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Aortic Valve Calcification in Low-Gradient Aortic Stenosis
Quick Takes
- Current guidelines suggest that a high aortic valve calcification (AVC) score on CT in patients with suspected low-flow low-gradient severe aortic stenosis (AS) may be appropriate to define severity, although the cutoff values used to define a high score were derived from a largely different population.
- This study finds that AVC score by CT has poor discrimination between moderate and severe AS in patients with suspected low-flow low-gradient AS undergoing dobutamine stress echocardiography and CT.
Study Questions:
What is the relationship between aortic valve calcification (AVC) and aortic stenosis (AS) severity in patients with suspected low-flow low-gradient AS?
Methods:
This multicenter observational study evaluated patients with moderate or severe AS undergoing both dobutamine stress echocardiography (DSE) and AVC by CT within 1 year. Suspected severe low-flow low-gradient AS was defined by an aortic valve area <1.0 cm2, a peak aortic valve velocity <4 m/s, and a mean aortic valve gradient <40 mm Hg. Patients with normal-flow (stroke volume index >35 mL/m2 for women or >40 mL/m2 for men) or high-gradient AS at rest were excluded. Receiver-operator characteristics curve analysis was used to evaluate the diagnostic performance of AVC for AS severity using DSE as a reference standard.
Results:
There were 214 patients in the study (median age 78 years, 25% female), and left ventricular (LV) ejection fraction was reduced (<50%) in 92% of patients. Severe AS was diagnosed by rest echocardiography and DSE in 106 subjects (49.5%), while moderate AS was observed in 108 subjects (50.5%). Moderate AS was determined by resting echocardiography in 77 individuals and was confirmed in 31 by DSE. A high AVC score was seen in 47 patients with severe AS (44.3%) and in 47 patients with moderate AS (43.5%). The sensitivity, specificity, and positive and negative predictive values of a high AVC value to identify severe AS were 44.3%, 56.5%, 50.0%, and 50.8%, respectively.
Conclusions:
A high AVC score on CT does not discriminate between moderate and severe low-flow low-gradient AS. The AVC score cannot be used to replace DSE to distinguish patients with low-flow low-gradient severe AS and pseudo-severe AS.
Perspective:
Patients with suspected severe low-flow low-gradient AS can be a challenging cohort to evaluate. There can be uncertainty about whether: 1) they truly have severe AS, 2) there is an error in the calculated aortic valve area, 3) gradients are underestimated, or 4) they have pseudo-severe AS (the latter in the setting of reduced LV function). Current guidelines provide a Class IIa recommendation that DSE may be appropriate in patients with suspected low-flow low-gradient severe AS and reduced LV function to further define the severity of AS. They also have a Class IIa recommendation that CT may be useful to evaluate for a high AVC score in patients with suspected low-flow low-gradient AS regardless of LV function, and state that a high calcium score can further define AS severity. However, the AVC cutoffs used to define a high value (Agatston score >1,200 for females and >2,000 for males) were validated in patients with normal-flow AS and/or normal or mildly reduced LV function, and may not apply to a population with suspected low-flow low-gradient severe AS.
This study asked a very practical question. In patients with suspected moderate or severe low-flow low-gradient AS, how well did a high AVC discriminate moderate from severe AS? The results of this study find that the accuracy of a high AVC to identify severe AS in this cohort is close to flipping a coin, with a very poor discriminatory performance. Of note, the study had a small proportion of women (25%), and most patients (92%) had reduced LV function. It remains less clear whether AVC may remain helpful in women, or in patients with normal LV function, and future study in these cohorts may be helpful. Based on the findings of this study, current guidelines endorsing the use of CT to measure AVC in patients with suspected low-flow low-gradient severe AS may merit revision.
Clinical Topics: Noninvasive Imaging, Valvular Heart Disease, Echocardiography/Ultrasound
Keywords: Aortic Valve Stenosis, Echocardiography, Stress
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