Pathology of Unstable Angina: Analysis of Biopsies Obtained by Directional Coronary Atherectomy.

Background: The transient and generally nonfatal nature of unstable angina has impaired the accumulation of pathologic data and the definition of the pathoanatomy of this syndrome. Methods: Atherectomy specimens from patients enrolled in CAVEAT were examined for the presence of thrombus, foam cells, cholesterol clefts, media, and adventitia. Comparison of the pathologic findings was made according to clinical presentation in the following categories: stable angina, unstable angina, and recent myocardial infarction. Results: Patients with unstable angina had. a slightly higher incidence of thrombus when compared with patients presenting with stable angina (36% vs. 26%, p =.14). Within the unstable angina population some subgroups demonstrated a greater incidence of thrombus, including those whose pain was associated with ECG changes (43%, p =.07). The incidence of thrombus was highest among patients who had a myocardial infarction within 30 days (53%, p =.004) or within 14 days (58%, p =.003). No difference between the patient groups was detected with respect to the other histologic findings. Conclusions: Atherectomy specimens from patients with unstable angina demonstrated a trend toward increasing incidence of thrombus, but this trend did not achieve statistical significance. Specimens from patients with a recent myocardial infarction did not demonstrate a significant increase in the presence of thrombus. While thrombus is a component of the pathophysiology of unstable angina in a significant number of patients, continued study is required to determine the other factors that are responsible.