Transcatheter mitral valve repair and replacement

Rationale for transcatheter therapy

Surgery to repair or replace the MV in patients with severe MR appears to improve survival in observational studies. The impetus for the development of transcatheter therapies for valvular heart disease arises from two major factors. First is the expectation that a transcatheter therapy can avoid the risks and discomfort associated with surgery, particularly the use of cardiopulmonary bypass and sternotomy or thoracotomy. Second is the patient’s desire to avoid the slower recovery associated with major surgery. However, these factors must be balanced with the efficacy of the transcatheter approach. A transcatheter approach that is less invasive, provides faster patient recovery, and has similar efficacy is always preferred to a surgical approach. However, a less efficacious approach, even if safer and associated with faster recovery, requires more complex shared decision making that takes into account the patient’s age, frailty, comorbidities, and goals of care.

Surgery is associated with mortality rates of 1% to 5% and additional morbidity rates of 10% to 20%, with morbidity including stroke, reoperation, renal failure, and prolonged ventilation. In one study of Medicare-age patients, more than 20% required rehospitalization during the first 30 days after surgery. The risks of surgery are particularly high in patients who are elderly or have LV dysfunction. ^, In a study of more than 30,000 patients undergoing MV replacement, the mortality rate increased from 4.1% for those younger than 50 years of age to 17.0% for octogenarians ( Fig. 20.1 ). Significant morbidity (i.e., stroke, prolonged ventilation, renal failure, reoperation, sternal infection) affected more than one third of the octogenarians. Predictors of risk in addition to age in this study included hemodynamic instability, severe symptoms, renal failure, and prior coronary artery bypass grafting surgery (CABG).

For patients with LV dysfunction and secondary MR, whether ischemic or functional, survival with or without surgery is not as good as for patients with preserved LV function and a diagnosis of primary MR. Whether the increased mortality rate is a consequence of the preexisting LV dysfunction or the MR contributes to the reduced survival remains a controversial issue. In vitro studies have demonstrated progressive adverse LV remodeling in sheep even after successful MR repair. Other studies have not shown benefit with annuloplasty repair of MR in dilated cardiomyopathy or at the time of revascularization with CABG. One study of MV repair during CABG reported a rate of recurrence for moderate or severe MR of close to 60% at 2 years. In cases of ischemic and nonischemic functional MR, age and comorbidities are the most important predictors of survival.

The major reason for surgery in most patients with ischemic MR is to provide symptomatic improvement, and in those with primary MR, the goal is to forestall the development of LV dysfunction. It also is essential to discuss the efficacy of surgery in terms of MR reduction. In relatively young patients (range, 55–60 years) with primary MR, long-term freedom from repeat surgery is well documented. ^, However, recurrent 3+ and 4+ MR may be observed in up to 30% of patients within 15 years. ^, Recurrent MR is even more common in patients with ischemic MR, providing a potential target for the development of transcatheter therapies.

Classification of percutaneous repair techniques

In keeping with the complexity of the MV apparatus, it is useful to consider the percutaneous approaches according to the major structural abnormalities that they address. Unlike the extensive toolbox available to the MV surgeon, transcatheter approaches are much more limited and often able to address only a single major element of the dysfunctional valve that contributes to MR.

The remainder of this chapter addresses these transcatheter approaches, with an emphasis on devices that have been approved in some part of the world, those that have entered first-in-human or phase 1 clinical investigation, and those with published data (i.e., clinical or preclinical). Some devices that have been evaluated in vivo without success or are no longer under development are discussed only as they relate to other current approaches. Table 20.1 lists the devices along with their manufacturers, state of development, and available published reports.