Aortic stenosis: Who should undergo surgery, transcatheter valve replacement?
ABSTRACTAortic stenosis, the most common valvular disease in the Western world, affects mainly people over age 60. It is characterized by years to decades of slow progression followed by rapid clinical deterioration and a high death rate once symptoms develop. Drug therapy for it remains ineffective, and surgical aortic valve replacement is the only effective long-term treatment. We discuss the indications for this surgery, with an emphasis on controversial conditions in which the indications are less well defined.
KEY POINTS
- The management of severe but asymptomatic aortic stenosis is challenging. An abnormal response to exercise stress testing and elevated biomarkers may identify a higher-risk group that might benefit from closer followup and earlier surgery.
- Even patients with impaired left ventricular function and advanced disease can have a good outcome from surgery.
- Dobutamine infusion can help ascertain which patients with low-flow, low-gradient aortic valve stenosis have true severe stenosis (as opposed to pseudostenosis) and are most likely to benefit from aortic valve replacement.
- Transcatheter aortic valve implantation will soon become the procedure of choice for patients at high risk for whom surgery is not feasible, and it may be an alternative to surgery in other patients at high risk even if they can undergo surgery.
Elderly patients
The risks of cardiac surgery increase with age. Older patients may be more deconditioned and have more comorbidities than younger patients, placing them at greater risk of a poor outcome.
Several retrospective studies of valve replacement in octogenarians have found that operative mortality rates range from 5.7% to 9% during isolated aortic valve replacement.58–60 Note that, using the STS score, the operative mortality risk increases only from 1.2% in a 70-year-old man with no comorbidities to 1.8% in an 80-year-old man undergoing aortic valve replacement plus coronary artery bypass grafting.61
As in younger patients, valve replacement results in a significant survival benefit and symptomatic improvement. Yet up to 30% of patients with severe aortic stenosis are not referred for surgery because surgery is believed to be too risky.62 The conditions most frequently cited by physicians when declining to refer patients for surgery include a low ejection fraction, advanced age, and advanced comorbidities. None of these is an absolute contraindication to surgery.
A recent retrospective study of 443 elderly patients (mean age 79.5) showed that those with left ventricular concentric remodeling, lower stroke volume, elevated left ventricular filling pressures, and mildly elevated pulmonary artery pressures have a very bad prognosis, with a mortality rate of 50.5% at 3.3 ± 2.7 years.63
Despite the higher operative mortality risk, these patients face a dismal prognosis when treated medically and should be referred to a cardiologist or cardiothoracic surgeon for an assessment of their operative risk and, potentially, for referral for catheter-based valve replacement.
Acutely ill patients
In critically ill patients with aortic stenosis and cardiogenic shock, the use of intravenous sodium nitroprusside increases cardiac output and decreases pulmonary artery wedge pressure, allowing patients to transition to surgery or vasodilator therapy. The mechanism seems to be an increase in myocardial contractility rather than a decrease in peripheral resistance. The reduction in filling pressure and concurrent increase in coronary blood flow relieves ischemia and subsequently enhances contractility.64
TRANSCATHETER AORTIC VALVE REPLACEMENT
Until recently, patients with severe aortic stenosis who were deemed to be at high surgical risk were referred for balloon valvuloplasty as a palliative option. The procedure consists of balloon inflation across the aortic valve to relieve the stenosis.
Most patients have improved symptoms and a decrease in pressure gradient immediately after the procedure, but the results are not durable, with a high restenosis rate within 6 to 12 months and no decrease in the mortality rate.65 (There is some evidence that serial balloon dilation improves survival.66)
The procedure has several limitations, including a risk of embolic stroke, myocardial infarction, and, sometimes, perforation of the left ventricle. It is only used in people who do not wish to have surgery or as a bridge to surgical aortic valve replacement in hemodynamically unstable patients.
Advances in transcatheter technologies have made nonsurgical valve replacement a reality that is increasingly available to a broader population of patients. The first percutaneous valve replacement in a human was performed in 2002.67 Since then, multiple registries from centers around the world, especially in Europe, have shown that it can be performed in high-risk patients with outcomes very comparable to those of surgical aortic valve replacement as predicted by the STS score and EuroSCORE.68,69 Procedural success rates have increased from around 80% in the initial experience to over 95% in the most current series.70
Results from randomized trials
The long-awaited PARTNER A and B trials have been published.
The PARTNER B trial17 randomized patients with severe aortic stenosis who were not considered by the STS score to be suitable candidates for surgery to standard therapy (which included balloon valvoplasty in 84%) or transcatheter aortic valve replacement. There was a dramatic 20% absolute improvement in survival at 1 year with transcatheter replacement, with the survival curve continuing to diverge at 1 year. The rate of death from any cause was 30.7% with transcatheter aortic valve replacement vs 50.7% with standard therapy (hazard ratio with transcatheter replacement 0.55; P < .001).
The major concerns about transcatheter aortic valve replacement borne out in the study are procedural complications, namely stroke and vascular events. At 30 days, transcatheter replacement, as compared with standard therapy, was associated with a higher incidence of major stroke (5.0% vs 1.1%, P = .06) and major vascular complications (16.2% vs 1.1%, P < .001).17
On the other hand, the PARTNER A trial randomized high-risk patients deemed operable by the STS score to either transcatheter or surgical aortic valve replacement. The rate of death at 1 year from any cause was similar in both groups (24.2% vs 26.8%; P = .44), but again at the expense of higher rates of vascular complications (11.0% vs 3.2%, P < .001 at 30 days) and stroke (5.1% vs 2.4%; P = .07 at 1 year) in the transcatheter group. However, the surgical group had higher rates of major bleeding (19.5% vs 9.3%; P < .001) and new-onset atrial fibrillation (16.0% vs 8.6%, P = .06).71
Transcatheter aortic valve replacement has modernized the way we treat aortic stenosis and without a shred of doubt will become the standard of therapy for severe symptomatic aortic stenosis in patients who are not candidates for surgery. For the high-risk operable patient, the benefit of avoiding a sternotomy should be weighed against the higher risk of stroke and vascular complications with the transcatheter procedure. The availability of smaller delivery systems, better expertise, and better vascular access selection should decrease the rate of complications in the future.
