Abstract: Aim To evaluate microvascular function and its relation to the genesis of chest pain and S T segment depression during exercise in patients with syndrome X. Methods Changes pacing-induced in transmural myocardial blood f low distribution were quantitatively assessed by 2-dimensional myocardial contrast echocardiog raphy. Myocardial blood flow distribution before and after pacing stress was assessed by measuring the ratio of the endocardial to epicardial gray level (ie, endo/epigray level ratio) in the territory of the left anteior descending coronary. Results Of 25 patients w ith a history of chest pain and normal coronary arteries with the negative ergonovine test, 11 had exercise-induced chest pain and ST segment depression(syndrome X), and 14 did not (controls). Pacing-induced chest pain and ST segment depression were observed in syndrome X, but not in controls. The endo/epigray level ratio in syndrome X significantly decreased after pacing (form 0.98 ±0.10 to 0.76 ±0.17, P <0.01), but not in controls (from 0.97 ±0.08 to 0.99 ±0.08, P >0.05). Conclusion Abnormal myocardial blood flow distribution may play an important role in exercise induced chest pain and ST segment depression in these patients.

Key words: angina pectoris, coronary arteries, myocardial blood flow distribution, myocardial contrast echocardiography