57. Reoperative Aortic Valve Surgery- Review of CT Surgery

Bogdan Kindzelski and Douglas Johnston

Overview

As the population ages, the rate of reoperation for valvular heart disease continues to increase. Reoperative surgical aortic valve replacement (SAVR) can be performed for a myriad of prosthetic valve complications including structural valve deterioration (SVD), prosthetic endocarditis, prosthetic thrombosis, severe patient prosthesis mismatch, or paravalvular leak. Surgical implantation of bioprostheses and transcatheter aortic valve replacement (TAVR) have been increasing rapidly at the expense of mechanical prostheses. This trend is not only seen in the elderly patient population, but also demonstrated in younger patients, ultimately yielding higher rates of SVD over time. Several factors may explain increased rates of bioprosthetic valve selection in the younger population: no need for lifelong anticoagulation, the extended durability of newer bioprostheses, and the availability of transcatheter valve-in-valve (TViV) options in cases of SVD.

Based on the 2020 AHA/ACC Guidelines the following are indications for reparative valve surgery:

• Repeat surgical intervention is indicated in patients with symptomatic severe stenosis of a bioprosthetic or mechanical prosthetic valve, unless surgical risk if high or prohibitive (Class I)
• In patients with intractable hemolysis or HF attributable to prosthetic transvalvular or paravalvular leak, surgery is recommended unless surgical risk is high or prohibitive (Class I)
• In asymptomatic patients with severe prosthetic regurgitation and low operative risk, surgery is reasonable (Class IIa)
• In patients with prosthetic paravalvular regurgitation with 1) either intractable hemolysis or NYHA III-IV symptoms and 2) who are at high or prohibitive surgical risk and 3) have anatomic features suitable for catheter-based therapy, percutaneous repair of paravalvular leak is reasonable when performed at a Comprehensive Valve Center (Class IIa)

The specific etiology for reoperation, relevant anatomy, and patient comorbidities are all critical to carefully assess for optimal outcomes. Reoperations are more challenging than primary cases due to more complex pathology and patient comorbidities, proximity of cardiovascular structures to the posterior table of the sternum, and risk of inadvertent injury during both re-entry and mediastinal dissection that is necessary for adequate exposure and safe conduct of the operation. Furthermore, outcomes are incrementally worse at a higher preoperative NYHA class. Concomitant coronary artery disease and pulmonary hypertension are also strong independent risk factors for worse outcome. Therefore, referral for reoperative AVR is paramount before significant myocardial depression or worsening pulmonary hypertension occurs. Nonetheless, risk-adjusted outcomes of a redo-SAVR have been shown to approach those of a primary operation for aortic valve replacement.

Preoperative Workup and Indications for Intervention

As for every reoperative cardiac surgery, a thorough preoperative workup should be undertaken to assess candidacy and risk. A heart-team approach allows for the optimal treatment options to be assessed for each individual patient. A thorough echocardiogram should be conducted with particular attention to hemodynamics of the prosthetic valve, cardiac chamber size, and overall LV/RV function. Severe prosthetic aortic stenosis is defined as aortic valve area <0.8 cm2, mean AV gradient ≥40 mm Hg, or dimensionless index <0.25, according to AHA guidelines. Studies have also shown LV global longitudinal strain as an independent predictor of longer-term adverse events. Additionally, specific attention to these echocardiographic findings should be entertained when evaluating a prosthetic prosthesis:

• Effective orifice area and any evidence of patient-prosthetic mismatch
• Obstruction due to thrombus, pannus ingrowth, leaflet thickening, or significant calcium burden
• Prosthetic valve endocarditis including vegetations and abscess formation
• Prosthetic regurgitation as a result of paravalvular leak, vegetation, or bioprosthesis leaflet tear
• Prosthetic valve dehiscence with evidence of valve ring rocking
• Mechanical structural failure (e.g., strut failure)

Cardiac structure proximity to the posterior sternum should be assessed using a CT scan. For high-risk sternal re-entry cases (e.g., sternal adherence of bypass grafts crossing midline, adherence of ascending aorta to the sternum, or pseudoaneurysm of the aorta or other great vessels within close proximity to the sternum) or calcified/porcelain aortas, alternative cannulation strategies should be considered and the femoral vessels and the right axillary artery should be appropriately assessed on imaging. Additionally, the location of the coronary arteries and coronary height should be thoroughly assessed. This can provide critical insight on risk of coronary occlusion, particularly with TViV options. Accurate size measurements of the aortic annulus are paramount as they may shed insight on the need for root enlargement procedures to prevent significant patient prosthesis mismatch. Furthermore, CT/MR imaging can provide information on whether any associated aortopathies exist that may require adjuvant aortic procedures. Coronary angiography should be pursued in each patient to evaluate the need for concomitant bypass grafting as well as the anatomic location, mobility, and degree of stenosis of previous bypass grafts should be carefully assessed.

A decision on pre- or post-sternotomy CPB initiation should be made based on anatomic features and surgeon preference. The main pillars of a successful strategy include a multi-disciplinary team approach with close collaboration between cardiovascular imaging, cardiology, cardiac surgery, cardiovascular anesthesia, perfusion, transfusion medicine, nursing, and other care participants. Image guidance and multi-disciplinary expertise are particularly important in high-risk anatomic scenarios. Certain high-risk cases may warrant adjuncts such as endovascular aortic balloon occlusion or percutaneous cardioplegic arrest before repeat sternotomy.

Surgical Aortic Valve Replacement

Per usual practice for reoperative cardiac surgery, prior to incision, external defibrillator pads should be applied to the patient, blood products should be readily available, the CPB pump should be primed, and a bailout strategy should be discussed with the team prior to attempt at re-sternotomy. A hemi-sternotomy approach may be used for reoperative aortic valve surgery and entails a partial sternotomy to the fourth intercostal space. Our preference is a standard full reoperative sternotomy to allow for optimal exposure and provide options for adjuvant maneuvers and procedures if needed. Vigilant myocardial protection should be adhered to with frequent re-dosing and use of retrograde, particularly in cases where aortic insufficiency is present or previous coronary bypass grafting was done. If a patent LITA graft is present then a decision needs to be made on whether to dissect, identify and clamp the graft or use a no-dissection surgical technique in which the graft is left unclamped with use of deep hypothermic cardioplegic arrest.

Following aortotomy and placement of a basket vent through the valve, removal of the previously implanted prosthesis should be done utilizing sharp dissection. Removal of any pledgets from the annulus is encouraged to allow for maximal area for new valve implementation. Annular debridement of any significant calcium should be undertaken and any annular injuries can be repaired with pledgeted interrupted sutures or a bovine pericardial patch if extensive. Removal of sutureless valves or previous TAVR valves can be particularly challenging and may require extensive aortic endarterectomy or replacement due to the neoendothelialization between the aorta and the device. In fact, patients who undergo SAVR after TAVR experience longer operative times and have a higher rate of morbidity and mortality. Operating on previously implanted allografts presents challenges, as well, due to the extensive calcific changes. Options include replacing the allograft with another homograft, doing a Bentall procedure (biologic or mechanical valved conduit), or performing an open valve-in-homograft approach, which entails resection of the degenerated or infected aortic homograft leaflets and seating a new valve within the aortic homograft valve annulus. In cases of endocarditis, aggressive debridement of all infected tissue must be performed with possible aortic root reconstruction or aorto-mitral curtain reconstruction (see below).

Proper sizing of the valve should be done prior to implementation, opting for the largest possible valve to avoid patient-prosthetic mismatch. A root enlargement procedure may be considered in cases where a less than ideal sized valve, (target EOA to BSA ratio of 0.85 cm²/m² or greater), can be fit (see AVR chapter for details on enlargement techniques). Following valve replacement, copious irrigation and standard aortotomy closure is done. For reoperative surgery careful monitoring of hemodynamics is required coming off-pump with inotropic support as needed. Hemostasis is integral as there is often more raw surface bleeding due to previous significant inflammatory and reactive changes.

Commando Procedure and Homograft Use in Cases of Infective Endocarditis

In patients with extensive endocarditis involving a previously implanted prosthetic aortic valve, depending on local invasion, a more extensive operation may be warranted. When the infection extends into the aortic root forming an abscess, a root and valve replacement, usually done with a homograft is warranted. Additionally, if CHB is present then permanent pacing wires should be implemented at the time of surgery.

Infection of the intervalvular fibrosa (IVF) presents with both mitral and aortic valve involvement. These cases require radical debridement and IVF reconstruction. A double-valve replacement with IVF reconstruction (Commando procedure) or aortic valve replacement with mitral valve repair and IVF reconstruction (hemi-Commando procedure) may be pursued based on final intraoperative mitral valve pathology. In both techniques, exposure is obtained by incising the roof of the left atrium (LA) into the aortic root. Following radical debridement of infected tissue, reconstruction of the IVF can be accomplished using a pericardial patch in the Commando procedure, while an anterior mitral leaflet extension of the implanted aortic allograft can generally be utilized with the hemi-Commando approach.

Valve-in-valve TAVR

Based on the 2020 AHA/ACC Guidelines the following are indications for TViV:

• For severely symptomatic patients with bioprosthetic aortic valve stenosis and high or prohibitive surgical risk, a transcatheter ViV procedure is reasonable when performed at a Comprehensive Valve Center (Class IIa)
• For patients with severe HF symptoms caused by bioprosthetic valve regurgitation who are at high to prohibitive surgical risk, a transcatheter ViV procedure is reasonable when performed at a Comprehensive Valve Center (Class IIa)

TViV is possible in stented or stentless bioprosthetic valves. Preoperative planning for TViV is critical. Adequate vascular access is needed: either femoral or transaxillary. In rare cases a transapical approach may still be used. Information that must be obtained includes: CT and echocardiographic imaging, previous operative reports detailing bioprosthetic valve type and size along with commercially available information about the true internal diameter, radiopaque markings, leaflet configuration, strut height, and rigidity. Careful measurements of the prosthetic valve geometry both pre and intraoperatively is important in order to avoid malpositioning, valve migration, and/or coronary obstruction. Patients with SVD and small bioprosthetic valves with an internal diameter <20 mm will have high postoperative gradients and worse outcomes. Therefore, these patients may be better suited with redo-SAVR and possible aortic root enlargement to optimize valve sizing.

Coronary obstruction during TViV has been shown to be associated with poor outcomes. The predominant mechanism of coronary obstruction during TViV involves the displacement of the bioprosthetic valve leaflet towards the sinuses of Valsalva, causing obstruction in the diastolic perfusion of the coronaries. The left coronary artery is more often involved. Preoperative characteristics associated with an increased risk of coronary obstruction include: lower height of the coronary ostium above the valve annulus, narrow sinuses, narrow or low sinotubular junction, tall and bulky leaflets, and externally fixed leaflets or stentless valves. Thus, patients at high risk for coronary obstruction may better benefit from redo-SAVR and if TViV is entertained should have wire access in the coronary arteries prior to valve deployment.

Comparisons between SAVR and TViV have shown similar outcomes in major morbidity and mortality. Several retrospective studies have shown slight differences among the two approaches including higher rates of paravalvular leak in the TViV group versus longer ICU and hospital stays along with greater rates of atrial fibrillation in the redo SAVR group.

Suggested Readings

1. Johnston DR, Soltesz EG, Vakil N, et al. Long-term durability of bioprosthetic aortic valves: implications from 12,569 implants. Ann Thorac Surg. 2015;99:1239-47.
2. Ejiofor JI, Yammine M, Harloff MT, et al. Reoperative Surgical Aortic Valve Replacement Versus Transcatheter Valve-in-Valve Replacement for Degenerated Bioprosthetic Aortic Valves. Ann Thorac Surg. 2016;102:1452-1458.
3. Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for the Management of Patients with Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2021;143(5):e72-e227.
4. Naji P, Shah S, Svensson LG, et al. Incremental Prognostic Use of Left Ventricular Global Longitudinal Strain in Asymptomatic/Minimally Symptomatic Patients With Severe Bioprosthetic Aortic Stenosis Undergoing Redo Aortic Valve Replacement. Circ Cardiovasc Imaging. 2017;10.
5. Kalra A, Raza S, Hussain M, et al. Aortic Valve Replacement in Bioprosthetic Failure: Insights From The Society of Thoracic Surgeons National Database. Ann Thorac Surg. 2020;110:1637-1642.
6. Fukuhara S, Brescia AA, Shiomi S, Rosati CM, Yang B, Kim KM and Deeb GM. Surgical explantation of transcatheter aortic bioprostheses: Results and clinical implications. J Thorac Cardiovasc Surg. 2021;162(2):539-547.e1.