Increased platelet aggregation response in cavalier king charles spaniels with mitral valve prolapse

Mitral valve prolapse (MVP) is a fundamental feature of myxomatous mitral v alve disease in the dog. In humans, primary MVP is associated with increase d platelet reactivity. In Cavalier King Charles Spaniels (CKCS). a breed pr edisposed to myxomatous mitral valve disease, there is a high prevalence of hypomagnesemia and platelet anomalies. such as thrombocytopenia and macrot hrombocytosis. The objective of this study was to evaluate platelet aggrega tion responses in CKCS and to determine the relationship between the platel et aggregation response and serum magnesium concentration. MVP, mitral regu rgitation (MR). and platelet count. In 19 CKCS with MVP and 7 control dogs (not CKCS). the platelet aggregation response to 3 different agonists was c ompared. The CKCS with >100.000 platelets/muL (n = 10) had a significantly higher maximum aggregation response with regard to all tested agonists than the CKCS with < 100.000 platelets/muL (n = 9) and control dogs (n = 7). Th e CKCS with < 100.000 plarelets/muL had a platelet aggregation response sim ilar to the control dogs. There was no correlation between degree of MVP an d platelet aggregation response. platelet diameter increased (P =.006) and serum magnesium concentration decreased (P =.04) with lower platelet concen tration. In conclusion. CKCS with MVP appeared to separate into 2 groups-1 group with < 100.000 platelets/muL, normal platelet aggregation. low serum magnesium concentration, and enlarged platelets, and another group with < 1 00.000 plarelets/muL. increased platelet aggregation. and normal serum magn esium concentration and platelet size.