pathologic effects are noted predominantly on the endocardium and cardiac valves,
particularly the mitral valve. During the acute phase of myocarditis, the left ventricle dilates, which causes
stretching of the annulus of the mitral valve. The mitral insufficiency thus produced is temporary and disappears
when the left ventricle regains its normal function. Rheumatic heart disease is a chronic and progressive
condition. The earliest permanent change is the fusion of the commissures, followed by thickening and fibrosis of
the valve leaflets. These pathologic events are responsible for the creation of the turbulent flow that, together
with the continuing rheumatic process, further enhances the progression of the disease and eventual
involvement of the subvalvular apparatus. The chords and papillary muscles become thickened, shortened, and
fused to each other and to the mitral leaflets. A continuous cycle of progression of pathologic changes and
increasingly disturbed flow is therefore created, eventually leading to severe mitral valve disease, notably mitral
stenosis or mixed stenosis and insufficiency with or without calcification.
Functional mitral regurgitation may be caused by ischemic or nonischemic cardiomyopathies. The leaflets and
subvavular structures are normal but leaflet coaptation is prevented by annular dilation, left ventricular wall
motion abnormalities or generalized cavity dilation, and/or papillary muscle dysfunction. Ischemic heart disease
and myocardial infarction may also lead to ischemic mitral valve prolapse due to papillary muscle or chordal
injury.
Bacterial endocarditis can affect both normal and abnormal heart valve leaflets. The infection may burrow
through and invade the mitral valve annulus. Infrequently, the endocarditis extends to the aortic valve and/or the
subvalvular apparatus of the mitral valve. It can destroy the mitral valve leaflet configuration, resulting in gross
mitral valve insufficiency.
SURGICAL ANATOMY OF THE MITRAL VALVE
The mitral valve forms the inlet of the left ventricle. It consists of two leaflets: the anterior (aortic) and posterior
(mural) leaflets, which are attached directly to the mitral annulus and to the papillary muscles by primary and
secondary chordae tendineae. A series of chordae tendineae originates from the fibrous tips of the papillary
muscles and inserts into the free edges and the undersurfaces of the mitral leaflets, thereby preventing the
prolapse of the leaflets into the left atrium during systole and contributing to the competency of the mitral valve.
The attachments of the leaflets to the annulus meet at the anterolateral and posteromedial commissures. One-
third of the mitral valve annulus provides attachment for the anterior leaflet, and the posterior leaflet arises from
the remaining two-thirds of the annulus. Although from the strict anatomic point of view the mitral valve consists
of two leaflets, there are multiple clefts within the posterior leaflet. These slits give rise to scallops of leaflet that
may prolapse and give rise to valvular insufficiency. Most surgeons and echocardiographers have adopted the
classification of Carpentier, which divides both the anterior and posterior leaflets into three functional segments
(Fig. 6.1).
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FIG. 6.1 Carpentier functional mitral valve components.
FIG. 6.2 Surgical anatomy of the mitral valve.
When the posterior annulus is studied from a strictly anatomic standpoint, it is attached to the left ventricular
myocardium through the interposition of a narrow membrane and is therefore actually slightly elevated above the
opening of the left ventricle. This subannular membrane extends underneath the posterior annulus to the region
of both commissures and merges with the fibrous skeleton of the heart. The anterior leaflet is continuous with the
adjoining halves of the left and noncoronary annuli of the aortic valve and also with the fibrous subaortic curtain
located beneath the commissure between the left and noncoronary aortic sinuses (Fig. 6.2).
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The annulus of the mitral valve is surrounded by many important and vital structures. The nearby left circumflex
coronary artery traverses around the mitral annulus in the posterior atrioventricular groove. The coronary sinus
also runs in the more medial segment of the same groove. The atrioventricular node and its artery, usually a
branch of the right coronary artery, run a course parallel and close to the annulus of the anterior leaflet of the
mitral valve near the posteromedial commissure. As mentioned earlier, the remainder of the anterior leaflet
annulus is contiguous with the aortic valve. These relationships have significant clinical implications during mitral
valve surgery (Fig. 6.3).
FIG. 6.3 Vital structures surrounding the mitral annulus.
Functional mitral regurgitation occurs secondary to annular or left ventricular changes with anatomically normal
leaflets and subvalvular structures. One etiology is simple annular dilation due to left ventricular enlargement. In
this case, the leaflet motion is normal, but the leaflets are pulled apart, preventing normal coaptation. Localized
left ventricular wall motion abnormalities result in displacement of the papillary muscles. This results in apical
tethering of the leaflets with restricted mitral leaflet motion in systole. In some patients, both mechanisms
contribute to functional mitral regurgitation.
Technical Considerations
Incision
A median sternotomy is the incision most commonly used. Standard aortic and bicaval cannulation is performed.
A right anterior thoracotomy with femoral cannulation affords good access to the mitral valve and spares the
midline sternotomy incision.
Myocardial Preservation
When satisfactory cardiopulmonary bypass has been established, the aorta is cross-clamped and cold blood
cardioplegic solution is administered into the aortic root to bring about prompt diastolic cardiac arrest. Further
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administration of blood cardioplegic solution is often administered by the retrograde method (see Chapter 3).
Aortic Insufficiency
Satisfactory administration of cardioplegic solution into the aortic root can only be accomplished if the aortic
valve is competent. Aortic insufficiency, if present, directs the cardioplegic solution into the left ventricular cavity,
causing distension and stretch injury to the myocardium. This can be prevented by administering cardioplegic
solution using the retrograde technique alone (see Chapter 3).
Exposure of the Mitral Valve
There are many different approaches for entering the left atrium to provide good exposure of the mitral valve.
Interatrial Groove Approach
The left atrium is opened with an incision just posterior to the interatrial groove (Fig. 6.4). The opening can be
extended inferiorly onto the posterior wall of the left atrium.
Fatty Fragments
There is always a variable amount of loose fatty tissue in the interatrial groove. Fragments of fat and loose tissue
may enter the left atrial cavity during the atriotomy. Similarly, when the atriotomy is being closed, fatty fragments
may invaginate through the closure into the left atrium.
FIG. 6.4 Surgical approach to the mitral valve.
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FIG. 6.5 Extension of the incision inferiorly to the back of the heart.
Extension of the Incision
Upward extension of the incision behind the superior vena cava should be avoided because subsequent closure
may be difficult. Generous inferior extension to the back of the heart provides satisfactory exposure of the mitral
valve in most cases (Fig. 6.5). Closure of this posterior extension of the incision is facilitated by suturing from
inside the left atrial cavity under direct vision.
Drainage of Cardioplegic Solution
At least one of the caval snares must be loosened during administration of cardioplegic solution to allow the
venous return from the coronary sinus to drain into the oxygenator. If both snares are down, cardioplegia may
distend the right heart. If the right atrium is not opened at any time, the cavae do not necessarily require snares
around them because venous drainage may be adequate.
Air Embolism
The aorta must be cross-clamped before opening the left atrium to avoid systemic air embolism.
Specially designed retractors are introduced into the left atrium. Optimal exposure is obtained when the retractor
held by the assistant pulls the atrial wall at least 1 cm from the mitral annulus upward and slightly to the patient's
left. Many self-retaining retractors are available to improve exposure of the mitral valve. They may be particularly
helpful if there is a shortage of assistants in the operating room.
Retractor Injury
Because the atrial wall may be somewhat friable, excessive pull on the retractor may produce a shearing tear of
the atrial wall edges, thereby complicating closure. On many occasions, two smaller retractors provide better and
safer exposure than a single large one because the assistant is able to divert the pulling force from one retractor
to the other to accommodate the surgeon's view (Fig. 6.6).
Transatrial Oblique Approach
If the left atrium is small, exposure of the mitral valve through the interatrial groove may be suboptimal. In
reoperative procedures, dense adhesions may make dissection hazardous, particularly near the region of the
interatrial groove. In such cases, an oblique transatrial approach provides excellent exposure of the mitral valve
(Fig. 6.7). The aorta is cross-clamped, and cardioplegic solution is administered as before. After the aorta is
clamped, an oblique incision is made on the right superior pulmonary vein with a long-handled no. 15 blade.
Warm blood will gush out to decompress the left atrium. This will allow expeditious cooling and arrest of the
heart.
The vena caval snares are secured. The opening in the right superior pulmonary vein is extended obliquely
across the right atrial wall. By gently retracting the right atrial wall edges, the incision can now be extended
across the interatrial septum and through the fossa ovalis just inferior to the limbus (Fig. 6.7B). At this time, a
retrograde cardioplegic cannula can be introduced into the coronary sinus under direct vision. It can be secured
with a fine purse-string suture of Prolene placed on the inside of the coronary sinus ostium, away from the
conduction tissues (see Chapter 3). In this manner, retrograde infusion of cardioplegic solution can supplement
the antegrade technique.
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FIG. 6.6 Use of two small retractors to avoid tearing the atrial wall edges.
FIG. 6.7 A: Incision on the right superior pulmonary vein extends across the right atrium. B: Transatrial incision.
Extension of the incision across the interatrial septum just to the limbus of the fossa ovalis. C: For additional
exposure, the septal incision is extended along the fossa ovalis.
Overextended Septal Incision
Extension of the septal incision far beyond the anterior limbus of the fossa ovalis may divide the mitral valve
annulus, making mitral valve replacement insecure. It could also create a passage outside the atrium into the
transverse sinus. The septal incision should therefore terminate just distal to the anterior margin of the fossa
ovalis. The septal incision can be extended inferiorly on the fossa ovalis if additional exposure is required (Fig.
6.7C).
The septal edges are retracted with two small retractors. This provides excellent exposure of the mitral valve
without distorting it, an important advantage when mitral valve reconstruction is being contemplated (Fig. 6.8).
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FIG. 6.8 Retraction of the septal edges to provide exposure of the mitral valve without distorting it.
Transatrial Longitudinal Septal Approach
When there are excessive adhesions from previous surgery, excellent exposure of the mitral valve can be
obtained through a longitudinal septal approach. Depending on the size of the right atrium, an oblique or
longitudinal incision is made on the right atrial wall. Excellent exposure of the right atrial cavity and interatrial
septum is thus obtained. A longitudinal incision is made along the posterior margin of the fossa ovalis and
extended both superiorly and inferiorly to provide good exposure of the mitral valve (Fig. 6.9A). The right
atriotomy incision can be extended across the base of SVC, onto the roof of the left atrium (Fig. 6.9B). This way,
the transatrial septal incision can also be extended into the roof of the left atrium (as far as the left atrial
appendage base) to provide excellent exposure of the left atrium (especially when left atrium is not dilated (Fig.
6.9C).
Extension of right atriotomy beyond the base of SVC (transection of SVC) will likely divide the SA nodal
artery. Post-operatively, many patients develop junctional rhythm for a few days until the sinus rhythm returns.
Few patients may require a permanent pacemaker if there is not a return of sinus rhythm after 7 to 10 days.
Proximity to the Mitral Annulus
The annulus of the mitral valve is at the muscular septal wall most anterior to the fossa ovalis. Therefore, the
longitudinal septal incision should be made posterior to the fossa ovalis, leaving a good margin of septal wall
between
the opening and the mitral annulus. This segment of the septum is retracted to provide excellent exposure of the
mitral valve.
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FIG. 6.9 A: Transatrial longitudinal septal approach. B: Extension of right atriotomy across the base of SVC to
the roof of the left atrium. C: Transatrial septal incision with extension to the roof of the left atrium (to the base of
the left atrial appendage) provides excellent exposure of the mitral valve.
OPEN MITRAL COMMISSUROTOMY FOR MITRAL STENOSIS
Mitral stenosis secondary to longstanding rheumatic fever has continued to be the dominant mitral valve disease
affecting large populations worldwide. The disease is now being seen with increasing frequency among
immigrants coming to the United States and Western Europe, where rheumatic heart disease had become
uncommon.
Mitral commissurotomy can be accomplished safely and precisely under direct vision. With the availability of
cardiopulmonary bypass, the closed technique is rarely used today except in third world countries.
A median sternotomy is the incision of choice, although the mitral valve can be approached through either a right
or left thoracotomy.
The left atrium is incised by one of the techniques described in the preceding text to expose the mitral valve. The
mitral leaflets are identified and, by means of two fine Prolene traction sutures, gently pulled upward toward the
left atrial cavity. At times, use of nerve hooks can also provide the same effect. Often this maneuver will stretch
the valve leaflets apart and show the line of commissural fusion as a furrow extending between them. If visibility
through the valve ostium is adequate, the chords and papillary muscles are examined for evidence of shortening
and fusion to each other and, especially, fusion to the undersurfaces of the valvular leaflets.
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FIG. 6.10 Technique for open mitral commissurotomy (see text).
A right-angled clamp is introduced through the mitral valve opening and placed directly below the fused
commissures. It is then opened gently beneath the leaflets to facilitate incision with a no. 15 blade onto the
commissures without severing the chordal attachments (Fig. 6.10). Occasionally, the papillary muscles are fused
to the undersurface of the leaflet, making commissurotomy hazardous. With the opened right-angled clamp in
place, the commissure is first incised near the annulus; this incision is extended inward over the clamp, cutting
vertically into the papillary muscle and the thickened, fused chords for a short distance.
Injury to Papillary Muscle
Care must be taken to divide the head of the papillary muscle fused to the undersurface of mitral leaflets straight
along its long axis. Oblique division may weaken or even result in a partial division of the papillary muscle,
necessitating its repair or reimplantation or even requiring mitral valve replacement.
Overextension of Commissurotomy
The extent of commissurotomy must be as complete as possible without producing valvular incompetence. If the
incision is extended too far toward the annulus, annuloplasty may become necessary (see Mitral Valve
Reconstruction section).
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CLOSED MITRAL COMMISSUROTOMY FOR MITRAL STENOSIS
Closed mitral commissurotomy is now rarely performed in most Western countries. Consequently, only a few of
the current generation of cardiac surgeons have had adequate experience with this technique. Nevertheless,
closed mitral valvotomy remains a good operation in selected subgroups of patients, and the long-term results
have been consistently satisfactory. In third world countries, closed valvotomy continues to be the preferred form
of therapy because of its simplicity and low cost compared with openheart procedures.
FIG. 6.11 Technique for closed mitral commissurotomy.
Technique
A left posterolateral or anterolateral thoracotomy is made through the bed of the fifth rib. The lung is retracted
posteroinferiorly, and a long incision is made anterior and parallel to the left phrenic nerve. The pericardium is
then suspended with traction sutures. The left atrial appendage is identified and excluded with a side-biting
clamp. A purse-string suture of 2-0 Prolene is placed around the left appendage. Another purse-string suture,
reinforced with pledgets, is then placed into the apex of the left ventricle. The left atrial appendage is incised
within the purse-string suture, and the surgeon's right index finger is introduced into the left atrium. The mitral
valve is palpated to detect calcification, the degree of mitral stenosis, or the presence of insufficiency (Fig. 6.11).
Tear in the Atrial Appendage
The index finger should be introduced gently, without undue pressure. If the atrial appendage tears, it will result
in brisk bleeding.
Blood Clot
Preoperative echocardiography is always performed to study the mitral valve pathology and to detect the
presence of a blood clot in the left atrial appendage. Nevertheless, before applying clamps to the appendage or
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