Plaque Morphology Predictors of Side Branch Occlusion After Main Vessel Stenting in Coronary Bifurcation Lesions: Optical Coherence Tomography Imaging Study.

The issue of transcatheter heart valve (THV) thrombosis is a poorly understood emerging entity of great clinical importance. There are now a number of papers describing both clinically apparent and silent THV thrombosis (1). The literature describes a very heterogenous cohort in terms of the timing of presentation (2 days to 24 months); however, the dominant mode of presentation is recurrent dyspnea coupled with an increase in transvalvular gradient, with or without visualized thrombus. In terms of etiology, this can broadly be divided into 3 categories: 1) patient-related factors leading to a predisposition for thrombosis; 2) valve-related factors inciting a prothrombotic state or causing changes in flow dynamics; and finally 3) procedural-related factors such as suboptimal stent deployment or leaflet microinjury resulting in a tendency for thrombus formation. The correspondence from Dr. Kounis and colleagues suggests hypersensitivity to a component of the stent alloy as a potential mechanism for thrombus formation. Hypersensitivity to metal components of alloys and polymers has been associated with inflammatory reactions with a variety of situations. The experience with coronary stents suggests nickel allergy may be associated with an excess of restenosis, but not thrombosis. There is little reported experience of valve replacements in the setting of nickel allergy. Lyell et al. (2) described a case of repeated valvular incompetence in a patient with severe nickel allergy. Subsequent placement with a nickel-free prosthesis lead to a normally functioning prosthesis at 22 months (2). Córdoba-Soriano et al. (3) reference 2 cases of THV thrombosis where testing for allergy to valve components was negative. In should be remembered that the vast majority of cases manifest as leaflet thickening with reduced motion or as a mobile mass associated with the leaflets (4). In only very rare cases has thrombosis been associated with the valve frame (5). Although there is some certainty as to how to treat this condition (4), there is as yet huge uncertainty as to how it occurs, and we should be well advised to keep an open mind.