Manouguian Procedure

Anatomy and Physiology

Anatomy

The aortic root connects the left ventricular outflow tract to the ascending aorta and out to the systemic circulation. The aortic root is a very complex system with multiple components that make this area very unique, as it has the ability to maintain hemodynamic conditions during varying demands. The aortic root is made up of very distinct parts that function in a well-coordinated fashion as a complete unit to propel fluids forward and also perfuse the coronary arteries. The aortic root is made up of the aortic valve with its semilunar leaflets and attachments, sinuses of Valsalva, the sinotubular junction, and the aortic annulus. The aortic root has three sinuses, the left and right sinuses give rise to their respected coronary arteries. The third sinus, which is called the noncoronary sinus, does not have a coronary artery arise from its sinus. The aortic valve has three leaflets named according to their location: left, right, and posterior. The leaflets may also be referred to from their respected coronary sinus. Between each leaflet lies a commissure which separates the leaflets. The sinotubular junction separates the aortic root from the ascending aorta. The aortic annulus is the area where the leaflets attach as there is no distinct anatomical or histological ring structure. The annulus is the smallest area in diameter between the left ventricle and aorta. The annulus is the area where the aortic valve is measured for the placement of the prosthetic valve. The aortic outflow tract is best viewed when looking down the tract into the annulus.[3][4]

Physiology 

The aortic valve and outflow tract anatomical components play a large role in the patient’s physiology, especially when there is pathological disease present. The discussion of aortic regurgitation and stenosis physiological components are discussed elsewhere. 

The size of the aortic valve replacement should be proportional to the patient’s body surface area to help maintain physiologic homeostasis of the aortic root. Patient prosthesis mismatch was first discussed in the 1970s. A patient prosthesis mismatch occurs when the effective orifice area of the newly inserted prosthetic valve is less than that of a normal human valve. The accepted patient prosthesis mismatch definition is defined as a prosthetic valve effective orifice area indexed to a body surface area less than 0.85 cm2/m^2. A severe patient mismatch is considered when it is less than 0.65 cm^2/m^2. When evaluating patients for patient prosthesis mismatch possibility in the pre-operative setting, we can multiply the patient's body surface area by 0.85 cm^2/m^2, which will give the minimum-sized effective orifice area that will ultimately tell us the smallest sized valve we can place while avoiding patient prosthesis mismatch. One of the main issues with patient prosthesis mismatch is the creation of very high transvalvular pressure gradients through the newly placed valve.

The high transvalvular gradients cause an interruption in the normal flow patterns through the root, thus causing an inability to maintain the cardiac output requirement. Patient prosthesis mismatch has been reported to be as high as 20% to 70% after aortic valve replacement, which has proven to have more cardiac events and poor outcomes in patients with higher patient prosthesis mismatch severity. Patient prosthesis mismatch is tolerated better in higher body mass index patients. If patients have impaired left ventricular function prior to surgery, it is imperative to avoid patient prosthesis mismatch as studies have shown impaired left ventricular function has decreased survival and more heart failure symptoms.[5][6][7]

Indications

The following are the indications of performing a Manouguian procedure:

• Enlargement of the aortic root, which may be small, calcified, or fibrotic in adults to avoid patient prosthesis mismatch

• Enlargement of small aortic roots in children when undergoing aortic valve replacement[8][9]

• Performing a root enlargement so a larger bioprosthetic valve may be placed in a patient who may later require a valve in valve replacement through transcatheter aortic valve replacement (TAVR)[10]

Equipment

When performing the Manouguian technique, the following are necessary: 

• Operating room

• Cardiopulmonary bypass machine

• Sterile drapes, gowns, gloves

• Cardioplegia

• Echocardiography ultrasound

• Swan-Ganz catheter

• Sternotomy saw

• Operative instruments and all supplies (sutures, pledgets)

• Graft material (dacron, glutaraldehyde prepared bovine pericardium, polytetrafluoroethylene)

Personnel

• Cardiac surgeon

• Anesthesia team

• Cardiologist

• OR nursing staff

• First assistant

• Perfusionist

• Scrub techs

• Echo tech

Preparation

Patients undergoing preoperative workup for aortic valve replacement should undergo multiple tests. The main imaging modality to assess the aortic outflow tract is a transthoracic cardiac echo, but it can also be viewed using transesophageal echo, computed tomography (CT) scan, or magnetic resonance imaging (MRI). The main goal is to view the entire aortic root in multiple different planes to get the most precise measurements. Patients will need to be assessed for associated coronary artery disease so they will need to undergo stress testing and left heart catheterization. After the cardiac angiogram is performed and the possible need for coronary bypass grafting or stenting is ruled out, the anatomy and course of the arteries should be studied in great detail to rule out any aberrant courses. An echocardiogram should be performed to look at the left ventricle for signs of hypertrophy and assess the overall function of the heart. The patient can also be evaluated for subaortic stenosis which can be addressed during a myectomy if needed. CT imaging and echocardiogram can identify any ascending aorta calcification or aneurysmal dilation. An electrocardiogram should be performed to assess for any preoperative cardiac electrical conduction abnormalities such as atrial fibrillation, which can also be addressed during the operation.[11] 

The choice of the aortic valve should be made prior to the operating room. There should be a long discussion with the patient regarding which type of valve is best for their anticipated longevity and if they can tolerate anticoagulation. If a patient prosthesis mismatch is possibly suspected after preoperative assessment with the prosthetic valve that was going to be placed, a decision will need to be made after discussing all the options. A different valve can be used that has a larger effective orifice area and a lower profile such as a newer mechanical valve, a stentless bioprosthetic valve, or an aortic root enlargement procedure can be continued with the placement of a larger prosthetic valve. The last option is to continue with the original plan of aortic valve size with acceptance of patient prosthesis mismatch and the associated clinical conditions.[12]

Preoperative planning should be aimed at reviewing all the imaging to give the patient the best chance at avoiding patient prosthesis mismatch. This includes discussing the best type of valve for the patient and the best aortic enlargement technique to provide the best overall outcome.[13]

Technique or Treatment

The patients are taken to the operating room, then prepped and draped in the usual sterile fashion. All preoperative imaging should be reviewed, and the decision to perform an aortic valve replacement with aortic enlargement procedure should be discussed after the findings of a small aortic annulus. A median sternotomy can be performed using a sternal saw. Cardiopulmonary bypass can be started with cannulation of the aorta and right atrium. A left heart venting catheter can be placed if needed. After cross-clamping the aorta and giving cold cardioplegia with circulatory arrest, the aorta can be examined. A transverse aortotomy can be performed with full exposure of the aortic valve and aortic root. The aortic valve can be fully excised with further examination of the aortic annulus. The annulus can then be measured intraoperatively with sizers. The measurements of the annulus and the patient's body surface can then be discussed to consider how much valve diameter they will gain by performing the Manouguian technique. Usually, patients can have a valve 1 to 2 sizes larger placed after performing the posterior aortic enlargement technique.

After making the decision to proceed with aortic root enlargement, either a modified Manouguian or a traditional Manouguian can be performed. To perform the modified Manouguian technique, an incision is made by extending through the commissure between the noncoronary cusp and the left coronary cusp onto the subaortic curtain. The traditional Manouguian involves making a similar incision between the noncoronary and left coronary cusps. The incision is then carried on to the anterior leaflet in the mitral valve and roof of the left atrium. The incision can almost be extended to the free edge of the mitral valve for added enlargement. Careful technique should be used to ensure the incision is made in the middle of the anterior leaflet. The newly created defect can be reconstructed with glutaraldehyde prepared bovine pericardium, autologous pericardium, or a Dacron patch. The patch can be cut into a diamond shape and can then be sewn in place using a running prolene suture starting at the apex of the reconstruction but allowing room for placement of the aortic valve sutures into the annulus. This allows for the widest aortotomy for placement of a larger sized aortic valve. At this point, the aortic annulus can then be remeasured.

The pledgeted valve sutures can be placed around the aortic annulus. The valve can then be sewn in place. The aortotomy can then be closed using the remaining patch for the closure of the aorta in a running continuous fashion. If the left atrial wall is small and able to be closed, it can be closed in continuity with the patch closure. If the left atrium is unable to be closed, a second patch will need to be used to close the left atrial defect.  A transesophageal echo can be performed to evaluate the new aortic enlargement and the valve. The patient can then be weaned from cardiopulmonary bypass with decannulation. The chest can then be closed with completion of the surgery.

Complications

Research has shown minimal added risk when performing this technique. Patients undergoing aortic root enlargement techniques do have higher perioperative morbidity and mortality when compared to those without enlargement. However, when strictly comparing only aortic valve replacements with aortic enlargement procedures with no added operative procedures, there was no difference noted. The aortic enlargement patient group was found to have lower risks of patient prosthesis mismatch. Despite longer on pump aortic cross-clamp time, patients who underwent aortic valve replacement with aortic enlargement procedure did not experience higher rates of myocardial infarction, stroke, complete heart block/permanent pacemaker implantation, or reoperation for bleeding.[14]

• Infection

• Bleeding

• Damage to aortic outflow tract structures

• Damage to the conduction system

• Damage to mitral valve causing significant mitral regurgitation[15]

• Detachment of aortic patch[16]

• Dysfunction of the aortic valve if enlargement too great 

• Patient prosthesis mismatch[5][17]

• Reduced exercise tolerance

• Delayed left ventricular regression

Clinical Significance

Aortic valve replacement with the Manouguian technique for placement of a larger aortic valve can be life-changing for patients as it allows them to have increased cardiac output while allowing placement of a larger aortic valve to help avoid patient prosthesis mismatch.[18]

While there have been multiple studies performed looking at the increased operative time, increased cross-clamp time, and safety of aortic root enlargement procedures, they have proven to add minimal cross-clamp time and do not add to the cost of the procedure. Many studies have shown that enlarging the aortic root even in the setting of calcified aortic walls is worth the risk of avoiding patient prosthesis mismatch as enlargement of the aortic root has proven to be safe and reproducible.[19][20]

If patients have undergone previous mitral valve surgery, they are not candidates for the Manouguian or Nicks technique. They could possibly undergo a Konno procedure, which does allow previous mitral valve replacement. 

Avoid enlarging the annulus too much as this can cause aortic valve dysfunction postoperatively. Likewise, if you put in a valve that is too large for the annulus, this can cause excessive pressure to be placed on the surrounding conduction system and cause cardiac dysfunction or heart block. 

Postoperatively all patients should undergo transthoracic echocardiography to not only view the new valve that was placed but to determine the new indexed effective orifice and pressure gradient across the valve.

Careful planning in the preoperative and intraoperative settings will allow the best overall outcome for aortic root enlargement techniques along with other operative interventions that need to be performed.

Enhancing Healthcare Team Outcomes

The Manouguian procedure has allowed for operative intervention in patients with small aortic outflow tracts and has helped to decrease patient-prosthesis-mismatch. All patients undergoing aortic valve replacement with the need for a possible root enlargement procedure should undergo preoperative discussion at interprofessional meetings to discuss complex cases.

Preoperative imaging with reviewing the patient's aortic root dimensions along with their body surface area will allow the team to prepare for the possible need for aortic root enlargement and valve sizing. While a successful aortic root enlargement may decrease the overall morbidity and mortality of the patient long term, it may increase the cross-clamp and bypass times, thereby potentially increasing the perioperative morbidity and mortality of the patient. For this reason, all healthcare team members must be in constant communication and efficient in their practice to enhance better outcomes. As with any other procedure, effective preparation will enhance the healthcare team outcomes.

Having a detailed plan in place, along with a preoperative discussion, will help to prevent any poor intraoperative decision making. The perfusionist and anesthesia team must be informed if longer cross-clamp times are needed to ensure adequate cardioplegia and hypothermia for the best myocardial protection. Postoperative management requires a team monitoring for many things such as post-op bleeding, arrhythmias, or other conduction issues, and pain control.

Nursing, Allied Health, and Interprofessional Team Interventions

An interprofessional team is needed in order to execute every successful procedure. Cardiac surgeons perform this procedure while general anesthesia from either an anesthesiologist or a certified registered nurse anesthetist (CRNA) is provided pre and post cardiopulmonary bypass. The perfusion team maintains the patient's hemodynamics while on cardio-pulmonary bypass. The OR staff, including the nurses and scrub techs, are also very important as they assist the surgeon throughout the entire case.

Postoperatively, cardiac intensivists help aid in the management of the patient's care along with cardiologists. Echo techs are available to evaluate the effectiveness of the valve through either transthoracic or transesophageal echocardiogram. Postoperatively, rehab specialists and physical therapy teams play a pivotal role in preparing the patient for discharge home. It is clear that the Manouguian procedure is one of great detail and requires precision. While there are various different roles that must be taken throughout the patients stay, interprofessional interventions and communication are vital to the success and outcomes of the patient.

Nursing, Allied Health, and Interprofessional Team Monitoring

Interprofessional monitoring is crucial to not only the success of the operation but to the overall outcomes of the patient's entire hospital course. To prevent any complications from occurring during the Manouguian procedure, all team members must be monitoring the patient. The anesthesia and perfusion teams are responsible for close-knit communication and keeping the patient stable throughout the procedure. This entails an adequate amount of sedation while maintaining stable perfusing vitals while on cardio-pulmonary bypass. The OR staff helps by obtaining the correct surgical supplies, prepping, positioning the patient, and helping throughout the operative case. While all team members have specific physical responsibilities, they are all responsible for monitoring the patient. Any complication may occur at any point in time. Having multiple people prepared for any event to occur helps to decrease poor outcomes.