Use of transcatheter aortic valve replacement (TAVR) for severe aortic stenosis (AS) has grown rapidly over the last decade and the technology has correspondingly matured. Nevertheless, recent data suggest that subclinical thrombosis may form on some leaflets of the TAVR prostheses following implant. The frequency, implications, and required treatment of this process are largely unknown, as is the relevance to surgical aortic valve replacement (SAVR).
Two single center registries, The Assessment of Transcatheter and Surgical Aortic Bioprosthetic Valve Thrombosis and its Treatment with Anticoagulation (RESOLVE) and the Subclinical Aortic Valve Bioprosthesis Thrombosis Assessed with Four-Dimensional Computed Tomography (SAVORY), collectively enrolled 890 non-consecutive patients who underwent 4D volume-rendered computed tomography (CT) at various intervals following TAVR (752 patients) or SAVR (138 patients) between 2014 and 2017 with the intent to explore the prevalence of subclinical leaflet thrombosis.
Relative to SAVR prostheses, a higher percentage of TAVR patients had thrombus detected (12% versus 4%, p=0.001) and those with confirmed leaflet thromboses were more likely to have mean prosthetic valve gradients on echocardiography of more than 20 mmHg (14% versus 1%, p<0.0001).
Patients taking anticoagulation at the time of their CT scans were less likely to have subclinical thrombosis than patients on no anticoagulants (4% vs 15%, p<0.0001), but there were no differences in subclinical thrombosis prevalence for patients on dual or mono antiplatelet therapy compared to none.
Among the 36 patients with reduced leaflet motion from subclinical valve thrombosis who underwent treatment with systemic anticoagulation, all had restoration of normal leaflet motion and valve gradients whereas 20 of 22 (91%) of those who were not anticoagulated had persistent or progressive reduced leaflet motion.
Those patients with subclinical thrombosis had significantly higher rates of transient ischemic attack (5% versus 1%, p=0.002) but not stroke (4% versus 2%, p=0.18).
Long term follow up of the large, randomized clinical trials for the early TAVR prostheses have consistently demonstrated excellent mean gradient gradients suggesting, that progressive subclinical leaflet thrombosis is likely not an endemic problem for TAVR. However, these data do support close monitoring of patients following TAVR and SAVR. How to manage subclinical leaflet thrombosis when found, and opportunities for prophylaxis remain largely speculative.
Chakravarty T, Søndergaard L, Friedman J, et al, on behalf of the RESOLVE and SAVORY Investigators. Subclinical lea et thrombosis in surgical and transcatheter bioprosthetic aortic valves: an observational study. Lancet 2017; published online March 19. http://dx.doi.org/10.1016/S0140-6736(17)30757-2.
Sandeep Krishnan, MD and James M. McCabe, MD
University of Washington, Seattle, USA