The Golden Age of Minimally Invasive Cardiothoracic Surgery

Hybrid & Catheter-based Therapies

Hybrid Coronary Revascularization

Hybrid coronary revascularization is a relatively new innovation that offers patients an alternative to traditional coronary artery bypass by employing a minimally invasive incision for LIMA–LAD bypass with stenting of other occluded coronaries during the same procedure. It should not be confused with the MIDCAB, which offers a minimally invasive incision, but no stenting.^[117]

Hybrid revascularization is the next logical step in the evolution of minimal access treatment of multivessel CAD. It is well established that utilizing a LIMA graft to the LAD for patients with CAD is more effective at decreasing symptoms and increasing patient survival than any other CAD therapy. Graft patency often lasts 10–15 years or more.^[117–121]

Hybrid revascularization allows for the benefit of both the surgical LIMA–LAD bypass graft and a minimally invasive incision, while percutaneous coronary intervention (PCI) is used for the treatment of non-LAD vessels. This combination of surgical LIMA–LAD and PCI affords the patient the best available therapy for any given set of cardiovascular lesions with minimal access and reduced heart manipulation.^[117] Early hybrid revascularization techniques completed PCI and coronary bypass grafting in two separate procedures with the bypass grafting being performed on- or off-pump on a patient-to-patient basis; however, hybrid revascularization is now performed simultaneously, with the PCI and coronary artery bypass grafting occurring during the same procedure and off-pump.

Hybrid revascularization is currently used almost exclusively for patients who are high risk, likely owing to MIDCAB or off-pump full sternotomy options being available for complete multivessel revascularization, with low morbidity and mortality in lower-risk patient groups.^[122] Widespread adoption of hybrid revascularization has been restricted largely by the elevated number of repeat PCIs owing to target vessel failure. These reinterventions are not customary in MIDCAB or off-pump CABG groups; however, the introduction of drug-eluting stents seems to have reduced the need for repeat PCI in hybrid revascularization patients; long-term follow-up is still required.^[122]

In addition, there are debates concerning the conflicting perioperative management for simultaneous surgical revascularization and PCI,^[122] high costs associated with the procedure and drug-eluting stents and other logistical concerns. Closer cooperative collaboration between cardiac surgeons and interventional cardiologists is necessary to obtain optimal patient outcomes in the future.^[117] As with many surgical techniques, patients with particular characteristics are better candidates for certain techniques. A patient-based approach for selection to hybrid revascularization must be used.

Other hybrid revascularization procedures in use include minimally invasive valve surgery combined with PCI to coronary lesions, the latter of which transforms a complex operation of valve surgery with concomitant coronary artery bypass grafting to a less invasive, minimal access valve surgery.^[117]

Transcatheter AVR

Replacement of the aortic valve is the only effective treatment for symptomatic aortic stenosis (AS) that alleviates symptoms and improves survival. Surgical AVR, whether utilizing traditional or minimally invasive techniques, has a low operative mortality in an otherwise healthy individual;^[123] however, the mortality rate associated with surgical AVR increases considerably with the addition of patient comorbidities, including left ventricular dysfunction and chronic conditions possibly exacerbated by cardiac surgery. Patients of increased age are at a much higher risk of mortality, presumably owing to the presence of multiple coexisting conditions that typically present in persons of advanced age. Transcatheter AVR was developed with the purpose of having a therapeutic solution to offer patients with severe symptomatic AS who are not candidates for surgical AVR.^[124]

Initial attempts at transcatheter AVR were complicated by vascular access difficulties and lack of suitable equipment. The initial technique employed for transcatheter AVR was the antegrade approach. Using this technique, the catheter is advanced via the femoral vein, threaded trans-septally and passed through the mitral valve en route to the aortic valve.^[125] Valve placement using this approach is simple, because the device crosses the smooth portion of the aortic valve; however, the overall technique is challenging owing to complicated navigation of the catheter and prosthetic valve across the mitral and aortic valves, the need for trans-septal puncture and the risk for mitral-valve injury. These issues prompted technical improvements in the delivery system and incited implementation of the transfemoral (retrograde) approach.^[124] In the transfemoral approach, the catheter is advanced to the stenotic aortic valve via the femoral artery. Valve deployment is accomplished by transcatheter introduction of a balloon- or self-expandable valve.^[11,126] Rapid ventricular pacing (roughly 180–200 beats per min) is used to reduce cardiac motion during critical deployment of the valve. The transfemoral approach is faster and less technically difficult than the antegrade approach, although it does still carry the risk of injury to the aortofemoral vessels.^[125]

The transapical approach is the most recently developed technique for transcatheter AVR. The transapical AVR requires the use of a hybrid operative suite. It employs a small left lateral thoracotomy and subsequently uses direct puncture and sheath insertion directly into the apex of the left ventricle. A guide wire is used to cross the aortic valve and the rest of the procedure follows the same steps of valve deployment as the transfemoral approach.^[125]

Benefits of transapical AVR involve more direct access to the stenotic valve and the avoidance of potential complications owing to peripheral access. Although beneficial, the transapical approach does require the use of general anesthesia and it also carries the risk of complications related to the puncture of the left ventricle.^[125]

The antegrade approach to transcatheter AVR is no longer employed. Transfemoral and transapical delivery routes can be selected based on certain patient characteristics, such as the quality of vascular access and the type of aortic valve prosthesis selected for the procedure.^[124]

The number of transcatheter AVRs has grown significantly in just a few years and initial published data have been promising.^[127–129] A multicenter, randomized trial, Placement of Aortic Transcatheter Valve (PARTNER), has completed enrollment. The trial includes patients with severe symptomatic AS who are poor or unsuitable surgical candidates. Its two treatment arms include an arm comparing outcomes of optimal medical management (including balloon valvuloplasty) with transfemoral AVR in patients considered 'inoperable' and an arm comparing outcomes of traditional surgical AVR with transfemoral AVR and traditional surgical AVR with transapical AVR in high-risk patients.^[124,126]

Data from the first arm comparing optimal medical management to transfemoral AVR in inoperable patients have recently been reported in 2010, with a primary end point of rate of death from any cause. The results of this arm demonstrated significantly reduced rates of all-cause mortality, reduction in the composite end point of death from any cause or repeat hospitalization and decreased incidence of cardiac symptoms. Conversely, there was a significant increase in the incidence of cerebrovascular accidents and other major vascular events associated with the transfemoral AVR approach, whose reasons have yet to be fully elucidated.^[126]

The final results of this trial will play a major part in determining the role of transcatheter AVR in the future. The results of the second arm are due to be released in early 2011. After these results are released, a continuation of the PARTNER trial will likely be underway, presumably with the purpose of studying outcomes in a lower-risk patient population.

Percutaneous Indirect Mitral Annuloplasty

The percutaneous treatment of mitral stenosis is well established;^[130] however, the percutaneous management of mitral regurgitation (MR) is still in early development and is a potential area of clinical benefit for both degenerative and functional MR patients.

The MitraClip® (Abbott Laboratories, Abbott Park, IL, USA) procedure is a percutaneous version of a surgical technique used in mitral valve repair, the Alfieri stitch. This surgical treatment involves suturing the midpoint of the two mitral valve leaflets together, which reduces regurgitant mitral valve flow.^[131]

The Evalve MitraClip uses clips placed percutaneously to approximate the surgical Alfieri stitch repair. Transesophageal echocardiographic guidance is used for the procedure. Trans-septal puncture is performed and the delivery system is delivered into the left atrium using the femoral vein. The device is guided toward the central part of the mitral valve. The arms of a clip are extended and used to grab the central portion of each of the two mitral valve leaflets. The clip arms are then closed to retain both leaflets within the clip. This approximates the Alfieri stitch described previously.^[131]

The Evalve technology can be used in some valves with degenerative disease, such as mitral valve prolapse or flail leaflet, provided certain anatomic requirements are met in order to ensure the ability of the clip to capture the two mitral valve leaflets. These anatomic requirements include adequate coaptation of the leaflets and a central MR jet origin along the line of leaflet coaptation. The MitraClip has also been used in patients with functional MR, where annular dilation is limited enough to allow sufficient leaflet coaptation for the clip to capture.^[131]

The Endovascular Valve Edge-to-Edge Repair Study (EVEREST II) trial was completed in 2010. This is the first randomized, multicenter trial of any percutaneous mitral valve therapy. Patients were randomized 2:1 (two MitraClip to one surgical mitral valve repair or replacement). Overall, 30-day safety was superior for the MitraClip and 1-year efficacy was reported as noninferior compared with surgical approach.^[132] However, the general consensus is that percutaneous mitral-valve repair is not as effective in preventing long-term MR as surgery and that the future role of percutaneous mitral-valve repair is still to be decided.

As with many surgical techniques, patients with particular risk factors are better candidates for certain techniques. A patient-based approach for selection to MitraClip implantation should be implemented.^[132]

Future Cardiol. 2011;7(3):433-446. © 2011 Future Medicine Ltd.

Cite this: The Golden Age of Minimally Invasive Cardiothoracic Surgery - Medscape - May 01, 2011.