Mitral Operation: Endoscopic Approach

INTRODUCTION

Mitral repair or replacement via median sternotomy is the gold standard for surgical interventions upon the mitral valve and remains the most common approach. However, mitral operation began with non-sternotomy approaches. In certain patients, such as those with severe peripheral vascular disease or unsuitable anatomy for limited access approaches, sternotomy is the only option. Here we describe our practice of endoscopic mitral valve surgery. This procedure may also be known as HeartPort or port access mitral surgery.

HISTORICAL PERSPECTIVE

While today median sternotomy is the most common approach to mitral valve surgery, mitral operations began with non-sternotomy approaches. Indeed, the first mitral operation in 1923 was through a transapical approach via thoracotomy. Thoracotomy approaches continued to dominate surgical approach to the mitral valve, particularly operations for mitral stenosis. This lasted until the routine establishment of sternotomy in the 1960s. In 2003, Casselman et al. described their approach to endoscopic mitral valve repair, declaring that “mitral valve surgery can now routinely be performed endoscopically.” Over the last several decades, endoscopic approach mitral surgery has expanded in its use substantially but has not yet supplanted median sternotomy, despite data showing comparative outcomes for mitral valve repair. There has also been a suggestion of improved outcomes such as shorter length of stay, reduced bleeding, better cosmesis, and possibly less postoperative pain. The hesitancy to use a thoracotomy approach is likely due to the learning curve of this procedure and, until recently, the anxiety surrounding the mitral valve repair. In this chapter, we will discuss many of these aspects with respect to our own substantial experience.

PATIENT SELECTION

One of the most important elements in minimal access mitral valve surgery is proper patient selection. This relates to two specific elements: clinical factors and vascular assessment. Body habitus is one of the most important elements in determining how challenging endoscopic access surgery will be. Patients who have a body mass index (BMI) above 40 or who have chest wall deformities may be challenging operative candidates from an endoscopic approach. These patients are best avoided in the early experience of new surgeons. For patients needing re-operative mitral surgery, including those with previous coronary artery bypass grafting (CABG), aortic valve replacement (AVR), or mitral valve replacement (MVR), thoracotomy is our preferred approach. This necessitates the use of the endoballoon, so again we would recommend against this technique early in one’s experience. In patients with a diminutive left atrium, thoracotomy provides excellent exposure as opposed to sternotomy. Standard elements of the preoperative assessment are shared with the approach to a patient undergoing sternotomy. These include left and right cardiac catheterizations to define any pulmonary hypertension, visualize the coronaries (including dominance and proximity of the circumflex artery), and the extent of mitral annular calcification. In some younger patients we will accept computerized tomographic angiogram (CTA) as a screening tool and not require catheterization. Elements which make a patient a higher-risk sternotomy candidate also make them a higher-risk endoscopic candidate. This includes poor left ventricular function, severe pulmonary hypertension, and severe lung disease. Early in one’s experience, it is advisable to select mitral cases requiring straightforward repair in patients with normal BMI and without chest wall deformity. For example, a repair requiring a P2 management (resection or chords) and annuloplasty band would be more appropriate than a complex bileaflet repair approach in a sick patient.

The second category of factors relates to the suitability of the patient for peripheral cannulation for cardiopulmonary bypass. First, the common femoral artery must be relatively free of calcification. We have not found vessel caliber to be an important factor and have not routinely placed an antegrade perfusion limb for the lower extremity. The abdominal and thoracic aorta should be of a reasonable quality without heavy calcification or severe tortuosity. In particular, “shaggy” calcium in the lumen of the aorta may be dislodged and result in ischemic stroke, while mural calcification is less problematic. Although in the first 1000 cases we did not routinely do computed tomography (CT) scans (non-con) of the chest, abdomen, and pelvis, that is currently part of our preoperative assessment. Much can be learned about the burden of atherosclerosis on the basis of the views of the descending thoracic aorta and arch on transesophageal echocardiogram (TEE).

SETUP

Here we briefly describe our setup. It is important to stress the impact the entire operative team has on the success of minimal access mitral surgery, including endoscopic approaches. Skilled and experienced physician assistants should train with the surgical proctors, as should the scrub team to learn how to conduct the operation together.

The anesthesiologists routinely provide double-lumen tracheal intubation, a 16 to 18 Fr superior vena cava (SVC) venous drainage cannula via the internal jugular vein. We do not use an endopulmonary vent. We routinely use this bi-caval cannulation method. There are groups, however, that use a single venous cannula from the groin. If this single venous cannula does not provide adequate venous drainage, then the surgeon will experience a couple of miserable hours with difficult exposure. The patient is prepared in the usual fashion, with a bump used to elevate the right hemithorax. The patient’s pertinent surface anatomy is marked, including the nipple and the site of the mid-sternum. The right costal margin and clavicle are marked to define the midpoint of the thorax. A pulmonary artery catheter is inserted. A complete echocardiographic assessment of the valve is performed including three-dimensional reconstruction.

Operation is begun in the groin crease, with exposure of the femoral vessels via a limited oblique incision. Only the anterior surface of these structures is exposed. This is to minimize dissection in order to limit nerve and lymphatic injury. Once we have secured sites for arterial and venous cannulation, we open the right hemithorax with an incision approximately 2 to 3 inches long, immediately below the right nipple (typically the fourth interspace). In women, we take care to place this just above the inframammary crease to prevent bra friction. The patient is now ventilated selectively through the left lung on single-lung anesthesia. We initially open the chest through a small wound and palpate the diaphragm to determine how close it is. If it is very close, the thoracotomy is placed one space higher up. If diaphragmatic retraction is necessary, a heavy braided retraction suture is placed in the central tendon and brought out to the chest wall under tension (it is important to tie this suture to prevent diaphragmatic bleeding). Care also must be taken not to place too much tension on the phrenic nerve by pulling the diaphragm down. The “working” port is then enlarged to approximately 2.5 inches. Reaching in the wound, the intercostal space two below the working port is identified. A trocar is inserted, and CO ₂ infusion begun. The left ventricular vent is subsequently placed through this trocar. A soft tissue wound protector is then placed through the working port, and the deflated lung is retracted. A good landmark to confirm that the incision will provide adequate exposure to the mitral valve is that the right-sided pulmonary veins should be evident in the center of the incision. A 5-mm camera port is placed in the same rib space as the thoracotomy, a bit more laterally. This initially contains a 0-degree thoracoscope which is later exchanged to a 30-degree thoracoscope. An angiocath is placed superomedially to the thoracotomy. Through this a 24-gauge steel wire is placed that will be used to retract annular sutures and enhance the surgeon’s view later (Vanermen maneuver). Finally, it may be necessary to place a retractor into the incision to facilitate exposure, although frequently the soft tissue retractor suffices ( Fig. 17.1 ).