Challenges in the management of aortic stenosis
The classic case of aortic stenosis is in an otherwise healthy middle-aged patient with symptomatic severe disease who is referred to a cardiac surgeon for surgical aortic valve replacement. Unfortunately, physicians who manage valvular heart disease do not encounter this straightforward scenario on a regular basis. Rather, patients come with comorbidities such as advanced age, pulmonary disease, renal dysfunction, coronary artery disease, and significant left ventricular dysfunction. They also come with severe aortic stenosis without symptoms.
In this issue of the Cleveland Clinic Journal of Medicine, Sawaya and colleagues1 review the management of aortic stenosis, focusing on clinically challenging scenarios such as low-flow, low-gradient aortic stenosis, low-gradient severe aortic stenosis with a normal ejection fraction, aortic stenosis in elderly patients, moderate aortic stenosis in patients undergoing other cardiac surgery, and transcatheter aortic valve replacement, according to the guidelines from the American College of Cardiology and American Heart Association.2
In addition to the situations covered in their review, a few other complicated situations in patients with severe aortic stenosis also merit discussion. We discuss these below.
ASYMPTOMATIC SEVERE AORTIC STENOSIS AND A NORMAL EJECTION FRACTION
Patients with aortic stenosis may be unaware of their decline in functional capacity, since the illness is gradually progressive. In these patients, exercise testing is often done, as it can uncover limitations and determine the need for aortic valve replacement. Another group of patients with asymptomatic severe aortic stenosis who need aortic valve replacement are those whose ejection fraction is less than 50%.
However, many patients with asymptomatic aortic stenosis pass the stress test with flying colors—no symptoms, no blood pressure changes, no arrhythmias—and have a normal ejection fraction. Managing these patients can be more complicated.
Lancellotti et al3 described a group of patients with asymptomatic severe aortic stenosis, a normal ejection fraction, an aortic valve area smaller than 1 cm2, and normal results on exercise testing. Rates of the primary end point (cardiovascular death or need for aortic valve replacement due to symptoms or left ventricular dysfunction) were assessed in subsets of patients grouped on the basis of two variables:
- Left ventricular stroke volume index (flow)—either normal or low (< 35 mL/m2) and
- Mean gradient—either high or low (< 40 mm Hg).
The prevalence rates and 2-year event rates (which were substantial) were as follows:
- Normal flow, high gradient—51% of patients; event rate 56%
- Normal flow, low gradient—31% of patients; event rate 17%
- Low flow, high gradient—10% of patients; event rate 70%
- Low flow, low gradient—7% of patients; event rate 73%.
Mihaljevic et al4 at our institution found that left ventricular hypertrophy at the time of surgery for aortic stenosis may have lasting negative consequences. In an observational study of 3,049 patients who underwent aortic valve replacement, severe left ventricular hypertrophy preceded symptoms in 17%. Additionally, the survival rate at 10 years in the group whose left ventricular mass was greater than 185 g/m2 was 45% at 10 years, compared with 65% in patients whose left ventricular mass was less than 100 g/m2. Left ventricular hypertrophy may, therefore, eventually become another factor that we use in defining the appropriateness of surgery in patients with severe but asymptomatic aortic stenosis.
Comment. Not all patients who have severe aortic stenosis, no symptoms, and a “normal” ejection fraction are the same. Our view of what constitutes appropriate left ventricular function in aortic stenosis has changed and now encompasses diastolic filling values, myocardial velocity, and patterns of hypertrophy in addition to ejection fraction. Surgery is already considered reasonable for patients with asymptomatic but “extremely severe” aortic stenosis (aortic valve area < 0.6 cm2, jet velocity > 5 m/sec, mean gradient > 60 mm Hg), and it may improve long-term survival.2,5
However, closer inspection of left ventricular mechanics may also identify another group of patients whose prognosis is worse than in the rest. It is possible that a more thorough evaluation of left ventricular mechanics, including strain imaging, will provide a more elegant way to risk-stratify patients and help clinicians decide when to intervene in this difficult group of patients.6
While these factors are not yet a part of the diagnostic algorithm, the work by Lancellotti et al3 and Mihaljevic et al4 sheds light on the idea that evaluation of advanced echocardiographic variables may provide clinical insights into whether patients should undergo aortic valve replacement.
