Valvular Heart Disease

Fritz J. Baumgartner

AORTIC VALVE DISEASE

Anatomy

The aortic valve is a tricuspid valve with a right, left and noncoronary cusp (Fig. 6.1). The right coronary orifice is in the sinus of Valsalva of the right coronary cusp; the left main coronary ostium is in the sinus of Valsalva of the left coronary cusp. The junction between the left and right coronary cusps is the intercoronary commissure; the junction between the right coronary cusp and the noncoronary cusp is the anterior commissure; the junction between the noncoronary cusp and the left coronary cusp is the posterior commissure.

As noted earlier, the membranous septum is just underneath the junction of the right coronary cusp and noncoronary cusp and immediately beneath this lies the bundle of His. This is an area which requires particular attention during surgery to prevent injury resulting in heart block. Subaortic extension of calcification of the aortic valve may lead to heart block because of involvement of this area.

Pathology

Aortic valve disease can result in aortic stenosis or aortic insufficiency. The most common cause of aortic stenosis is calcific aortic stenosis in a congenitally bicuspid aortic valve (Fig. 6.2). Nearly as common is senile calcific aortic stenosis with severe calcification secondary to age. The third important cause of aortic stenosis is rheumatic fever. Aortic insufficiency has a more varied etiology. Rheumatic disease is the most common cause of aortic insufficiency. Unlike rheumatic aortic stenosis, commissural fusion is not present in rheumatic insufficiency and the leaflets are only minimally thickened. With rheumatic aortic stenosis, the leaflets are markedly thickened. The basic pathology of aortic insufficiency related to rheumatic disease is related to shortening of the cusps.

Other causes of aortic insufficiency include bicuspid or unicuspid aortic valves, endocarditis, and annular ectasia from a chronic aortic aneurysm or from acute dissection. The normal area of the aortic valve is 2-3 cm2. An area less than 0.8 cm2 can be considered severe stenosis, as is a gradient across the aortic valve of greater than 50 mm mean gradient.

The indications for surgery for aortic stenosis include the classic symptoms of syncope, angina or heart failure. Of these, angina is the most common symptom

Fig. 6.1. Aortic valve anatomy.

INTERCORONARY COMMISSURE 1

AV MODE/ BUNDLE OF HIS

COMMISSURE COMMISSURE

INTERCORONARY COMMISSURE 1

COMMISSURE COMMISSURE

occurring in half of patients requiring aortic valve replacement for aortic stenosis. All three symptoms are present in about a third of patients presenting with symptomatic aortic stenosis. These symptoms usually exist when the aortic valve gradient is greater than 50 mmHg or the area of the valve is less than 1 cm2.

Indications for operating on patients with aortic insufficiency are much more complex and less clear-cut than for stenosis. Generally, Class III or Class IV heart failure status is an indication for surgery. For Class I or Class II New York Heart Association classification, surgery is only performed if there are signs of left ventricular dysfunction; for example, if the left ventricular ejection fraction is less than 40% or if the ventricular function worsens after a stress test. The ejection fraction while undergoing a stress test is the most important parameter in evaluating whether to operate in aortic insufficiency (or mitral regurgitation for that matter). As an example, if a patient can increase his ejection fraction from 40 to 50% with exercise, then even though his ejection fraction is moderately diminished and the patient has Class I-II symptoms, the valve probably does not need to be replaced. If, however, he is unable to increase his ejection fraction with exercise, this is a sign of impending cardiac demise and a valve replacement is indicated. Other parameters that support aortic valve replacement in patients with Class I or Class II symptoms are left ventricular enlargement with a cardiac/thoracic ratio of greater than 0.55, or left ventricular enlargement with left ventricular end diastolic dimension of greater than 50 mm. It should be noted that aortic insufficiency is a very insidious disease. This is because it is a volume overload problem of the left ventricle, rather than a pressure overload problem as with aortic steno-

sis. Aortic insufficiency progresses insidiously with even severe regurgitation not causing the symptoms in a patient until there is marked myocardial dysfunction. Once the patient starts to develop myocardial dysfunction and diminished ejection fraction, one can be assured that the aortic insufficiency has progressed far and that surgery is needed. There may be a point where the ejection fraction may be so bad with aortic insufficiency that aortic valve replacement will lead to the patient's demise. This is not true for aortic stenosis and one should consider aortic valve replacement in all patients with severe aortic stenosis, no matter how bad the ejection fraction because these patients will almost certainly do better after the aortic valve replacement. This may not be true for the longstanding ventricular dysfunction associated with aortic insufficiency.

For aortic insufficiency associated with annular ectasia from chronic aneu-rysm or acute dissection, replacement of the ascending aorta may be required as well as valve replacement. A composite graft replacement of the ascending aorta with an aortic valve replacement and reimplantation of the coronary arteries into the graft is a Bentall procedure. The details will be described in the section on Aortic Aneurysm and Dissection. In brief, cardiopulmonary bypass is established with an arterial line either in the aorta or femoral artery for the bypass. The aorta is cross-clamped and opened and cardioplegia solution infused into the coronary orifices directly or alternatively retrograde cardioplegia solution is infused. A Dacron graft which has a mechanical valve sewn into it by the manufacturer is used. The aortic valve replacement is performed first, followed by reimplantation of the coronary orifices, followed by sewing the distal anastomosis.

Technique of Aortic Valve Replacement (Fig. 6.3)

A standard median sternotomy is performed. The aorta is cannulated and then the right atrium is cannulated with a two-stage cannula drawing blood from both the inferior vena cava and right atrium. An antegrade plegia cannula is placed followed by a retrograde plegia cannula in the coronary sinus. Cardiopulmonary bypass is instituted. A left ventricular vent is placed via the right superior pulmonary vein. Cross-clamp is placed and antegrade cold blood cardioplegia given initially, then switched to retrograde cold blood cardioplegia. If the patient has severe aortic insufficiency, then no antegrade plegia is given and retrograde plegia is used from the start. This is given in an intermittent fashion since it is cold blood and there is no need for continuous plegia administration. Every 20 minutes, more plegia solution is given. With the heart arrested, the aortic root is opened approximately 2 cm proximal to the annulus in an oblique fashion. The aortic valve is excised, the annulus sized and pledgetted 2-0 Ethibond sutures are placed from the ventricle to the aortic side, except at the commissures at which point the stitches are placed from the aorta into the ventricular side to approximate the level of the annulus. This seats the valve in the supra-annular position.

If a suture breaks when placing the aortic valve it is not a simple matter to place another stitch into the annulus of the aorta and up into the sewing ring of the valve, because the pledgets are placed from the ventricular up into the aortic aspect. If a suture does break, several techniques are available. First of all, the pledget

Ventricular Pledgets

Fig. 6.3. Aortic valve replacement. (a) Exposure of the aortic valve through an oblique aortotomy. (b) Resection of the native aortic valve. The CUSA ultrasonic dissector may be very effective for managing a heavily calcified annulus. (c) Commissural sutures are placed from the aortic into the ventricular direction. The remaining sutures are placed from the ventricular into the aortic direction. (e) The sutures are placed through the prosthetic sewing ring and the valve seated and sutures tied. (f) The final position of the prosthetic (St. Jude) aortic valve. Note that the valve position is supra-annular and the valve leaflets are perpendicular to the septum.

Fig. 6.3. Aortic valve replacement. (a) Exposure of the aortic valve through an oblique aortotomy. (b) Resection of the native aortic valve. The CUSA ultrasonic dissector may be very effective for managing a heavily calcified annulus. (c) Commissural sutures are placed from the aortic into the ventricular direction. The remaining sutures are placed from the ventricular into the aortic direction. (e) The sutures are placed through the prosthetic sewing ring and the valve seated and sutures tied. (f) The final position of the prosthetic (St. Jude) aortic valve. Note that the valve position is supra-annular and the valve leaflets are perpendicular to the septum.

must be removed because it is free floating in the ventricle and could embolize. Sometimes, however, it may be wedged between the valve sewing ring and the annulus and therefore it may not be possible to retrieve the pledget. If the stitch breaks in the region of the noncoronary cusp, it will be possible to place a pledgetted suture from outside of the aorta, through the aorta and then up through the sewing ring of the valve. If the stitch breaks in the region of the left coronary cusp or right coronary cusp, one may not be so fortunate because placing such a pledget stitch in these cusps may result in tacking down the right or left coronary artery. This is why the sutures are initially tied down first in the right coronary cusp then the left coronary cusp prior to tying down the noncoronary cusp sutures. If a right coronary cusp stitch breaks or a left coronary cusp stitch breaks, then the valve can be lifted and it is a simple matter to place another stitch. If the right coronary cusp sutures are tied followed by the left coronary cusp sutures and then a break occurs when tying down the noncoronary cusp stitches, one can still salvage the situation by driving a pledgetted stitch from the outside of the aorta up through the aortic valve sewing ring. Each move done in cardiac surgery should have a function based on a knowledge of efficiency for the best possible outcome for the patient.

The aorta is closed, and prior to completing the closure the left ventricular vent is stopped and 10 cm pressure applied to the lungs to expel air. Then higher suction is placed on the left ventricular vent and aortic root vent is applied to further evacuate air. Then the cross-clamp is removed. The left ventricular vent is once again shut off and needle aspiration of the dome of the left atrium and the left ventricle performed. With the rhythm obtained and bleeding controlled, the left ventricular vent is once again shut off and removed and the patient weaned from cardiopulmonary bypass.

Small Aortic Annulus

The management of a small aortic annulus may be difficult. A homograft may be used with minimal gradient (down to 16 mm size) but if a prosthetic must be used (i.e. St. Jude's mechanical) then the valve diameter in general should be greater than or equal to 21 mm at least, lest there be a large gradient across the valve with inadequate cardiac output during exercise. This judgment depends on the size of the patient and whether or not a higher cardiac output would be necessary, i.e. such as an athlete versus a sedentary patient. St. Jude's aortic valves of 17 mm size are available and are generally unacceptable in this size except for small or sedentary patients. As a rule of thumb, patients with a body surface area (BSA) less than 1.7 will manage with a 19 mm valve. Those between 1.7-2.0 m2 will do best with a 21 mm valve, and those greater than 2.0 m2 generally need a 23 mm valve.

The St. Jude HP® (Hemodynamic Plus) valve achieves a larger orifice for a given valve size (see section on Mechanical and Bioprosthetic Cardiac Valves). The result is an effective increase in the valve orifice area by nearly one valve size (i.e. a St. Jude 19 mm HP valve has nearly the orifice size of a standard St. Jude 21 mm valve). The HP valve is not recommended for the heavily calcified valve annulus, although we have used the valve safely after annular decalcification using the ultrasonic dissector (CUSA). The use of the HP valve markedly reduces the requirement for surgical enlargement of the aortic annulus.

Nonetheless, other surgical techniques may be necessary to seat a larger valve greater than or equal to 21 mm:

1) Simply placing the sutures from the direction of the ventricle up into the aorta with the pledget seated on the ventricular aspect allows for one valve size larger. This is because the sewing ring of the aortic valve thus sits in a supra-annular position. The pledgetted sutures were placed from the aorta down into the ventricle, the valve would be seated intra-annular. At Harbor, we typically place the stitches such that the valve seats in the supra-annular position. This is also found to be highly effective for the HP valve.

2) Supra-annular and annular patch enlargement can be performed by incising down the junction between the noncoronary and left coronary cusp (Manouguian procedure). By splitting this posterior commissure, one is able to then sew in an albumin-treated Dacron patch to enlarge the annulus (Fig. 6.4). Pledgetted sutures are then passed through the Dacron in standard fashion, as if there were an annulus present there, and the valve can be seated.

3) A less ideal method is the supra-annular patch enlargement by incising down into the noncoronary sinus but not actually into the annulus. This merely enlarges the supra-annular portion but not the annulus itself.

4) A Konno aortoventriculoplasty may also be performed. This is a procedure best done by pediatric cardiac surgeons and consists of a vertical aortotomy followed by incision just to the right of the commissure between the left and right coronary cusps. The right ventricle is opened with an oblique incision and the interventricular septum is then incised, thus splaying open the annulus. A piece of Dacron is sewn into the interventricular septum and up into the annulus and then used to cover the aorta. The right ventriculotomy is covered with a pericar-dial patch. This is rarely needed if ever.

(5) Another method primarily of historic interest is placement of a valved conduit from the left ventricular apex to abdominal aorta.

MITRAL VALVE DISEASE

Anatomy

The mitral valve is a bi-leaflet structure and as described before the surface area of the anterior leaflet is much greater than that of the posterior leaflet, although the posterior leaflet extends along more of the circumference of the annulus than the anterior leaflet (Fig. 6.5).

The left fibrous trigone has the greatest risk of structural injury to the aortic valve in the region of the noncoronary cusp and left coronary cusp. The right fibrous trigone is in the region of the AV node and bundle of His. At approximately the 7 to 8 o'clock position on the mitral annulus is the region of the AV

Fig. 6.4. Aortic annular enlargement. Posterior commissure between the left and noncoronary cusps is split down to the anterior leaflet of the mitral valve and a Dacron patch is used to enlarge the annulus. Generally, this enables the next larger valve size to be placed.

Fig. 6.4. Aortic annular enlargement. Posterior commissure between the left and noncoronary cusps is split down to the anterior leaflet of the mitral valve and a Dacron patch is used to enlarge the annulus. Generally, this enables the next larger valve size to be placed.

groove and circumflex coronary artery and coronary sinus. It is at this point that the greatest risk to these structures exist, and disruption at this point may lead to catastrophic AV disruption leading to an actual separation of the left atria and left ventricle, i.e. separation of the back wall of the heart itself.

Pathology

Mitral valve disease can be classified as mitral stenosis or mitral regurgitation. Mitral stenosis is nearly always rheumatic in etiology although functionally it may result from such things as a large left atrial myxoma plugging up the mitral valve in a ball-valve type action. Mitral stenosis may lead to increased pulmonary vascular resistance due to spasm of the pulmonary arteries as well as back pressure directly from the mitral valve to the left atrium and then to the pulmonary veins. The elevated pulmonary vascular resistance may lead to right heart failure or tri-cuspid regurgitation.

Mitral regurgitation, like aortic regurgitation, is due to a variety of causes. The most common cause of mitral regurgitation is mitral valve prolapse. This occurs from myxomatous valve degeneration or from localized idiopathic chordal rupture resulting from localized myxomatous degeneration (usually in the postero-medial portion of the posterior leaflet).

The next most common cause of mitral regurgitation is rheumatic mitral regurgitation. If a patient has combined mitral stenosis and mitral regurgitation, the cause is nearly always rheumatic. Rheumatic mitral regurgitation results from two possible etiologies. One is the acute rheumatic process resulting in annular dilation from myocarditis. This occurs from the actual rheumatic infection. However, the most common cause is from the chronic sequelae of rheumatic fever resulting in severe valve thickening, especially involving the posterior leaflet, as well as rolling of the leaflet edges. The chordae may be elongated but more typically are shortened, thickened and fused, and sometimes they are so short that the papillary muscles actually appear to be fused up to the valve leaflet. When describing rheumatic mitral valve leaflets, one must assess the commissural fusion, leaflet thickening, leaflet calcification, leaflet fibrosis and chordal shortening. Other

JUNCTION OFRCC AND NCC OF AORTIC VALVE

JUNCTION OFRCC AND NCC OF AORTIC VALVE

CIRCUMFLEX ARTERY GREAT CARDIAC VEIN AV GROOVE

Fig. 6.5. Mitral valve and neighboring structures.

causes of mitral regurgitation are ischemic mitral regurgitation which has been extensively described previously. Endocarditis is another etiology of mitral regurgitation.

The normal mitral valve area is 4-6 cm2. Symptoms typically start when the area is less than 2 cm2. If less than 1 cm2, the patient is generally symptomatic at rest (New York Heart Association Class IV). The indications for operation for mitral stenosis is New York Heart Association Class III or IV failure. These patients generally require a mitral valve replacement. New York Heart Association Class II patients generally require commissurotomy but do not necessarily require a valve replacement. Generally, a patient who has a mitral valve area less than 1.5 cm2 or a gradient across the mitral valve of greater than 15 mm requires some mitral valve procedure, be it a commissurotomy or a mitral valve replacement. For mitral regurgitation, the indications again are more vague than those for mitral stenosis. The indications for mitral regurgitation are the same as those for aortic insufficiency. Like aortic insufficiency, mitral regurgitation is a condition of volume overload of the ventricle. New York Heart Association Class III or IV is an indication for mitral valve replacement for mitral regurgitation. Those New York Heart Association Class I or II patients are generally not operated on for mitral regurgitation unless they have signs of impending heart failure and have diminution of ventricular function indices such as diminished left ventricular ejection fraction of less than 40% or an ejection fraction which worsens after a stress test. Left ventricular enlargement with an enlarged cardiac to thoracic ratio is an indication for surgery as it is in aortic insufficiency. Again, once a patient develops signs of failure with mitral regurgitation, the disease has been longstanding and the changes may not be reversible.

An interesting phenomenon that occurs postoperatively in patients who undergo mitral valve replacement for mitral regurgitation is that their ejection fraction may actually worsen. This is because of the increased afterload after mitral valve replacement. In other words, one has eliminated the path of least resistance from the ventricle back up into the atrium and now the ventricle can only eject out of the aorta. This results in a higher left ventricular filling pressure on the Starling's curve and may result in a reduced ejection fraction (Fig. 6.6). There is some evidence that preservation of the chordae maintains left ventricular geometry and prevents this increase in left ventricular and diastolic filling pressure, thus keeping the patient on a favorable p ortion of the Starling curve. Hence, chordal preservation is recommended in cases of mitral valve replacement for mitral regurgitation.

After aortic valve replacement for aortic insufficiency, conversely ejection fraction can improve as left ventricular filling pressure decreases because of relief of the aortic insufficiency. Therefore one may move to a more favorable position on the Starling's curve.

Technique of Mitral Valve Replacement

A standard median sternotomy incision is performed. The aorta is cannulated. Separate cannulas are placed in the superior vena cava and inferior vena cava, i.e.

AFTER MVR FOR MITRAL REGURG

LV END DIASTOLIC VOLUME (LVEDV)

PRIOR TO MVR FOR MITRAL REGURG I

AFTER MVR FOR MITRAL REGURG

Fig. 6.6. Starling curve depicting a shift of myocardial performance to a less favorable position after mitral valve replacement for mitral regurgitation. The decom-pr ession of the left ventricle into the left atrium has been eliminated, increasing the LVEDV and worsening the ejection fraction.

bi-caval cannulation, because this permits increased mobility of the left atrium which improves exp osure of the mitral valve. The most common difficulty associated with mitral valve replacement is inadequate exp osure of the valve. Techniques that can be used to improve visualization of the mitral valve include incision along the superior vena cava and inferior vena cava to mobilize these; separate cannula-tion of the superior and inferior vena cava; mobilization of the right superior pulmonary vein to prevent tethering down of the left atrium; and extensive mobilization of the undersurface the rectus fascia and inferior portion of the wound to improve the opening into the chest.

After the aorta and cavae are cannulated, an antegrade plegia cannula is placed followed by a retrograde plegia cannula through the right atrium into the coronary sinus. After cardiopulmonary bypass is instituted, 10 cm pressure is applied to the lungs and a left atrial vent is placed via the right superior pulmonary vein and put on active suction. The aorta is cross-clamped and antegrade plegia is used to arrest the heart followed by retrograde cold blood cardioplegia. The left atrial vent is turned off and an incision is made in the left atrium alongside the groove just anterior to the right superior pulmonary vein. This groove corresponds to the interatrial septum (Fig. 6.7a).

The incision in the left atrium is extended proximally underneath the superior vena cava and distally underneath the inferior vena cava. Another approach is the transatrial, transeptal approach of Dubost (Fig. 6.7b). A mitral valve retractor is positioned and held by the first assistant. A traction stitch is placed in the anterior leaflet and mitral valve and pulled down to improve exposure of the mitral valve (Fig. 6.8). A knife is used to incise the base of the anterior mitral leaflet just sufficiently to place 2-0 pledgetted Ethibon stitch in the annulus at 12 o'clock to put downward traction on the annulus to improve exposure. This is a critical maneuver in cases of difficult mitral valve exposure and makes a sometimes impossible task fairly easy. The pledgetted Ethibond stitches are placed from the atrial into the ventricular aspect as the anterior leaflet is serially excised out. This permits seating of the valve eventually in the intra-annular position rather than the supra-annular position, differing from aortic valve replacement. This is the recommended valve seating arrangement suggested by St. Jude's corporation, since

Fig. 6.7a. Mitral valve exposure. Standard mitral exposure. Left atriotomy begins just anterior to right superior pulmonary vein. This affords excellent exposure of the mitral valve in most cases.

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