Aortic valve replacement is the standard treatment for patients with severe or symptomatic aortic insufficiency or aortic stenosis. In the past, the standard method of replacing the aortic valve has been via a median sternotomy approach. However, in some patients, this midline anterior chest incision may not heal properly, cause pain, and be associated with a prolonged recovery. In patients with osteoporosis or diabetes, the thinned out sternum may take a long time to heal and be associated with a significant amount of pain.
Over the past two decades, surgeons have developed alternative access routes to the aortic valve. The two main approaches to the aortic valve include a mini-thoracotomy and the minimally thoracoscopic approach. A third way of implanting the aortic valve is via a percutaneous approach combined with a mini-anterior thoracotomy. All these surgical approaches to the heart require general anesthesia, use of transesophageal echocardiogram, and full cardiac monitoring. In addition, the perfusionist must have the open heart-lung machine ready in case a complication occurs and there is a need to convert to a median sternotomy. The operating room is fully prepared in the same way as when a conventional aortic valve surgery is going to be performed.
The minimally invasive aortic valve surgery is performed by making a 4 cm to 6 cm incision on the anterior chest wall (to the left of the sternum) which gives direct access to the left ventricle. Another variation is to make a 4 cm to 6 cm horizontal incision in the right third intercostal space to access the root of the aorta. In both these scenarios, the femoral vessels are used to place the patient on the heart-lung machine. The most difficult part of the surgery is getting proper access to the aortic root. The rest of the procedure is then done the same as a conventional aortic valve replacement.
Percutaneous aortic valve surgery is performed by making a 6 cm incision at the left costal margin and accessing the heart. A transesophageal probe is placed in the esophagus, and special instruments are used to make a hole in the left ventricle apex, and a valve-containing device is guided to the aortic annulus. The stenotic valve is dilated first. Once the device is in place, the valve is released at the aortic annulus, and the instruments are removed. The hole in the ventricle is closed with sutures.There also is a robotic-assisted valve surgery procedure where three to five small incisions are made, and the surgeon uses robotic arms to conduct the surgery. Again, the most difficult part of this technique is to perform the actual aortic valve anastomosis. Most experts believe that the robotic surgery should be combined with an open incision so that the surgeon can manually perform the aortic anastomosis. The minimally aortic valve surgeries are also more expensive than the routine method of replacing the aortic valve as they require expensive disposable equipment.
The human heart has four different anatomical valves that play a role in the regulation of blood flow into and out of the myocardium. The two semilunar valves include the pulmonic and aortic valves, and the two atrioventricular valves include the mitral and tricuspid valves.
Except for the mitral valve, all the cardiac valves are tri-leaflet. Each of the heart valves is surrounded by a complete or partial fibrous ring (annulus), which helps supports the valves. The aortic valve is located between the ascending aorta and the left ventricular outflow tract. It is a very important valve and closely approximates other myocardial structures like the mitral valve posterolaterally, the pulmonic valve anteriorly, and the tricuspid valve posteromedially.
Percutaneous aortic valve replacement is indicated for the following patients:
The procedure is contraindicated in patients with severe aortic valve calcification and severe peripheral vascular disease.
In general, aortic valve surgery is done for all symptomatic patients and those with severe aortic stenosis.
The median sternotomy approach to the aortic valve is associated with an increased risk of perioperative complications; thus an alternative surgical approach to the aortic valve, such as a mini-thoracotomy or a left lateral thoracotomy, may be safer sometimes. Other relative contraindications to median sternotomy include COPD, obesity, or prior radiation exposure to the anterior chest.
The new tri-leaflet aortic valve can either be sutured or attached to the annulus by first expanding the annulus and then deploying a stent mounted catheter system. The initial percutaneously implanted aortic stent valves failed because they were too large, but over the years, the newer generation of aortic valves have a better profile and hemodynamic performance. The smaller catheter-based valves do not obstruct the coronary arteries or interfere with the function of the mitral valve. However, they still need to be accurately placed at the annulus.
The following is a summary of the different types of aortic valves that are currently available:
To deploy the stent valve, either expand the balloon on a balloon-expandable stent or withdraw the sheath that releases a self-expanding stent.
Once the valve is deployed it must remain secure around the diseased aortic valve and be able to resume hemodynamic function right away
Once the valve is functioning, its hemodynamic performance should be arranged in the same way as the valves that are implanted via a median sternotomy. The left ventricular outflow gradient must be 10 mmHg or less and the aortic valve area should be between 1.5 and 2.0 cm2. Once the prosthetic valve has been deployed, it is vital that it does not occlude the native coronary vessels or affect the function of the mitral valve which is located just underneath the aortic valve. In addition, the newly seated valve should be firmly seated on the aortic annulus and prevent the development of a paravalvular leak or aortic insufficiency.
General anesthesia for sternotomy is dependent upon the type of operation to be performed. If single lung ventilation is required, patients should be intubated with a double lumen endotracheal tube.
The patient must be sufficiently sedated and paralyzed before opening the chest to avoid tachyarrhythmias and hypertension during anesthesia. In patients with severe aortic stenosis, the surgeon must be scrubbed and ready to open the chest in case an arrest occurs.
The lungs are usually deflated before sternal division.
Today, several minimally invasive approaches to the aortic valve aim to avoid a full median sternotomy. Of these incisions, the right parasternal approach appears to be the most widely used. However, it is important to remember that the median sternotomy is still the gold standard for replacing the aortic valve.
Complications may include:
In general, the minimally invasive procedures are not the standard of care for aortic valve replacement. These procedures are done in patients who are too ill to undergo a formal median sternotomy and use of a heart-lung machine. Short-term results of these minimally aortic valve replacement procedures are fraught with complications. Complications of minimally valve surgery include bleeding, failure of the procedure to work, immediate opening of the chest due to a complication, thrombosis of the valve, perforation of the esophagus, and damage to the femoral vessels (usually dissection). The recovery of the patient is done in the same way as a normal open-heart surgery patient.
Several large clinical trials have been performed on the use of the percutaneous method of aortic valve implantation, and early results indicate that the morbidity and mortality are the same as the conventional technique. However, more long-term data are needed to determine if the results are durable and sustained for at least a decade.
A multidisciplinary approach to minimally invasive aortic surgery
Even though there are several ways for cardiac surgeons to operate on the aortic valve, the gold standard is the open procedure. The minimally invasive procedures do offer some advantages but they also require expensive equipment, extensive exposure to radiation and one must have an operating room on standby in case something goes wrong. Healthcare workers who see patients with valvular disorders must be aware that these minimally invasive procedures are only done for very ill patients who are not fit for the open procedure. In the end, a multidisciplinary team must fully evaluate the patient and decide which is the ideal procedure for him/her.