From the Guidelines
Low flow low gradient aortic stenosis is a challenging subtype of aortic stenosis where the valve is severely narrowed, but due to reduced cardiac output, the pressure gradient across the valve appears deceptively low. This condition typically presents with a valve area less than 1.0 cm², a mean gradient less than 40 mmHg, and a stroke volume index less than 35 mL/m², as defined by recent guidelines 1. It occurs in two main variants:
- Classical low flow low gradient AS with reduced ejection fraction (typically below 40%), often due to myocardial dysfunction;
- Paradoxical low flow low gradient AS with preserved ejection fraction, usually caused by small ventricular size, restrictive physiology, or significant hypertrophy. Diagnosis requires careful echocardiographic assessment, often supplemented by dobutamine stress echocardiography to distinguish true stenosis from pseudostenosis, as recommended by the 2024 ACC/AHA clinical performance and quality measures for adults with valvular and structural heart disease 1. Management depends on confirming true stenosis and assessing surgical risk, with valve replacement (either surgical or transcatheter) recommended for true severe stenosis, as supported by the 2023 ESC/EACTS guidelines versus ACC/AHA guidelines for the management of severe aortic stenosis 1. Patients with pseudostenosis may be managed medically. The condition carries a poorer prognosis than high-gradient aortic stenosis, particularly when left untreated, due to the combination of valve obstruction and myocardial dysfunction, highlighting the importance of accurate diagnosis and timely intervention 1.
Some key points to consider in the diagnosis and management of low flow low gradient aortic stenosis include:
- The use of dobutamine stress echocardiography to distinguish true stenosis from pseudostenosis, as recommended by the 2014 AHA/ACC guideline for the management of patients with valvular heart disease 1.
- The importance of assessing surgical risk and considering valve replacement (either surgical or transcatheter) for true severe stenosis, as supported by the 2020 ACC/AHA guideline for the management of patients with valvular heart disease 1.
- The need for careful echocardiographic assessment and integration of multiple sources of data to confirm the diagnosis and guide management, as emphasized by the 2017 ACC expert consensus decision pathway for transcatheter aortic valve replacement in the management of adults with aortic stenosis 1.
Overall, the management of low flow low gradient aortic stenosis requires a comprehensive and multidisciplinary approach, taking into account the latest evidence and guidelines to optimize patient outcomes.
From the Research
Definition of Low-Flow Low-Gradient Aortic Stenosis (AS)
- Low-flow low-gradient aortic stenosis (AS) is a subset of severe aortic stenosis characterized by a small aortic valve area (≤1.0 cm2) and low mean transvalvular pressure gradient (<40 mmHg) 2, 3.
- It is divided into two categories: classical low-flow low-gradient AS with reduced left ventricular ejection fraction (LVEF) and paradoxical low-flow low-gradient AS with preserved LVEF 2, 3.
Diagnostic Challenges
- The primary diagnostic challenge in patients with low-flow low-gradient AS is to confirm that AS is truly severe and not pseudosevere 2, 4.
- Dobutamine stress echocardiography and multidetector computed tomography are used to distinguish true-severe from pseudo-severe stenosis and assess the existence of flow (contractile) reserve 2, 3, 4, 5.
Management and Treatment
- The management of symptomatic true severe low-flow low-gradient AS is mainly by aortic valve replacement (AVR), whether surgical or transcatheter approach 2, 3, 4.
- Patients with low-flow low-gradient severe AS have a generally worse prognosis and higher mortality compared with patients with high-gradient severe AS 2.
- Early recognition and correct diagnosis of a patient with low-flow low-gradient AS is crucial to improve their mortality and morbidity 2.