Minimally Invasive Mitral Valve Surgery

Anatomy and Physiology

Anatomy of the Mitral Valve

The mitral valve is a critical structure located between the left atrium and the left ventricle of the heart, consisting of several key anatomical components:

• Valve leaflets
  • The mitral valve has 2 leaflets: anterior (or aortic) and posterior (or mural).
  • These leaflets are thin, fibrous structures that open and close to regulate blood flow between the left atrium and ventricle.
• Chordae tendineae
  • These strong, fibrous cords attach the mitral valve leaflets to the papillary muscles in the left ventricle.
  • They prevent the valve leaflets from prolapsing into the left atrium during ventricular contraction.
• Papillary muscles
  • These muscles are located in the left ventricle and are attached to the chordae tendineae.
  • Their contraction during systole (ventricular contraction) helps maintain tension on the chordae tendineae, thereby preventing mitral valve prolapse.
• Annulus
  • The mitral valve annulus is a fibrous, saddle-shaped structure that surrounds the valve orifice, provides attachment for the valve leaflets, and helps maintain the valve's shape and integrity during the cardiac cycle.

Physiology of the Mitral Valve and Associated Pathologies

The mitral valve has an essential function in pressure and volume homeostasis for the heart, showing dynamic changes in geometry during the cardiac cycle.[6] 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 3-dimensional echocardiography have allowed for enhanced visualization of the mitral valve pathology to classify mitral valve pathology better.[7] Mitral valve pathologies primarily involve conditions like mitral stenosis (narrowing of the valve opening) and MR (leakage of blood back into the left atrium), which are further discussed below:

• Mitral stenosis

  • Mitral stenosis occurs when the mitral valve leaflets thicken and become stiff, reducing the valve's ability to open fully during diastole (ventricular relaxation). This obstruction impedes blood flow from the left atrium to the left ventricle, causing increased pressure in the left atrium and in overall pulmonary circulation.
  • Reduced diastolic filling of the left ventricle leads to decreased stroke volume and cardiac output. The elevated left atrial pressure may cause pulmonary congestion, leading to symptoms such as dyspnea, orthopnea, and pulmonary edema.
  • This condition is most commonly due to rheumatic heart disease.[8] 
  • The preferred modality for treating mitral stenosis is percutaneous balloon mitral valvuloplasty to increase the valve area and relieve the pressure gradient between the left atria and left ventricle.[8]

• Mitral regurgitation

  • MR occurs when the mitral valve leaflets fail to close properly during systole, allowing blood to leak back into the left atrium from the left ventricle. This leakage increases the volume load on the left atrium and may cause left ventricle volume overload.
  • During systole, some blood flows back into the left atrium instead of being pumped into the systemic circulation. This reduces the effective forward stroke volume and can lead to symptoms of heart failure such as fatigue, dyspnea, and, eventually, left ventricular dysfunction.
  • MR can be defined as primary or secondary due to the underlying pathology.
    • Primary
      • Per the European Society of Cardiology statement, primary MR 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.[9]
    • Secondary
      • 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.[10]
      • Causes of secondary MR include dilated cardiomyopathy, ischemic cardiomyopathy, and annular dilation that causes an increase in the mitral annulus diameter.[10]
  • Management options differ between primary and secondary MR, requiring proper evaluation and classification of the pathology.

Indications

Indications for Minimally Invasive Mitral Valve Surgery Overview and Guidelines

According to the American College of Cardiology and the European Society of Cardiology recommendations, the management of MR is determined by the severity and pathology of the disease.[11][12] For acute MR, a trial of medical therapy is indicated. Patients who are asymptomatic with a left ventricular ejection fraction (LVEF) greater than 60% can be monitored without immediate surgical intervention. However, patients with chronic MR who exhibit symptoms despite medical management or who have poor ventricular function should be considered for surgery due to their poor prognosis. Mitral valve repair remains the gold standard surgical technique for treating significant MR, offering high patient satisfaction, shorter hospital stays, low perioperative morbidity and mortality rates, and excellent long-term outcomes.[13][14] 

Primary MR

For primary MR, surgery is recommended for patients who are symptomatic with chronic severe MR (stage D) and LVEF greater than 30%. Surgery is also indicated for patients who are asymptomatic with left ventricular dysfunction, characterized by a left ventricular end-systolic dimension (LVESD) of 40 to 45 mm or greater or LVEF less than 60% (class I, level B). The primary treatment of primary MR is surgical repair. However, the European guidelines suggest that the percutaneous edge-to-edge procedure may be considered for patients with symptomatic severe primary MR who meet the echocardiographic eligibility criteria and are deemed inoperable or at high surgical risk by the heart team (class IIb, level C).[12] 

Secondary MR

In cases of secondary MR, surgical correction has not demonstrated improved survival. However, percutaneous edge-to-edge repair has shown benefits in improving the quality of life and survival for patients with heart failure and moderate to severe MR who remain symptomatic despite optimal medical management. 

Minimally Invasive Mitral Valve Surgery

Minimally invasive mitral valve surgery indications have expanded significantly, particularly in high-volume institutions. This approach now includes patients who are more fragile and high-risk, as well as those with increasingly complex mitral valve disease, such as infective endocarditis. More than 50% of patients with infective endocarditis require surgical intervention to prevent severe complications such as heart failure, uncontrolled infection, and systemic embolism. Both American and European guidelines advocate for early surgical intervention when necessary. Advances in early surgical planning, intensive care, and postoperative management have significantly improved outcomes for these patients, although perioperative mortality and morbidity rates remain high. The rationale for using a minimally invasive approach in those who are high-risk is to reduce surgical trauma, facilitate quicker postoperative recovery, and lower the risk of surgical wounds and hospital-acquired infections.[3]

Minimally invasive surgical techniques for mitral valve repair, such as right minithoracotomy, robotic-assisted repair, and percutaneous edge-to-edge mitral valve repair, are increasingly favored due to their benefits in reducing postoperative complications and enhancing recovery, especially in patients who are not ideal candidates for traditional open surgery. As technology advances and transcatheter aortic valve replacement becomes more popular, devices for TMVR are being developed as future therapeutic options, further expanding therapeutic possibilities for patients with MR.

Contraindications

When considering minimally invasive surgical mitral repair versus TMVR, many factors must be weighed. Minimally invasive techniques, such as minithoracotomy and robotic surgery, offer benefits over traditional surgical methods, including less postoperative pain, shorter recovery times, and better cosmetic results.[4] However, these approaches are technically complex and require significant practice to achieve comparable outcomes.[15] 

Despite the advantages, not all patients are suitable candidates for minimally invasive mitral valve surgery. Specific contraindications must be considered. While minimally invasive mitral valve surgery via mini-thoracotomy can be performed along with atrial fibrillation ablation or right-sided heart procedures, concomitant surgeries such as coronary artery bypass grafting (CABG) and aortic valve replacement necessitate a traditional median sternotomy approach.[16] Other contraindications for minimally invasive mitral valve surgery include:

• Previous right thoracotomy
• Significant aortic root dilatation
• Moderate to severe aortic regurgitation
• Right ventricular dysfunction
• Fixed pulmonary hypertension (greater than 60 mm Hg)
• Severe generalized peripheral artery disease
• Calcification of the aortic root or mitral annulus
• Symptomatic cerebrovascular disease or recent stroke
• Significant bleeding disorders
• Severe liver dysfunction

For robotic mitral valve repair, relative contraindications include:

• Mild aortic stenosis or regurgitation
• Limited peripheral artery disease
• Variable pulmonary hypertension (greater than 50 mm Hg)
• Chest deformity (eg, pectus excavatum or scoliosis)
• Coronary artery disease
• Moderate pulmonary dysfunction [17] 

Given that mitral valve disease is more prevalent in patients 65 and older, many patients are not suitable candidates for surgical intervention. They may instead be referred for percutaneous edge-to-edge mitral valve repair. This transcutaneous approach provides an alternative for patients with MR who are not candidates for traditional surgery. However, this procedure is contraindicated in patients who cannot tolerate procedural anticoagulation or postprocedural antiplatelet therapy, those with active endocarditis, rheumatic mitral valve disease, and those with intracardiac or venous thrombus.

Personnel

Treating mitral valve disease requires effective multidisciplinary communication. One key distinction between the minimally invasive surgical approach and percutaneous edge-to-edge mitral valve repair is the team performing the procedure. Cardiothoracic surgeons conduct minimally invasive and robotic surgeries, while interventional cardiologists typically handle transcatheter repairs. In cases where complications arise during percutaneous edge-to-edge mitral valve repair, cardiothoracic surgery collaborates with interventional cardiology to convert the procedure to a mediastinotomy if necessary. This collaboration ensures comprehensive care and enhances patient outcomes.   

Preparation

In preparation for minimally invasive mitral valve surgery, a patient must undergo a comprehensive diagnostic workup and therapeutic medical management by a cardiologist. This includes an echocardiogram, which can be performed via a transthoracic or transesophageal approach to visualize the heart structures and understand the anatomy of the mitral valve. Additional workup involves optimizing the management of other comorbidities. Since general anesthesia is required for both minimally invasive surgery and percutaneous edge-to-edge mitral valve repair, patients need clearance from their cardiologist before the procedure.

For a surgical mitral valve repair, the patient will meet with the cardiothoracic surgeon and anesthesiologist before the procedure to prepare for the operating room. Patients scheduled for percutaneous edge-to-edge mitral valve repair will meet with an interventional cardiologist and anesthesiologist to prepare for a hybrid operating room. This preoperative coordination ensures that all patient care aspects are meticulously planned and managed, optimizing surgical outcomes and patient safety.

Technique or Treatment

Minimally invasive mitral valve surgery avoids a full sternotomy and can be performed through several approaches, including a partial sternal split (lower J-shaped, or less commonly, upper hemisternotomy), a right mini-thoracotomy incision, and multiple smaller incisions for a robotic approach.[17] The standard incision for a mini-thoracotomy is made in the fourth intercostal space, but newer techniques utilize periareolar incisions for select patients. Robotic instrumentation can facilitate an endoscopic approach with incisions no larger than 1.5 cm for instrument placement. Complete procedural details are beyond the scope of this review and discussed elsewhere.[4][17] Myocardial protection and cardioplegia delivery are crucial, as cross-clamp and pump times are longer compared to open mitral valve surgery.

Right Mini-thoracotomy Approach

The most common approach is through a right mini-thoracotomy.[4] This requires cardiopulmonary bypass, usually achieved through peripheral femorofemoral cannulation, though direct aortic cannulation via the mini-thoracotomy incision is also an option.[18] Special techniques for cardiopulmonary bypass include vacuum assist, smaller cannulas, and transthoracic aortic cross clamps. A partial sternal split approach allows for central aortic cannulation, while a limited right thoracotomy or multiple smaller incisions for a robotic procedure requires femoral arterial and venous cannulation.[4]

Percutaneous Edge-to-Edge Mitral Valve Repair

This approach benefits from not requiring cardiopulmonary bypass and involves a 5-step process using transesophageal echocardiography guidance:

• Baseline imaging
• Transseptal puncture
• Positioning of the clip in the left atrium above the affected mitral leaflet
  • Multiple clips may be deployed to achieve a good result.[19]
• Leaflet grasp and deployment of the device
• Postdeployment assessment 

TMVR

TMVR devices are currently undergoing clinical trials in the US. Results from the first-in-human study conducted in Vancouver, Canada, between August 2017 and August 2018 showed promise. The Abbott Tendyne TMVR device 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 MR (SUMMIT) clinical trial in the US for potential approval. Various techniques and the success of TMVR devices are still being investigated. These minimally invasive approaches offer significant advantages, including reduced postoperative pain, shorter recovery times, and better cosmetic results. However, they are technically complex and require considerable expertise to achieve outcomes comparable to traditional surgery.

Complications

Due to increased technical demands, minimally invasive mitral valve surgery typically requires longer cardiopulmonary bypass times than conventional sternotomy. Few underpowered randomized comparisons exist between traditional and minimally invasive techniques regarding clinical outcomes and postoperative complications. Studies suggest that the increased cardiopulmonary bypass time, with retrograde flow in the aorta, presents a stroke risk similar to traditional approaches.

The risks of mortality, renal failure, wound infection, reoperation for bleeding, aortic dissection, myocardial infarction, atrial fibrillation, and 30-day readmission are reported as not statistically different between minimally invasive and conventional surgical approaches when surgically appropriate indications and proper patient selection are present. Stroke rates for minimally invasive mitral valve repair have been reported between 1% and 2.6%. Peripheral cannulation can lead to soft tissue infections in 1% to 7% of patients.[20] Additionally, a small subset of patients may require conversion to median sternotomy intraoperatively due to complications.

The percutaneous edge-to-edge mitral valve repair device is relatively safe, as the Endovascular Valve Edge-to-Edge Repair Study (EVEREST) trial demonstrated.[21] This device shows low rates of resuscitation, myocardial infarction, renal failure, and pulmonary embolism, ranging from 0% to 1%. Stroke risk is between 0.4% and 1.4%, and significant bleeding risk is between 1.1% and 7.4%. Major bleeding is a frequent complication due to the necessity of anticoagulation.

Procedural complications include the potential dislocation of an existing pacemaker during transseptal puncture, which can be mitigated by verifying the location with fluoroscopy and echocardiography. Transseptal puncture generally does not require closure as the risk of pericardial tamponade postoperatively is low. Single-leaflet device detachment, occurring in 0% to 4.8% of cases, is the most common implantation complication. Rare complications include clip embolization requiring surgical retrieval, thrombus formation on the clip, and direct leaflet damage. Mitral stenosis may result from clip placement but is considered acceptable based on the interventional team's judgment. Achieving an adequate reduction of MR may warrant accepting a higher transmitral valve gradient, resulting 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 provides essential treatment options for those at higher risk for surgery. Available data suggest that procedural and long-term outcomes and the safety of the minimally invasive approach are comparable to conventional mitral valve surgery. Therefore,  a minimally invasive approach should always be considered for patients requiring surgery for primary MR.

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

Enhancing Healthcare Team Outcomes

Successful minimally invasive mitral valve surgery hinges on a highly skilled and coordinated interprofessional team. Physicians, including cardiothoracic surgeons and cardiologists, must possess expertise in advanced surgical techniques and patient assessment to determine suitability for minimally invasive approaches. Advanced practitioners, such as nurse practitioners and physician assistants, play a crucial role in preoperative evaluations, postoperative care, and patient education. Nurses are integral in providing perioperative care, monitoring patient status, and ensuring adherence to postoperative protocols. Pharmacists contribute by managing medications, particularly anticoagulation therapy, critical for patient safety and optimal outcomes.

Effective interprofessional communication and care coordination are vital for enhancing patient-centered care. Regular team meetings and multidisciplinary tumor boards facilitate comprehensive treatment planning and promptly address any complications. Utilizing standardized communication tools ensures precise and consistent information exchange among team members. Coordinated care plans that include detailed preoperative workups, intraoperative management strategies, and postoperative follow-up protocols help optimize patient outcomes. The healthcare team can minimize risks, reduce recovery times, and improve patient safety and satisfaction by working collaboratively.