From the Guidelines
Low flow low gradient aortic stenosis is diagnosed through a comprehensive approach combining echocardiography, dobutamine stress testing, and clinical assessment, with the most recent guidelines suggesting that true severe aortic stenosis is confirmed when the valve area remains less than 1.0 cm² despite increased flow, while the gradient increases above 40 mmHg, as recommended by the 2020 ACC/AHA guideline for the management of patients with valvular heart disease 1.
Diagnostic Approach
The diagnostic approach for low flow low gradient aortic stenosis involves:
- Initial evaluation with echocardiography showing a valve area less than 1.0 cm², mean gradient less than 40 mmHg, and reduced stroke volume index (less than 35 mL/m²) 1
- Dobutamine stress echocardiography as the key diagnostic test, administered at incremental doses from 5 to 20 μg/kg/min while monitoring for changes in valve area and gradient 1
- Assessment of contractile reserve during dobutamine testing, with a stroke volume increase >20% indicating a better prognosis 1
- Cardiac CT may be used to quantify valve calcification, with sex-specific Agaston unit thresholds for diagnosis of severe AS being 1300 in women and 2000 in men 1
Key Diagnostic Criteria
The key diagnostic criteria for true severe aortic stenosis include:
- Valve area remaining less than 1.0 cm² despite increased flow 1
- Gradient increasing above 40 mmHg with increased flow 1
- Presence of contractile reserve, indicated by a stroke volume increase >20% during dobutamine testing 1
- Valve calcification, with sex-specific Agaston unit thresholds for diagnosis of severe AS being 1300 in women and 2000 in men 1
Clinical Considerations
Clinical considerations in the diagnosis of low flow low gradient aortic stenosis include:
- Evaluation of comorbidities, as patients often have multiple cardiac conditions contributing to their presentation 1
- Consideration of systemic hypertension, which may affect the accuracy of diagnostic measurements 1
- Use of dobutamine stress echocardiography to distinguish between pseudo-severe and true severe aortic stenosis 1
From the Research
Diagnosis of Low Flow Low Gradient Aortic Stenosis
To diagnose low flow low gradient aortic stenosis, several diagnostic modalities can be used, including:
- Dobutamine stress echocardiography (DSE) to assess contractile reserve and severity of aortic stenosis 2, 3, 4, 5
- Multidetector computed tomography (CT) to evaluate aortic valve calcification and severity of aortic stenosis 2, 4, 5
- Echocardiography to measure aortic valve area, mean transvalvular pressure gradient, and left ventricular ejection fraction (LVEF) 2, 3, 4, 5
Diagnostic Challenges
The diagnosis of low flow low gradient aortic stenosis can be challenging due to the discrepancy between the small aortic valve area and low mean transvalvular pressure gradient 2. Additionally, the presence of severe left ventricular dysfunction can make it difficult to accurately assess the severity of aortic stenosis 5.
Role of Dobutamine Stress Echocardiography
DSE can be used to distinguish between true-severe and pseudo-severe aortic stenosis, and to assess contractile reserve in patients with low flow low gradient aortic stenosis 3, 4, 5. However, the diagnostic accuracy of DSE can vary depending on the level of LVEF, with higher accuracy in patients with LVEF <35% 5.
Safety of Dobutamine Stress Echocardiography
DSE can be safely performed in patients with aortic stenosis, although serious cardiac arrhythmias can occur, particularly in patients with severe left ventricular dysfunction 6. The use of atropine during DSE may also increase the risk of adverse side effects 6.