Minimally Invasive, Mini-Thoracotomy Aortic Valve Replacement

The right minithoracotomy can be used in most subsets of patients requiring an aortic valve replacement (AVR). Definitive contraindications to a right anterior thoracotomy approach include patients with a severely calcified aorta (porcelain aorta), evident preoperatively by cardiac catheterization or computed tomography (CT) scan or intraoperatively by palpation, patients who cannot be safely cannulated peripherally due to peripheral vascular disease or centrally due to calcium in the aorta, and patients who require a valve-sparing operation. The aforementioned groups require greater exposure of the operative field. Patients who present with previous right thoracic surgery or dense adhesions from an inflammatory reaction may undergo a minithoracotomy approach. In this particular group, minimal dissection is performed in the pleural cavity, and the pericardial space is immediately entered and exposed.

The benefits of the minithoracotomy over a standard sternotomy AVR have also been seen in higher-risk patients, including older patients (> 75 years old), obese patients (body mass index [BMI] > 30 kg/m ² ), patients with chronic obstructive pulmonary disease (COPD), and patients with a low ejection fraction (< 35%). Several studies have demonstrated a lower morbidity and mortality in these higher-risk patients. An extended application of this procedure can be offered to patients who require replacement of the ascending aorta and hemiarch along with an AVR. Most of these procedures are performed under deep hypothermic circulatory arrest and retrograde cerebral perfusion. In patients requiring a full root replacement due to aneurysmal disease or a small aortic annulus, an aortic root replacement with reimplantation of the coronaries can also be performed. In addition, reoperative aortic valve surgery in patients with prior valve surgery or coronary revascularization via a right minithoracotomy approach is feasible. All these procedures are more technically challenging and require additional experience. Other applications include AVR with aortic root enlargement, AVR with a septal myectomy, and AVR with a single bypass to the proximal or distal right coronary artery (RCA). The posterior descending artery is difficult to visualize with this approach. In patients with coronary artery disease amenable to percutaneous intervention, a hybrid approach is preferable. A percutaneous intervention can be performed at any time prior to the minimally invasive valve surgery. A minithoracotomy approach can be offered to patients receiving dual antiplatelet therapy.

The preoperative workup includes routine blood work, chest radiography, cardiac catheterization, and echocardiography. A routine CT angiogram is not necessary unless severe peripheral vascular disease is suspected by history or physical examination, although a CT angiogram is highly recommended when initiating a minimally invasive program. Stroke rates are low in patients undergoing femoral cannulation, despite the use of retrograde arterial perfusion, and are comparable to rates in patients undergoing a sternotomy valve procedure.

Routine CT scans of the chest are not necessary either, although others have defined inclusion criteria based on CT scan findings, which may be beneficial initially. Chest CT scans may also potentially diminish the incidence of conversions.

The anatomy of certain patients can pose additional challenges when performing the procedure via a right minithoracotomy approach. A chest x-ray demonstrating the right border of the heart adjacent to the right border of the vertebral column may be associated with the heart being displaced toward the left side of the chest. This is also true for patients with a pectus excavatum. If the angle of the aorta and ventricle lie at 90 degrees on the ventriculogram (cardiac catheterization), visualization of the aortic valve may be more challenging. Visualization of the aortic valve is usually more challenging in patients with a bicuspid aortic valve. Although challenging, these anatomic variants are not definitive contraindications for the surgery.

A single-lumen endotracheal tube is inserted, and double-lung ventilation is used throughout the operation. If visualization of the heart is impaired by the lungs, the lungs are temporarily deflated, or cardiopulmonary bypass can be initiated early in the procedure.

Single-lung ventilation with a double-lumen endotracheal tube or bronchial blocker is not performed unless significant pleural adhesions limit visualization and dissection. Cases of unilateral reexpansion pulmonary edema secondary to single-lung ventilation have been reported.

The preoperative preparation includes insertion of a left radial arterial line and right internal jugular or left subclavian vein Swan-Ganz catheter. A left radial arterial line is always preferred in case right axillary artery cannulation is required. Patients undergoing reoperative aortic valve surgery will have a temporary transvenous pacemaker inserted after the induction of anesthesia.

The patient is induced with a muscle relaxant (fentanyl and midazolam). A volatile agent is administered throughout the surgery. Remifentanil is started immediately prior to exposing the artery and vein for cannulation. Heparin (300-400 units/kg) is also given at this time in preparation for cannulation. The dosage of remifentanil is increased prior to the chest incision. While on cardiopulmonary bypass, the remifentanil dose is lowered, and midazolam is administered. After weaning from cardiopulmonary bypass, remifentanil is continued at a low dose. At completion of the operation, the patient is transported to the intensive care unit and continued on remifentanil.

Every patient should have a thorough intraoperative two-dimensional (2D) and three-dimensional (3D) transesophageal echocardiographic assessment. The sizes of the aortic annulus and ascending aorta are measured. Left ventricular function is assessed. The mitral valve is visualized and analyzed. If mitral valve pathology requiring repair or replacement is identified, patient positioning may need to be changed. Assessment of atherosclerotic disease in the ascending and descending aorta is performed. Evidence of a grade 4 or 5 free-floating atheroma in the descending aorta would preclude femoral cannulation and retrograde arterial perfusion. Positioning of the venous cannula in the superior vena cava (SVC) is performed with transesophageal echocardiography (TEE). A bicaval midesophageal view done at 80 to 100 degrees is used for placement of the venous cannula into the SVC. TEE is also used in reoperative aortic valve surgery for insertion of a retrograde cardioplegia cannula. A midesophageal, four-chamber view at 0 degrees is used for guiding placement of a retrograde cannula into the coronary sinus if necessary.

Intraoperative fluoroscopy can also be used to aid placement of the venous guidewire and cannula when the wire cannot be visualized by TEE. Intraoperative iliac and abdominal aortic angiograms with fluoroscopy are obtained when there is uncertainty after insertion of the femoral arterial cannula or when calcified plaques are encountered during cannulation.