Mean platelet volume is an independent risk factor for myocardial infarction but not for coronary artery disease

The elegant work by Endler et al (2002) showed that an increased mean platelet volume (MPV) was associated with a greater risk of myocardial infarction (MI) in patients with coronary artery disease. This effect was independent of several well-established risk factors (e.g. hypertension, smoking and dyslipidaemia). We have shown that platelet activation (in vivo and in vitro) results in an increase in MPV (Mikhailidis et al, 1990; Barradas et al, 1992). In vitro, this increase tends to be reversible; it is essentially aspirin resistant and it occurs during the platelet shape change (PSC; an early phase of platelet activation that precedes aggregation). We reproducibly assessed PSC with a high-resolution (0·07 fl) channelyser (Jagroop et al, 1996). We also matched the changes in MPV with platelet morphology using electron microscopy (Jagroop et al, 2000). Nevertheless, an EDTA method (like that of Endler et al, 2002) is ideal for clinical use in contrast to our slower (research) technique that requires the preparation of platelet-rich plasma. It remains to be established if platelet activation contributed to the increased MPV observed by Endler et al (2002) in the patients with a greater risk of MI. The effect of drugs on MPV was poorly documented. Our preliminary findings suggest that the administration of clopidogrel to patients with peripheral arterial disease significantly inhibits the ADP-induced increase in MPV, in vitro. This inhibition was enhanced when aspirin was administered together with clopidogrel. There is an urgent need for a practical test to identify which patients would benefit from a change in antiplatelet drug or the addition of a second one. Such a test would also allow the routine assessment of the antiplatelet effect of other drugs, like antihypertensives (e.g. in the studies cited by Endler et al, 2002) and lipid-lowering drugs (Milionis et al, 1999). Dr D. P. Mikhailidis has participated in advisory panels, received research grants and was sponsored for educational meetings by Sanofi-Synthelabo, the manufacturers of clopidogrel.