Platelet Aggregation and High-Intensity Transient Signals (HITS)
in a Sheep Model of Mitral Valve Replacement
Lucia Raco PhD, Philip R. Belcher FRCS, Iain Sim PhD, Anne McGarrity PhD,
Gillian M. Bernacca PhD, David J. Wheatley FRCS

High-intensity transient signals (HITS) were detected at three and six months in the carotid artery in 20 sheep implanted with either a mechanical or a biological mitral valve prosthesis. At the same times, platelet aggregates were counted in arterial blood. A 5HT_2a antagonist was given to alter platelet aggregate count. The mechanical group showed the anticipated greater frequency of HITS, and this was unaffected by changes in the number of platelet aggregates. Platelet aggregates decreased following 5HT_2a antagonist administration in all animals. Platelet aggregate numbers tended to increase as structural deterioration became evident in the bioprostheses. The lack of association between HITS counts and platelet aggregates suggests it is unlikely that HITS are caused by platelet aggregates in this setting.