Changes in platelet size and count in unstable angina compared to stable angina or non-cardiac chest pain

Aims An increase in platelet aggregability is associated withunstable angina and myocardial infarction. Platelet size andactivity correlate and mean platelet volume was found to beincreased before acute myocardial infarction. We measured themean platelet volume and platelet count in patients with stableangina, unstable angina and non-cardiac chest pain. Methods and results We studied 981 patients (734 men; 247 women)defined clinically as stable angina (n=688), unstable angina(n=108) and unstable angina requiring immediate angioplasty(n=52). After coronary angiography the patients were subdividedinto single (n=269), double (n=304) and triple-vessel disease(n=311) and the control group of non-cardiac chest pain (n=97).There was no significant difference in platelet count betweenthe control group and patients with 1, 2, or 3-vessel disease.However, the platelet size in patients with coronary arterydisease was significantly larger (single: 8·7±1·19fl;double: 8·7±1·12fl; triple-vessel disease:8·8±1·18fl) than the control group (8·2±0·95fl)(P<0·01). Patients with stable angina similarly hadno significant difference in platelet count compared to thecontrol group but did have a significantly increased mean plateletvolume (8·7±1·13;P<0·01). Incontrast, patients with unstable angina had a decreased plateletcount (245±56x10/l) compared to either stable angina(262±62x10/l;P<0·05) or the control group (261±58x10/l;P<0·05);furthermore, the mean platelet volume (9·4±1·23fl)was significantly greater than for stable angina (P<0·01).Patients with unstable angina requiring immediate PTCA had aneven lower platelet count (231±55x10/l) and higher meanplatelet volume (10·4±1·03fl) (P<0·01)than the rest of the population with unstable angina. Conclusions In stable angina the platelet count is unchangedcompared to patients with normal coronary arteries but the plateletsize is increased. However, in unstable angina there is a decreasein platelet count and an even larger increase in platelet size.We interpret this as meaning that unstable angina might be associatedor preceded by an increase in platelet destruction rate thatis not completely compensated for by an increase in plateletproduction rate. The large, more reactive platelets might becausally related to an ongoing coronary artery obstruction inunstable angina.