68. Minimally Invasive Cardiac Surgery- Review of CT Surgery

Lauren Barron, Puja Kachroo, and Ralph Damiano

Minimally invasive cardiac surgery is a field with evolving techniques, instrumentation and device development that has had outcomes on par with traditional “open” surgery. This review chapter is intended to introduce the principles and techniques of minimally invasive coronary revascularization and valve interventions and is not meant to be comprehensive. We will also highlight patient selection as a key factor as well as describe potential risks and benefits of minimally invasive approaches.

Minimally invasive coronary revascularization

MIDCAB

Minimally invasive direct coronary artery bypass (MIDCAB) is a single bypass utilizing the left internal mammary artery (LIMA), indicated primarily for patients with left anterior descending (LAD) artery disease. This approach is performed through a left anterior thoracotomy on a beating heart (with the option of cardiopulmonary bypass (CPB) support).

Patient selection

MIDCAB is ideal for patients with single vessel ostial or proximal LAD disease or even occlusion. It can also be considered in patients who have multi-vessel disease as part of a hybrid approach with PCI before or after the bypass. A good mid or distal LAD target should be identified preoperatively. Ideally, this approach should be avoided in patients with previous chest surgery or radiation and those with significant proximal left subclavian artery stenosis or a left sided arteriovenous fistula.  

Technique

Preoperative CT scan or cardiac catheterization is used to identify the coronary lesion and anatomy relative to the anterior interspaces. The patient is positioned supine with the arms at the side with a slight bump under the left scapula. Generally, the 4^th intercostal (ICS) is selected for a limited (5cm) left anterior thoracotomy from the nipple to the anterior-mid axillary line. A bronchial blocker may be beneficial. A specialized retractor designed to lift the superior ribs is utilized for takedown of the LIMA (either skeletonized or pedicled). Heparin is administered and the LIMA is divided. The pericardium is opened lateral to the pulmonary artery and parallel to the phrenic nerve over the LAD. Care must be taken to not open it widely as this may lead to partial cardiac herniation postoperatively. A stabilizer is introduced either from the subxiphoid space or laterally and positioned on either side of the LAD. The anastomosis may be performed either with temporary occlusion of the LAD or with the use of an intracoronary shunt.

Outcomes

American Heart Association guidelines give a class IIA recommendation for surgical revascularization in isolated LAD disease which is upgraded to class I recommendation when a large viable myocardial territory is involved. In addition to conventional coronary artery bypass grafting (CABG), there are also class Ia recommendations to support PCI for isolated LAD disease. When comparing MIDCAB to PCI for isolated LAD disease, MIDCAB was superior to PCI at 6 months with fewer target vessel interventions and fewer major adverse cardiac events. Rates of stroke and overall mortality were equivocal.

MICS CAB

Multi-vessel minimally invasive coronary artery bypass (MICS CAB) is a minimally invasive approach that can potentially address complete revascularization.

Patient Selection

MICS CAB can be considered for patients with multi-vessel CAD that meet the standard criteria for revascularization. There are a number of relative and absolute contraindications due to the increased technical demands and limited exposure of this approach.

• Absolute contraindications
  • Hemodynamic instability
    • Severe pectus deformity
    • Inability to tolerate single lung ventilation
    • Complete intramyocardial LAD
    • Relative contraindications
      • Significant left subclavian artery stenosis
      • Left sided arteriovenous fistula
      • Redo surgery
      • Severely diminished left ventricular function
      • Severe emphysema
      • Morbid obesity
      • Severe peripheral arterial disease
      • Right coronary artery or left circumflex artery stenosis without distal target

Technique

The major technical differences between MIDCAB and MICS CAB are based on exposure of all myocardial territories and the ascending aorta. In contrast to the MIDCAB incision, the MICS CAB utilizes a more lateral left 5^th ICS anterior thoracotomy beginning at the midclavicular line and extending laterally. Similar to the MIDCAB, the pericardial incision begins 2cm anterior to the phrenic nerve but is considerably longer extending cephalad to the level of the left atrial appendage and anterocaudally toward the diaphragmatic reflection. This allows for visualization of all myocardial territories. In addition to the LIMA, this approach utilizes additional conduits with proximal anastomoses performed onto the ascending aorta under direct visualization for complete revascularization. Several adjustments can be made to bring the aorta into view and are described in the selected readings. This approach can also be performed on or off CBP on a beating heart.

Outcomes

In a large series of 450 patients, operative mortality for MICS CAB was 1.3% and graft re-intervention rates at 18 months were 3% compared to 2.5% and 5.2% respectively in standard CABG. MICS CAB results has reported lower blood transfusion requirements, lower surgical site infections and faster return to full physical function. The selection bias introduced by the contraindications list highlights the value of the ongoing Minimally Invasive coronary surgery compared to STernotomy coronary artery bypass grafting (MIST) trial. The technical complexity of this approach has limited its use to a few high-volume centers. Therefore, the ability to develop recommendations from the MIST trial outcomes may be limited.  

Endoscopic CAB

Totally endoscopic coronary artery bypass (TECAB) is performed utilizing a robotic surgical system or thoracoscopic approach, with or without CPB, on a beating heart. Robotic-assisted coronary artery bypass (RA-CAB) is an alternate term frequently utilized in the literature. This term includes TECAB as well as endovascular LIMA harvest followed by a MIDCAB.

Patient Selection

The criteria are similar to those described above for MICS CAB. The use of cardiac CT to predict the intrathoracic working space and location of the LAD has further optimized patient selection and port placement for TECAB.

• Relative contraindications
• Small AP diameter (ratio AP/transverse <45)
• <2cm between the chest wall and LAD
• Laterally displaced LAD

Technique

Visualization is achieved utilizing a 30⁰ endoscope in the left 5th ICS with CO₂ insufflation and single lung ventilation. Instrument ports are triangulated in the 3^rd and 7^th ICS with the fourth robotic arm reserved for the endostabilizer placed in the subxyphoid space. LIMA dissection is similar to MIDCAB except that the pedicle is not ligated until the coronary target is exposed in order to prevent torsion. Similar to conventional CABG, it is critical to maintain appropriate tension on the suture ensuring a watertight anastomosis without damaging the coronary target. This can be challenging with the lack of haptic feedback provided by current robotic systems. The main difference from MICS CAB is that the coronary anastomoses are performed endoscopically rather than under direct visualization.

Outcomes

There are several limitations to comparing robotic and conventional coronary revascularization and there are no randomized trials to date. The patient population referred for conventional CABG has significantly more comorbidities than the average robotic candidate who generally has 1-2 vessel disease, without prior chest interventions, and with pulmonary function sufficient to tolerate single lung ventilation. In this healthier population, it is reasonable to expect better outcomes rather than equivalence. Data from the STS database over a 6 year period comparing RA-CAB with conventional CABG did not demonstrate a benefit from the robotic approach. Robotic approaches and MIDCAB share similar advantages and disadvantages when compared to conventional CABG. However, robotic surgery also includes a steep learning curve that often results in longer operative times, occasional conversion, and increased resource utilization. As the learning curve flattens, the results of revascularization approach equivalence when compared to those of other minimally invasive CABG approaches. The adoption of TECAB has been limited due to its technical complexity.

Hybrid Approach

The hybrid approach combines surgery and percutaneous coronary intervention (PCI) to offer a more complete revascularization.

Patient selection

Currently, there are no class Ia recommendations regarding this approach; however, there are some unique patient populations who may benefit from a hybrid approach for complete revascularization. A multidisciplinary team (interventional cardiologists and cardiac surgeons) approach is critical for patient selection. It should be considered for patients with multi-vessel disease involving the LAD who are poor candidates for sternotomy, have poor conduit options outside of the LIMA, or limited life expectancy. A reverse hybrid approach, which is PCI followed by MID CAB, should be considered in young patients with multi-vessel disease presenting with ACS involving a non-LAD territory.

Technique

The LIMA to LAD graft is performed utilizing a minimally invasive technique. The timing of PCI intervention is flexible. Simultaneous hybrid revascularization involves surgical grafting of the LIMA to LAD followed by PCI performed in a hybrid OR suite. This technique has the advantage of allowing immediate angiographic evaluation of the graft and reduced myocardial ischemia risk during the PCI intervention that follows. Surgical grafting followed by PCI days to weeks later is the standard hybrid approach and offers many of the same advantages as the 1-step approach. It provides the additional benefit of decreased risk of surgical bleeding, but these patients are at risk for ischemic events in the non-revascularized myocardium during the waiting period. The final approach, the reverse hybrid approach, is PCI followed by surgical grafting of LAD. This approach is utilized in patients who present with acute coronary syndrome involving non-LAD lesions but who have significant LAD disease. Most often patients undergo PCI 30 days prior to CABG, but this does not completely mitigate the risk of bleeding and stent thrombosis owing to the complex antiplatelet management.

Outcomes

When compared to conventional surgical revascularization utilizing vein grafts, the hybrid approach offers similar mortality and rates of major adverse cardiovascular events but may require more repeat coronary interventions.

Minimally Invasive Valve Surgery

Minimally invasive aortic valve replacement (AVR) is the replacement of the aortic valve either through a hemi-sternotomy or right anterior thoracotomy approach.

Patient selection

The hemi-sternotomy approach is reasonable to consider in most patients. Patients should have adequate femoral access for peripheral cannulation for the thoracotomy approach. Pneumonectomy presents a relative contraindication for both approaches with the displacement of the heart and great vessels making visualization a challenge through a hemi-sternotomy. Chest wall deformity and adhesions from prior lung surgery typically prevent adequate visualization through a thoracotomy. Any condition with similar anatomic distortion or potential for significant adhesive disease of the right pleura or mediastinum should be approached with caution.

Technique

The hemi-sternotomy involves making a 6-8cm vertical upper midline sternotomy using a standard sternal saw. Depending on patient anatomy the distal extent of the sternotomy is usually in the 3^rd or 4^th ICS. This provides exposure to the aortic root and right atrial appendage for cannulation. If access to the right atrium is limited, then the femoral vein can also be utilized for access. Alternatively, the aorta can be approached via a right anterior thoracotomy at the 2^nd or 3^rd ICS in the mid clavicular line. Some investigators have suggested that utilization of rapid deployment aortic valves offers a means to further simplify this approach.

Minimally invasive exposure presents limited access to the diaphragmatic surface of the right ventricle and posterior and lateral left ventricle. Because of this, placement of the retrograde cardioplegia cannula, if utilized, must be adjusted to accommodate a steeper angle of entry and confirmed with TEE rather than palpation. Alternatively, the retrograde cannula can be placed into the coronary sinus via the internal jugular vein by anesthesia preoperatively. Another significant alteration to the standard AVR is subxiphoid drain placement. Due to the limited space, these are typically placed with the heart decompressed on bypass through a retrosternal tunnel that is taken through the pericardium under direct visual or tactile guidance.

Outcomes

There have been no significant differences in early mortality, stroke, or reoperation for bleeding when compared to conventional AVR. Minimally invasive AVR by either approach has been associated with shorter LOS (1-2 days), less pain, and fewer transfusions. The thoracotomy approach has been associated with a reduction in the incidence of postoperative atrial fibrillation and a reduction in wound infections. If peripheral cannulation is used, minimally invasive AVR may increase the risk for vascular complications compared to conventional AVR.

Mitral Valve Surgery

Patient selection

There are several relative and absolute contraindications to a minimally invasive mitral valve surgery centered on the technical modifications necessary for this approach.

• Absolute contraindications
  • Chest wall deformities limiting exposure
    • Severe aortic insufficiency
    • Need for coronary revascularization
    • Heavily calcified mitral annulus
    • Severe peripheral arterial disease
    • Inability to tolerate single lung ventilation
    • Relative contraindications
      • Prior history of right sided thoracic surgery
      • Severely diminished left ventricular function
      • Severe emphysema
      • Morbid obesity

Technique

For minimally invasive and robotic techniques, the mitral valve is approached through a 4-6 cm right anterior thoracotomy in the 4^th ICS. This is considered the “working port” for both endoscopic and robotic approaches. Visualization is achieved utilizing a 2D endoscope in the 3^rd or 5^th ICS. Mitral valve exposure usually is achieved via an atrial lift system in the right parasternal 4^th ICS. Aortic occlusion can be performed under direct visualization utilizing a transthoracic vascular clamp through a right axillary incision or an aortic endoballoon (EndoClamp/IntraClude, Edwards Lifesciences, Irvine, CA, USA) placed with TEE guidance. For standard cross clamping, care must be taken to avoid injury to the pulmonary artery during clamp placement. While more costly, endoballoon aortic occlusion has the advantage of being able to deliver antegrade cardioplegia. It must be precisely placed and remain stable to avoid occluding the innominate artery, causing embolization, or migration towards the ventricle. Its use however has been associated with a higher risk of stroke in some series.

Mitral valve disease often presents with concomitant atrial fibrillation. A minimally invasive MAZE procedure can safely be performed at the time of mitral valve repair/replacement without significant additional morbidity. A description of the tools, technique, and outcomes can be found in the suggested readings for this chapter but will not be described here.

Outcomes

When comparing conventional and minimally invasive mitral valve surgery, there have been no significant differences in mortality, reoperation, valve function, or new onset atrial fibrillation. The risk of stroke is equivalent between the techniques when traditional cross clamping is used. With respect to operative time, minimally invasive mitral valve surgery generally has longer cross clamp and bypass times but is associated with decreased ICU and hospital length of stay as well as decreased need for transfusion.

Suggested Readings

1. Lancaster TS, Melby SJ, Damiano RJ Jr. Minimally invasive surgery for atrial fibrillation. Trends Cardiovasc Med. 2016 Apr;26(3):268-77.
2. Guenther TM, Chen SA, Balkhy HH, Kiaii B. Robotic Coronary Artery Bypass Grafting: The Whole 9 Yards. Innovations (Phila). 2020 May/Jun;15(3):204-210. doi: 10.1177/1556984520922931. Epub 2020 May 18. PMID: 32419555.
3. Rodriguez M, Ruel M. Minimally Invasive Multivessel Coronary Surgery and Hybrid Coronary Revascularization: Can We Routinely Achieve Less Invasive Coronary Surgery?. Methodist Debakey Cardiovasc J. 2016;12(1):14-19. doi:10.14797/mdcj-12-1-14
4. Marin Cuartas M, Javadikasgari H, Pfannmueller B, et al. Mitral valve repair: Robotic and other minimally invasive approaches. Prog Cardiovasc Dis. 2017;60(3):394-404. doi:10.1016/j.pcad.2017.11.002
5. Chang C, Raza S, Altarabsheh SE, et al. Minimally Invasive Approaches to Surgical Aortic Valve Replacement: A Meta-Analysis. Ann Thorac Surg. 2018 Dec;106(6):1881-1889.