Continuing Education Activity

The advent of minimally invasive mitral valve repair in recent years provides a necessary therapeutic option for patients with symptomatic mitral valve disease. This activity reviews the basics of minimally invasive mitral valve surgery, the indications and indications and contraindication, technique utilized, and role of the interprofessional team in the procedure in cardiovascular medicine.

Objectives:

• Identify the indications and contraindications of minimally invasive mitral valve surgery.
• Describe the technique of minimally invasive mitral valve surgery.
• Outline the potential complications of minimally invasive mitral valve surgery.
• Summarize some interprofessional strategies that the healthcare team can employ when a patient receives a minimally invasive mitral valve repair procedure.

Introduction

Medical advances have helped the US population live longer with more comorbidities than previously possible. As the aging population expands, the incidence of degenerative heart disease and valvular disease has increased.[1] Mitral valve disease is one of the most common valvular anomalies and often concomitant with aortic valve disease. Due to the center of the heart and association with other comorbidities that increase frailty, many patients are at high surgical risk and necessitate alternative therapeutic options.[1] Up to 50% of patients with moderate to severe mitral regurgitation (MR) are not considered surgical candidates.[2] Medical management in mitral regurgitation has poor outcomes with a 1-year mortality rate of 20%, a 5-year mortality rate of 50%, and a high hospitalization rate due to heart failure.[2]

The advent of minimally invasive mitral valve repair in recent years provides a necessary therapeutic option for patients with symptomatic mitral valve disease. Additionally, studies of minimally invasive mitral valve repair have been shown to preserve cardiac structure and function when implemented early. Minimally invasive surgical mitral valve repair has become routine for the treatment of MR.[3] 

Enhancements of minimally invasive surgical techniques improved surgical trauma and postoperative recovery, resulting in increased acceptance of these techniques.[3] Different minimally invasive techniques include robotic repair, minimally invasive mitral valve surgery using a right mini-thoracotomy, percutaneous edge-to-edge mitral valve repair, and transcatheter mitral valve replacement. Many patients with symptomatic MR have a poor prognosis due to older age and comorbidities. Minimally invasive surgical approaches to mitral valve repair have provided important treatment options in these higher-risk surgical patients. The emergence of transcatheter mitral valve repair and replacement options further pushes the boundary of possibilities. Hence, patients who are not surgical candidates can live longer than previously possible.[4]

Anatomy and Physiology

The mitral valve has an important function in pressure and volume homeostasis for the heart. Mitral valve disease can be detrimental and lead to complications like heart failure or atrial fibrillation from left atrial enlargement. Advances in cardiac imaging with three-dimensional echocardiography have allowed for better visualization of the mitral valve to be able to better classify mitral valve pathology.[5] The mitral valve has a saddle-shaped annulus and shows dynamic changes in geometry during the cardiac cycle.[6]

The most common mitral valve pathologies are mitral stenosis (MS) and mitral regurgitation. Mitral stenosis is caused by an abnormal thickening of the mitral valve that is most commonly due to rheumatic heart disease.[7] The preferred modality for the treatment of mitral stenosis is percutaneous balloon mitral valvuloplasty to increase the valve area and relieve the pressure gradient between the left atria and left ventricle.[7] Mitral regurgitation can be defined as primary or secondary due to the underlying pathology. Per the European Society of Cardiology statement, primary regurgitation is caused by a defect in the mitral valve apparatus that can be due to a degenerative process like mitral prolapse, flail leaflet, or endocarditis.[8]

Secondary MR is also known as ‘functional MR’ and is defined as an imbalance between closing and tethering forces on the mitral valve secondary to structural heart changes with a structurally normal mitral valve apparatus.[9] Causes of secondary MR include dilated cardiomyopathy, ischemic cardiomyopathy, and annular dilation that causes an increase in the mitral annulus diameter.[9] Management options differ between primary and secondary mitral regurgitation, requiring proper evaluation and classification of the pathology.

Indications

According to the American College of Cardiology/European Society of Cardiology recommendations, the management of MR is determined by the severity and pathology of the disease.[10][11] A trial of medical therapy is indicated for acute MR, and asymptomatic patients with LVEF>60% can be followed. Chronic mitral regurgitation with symptoms despite medical management or poor ventricular function should be considered for surgery due to the poor prognosis. Mitral valve repair is the gold standard surgical technique for the treatment of significant MR with results of high patient satisfaction, short hospital stay, low perioperative morbidity and mortality rates, and excellent long-term outcomes.[12] 

For primary MR, mitral valve surgery is recommended for symptomatic patients with chronic severe primary MR (stage D) and LVEF greater than 30% or in asymptomatic patients with LV dysfunction (left ventricular end-systolic dimension >=40-45 mm) and/or LVEF <60%) (I B). Primary treatment of primary MR is surgical repair, and percutaneous edge-to-edge mitral valve repair is considered for patients who are poor surgical candidates. Several other guideline recommendations for primary and secondary MR exist and are best referred to in the guideline statements.[10][11] 

Surgical correction or percutaneous edge-to-edge mitral valve repair can be considered for secondary MR. The European guidelines recommend that percutaneous edge-to-edge procedure may be considered in patients with symptomatic severe primary MR who fulfill the echocardiographic criteria of eligibility and are judged inoperable or at high surgical risk by the heart team, avoiding futility (IIb C).[11] 

Surgical correction of secondary MR has not shown improved survival, while percutaneous edge-to-edge repair improved quality of life and survival in patients with heart failure and moderate to severe MR who remained symptomatic despite optimal medical management. As transcatheter aortic valve replacement becomes more popular, devices for transcatheter mitral valve replacement are being developed as future therapeutic options.

Contraindications

When considering a minimally invasive surgical mitral repair versus transcatheter mitral valve repair approach, many factors come into play. When compared to a traditional surgical technique, the minimally invasive mini-thoracotomy and robotic surgery show benefit due to less postoperative pain, shorter recovery time, and better cosmetic result.[3] However, minimally invasive surgery is technically complex and requires practice to achieve similar outcomes.[13] 

Many patients are not surgical candidates and would not qualify for a variety of reasons. Although minimally invasive mitral valve surgery via mini-thoracotomy can be conducted in conjunction with atrial fibrillation ablation or right-sided heart procedures, concomitant procedures like coronary artery bypass and aortic valve surgery require a traditional median sternotomy approach. Other contraindications for minimally invasive MV surgery include previous right thoracotomy, significant aortic root dilatation, moderate to severe aortic regurgitation, right ventricular dysfunction, fixed pulmonary hypertension (>60 mmHg), severe generalized peripheral artery disease, calcification of the aortic root or mitral annulus, symptomatic cerebrovascular disease or recent stroke, significant bleeding disorders, and severe liver dysfunction.[14] 

Relative contraindications for robotic mitral valve repair include mild aortic stenosis or regurgitation, limited peripheral artery disease, variable pulmonary hypertension (>50 mmHg), chest deformity (pectus/scoliosis), coronary artery disease, and moderate pulmonary dysfunction.[14] 

As mitral valve disease is more prevalent in the elderly population, many patients are not surgical candidates and can be referred for mitral valve repair with the percutaneous edge-to-edge repair. Edge to edge repair has provided a transcutaneous mitral valve repair option for mitral regurgitation. Currently, this procedure is contraindicated in patients who cannot tolerate procedural anticoagulation or post-procedural antiplatelet medication, active endocarditis, rheumatic mitral valve disease, and intracardiac or venous thrombus.

Personnel

As with many aspects of medicine, the treatment of mitral valve disease requires multi-disciplinary communication. One of the key differences between the minimally invasive surgical approach and percutaneous edge-to-edge mitral valve repair is the team performs the procedure. Cardiothoracic surgeons conduct minimally invasive surgery and robotic surgery. Interventional cardiologists typically do the transcatheter repair. Cardiothoracic surgery works with interventional cardiology if complications arise, and the percutaneous edge-to-edge mitral valve repair must be converted to a mediastinotomy.

Preparation

In preparation for minimally invasive mitral valve surgery, a patient must undergo a full workup with diagnostic workup and therapeutic medical management by a cardiologist. The workup typically includes an echocardiogram to visualize the structures of the heart from a transthoracic approach or transesophageal approach as needed to understand the anatomy of the mitral valve. Further workup includes optimal management of other comorbidities. General anesthesia is required for minimally invasive surgery as well as the percutaneous edge-to-edge mitral valve repair. Patients will need clearance from their cardiologist before the mitral valve procedure.

For a surgical mitral valve repair, the patient would meet with the cardiothoracic surgeon and anesthesiologist before the procedure and prepared for the operating room. Patients planned for percutaneous edge-to-edge mitral valve repair would meet with an interventional cardiologist and anesthesiologist for preparation for a hybrid operating room.

Technique or Treatment

Minimally invasive surgery does not include a full sternotomy. Approaches include a partial sternal split (lower J shaped or less commonly upper hemi-sternotomy), limited right thoracotomy incision, and multiple smaller incisions for a robotic approach.[14]

A minimally invasive approach using the right mini-thoracotomy is the most common.[3] Cardiopulmonary bypass is required for surgical intervention and is achieved through peripheral femoro-femoral cannulation, most commonly or direct aortic cannulation via the mini-thoracotomy incision.[15] Cardiopulmonary bypass requires special techniques like vacuum assist, smaller cannulas, transthoracic aortic cross clamps. A partial sternal split approach allows central aortic cannulation for bypass. A limited right thoracotomy incision or multiple smaller incisions for a robotic procedure requires femoral arterial and venous cannulation.[3] 

The mini-thoracotomy incision is standardly made in the fourth intercostal space, and newer techniques with periareolar incision have been developed for select patients. Robotic instrumentation can be used for an endoscopic approach that refers to incisions no larger than 1.5 cm for endoscopic instrument placement. Complete procedural details are beyond the scope of this review and discussed elsewhere.[3][14] Importantly, myocardial protection and cardioplegia delivery are of increased importance as a cross-clamp and pump times are longer than with open mitral valve surgery.

The percutaneous edge-to-edge mitral valve repair procedure provides a benefit over the surgical approach as the cardiopulmonary bypass is not necessary. The procedure uses transesophageal echocardiography guidance and is divided into a five-step process:

1. Baseline imaging
2. Trans-septal puncture
3. The positioning of the clip in the left atria above the affected mitral leaflet
4. Leaflet grasp and deployment of the device
5. Post-deployment assessment. Multiple clips may be deployed to achieve a good result.[16]

Transcatheter mitral valve replacement (TMVR) devices are undergoing clinical trials in the US for future use. The first-in-human study was conducted in Vancouver, Canada, between August 2017 and August 2018 and showed promise. The first TMVR device, Abbott Tendyne, was approved for use in Europe in January 2020 and is undergoing the Safety and Effectiveness of Using the Tendyne Mitral Valve System for the Treatment of Symptomatic Mitral Regurgitation (SUMMIT) clinical trial in the US for possible approval. Many techniques and the success of the TMVR devices are currently under investigation.

Complications

A minimally invasive surgical approach to the mitral valve requires longer cardiopulmonary bypass timing than a conventional sternotomy approach due to the increased technical demand. Only a few under-powered randomized comparisons of traditional and minimally invasive techniques to valve surgery concerning clinical outcomes and postoperative complications. The increased cardiopulmonary bypass time with the retrograde flow in the aorta has been reported to have a similar risk of stroke than the traditional surgical approach.

The risk of mortality, renal failure, wound infection, reoperation for bleeding, aortic dissection, myocardial infarction, atrial fibrillation, and readmission at 30 days has been reported as not statistically different when comparing minimally invasive surgical approaches to conventional surgical methods, when surgically appropriate indications exist and with proper patient selection. A feared complication of cardiopulmonary bypass is stroke, and rates for minimally invasive surgical mitral valve repair complicated by stroke have been reported as occurring in 1% and 2.6% of patients. Peripheral cannulation can lead to soft tissue infections occurring in between 1% and 7% of patients.[17] A small subset of patients will require median sternotomy intraoperatively due to complications of the procedure.

The percutaneous edge-to-edge mitral valve repair device is relatively safe, as shown by the Endovascular Valve Edge-to-Edge Repair Study (EVEREST) trial.[18] This device has low rates of need for resuscitation, myocardial infarction, renal failure, and pulmonary embolism listed between 0 and 1%. The risk of stroke is between 0.4% and 1.4%, and the risk of significant bleeding is between 1.1% and 7.4%. Major bleeding is among the most frequent complications due to many patients requiring anticoagulation with therapeutic agents.

Procedural complications can lead to dislocation of an existing pacemaker during transseptal puncture, which can be avoided by double-checking location with fluoroscopy and echocardiogram during the procedure. A transseptal puncture does not require closure as the risk of pericardial tamponade post-operatively is low. The most common device implantation complication is single-leaflet device detachment seen between 0% and 4.8% of cases. Other rare complications include clip embolization requiring surgical retrieval, thrombus formation on the clip, and direct leaflet damage. Mitral stenosis can result from the percutaneous clip placement but is considered an acceptable complication based on the interventional team’s judgment. It may be acceptable to accept a higher trans-mitral valve gradient to achieve an adequate reduction of mitral regurgitation, and the trade-off results in better long-term outcomes.

Clinical Significance

A minimally invasive surgical approach to mitral valve repair is the preferred option for mitral valve surgery in surgically acceptable candidates and has provided essential treatment options in the higher risk surgical patients. Available data suggest that procedural and long-term outcomes and the safety of the minimally invasive approach are comparable to conventional mitral valve surgery. In patients requiring surgery for primary MR, a minimally invasive approach should always be considered.

The percutaneous edge-to-edge mitral valve repair procedure may be considered in patients with symptomatic severe primary MR who fulfill the echocardiographic criteria of eligibility and are judged inoperable or at high surgical risk by the Heart Team. For secondary MR, surgical repair is not typically recommended. As transcatheter aortic valve replacement becomes more popular, devices for transcatheter mitral valve replacement are being developed as future therapeutic options. Future research should study the best approach for minimally invasive surgery and provide comparative data with transcatheter and open surgical options, with regards to safety and efficacy for both primary and secondary MR.

Enhancing Healthcare Team Outcomes

As with any other procedure, patient-centered optimal care is critical for the success of minimally invasive mitral valve surgery. This approach starts with the Heart Team's appropriate patient selection for the procedure with a careful and comprehensive discussion between the cardiologist, cardiothoracic surgeon, and the patient. All minimally invasive non-sternotomy mitral valve surgical approaches require femoral arterial and venous cannulation. Careful evaluation and exclusion of atheromatous peripheral vascular disease are required, and patients with severe peripheral vascular disease are excluded. Careful post-procedural follow-up with repeat imaging to assess improvement in MR, clinical status follow-up, rehabilitation therapies.