Aortic Root Enlargement Techniques
Keywords: Aortic Root Enlargement Techniques, Operations for Valvular Heart Disease
This chapter discusses the commonly used aortic root
enlargement techniques that increase the diameter of the aorta with small
annulus and allow the implantation of larger prosthetic valves with better
hemodynamic performance. In addition, some other surgical considerations in
patients with small aortic root will also be discussed.
Introduction
· Aortic valve replacement (AVR) is
one of the most commonly performed operations in cardiac surgery. It is not
only effective in alleviating symptoms in patients suffering from aortic valve
disease, but also improves survival. However, in patients with a small aortic
annulus, the benefits of this operation are dependent on the surgeon’s ability
to avoid patient-prosthesis mismatch (PPM). PPM was first described by
Rahimtoola in 19781 as: “Mismatch can be considered to be present when the
effective prosthetic valve area, after insertion into the patient, is less than
that of a normal human valve.” Pibarot and Dumesnil2 defined PPM as
a prosthetic valve effective orifice area (EOA) indexed to a body surface area
of less than 0.85 cm2/m2. PPM has been shown to be
associated with a number of adverse outcomes, including worse hemodynamic
performance, reduced left ventricular mass regression, and lower survival. If
PPM is anticipated with the type of prosthesis that is being planned, the
surgeon can either implant another type of prosthesis with a larger EOA, such
as a stentless bioprosthesis, a new-generation mechanical prosthesis, or an
aortic homograft, or he or she can surgically enlarge the aortic root to
accommodate a larger prosthesis of the same type.
·
The well-known and documented
repercussions regarding PPM3 have heightened the desire of surgeons to master
aortic root enlargement techniques. In this chapter, we will discuss the
commonly used aortic root enlargement techniques, including posterior enlarging
techniques, such as the Nicks4 and Manougian5 procedures,
and anterior enlarging strategies such as the Konno-Rastan
aortoventriculoplasty and Ross-Konno AVR procedure.6-8 These
techniques increase the diameter of the aorta with a small annulus and allow
the implantation of larger prosthetic valves with better hemodynamic
performance. In addition, some other surgical considerations9-11 in
patients with a small aortic root will also be discussed.
· It is important to evaluate adult
patients for concomitant coronary artery disease with stress testing and left
heart catheterization. The coronary angiogram should be carefully studied for
anomalous origin of either main coronary artery, and the location of the first
septal branch of the left anterior descending artery should be identified if
the pulmonary autograft operation is under consideration.
· The echocardiogram should be
reviewed for evidence of left ventricular hypertrophy and to assess left
ventricular function. Careful preoperative measurement of the aortic annulus
can guide intraoperative valve sizing to avoid PPM and to identify patients in
whom aortic root enlargement is likely. Concomitant subaortic stenosis should
be identified because this can be addressed with myotomy/myectomy if required.
·
The echocardiogram can also
demonstrate concomitant poststenotic dilation of the ascending aorta or a true
ascending aortic aneurysm. If the pulmonary autograft operation is under
consideration, the pulmonary valve should be interrogated for insufficiency or
other abnormalities. It is important to note mitral valve structure and degree
of insufficiency on the preoperative echocardiogram because these may be
altered with aortic root enlargement.
·
Adult congenital patients, in
particular, who may have a history of associated arch anomalies may require a
computed tomography (CT) or magnetic resonance imaging (MRI) scan to ensure
that these structures and potential anatomic anomalies are well defined.
· A resting electrocardiogram should
be reviewed to identify any preoperative conduction abnormalities. Patients
should be evaluated for concomitant atrial fibrillation or other rhythm
disturbances that can be addressed during the operation.
·
The aortic root consists of the
aortic annulus, aortic cusps, aortic sinuses, and the sinotubular junction. The
aortic root represents the outflow tract from the left ventricle. It provides
supporting structures for the leaflets of the aortic valve and forms a bridge
between the left ventricle and ascending aorta. All aortic root enlargement
procedures are described based on an anatomic understanding of the coronary
artery ostia, coronary sinuses, and commissures. Special attention should be
paid to the relationship of these structures to the conduction system, the
mitral valve and its apparatus, and the interventricular septum. In addition,
the ability to distinguish the membranous portion of the septum is of critical
importance.
· The left ventricular outflow tract
is best appreciated when viewed directly down into the aortic annulus. The
aortic valve and pulmonary valve, although closely related, have different
planes. The infundibular portion of the right ventricle elevates the plane of
the pulmonary valve and trunk above the aortic valve, placing the pulmonary
valve higher and more posterior. The aortic valve shares fibrous continuity
with the anterior leaflet of the mitral valve (Fig. 11.1).
· The space between the fibrous
attachments of the aortic valve leaflets is termed the interleaflet triangle.
These triangles are more flexible than the other segments of the aortic root
(Fig. 11.2). The commissure between the right and left coronary cusps is
usually located directly across from the pulmonary artery, with a mirror image
configuration of the pulmonary valve cusps. The commissure between the right
coronary cusp and noncoronary cusp is located anteriorly and is closely related
to the interventricular septum and the conduction system. The commissure
between the left coronary cusp and noncoronary cusp is located more posterior
and to the right. This commissure is located opposite the middle portion of the
anterior leaflet of the mitral valve (see Fig. 11.2).
·
Various portions of the aortic
valve are above, at, and below the true aortic annulus. The tops of the
commissures rest above the aortic annulus, well into the sinus portion of the
aorta. The central portions of the leaflets meet below the aortic annulus
during diastole, within the left ventricular outflow tract. The true
aortoventricular junction is between these two levels (Fig. 11.3).
· The right coronary artery arises
from the right coronary sinus and courses rightward in the atrioventricular
groove. The left main coronary artery is short and branches immediately into
the left circumflex and left anterior descending arteries. The left circumflex
artery courses laterally in the atrioventricular groove, being near the
posterior mitral annulus. The left anterior descending artery lies posterior to
the pulmonary artery in its proximal portion before coursing down the anterior
interventricular groove. The first septal branch of the left anterior
descending artery lies directly behind the posterior leaflet of the pulmonary
valve (Fig. 11.4).
Step 3. Operative Steps
· Of paramount importance,
regardless of any proposed technique, is exposure of the left ventricular
outflow tract. In many cases a complete division of the ascending aorta,
approximately 1 cm above the sinotubular junction, provides excellent exposure to
the aortic valve and left ventricular outflow tract. Alternatively, a
spiraling-type incision down into the noncoronary sinus may be used if
extensive enlargement is not anticipated.
·
The aortic valve is excised and
the annulus is débrided. A careful determination is made as to the minimum size
of prosthesis that would be acceptable for the patient’s body size. If root
enlargement is indicated to achieve an adequately sized prosthesis, the
appropriate technique is used.
2. Root Enlargement
· Posterior enlargement of the
aortic root is performed by either the Nicks-Nunez or Rittenhouse-Manouguian
technique (Fig. 11.5). Both approaches are arguably the most commonly accepted
and widely used techniques for aortic root enlargement and will be a large
focus of this chapter. The Nicks-Nunez method is a vertical incision through
the commissure between the left coronary cusp and noncoronary cusp, extending
down into the interleaflet triangle. Limiting the incision to just the
interleaflet triangle can enlarge the root sufficiently by 2 to 3 mm. If
greater enlargement is required, the incision can be extended further into the
anterior leaflet of the mitral valve and the roof of the left atrium. The
Rittenhouse-Manouguian method is a vertical incision through the midportion of
the noncoronary sinus, through the aortic annulus and into the anterior leaflet
of the mitral valve and roof of the left atrium. The incisions in the anterior
leaflet of the mitral valve can be extended almost to the free edge of the
leaflet, dramatically enlarging the outflow tract.
· Anterior enlargement of the aortic
root, or aortoventriculoplasty, is performed according to the technique
described by Konno and Rastan (Fig. 11.6). A vertical aortotomy is performed,
and the incision is continued into the right coronary sinus, well leftward of
the right coronary artery. The incision is then extended through the aortic
annulus, near the commissure, between the right and left coronary leaflets. The
incision is carried into the interventricular septum only as far as necessary
to achieve the desired enlargement. Deep incisions place the first septal
branch of the left anterior descending artery at risk for injury. A second
incision is made on the right ventricular free wall to enlarge the right
ventricular outflow tract.
· After the aortic root has been
enlarged sufficiently, a diamond-shaped patch of autologous pericardium,
prosthetic material, or composite of both is fashioned. One end of the patch is
inserted into the distal end of the enlargement at the level of aortic-mitral
continuity if the incision is only into the interleaflet triangle. Interrupted
sutures with pledgets are preferred because the interleaflet triangle lacks
fibrous strength. The sutures are then passed through the sewing ring of the
aortic valve prosthesis. The remainder of the valve sutures are placed through
the aortic annulus in standard fashion (Fig. 11.7).
·
The patch is then tailored for
closure of the aortotomy if a spiraled incision has been used, or it is
transected flat at the level of the transverse aortotomy and incorporated as
part of the reanastomosis of the aortic root to the ascending aorta (Fig.
11.8).
·
If the incision has been carried
farther into the left ventricular outflow tract by crossing into the anterior
leaflet of the mitral valve and left atrium, reconstruction is begun by placing
the patch into the deepest portion of the incision. The defect in the anterior
leaflet is repaired with the patch. Interrupted sutures without pledgets are
used for accuracy and strength (Fig. 11.9).
· At the level of the aortic
annulus, interrupted sutures with pledgets are placed and passed, first through
the patch and then through the prosthetic valve. The remainder of the valve
sutures are placed through the aortic annulus in standard fashion. If the left
atrial wall is flexible, and the defect is small, the left atrial wall can be
approximated directly to the patch. Otherwise, a second patch is fashioned to
reconstruct the left atrial defect (Fig. 11.10).
· The patch is then tailored for
closure of the aortotomy or incorporated as part of the aortic reanastomosis,
as previously described.
· After enlargement of the root by
extending the incision across the noncoronary portion of the aortic annulus
into the anterior leaflet of the mitral valve and roof of the left atrium, a
diamond-shaped patch of either autologous pericardium or prosthetic material
(e.g., polytetrafluoroethylene [PTFE] or Dacron) is fashioned. As with the
Nicks-Nunez method, reconstruction is begun by placing the patch into the
deepest portion of the incision. The defect in the anterior leaflet is repaired
with the patch, using interrupted or continuous sutures without pledgets for
accuracy and strength (Fig. 11.11).
· At the level of the aortic
annulus, interrupted sutures with pledgets are placed and passed, first through
the patch and then through the prosthetic valve (Fig. 11.12A). The remainder of
the valve sutures are placed through the aortic annulus in standard fashion
(see Fig. 11.12B). If the left atrial wall is flexible, and the defect is
small, it can be approximated directly to the patch. Otherwise, a second patch
is fashioned to reconstruct the left atrial defect (see Fig. 11.12C).
·
The patch is then tailored for
closure of the aortotomy if a spiraled incision has been used, or it is
transected flat at the level of the transverse aortotomy and incorporated as
part of the reanastomosis of the aortic root to the ascending aorta.
·
The aortic root is mobilized by
careful dissection anteriorly between the right coronary sinus and the
pulmonary artery. This dissection is performed to the left side of the right
coronary artery and is carried down to the level of the aortic annulus. The
aortic root is enlarged with an incision through the right coronary portion of
the aortic annulus, near the commissure, between the right and left coronary
cusps. The incision is deepened into the interventricular septum, and a
matching incision is made on the right ventricular free wall to enlarge the
right ventricular outflow tract (Fig. 11.13).
· A diamond-shaped patch of
prosthetic material is fashioned and placed deep into the inter- ventricular
septal incision. Continuous sutures are used to attach the patch to the
ventricular muscle, up to the level of the aortic annulus (Fig. 11.14).
· A second triangular patch is
fashioned. Interrupted sutures with pledgets are used to attach the base of the
triangular right ventricular outflow tract patch to the junction of the
diamond- shaped left ventricular outflow tract patch at the level of the aortic
annulus. The sutures are then passed through the sewing ring of the prosthetic
valve (Fig. 11.15). The remainder of the valve sutures are placed through the
aortic annulus in standard fashion, and the prosthesis is secured into
position.
· The right ventricular outflow
tract patch is then folded over the right ventricular free wall defect, and
continuous sutures are used to attach the patch to the ventricular muscle. The
left ventricular outflow tract patch is tailored to close the defect in the
aorta using the continuous suture technique (Fig. 11.16).
· The aortic allograft is prepared
with the attached, intact, anterior leaflet of the mitral valve. A small rim of
donor left atrial tissue is also usually present and should be retained on the
allograft. The remnants of the chordae are removed from the allograft anterior
leaflet. In this fashion, the allograft can be used to reconstruct very large
defects of the aortic root and enlarge the root substantially.
· The aortic valve and sinus tissue
are removed. The coronary arteries are mobilized on generous buttons of sinus
tissue. The left ventricular outflow tract is enlarged posteriorly with either
a Nicks-Nunez or Rittenhouse-Manouguian incision extending down into the
anterior leaflet of the mitral valve (Fig. 11.17).
·
The anterior leaflet of the
allograft is inserted into the defect in the patient’s anterior leaflet and
attached using interrupted sutures, without pledgets, for accuracy and
strength. Care and precision are used for this reconstruction to avoid
distorting the mitral valve and causing undue tension (Figs. 11.18 and 11.19).
· The allograft is attached to the
left ventricular outflow tract using interrupted sutures for accuracy. This
proximal suture line is then reinforced with biologic glue. If the left atrial
wall is flexible, and the defect is small, it can be approximated directly to
the rim of the atrial wall of the allograft. Otherwise, a patch of autologous
pericardium or allograft aorta is fashioned to reconstruct the left atrial
defect (Fig. 11.20).
· The coronary artery buttons are
attached in the appropriate position to the aortic allograft with continuous
sutures. The allograft is attached to the ascending aorta with continuous
sutures, and all suture lines are reinforced with biologic glue.
· Severe hypoplasia of the left
ventricular outflow tract in young patients can be successfully managed with
combined aortoventriculoplasty and pulmonary autograft replacement of the
aortic valve.
· Bicaval cannulation and
cardiopulmonary bypass are initiated, and a transverse aortotomy is performed
after cardioplegic arrest. The aortic valve is excised, and the annulus is
débrided. The sinus tissue is removed, and the coronary arteries are mobilized
on generous buttons of sinus tissue. The pulmonary artery is carefully
dissected off the aorta and top of the right ventricle until the ventricular
muscle fibers are identified, running in a perpendicular orientation. This
portion of the dissection is begun at the commissure between the left and right
coronary cusps and carried underneath the pulmonary artery. The pulmonary
artery is transected near the bifurcation, and the pulmonary valve is carefully
inspected.
·
A small right-angled clamp is
passed well below the pulmonary annulus, along the line with the anterior
commissure. The clamp is pushed out through the right ventricular free wall,
and the right ventricle is divided well below the pulmonary annulus, with
direct visualization of the pulmonary valve leaflets. Scissors are used to
divide the right ventricular outflow tract anteriorly, leaving a generous
portion of the free wall with the autograft. Sharp dissection of the
ventricular septum with a knife is used to separate the pulmonary trunk from
the right ventricle to protect the first septal branch of the left anterior
descending coronary artery.
· A vertical incision is made
through the aortic annulus, near the commissure between the right and left
coronary leaflets. The incision is carried into the interventricular septum to
enlarge the left ventricular outflow tract (Fig. 11.21). The right ventricular
muscle portion of the autograft is inserted deep into the left ventricular
outflow tract (Fig. 11.22A), and interrupted sutures are used to attach it to the
defect in the interventricular septum (see Fig. 11.22B). The autograft is then
attached to the aortic annulus with interrupted sutures. The sutures are
secured, and the suture line is reinforced with biologic glue.
· The coronary arteries are
reimplanted onto the autograft in the appropriate position using a continuous
suture technique. The autograft is anastomosed to the ascending aorta with a
continuous suture technique, and the suture lines are reinforced with biologic
glue.
· The right ventricular outflow tract
is measured, and an appropriately sized pulmonary homograft is selected. The
distal end of the pulmonary homograft is attached to the bifurcation of the
patient’s pulmonary artery with continuous sutures. The proximal portion of the
pulmonary homograft is attached to the right ventricular outflow tract using
continuous sutures. Part of the suture line may include the pulmonary
autograft. If additional enlargement of the right ventricular outflow tract is
necessary, a patch of autologous pericardium is used to augment the right
ventricular free wall.
· In patients for whom the
conventional posterior root enlargement technique is not wide enough to implant
a prosthetic valve of desired size, two-directional enlargement involving a
combination of both posterior and anterior enlargement techniques could be used9
(Fig. 11.23). For this technique, the posterior enlargement is performed first,
and then an additional aortotomy is made anteriorly and extended to the
ventricular septum. The aortic annulus could be enlarged by 68% after this
two-directional enlargement technique.
· The aortotomy is made obliquely
toward the noncoronary sinus. The aortic annulus is measured with dilators
after removal of the aortic valve, and posterior enlargement is performed
according to the Nicks or Manouguian procedure. An additional anterior
enlargement is then made just to the commissure, between the left and the right
coronary cusps. Reconstruction of the annulus and repair of the aortotomy are
carried out with a bifurcated Dacron patch.
· In patients for whom the
preoperative evaluation has also revealed subaortic narrowing or obstruction, a
concomitant myotomy or myectomy may be an option, in addition to AVR. Exposure
is obtained by either an aortotomy or a complete transection of the ascending
aorta. The coronary artery ostia are then identified to avoid any iatrogenic
injury. In addition, the valve leaflets, commissures, and area of the presumed
conduction system are also well identified and protected during the process of
myectomy or myotomy.
· Optimal visualization of the
ventricular septum is facilitated by posterior displacement of the anterior
wall of the left ventricle with a sponge or sponge stick. A small suction
cannula may also be placed across the aortic annulus to retract the anterior
mitral valve leaflet and papillary muscles posteriorly and rightward away from
the ventricular septum. The myotomy or myectomy incision is made using a no. 11
blade scalpel, beginning the incision at the midventricular level and extending
upward to within 8 to 10 mm of the nadir of the annulus of the right coronary
cusp (Fig. 11.24). Any incision made at the base of the ventricular septum that
is more rightward than the nadir of the right cusp will injure the membranous
septum and conduction tissue, with concerns for resultant complete heart block.
A second longitudinal incision parallel to the first incision is made to be
carried up to within 8 to 10 mm of the aortic annulus, at the commissure
between the right and left coronary cusps. The area to the left of this incision
is the left ventricular free wall. These two incisions are joined superiorly,
and a hook may be used to allow for better traction of the proposed resected
muscle, which can be easily elevated. A deep wedge of septum is then resected,
beginning at the base of the septum and working toward the midventricle.
· By carefully understanding
preoperative transthoracic echocardiography (TTE) and/or transesophageal
echocardiography (TEE) measurements, care can be taken to avoid the iatrogenic
creation of a ventricular septal defect.
·
In patients with a small aortic
annulus that needs aortic root replacement, Bentall-type aortic upsizing
procedures can be considered.
Step 5. Postoperative Care
· Standard postoperative management
in the intensive care unit includes ventilator support, continuous cardiac
output monitoring with a pulmonary artery catheter, and other routine care
measures for a cardiac surgical patient. Right and left atrial pressure lines
are useful for direct continuous measurement of atrial pressures.
· A judicious balance between fluid
resuscitation and inotropic support is required. Many of these patients have
left ventricular hypertrophy, and administration of relatively small amounts of
intravenous fluids will drastically alter filling pressures. In addition, the
thick ventricular myocardium is sensitive to inotropes and may be irritable
after intraoperative myocardial ischemia. The preoperative status of left
ventricular hypertrophy and function, in addition to the appearance of the left
ventricle on TEE during completion of the procedure, will allow for a framework
to drive decision making.
· Efforts should be made to avoid
hypertension because this will place undue strain on the suture lines of the
left ventricular outflow tract reconstruction. Placement of an intraaortic
balloon pump is preferable to high doses of inotropes and aggressive fluid
resuscitation.
· A high index of suspicion for
coronary insufficiency should be held for every patient, whether a full root
replacement or simple AVR was performed. Full root replacement with coronary
reimplantation can result in kinking of a coronary artery. Prosthetic valve
replacement can result in coronary ostial obstruction by a valve stent or
sewing ring.
· The typical presentation of
coronary insufficiency is the inability to wean from cardiopulmonary bypass.
Intraoperative TEE is essential to demonstrate impaired ventricular function,
with or without electrocardiographic evidence of coronary ischemia. If a simple
valve replacement was performed, the prosthesis should be removed and
reinserted or a different prosthesis selected. If a full root replacement was
performed, the safest approach is to perform coronary artery bypass surgery on
the affected coronary artery.
Step 6. Pearls and Pitfalls
·
Careful and thoughtful
preoperative and intraoperative planning will avoid PPM. A value of less than
0.85 is indicative of PPM and may result in reduced recovery of the left
ventricle early and late after operation. Effort should be made to keep the
ratio above 1.0 for all patients.
· Root enlargement and root
replacement operations are extensive operations, with multiple suture lines
outside the heart exposed to systemic arterial pressure. The application of
biologic glue can help control intraoperative bleeding by sealing the needle
holes. Biologic glue does not seal gaps in an anastomosis, and this feature
allows identification of areas that require additional suture or pledgets to
control hemostasis. A thorough survey of all suture lines, especially those
located in the difficult to reach and visualized posterior locations and around
the coronary buttons, should be completed prior to the administration of
protamine and other blood products.
· The first septal branch of the
left anterior descending artery should be meticulously preserved during
pulmonary autograft harvest and pulmonary homograft implantation. Injury to the
first septal branch can result in significant left ventricular dysfunction,
which may not fully recover over time.
·
The incisions described in this
chapter for root enlargement are placed in areas of the aortic root that avoid
the conduction system. Particular attention should be paid to the area below
the commissure, between the right and noncoronary leaflets, extending leftward
under the right coronary artery ostium, to avoid injury to the conduction
system. In addition, attempts to insert a rigid valve prosthesis tightly into a
small aortic annulus can produce excessive pressure on the conduction system,
resulting in dysfunction or heart block.
·
Due to the significant challenges
of future reoperation on the aortic root following any form of enlargement
procedure, great care should be taken to ensure appropriate decision making
regarding prosthesis selection. Surgeons should be well versed in the long-term
outcomes of the various valve prostheses that may be used in the operation.
· Surgeons should be prepared to
perform extensive reconstruction of the aortic root and ascending aorta, as
indicated during surgery. The best long-term outcomes can be expected by
addressing all associated pathologic processes at the initial operation, rather
than leaving behind conditions that could result in early reoperation.
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