Surgical aortic valve replacement (AVR) is a routinely performed procedure for the treatment of patients suffering from severe aortic stenosis. Despite its excellent results, patient prosthesis mismatch (PPM) may ensue when a small-sized valve is implanted in a small aortic root. The increased pressure gradient across the valve with decreased exercise tolerance and delayed regression of left ventricular hypertrophy are among the complications encountered. Various procedures have been described in the literature to enlarge the aortic root to be able to implant a bigger valve thus avoiding PPM.
There are many options for small aortic root, involving posterior aortic root enlargement (ARE) including Nicks, Manougian, Konno-Rastan (anterior enlargement), and sutureless valves. One of the easily performed techniques is the Nicks procedure. The Nicks procedure for aortic root enlargement avoids PPM, allows for a valve in valve placement in the future, and helps to prevent structural valve deterioration.
The aortic root consists of the outflow tract from the left ventricle, the aortic valve, and the junction with the ascending aorta. The aortic valve is a semilunar valve with three leaflets (cusps). The leaflets consist of a right, left, and non-coronary leaflets. Two coronary arteries arise from above their respected leaflets. The aortic valve does not have a discrete annulus like other valves. The non-coronary cusp and left cusp are positioned near the aortomitral valve continuity. Below the commissure of the non-coronary cusp and left cusp lies the subaortic curtain, which is quite fibrous. On the right side of this commissure, the non-coronary cusp is attached superiorly on the left ventricular outflow tract. This area is related to the right atrial wall.
Along the non-coronary cusp and right coronary cusp before reaching the commissure, this area is above the wall containing the atrioventricular node. Nicks procedure is classified as one of the posterior aortic root enlargement procedures along with the Nunez and Manougian techniques. In Nicks procedure, a longitudinal incision is made through the non-coronary leaflet but not through the fibrous body between the aortic valve and the anterior leaflet of the mitral valve. This technique helps to increase the size of the aortic valve by 1 or 2 sizes upwards.
Patient prosthesis mismatch (PPM) was first discussed in the late 1970s. PPM occurs when the aortic annulus is too small, and this causes the prosthetic valve effective orifice area (EOA) when compared to the body surface area to be less than 0.85 cm/m. PPM is associated with poor outcomes such as poor hemodynamic performance, reduced left ventricular mass regression, and decreased survival rates among those with PPM.
When PPM is thought to be a possible occurrence, the surgeon can enlarge the aortic root or place a stentless bioprosthetic aortic valve or a newer aortic mechanical valve. Even though a prosthetic valve may appear to fit snug in the annulus, this may cause an unacceptable hemodynamic response. A high transvalvular gradient will impair left ventricular remodeling, which overall leads to higher morbidity and mortality, especially in patients with decreased left ventricular function.
The following are some common indications of performing Nicks procedure:
In the technique for the procedure originally reported by Nicks et al., a tongue of woven Dacron material, cut from a prosthetic tubular arterial graft was used for the aortic root enlargement. The patch was used with its natural curvature facing the lumen. However, other substitutes can be used like autologous pericardium either treated with glutaraldehyde or untreated or bovine pericardium. The following are the requirements for carrying out Nicks procedure successfully:
Nicks procedure is considered the easiest and safest of the posterior enlargement techniques because it avoids the fibrous trigone between the aortic valve and anterior mitral leaflet, and it does not enter the left atrium. Yet, it still would need a surgeon with expertise for performing it. An appropriate team is comprised of the following:
Preoperatively, identification of small aortic root can be made by echocardiography, either transthoracic or transoesophageal, computed tomography (CT), or magnetic resonance imaging (MRI). Minimum prosthetic aortic valve size is identified based on a given patient's BSA to prevent prospective mismatch as defined by an indexed effective orifice (iEOA) area of at least 0.85 cm/m, according to published normal reference values of effective orifice area (EOA) for each valve type and size.
Pre-op imaging is used to measure intraoperative sizing to help try and avoid PPM at all costs. Imaging is also needed to review any signs of subaortic stenosis so that this can be addressed intraoperatively if needed. The patient should also be evaluated for any need for coronary artery bypass grafting with left heart cath and stress testing.
A routine median sternotomy is performed. During the opening of the pericardium, the anterior portion may be excised and prepared with glutaraldehyde to use during the aortic root enlargement. This is followed by cannulation and left ventricle venting. The oblique incision in the ascending aorta (as described later) is done. Valve leaflets are excised, and measurement using the valve sizers comes after. If a sizer, matching the minimum valve according to the patient's BSA to avoid patient prosthesis mismatch, cannot be achieved, then an aortic root enlargement should be undertaken.
The patient is taken to the operating room. All preoperative lines are placed ( Cordis, Swan Ganz, A-line). A midline sternotomy is performed with the division of the thymus and opening of the pericardium. Heparin can then be given, and the level is confirmed by an activated clotting time. The ascending aorta is then visualized, and a place for cannulation is decided. Aortic cannulation is then carried out with the placement of venous bi-caval cannulation. A vent catheter can then be placed. The cooling of the patient then ensues. Once the patient reaches the desired temperature, the aorta can be cross-clamped, and the cardioplegia can be given.
Aortotomy for AVR is oblique, extending into the non-coronary sinus. The aortotomy can be further elongated to the annulus but not through it because widening the apex with pericardium permits the insertion of a rather larger valve. Further extension of the incision beyond the aortic annulus onto the anterior mitral leaflet can lead to a larger valve to be inserted. Once across the annulus, the incision is directed posteriorly towards the center of the anterior leaflet of the mitral valve. A teardrop-shaped patch of the autologous or bovine pericardium is sutured to the base of the incision with a 4-0 polypropylene suture, with the broader end of the patch at the apex.
After completion of the suture line above the level of the divided annulus, the valve prosthesis is sutured in situ in a supra-annular position with 2-0 pledged mattress separate sutures. Sutures of the valve are passed full-thickness from outside the patch to inside. The outstanding part of the patch is then accustomed to facilitate closure of the aortotomy. Possible restriction of leaflet motion may be expected when a bileaflet mechanical prosthesis is inserted with this technique; therefore, leaflet mobility must be thoroughly inspected. It may be needed to rotate the prosthesis to reach optimal valve closure.
Researchers have shown that posterior aortic root enlargement techniques, including the Nicks procedure, can be easily applied without additional risks. Aortic root enlargement patients have a statistically significant higher risk for perioperative mortality compared to those without ARE. However, when patients who underwent concomitant procedures were excluded, despite the presence of a higher risk, the difference was statistically non-significant. It was also observed that, despite longer CPB time and aortic cross-clamp time, patients who underwent AVR with ARE did not experience higher rates of myocardial infarction, stroke, complete heart block/permanent pacemaker implantation, or reoperation for bleeding. On the contrary, patients who underwent AVR with ARE had a higher overall mean of iEOA and a lower overall rate of PPM.
Valve selection for the small aortic root is dependent on many variants. Considerations include age, body surface area (BSA), size of the aortic root, size of the prosthesis after excision of the native valve, its EOA, and valvular outflow tract of each patient. Choosing the appropriate valve for a specific patient requires calculating the indexed EOA (EOA/BSA). An indexed EOA <0.85 leads to an increased gradient over the prosthetic valve leading to PPM. When iEOA is >0.85, it leads to improved left ventricular remodeling and decreased long-term risk of morbidity including arrhythmias, heart failure, and mortality.
Small aortic root and its management by aortic root enlargement are directed to provide the patient with improved hemodynamics postoperatively. In cases of small aortic valve prostheses, a high gradient across it will lead to symptoms mimicking those of aortic stenosis and patient prosthesis mismatch. PPM is associated with increased perioperative and overall mortality. Its impact on mortality is directly proportional to the severity of PPM, hence making the operation useless and sometimes harmful in the first place.
Nicks procedure provides a solution to the challenging nature of small aorta. While the principle of patient prosthesis mismatch is an area of debate, the recent development in the transcatheter valve in valve implantation has reignited the interest for the bigger valve. It is always advisable to discuss these complex cases in interprofessional team meetings, including cardiac surgeons, cardiologists, and anesthesiologists, for improved decision making. Good preoperative preparation comes along with diagnosing the small aorta and calculating the patient's body surface area and establishing the target valve size.
To achieve better outcomes intraoperatively, the surgical steps have to be outlined before beginning the case to the whole team. Thus saving time on intraoperative decision making and to account for extra steps such as patch preparation, especially if autologous pericardium is needed or in cases where the assistant will begin the case. Also, the surgical nurse can prepare the patch, glutaraldehyde if needed, 4-0 polypropylene sutures, and extra hemostatic agents for the anastomotic line. Discussion with the perfusionist regarding longer cross-clamp time can affect factors such as type of cardioplegia and degree of hypothermia for optimal myocardial protection.
In the postoperative period, a clear plan with the intensive care unit must be established. The strict control of blood pressure after weaning of sedation will avoid increased tension over the anastomotic line and the risk of postoperative bleeding. Monitoring the heart rhythm for possible conduction complications postoperatively is required. The nurse in charge will monitor the pain and provide adequate pain relief. Thus, further emphasizing the need for an interprofessional approach to the management of aortic root enlargement must be taken into account. The need for meticulous planning and discussion with other professionals involved in the management of the patient is highly recommended to lower the morbidity and improve outcomes.
The Nicks procedure requires an interprofessional team consisting of cardiac surgeons, anesthesiologists or nurse anesthetists, cardiologists, cardiac intensivists, multiple nurses, pharmacists, scrub techs, and many other staff members to be in constant communication to provide the absolute best care. Each of these team members plays a pivotal role in the management and potential outcomes of the patient.
Postoperative care is vital in the management of postoperative cardiac patients. Nursing, cardiac rehab specialist, and physical therapists play a pivotal role in multiple interventions that are needed to provide care for the patients. Interprofessional team management with good communication provides the best overall outcomes for postoperative cardiac patients.
Interprofessional team monitoring is critical for the success of the operation and the overall patient outcome. Every team member is responsible for monitoring for any complications that may arise. The patient should be monitored closely for postoperative bleeding via chest tube output, cardiac arrhythmias, hemodynamic instability, or any incision site complications.
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