Asymptomatic Severe Aortic Stenosis
Asymptomatic Severe Aortic Stenosis
Abstract & Commentary
By Michael H. Crawford, MD, Editor
Sources: Lancellotti P, et al. Clinical outcome in asymptomatic severe aortic stenosis: Insights from the new proposed aortic stenosis grading classification. J Am Coll Cardiol 2012;59:235-243. Flachskampf FA, Kavianipour M. Varying hemodynamics and differences in prognosis in patients with asymptomatic severe aortic stenosis and preserved ejection fraction. J Am Coll Cardiol 2012;59:244-245.
The management of asymptomatic patients with severe aortic stenosis (AS) is controversial. Patients meeting standard echocardiographic criteria for severe stenosis have a variety of pressure gradients and flow rates that can be divided into four categories based on normal flow vs low flow (NF vs LF) and low gradient vs high gradient (LG vs HG), where LF is defined as a stroke volume index (SVI) of < 35 mL/m2 and LG is a mean gradient < 40 mmHg. These investigators studied 150 consecutive patients (mean age, 70 years) with an echo aortic valve area (AVA) < 1.0 cm2, a normal exercise test, and an ejection fraction (EF) > 55%. These patients were followed every 6-12 months for 2 to 48 months (mean, 27). The primary composite endpoint was the time to the occurrence of cardiovascular (CV) death or the need for aortic valve replacement (AVR) due to the development of symptoms or EF < 50%. At baseline, the patients were divided into four groups: NF/HG seen in 52%, NF/LG in 31%, LF/HG in 10%, and LF/LG in 7%. B-type natriuretic peptide (BNP) was lowest in the NF/LG group and significantly different from the LF/HG group (22 vs 114) and the LF/LG group (22 vs 78), both P < 0.001. At 2 years follow-up, the event-free survival was 83% in the NF/LG group; 44% in NF/HG; 30% in LF/HG; and 27% in LF/LG (P < 0.001). By multivariate analysis, LF/LG (hazard ratio [HR] 5.3, 95% confidence interval [CI] 2-14, P < 0.05) and LF/HG (HR 2.4, CI 1.02-5.55, P = 0.001) were independent predictors of a poor prognosis compared to NF/HG, with LF/LG having the worst prognosis. The authors concluded that this categorization of asymptomatic severe AS patients allows for an improved determination of CV risk in subgroups of these patients.
Commentary
The management of the asymptomatic patient with echo-Doppler evidence of severe AS can be simple, wait for symptoms, or more nuanced. The traditional approach involves careful scrutiny of the echo to be sure severe AS is present, confirmation of symptom status with a cautious exercise study, and weighing other prognostic factors such as the degree of calcification of the valve. Concern for sudden death is not a consideration, as it has been very low in most studies and was 2% in this one. This study investigates the use of hemodynamic classification to aide in predicting who might benefit from an early decision for surgery. This approach assumes that if factors predictive of the need for surgery in an observational study are used to perform early surgery that the outcomes will be better in these asymptomatic patients. This concept has never been proven in a prospective randomized trial nor is it likely to be. So, does this study add any useful information to our clinical judgment in such cases?
The hemodynamic groups are based on the combination of gradient and SVI. About one-third of the patients had NF (SVI > 35 mL/m2) and a low gradient (mean < 40 mmHg). These patients had the best event-free survival of valve replacement and probably did not have severe AS. A valve area of < 1.0 cm2 was part of the definition of severe AS and many believe that severe AS should be defined at 0.8 cm2 or lower. A majority of the patients had normal flow and a high gradient and they had a lower event-free survival (44%). These represent severe AS patients with normal LV function and should be considered for surgery. The other two groups represented < 20% of the study population, which weakens any conclusions about their prognosis. However, the LF/LG group had the worst prognosis with a 27% event-free survival and an HR of 5.3 (P < 0.05). The LF/HG group had similar outcomes (HR 2.4, P < 0.001). Thus, in aggregate any asymptomatic patient with a valve area < 1.0 cm2 and an EF > 55% who has either an HG (mean > 40) or LF (SVI < 35 mL/m2) should be considered for surgery.
The groups with a low SVI probably have LV dysfunction that is not detected by EF. To be fair, an EF of 50-55% is abnormal by echo, but most guidelines use the 50% cutoff since this value is closer to the lower limit by angiography. In this study, BNP was a predicator, but was not an independent predicator in the multivariate analysis. Other LV function indices, such as end diastolic volume, left atrial size, and tissue Doppler longitudinal strain, had some predictive value, but the HRs were ≤ 1.12. Other factors not investigated in this study were coronary artery disease status and pulmonary hypertension. Both would likely affect outcomes and the risk of surgery.
The management of asymptomatic patients with severe aortic stenosis (AS) is controversial. Patients meeting standard echocardiographic criteria for severe stenosis have a variety of pressure gradients and flow rates that can be divided into four categories based on normal flow vs low flow (NF vs LF) and low gradient vs high gradient (LG vs HG), where LF is defined as a stroke volume index (SVI) of < 35 mL/m2 and LG is a mean gradient < 40 mmHg.Subscribe Now for Access
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