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Prognosis of Severe Low-Flow, Low-Gradient Aortic Stenosis by Echo Parameters
Quick Takes
- In this cohort of patients with low-gradient severe aortic stenosis, low stroke volume index and low flow rate on TTE were independently associated with clinical events.
- Patients with LV systolic dysfunction, low stroke volume index, and low flow rate were at highest risk of adverse outcomes.
Study Questions:
Among patients with severe aortic stenosis (AS), does characterization of flow state by transthoracic echocardiography (TTE) improve risk stratification?
Methods:
This single-center, retrospective cohort study, conducted at a suburban Australian hospital, included consecutive patients with severe AS (aortic valve area index [AVAi] <0.6 cm2/m2) on TTE from 2013-2019. Patients meeting this criterion were considered to have low-flow, low-gradient AS (LFLG-AS) if they had mean aortic valve gradient <40 mm Hg (low gradient), as well as stroke volume index (SVi) <35 ml/m2 and/or flow rate (FR) <200 ml/s. Patients were subclassified as having either classical LFLG-AS (left ventricular ejection fraction [LVEF] <50%) or paradoxical LFLG-AS (LVEF ≥50%). The primary outcome was a composite of all-cause mortality, hospitalization due to heart failure, and aortic valvular intervention.
Results:
Among 621 patients with severe AS, 345 had LFLG-AS (141 classical, 203 paradoxical). Over a median follow-up period of 11.6 months, survival among all patients with severe AS was 80.4% at 1 year and 70.8% at 2 years. The estimated probability of freedom from the composite outcome was highest among patients with low gradient and normal SVi and FR (72.5%) and lowest among those with low gradient, low SVi, and low FR (50.2%). In multivariable analyses, low SVi and low FR were independently associated with the composite endpoint, and patients with low LVEF, low SVi, and low FR had the highest risk of the composite endpoint (hazard ratio [HR], 2.65; 95% confidence interval [CI], 1.61-4.38; p < 0.001) and all-cause mortality (HR, 3.07; 95% CI, 1.65-5.69; p < 0.001). In a risk prediction model including clinical and echocardiographic variables, adding SVi improved classification accuracy, with net reclassification index 0.089 (95% CI, 0.045-0.133; p = 0.04). Adding FR to this model did not significantly improve classification accuracy. With regard to receiver operating characteristic analysis, a risk prediction model including AVAi, LVEF, and clinical variables was not significantly improved by the addition of either SVi or FR.
Conclusions:
In LFLG-AS, low SVi and low FR were both independently associated with clinical events, although only SVi improved risk classification in this cohort. Patients with low LVEF, low SVi, and low FR were at highest risk of adverse outcomes.
Perspective:
Multiple prior studies have shown that a low-flow state, most commonly identified by low SVi in clinical practice, is predictive of adverse events in AS. The authors point out that their findings contrast to some extent with those of Vamvakidou and colleagues ( JACC Cardiovasc Imaging 2019;9:1715-24), who found that low FR but not low SVi was predictive of mortality among patients with low-gradient severe AS undergoing aortic valve intervention. It is important to keep in mind that both SVi and FR are calculated based on stroke volume, which is derived from the LV outflow tract (LVOT) pulse wave Doppler measurement and LVOT diameter. Therefore, both variables are subject to similar errors, commonly including mismeasurement of the LVOT diameter (which should ideally be measured at or very close to the annulus) and placement of the pulse wave Doppler sample volume too apically. To maximize recognition of a low-flow state, assessment of both SVi and FR may be reasonable, though this strategy should be evaluated in prospective studies.
Clinical Topics: Cardiac Surgery, Geriatric Cardiology, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Prevention, Valvular Heart Disease, Aortic Surgery, Cardiac Surgery and Arrhythmias, Cardiac Surgery and Heart Failure, Cardiac Surgery and VHD, Acute Heart Failure, Interventions and Imaging, Interventions and Structural Heart Disease, Echocardiography/Ultrasound
Keywords: Aortic Valve Stenosis, Cardiac Surgical Procedures, Diagnostic Imaging, Echocardiography, Geriatrics, Heart Failure, Heart Valve Diseases, Risk Assessment, Secondary Prevention, Stroke Volume, Ventricular Function, Left
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