Low-Flow Severe Aortic Stenosis: Evolving Role of Transcatheter Aortic Valve Replacement
The definition of severe aortic stenosis has classically and retrospectively been based on the natural history of patients with medically managed aortic stenosis and preserved left ventricular function in an era where surgical aortic valve replacement was the sole therapy. We now recognize that this disease is more heterogeneous and includes important subsets of patients with low stroke volume index (low flow) and low-gradient with reduced (classical) or preserved (paradoxical) ejection fraction. These patients pose diagnostic and treatment dilemmas, requiring a comprehensive assessment with integration of multimodality imaging, testing, and clinical assessment. Surgery in these patients has been associated with higher operative mortality and lower long-term survival. Transcatheter aortic valve replacement (TAVR), because of its less-invasive nature, avoidance of the detrimental effects of cardiopulmonary bypass, and larger effective orifice area, offers several potential advantages. Studies of TAVR in low-flow severe aortic stenosis patients have demonstrated that TAVR has a significant mortality benefit compared with medical therapy and a similar benefit compared with surgery. Both low flow and low ejection fraction have emerged as important factors in predicting mortality post-TAVR, with particularly poor survival when flow or ejection fraction fail to improve. The recognition, diagnosis, and treatment of patients with low-flow severe aortic stenosis remains challenging. It is likely that TAVR will play an increasingly important role in the management of these patients.