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.
OTHER INDICATIONS FOR SURGICAL AORTIC VALVE REPLACEMENT
For patients with severe but asymptomatic aortic stenosis, surgical referral is standard practice in several circumstances.
Asymptomatic severe aortic stenosis with a low ejection fraction
Early studies found significant differences in survival beginning as early as 3 years after valve replacement between those whose preoperative ejection fraction was greater than 50% and those with a lower ejection fraction.4 Delaying surgery in these patients may lead to irreversible left ventricular dysfunction and worse survival.
Recommendation. The AHA and the ACC recommend surgical aortic valve replacement for patients who have no symptoms and whose left ventricular ejection fraction is less than 50% (class I indication, level of evidence C).10,11
Asymptomatic severe aortic stenosis in patients undergoing other cardiac surgery
Recommendation. Even if it is causing no symptoms, a severely stenotic aortic valve ought to be replaced if the ejection fraction is greater than 50% and the patient is undergoing another type of heart surgery, such as coronary artery bypass grafting, aortic surgery, or surgery on other heart valves (class I indication, level of evidence B).10,11
Asymptomatic moderate aortic stenosis in patients undergoing other cardiac surgery
When patients with a mildly or moderately stenotic aortic valve undergo other types of cardiac surgery, the decision to replace the valve is more difficult. Clinicians have to consider the increase in risk caused by adding aortic valve replacement to the planned surgery compared with the future likelihood of aortic stenosis progressing to a severe symptomatic state and eventually requiring a second cardiac surgery.
We have no evidence from a large prospective randomized controlled trial regarding prophylactic valve replacement at the time of coronary bypass surgery. However, a review of outcomes from the STS database between 1995 and 2000 found that patients under age 70 with a peak aortic gradient greater than “about 28 mm Hg” (correlating with a moderate degree of stenosis) benefited from prophylactic valve replacement at the time of coronary artery bypass surgery.18
These conclusions were supported by a subsequent retrospective analysis that found a significant survival advantage at 8 years in favor of prophylactic valve replacement at the time of bypass surgery for those with moderate (but not mild) aortic stenosis.19
Recommendation. The AHA and ACC give a class IIb endorsement, level of evidence B, for aortic valve replacement in patients with asymptomatic moderate aortic stenosis undergoing coronary bypass, valve, or aortic surgery.10,11
SEVERE ASYMPTOMATIC STENOSIS: WHICH TESTS HELP IN DECIDING?
A patient without symptoms presents a greater challenge than one with symptoms.
If surgery is deferred, the prognosis is usually excellent in such patients. Pellikka et al20 found that patients with severe asymptomatic aortic stenosis who did not undergo surgery had a rate of sudden cardiac death of about 1% per year of follow-up. However, physicians worry about missing the rapid development of symptoms of aortic stenosis in patients who previously had none. Pallikka et al also found that, at 5 years, only 20% of patients had not undergone aortic valve replacement or had not died of cardiovascular causes.20
Many researchers advocate surgical aortic valve replacement for severe asymptomatic aortic stenosis. However, the operative risk is 3% overall and has to be weighed against the 1%-per-year risk of death in patients who do not undergo surgery. Therefore, we need a way to identify a subgroup of patients without symptoms who are at higher risk.
Exercise stress testing
Some patients might subconsciously adapt to aortic stenosis by reducing their physical activity. In these “asymptomatic” patients, exercise stress testing can uncover symptoms in around 40%.21
In a group of people with severe asymptomatic aortic stenosis, a positive treadmill test (defined as an abnormal blood pressure response, ST segment changes, symptoms such as limiting dyspnea, chest discomfort, or dizziness on a modified Bruce protocol, or complex ventricular arrhythmias) strongly predicted the onset of symptoms or the need for surgery. At 24 months, only 19% of those who had had a positive exercise test result remained alive, symptom-free, and without valve replacement, compared with 85% of those who had had a negative test result.22
Subsequent study found that symptoms with exercise were the strongest predictor of the onset of symptoms of aortic stenosis, especially among patients under age 70, in whom the symptoms of fatigue and breathlessness are more specific than in the elderly.23
Recommendation. Exercise testing is recommended in patients with severe asymptomatic aortic stenosis (class IIa indication, level of evidence B) as a means of identifying those who are likely to develop symptoms or who might benefit from surgery. Surgery for those who have an abnormal exercise stress response receives a class IIb, level of evidence C recommendation from the ACC/AHA and a class IC from the European Society of Cardiology.24,25
Exercise stress echocardiography to measure change in transvalvular gradient
Emerging data suggest that exercise stress echocardiography may provide incremental prognostic information in patients with severe asymptomatic aortic stenosis. In fact, two studies showed that an exercise-induced increase in the transvalvular gradient of more than 20 mm Hg26 or 18 mm Hg27 predicts future cardiac events. This increase reflects fixed valve stenosis with limited valve compliance.
Other echocardiographic variables
Additional data have shown that severe aortic stenosis (valve area < 0.6 cm2), aortic velocity greater than 4.0 m/s, and severe calcification confer a higher risk of developing symptoms.28,29
Recommendation. The ACC and AHA say that surgical aortic valve replacement may be considered in patients without symptoms who have a high likelihood of rapid progression of aortic stenosis (ie, who are older or have severe calcification or coronary artery disease) or if surgery might be delayed at the time of symptom onset (class IIb, level of evidence C).
Aortic valve replacement can also be considered for extremely severe aortic stenosis (valve area < 0.6 cm2), mean gradient > 60 mm Hg, and velocity > 5.0 m/s if the operative mortality rate is 1.0% or less (class IIb, level of evidence C).
Brain natriuretic peptide levels
Measuring the brain natriuretic peptide (BNP) level may help if symptoms are unclear; higher levels suggest cardiac decompensation.28
One study showed that BNP levels are higher in patients with symptomatic aortic stenosis than in those with asymptomatic severe disease, and correlate with symptom severity.30 In addition, in two other studies, higher BNP and N-terminal BNP levels were shown to predict disease progression, symptom onset, and poorer event-free survival.31,32
In severe asymptomatic aortic stenosis, natriuretic peptides may provide important prognostic information beyond clinical and echocardiographic evaluation. Furthermore, in a recent study, Monin et al33 proposed a risk score that integrates peak aortic jet velocity, BNP level, and sex (women being at higher risk) in predicting who would benefit from early surgery in patients with severe asymptomatic aortic stenosis.33
