Pain threshold and tolerance in women with syndrome X and women with stable angina pectoris.

A recent report showed that during Holter monitoring of patients with syndrome X (typical anginal pain, positive exercise test response [at least 0.1 mV of ST-segment depression], no evidence of coronary spasm and angiographically normal coronary arteries), 50% of episodes of ischemic ST-segment depression were painful. This proportion is considerably higher than that in patients with chronic stable angina, which is about 30%. A significantly lower threshold and tolerance to painful stimuli was seen in a group of patients with chronic stable angina in whom 50% of episodes were painful compared with a group in whom only 5% of episodes were silent. Hence, patients with syndrome X may have enhanced sensitivity to painful stimuli. To investigate whether this difference was due to a lower threshold for painful stimuli in general, 12 patients with syndrome X and 10 (age- and sex-matched) with chronic stable angina were studied using the same battery of painful stimuli. Patients with syndrome X had a significantly lower threshold and tolerance for forearm ischemia (-36%, p less than 0.05, and -40%, p less than 0.001) and electrical skin stimulation (-37%, p less than 0.01, and -35%, p less than 0.001); the cold pressor test did not show significant differences (-7%, p = 0.391, and -1%, p = 0.818). Thus, patients with syndrome X in this study had significantly lower threshold and tolerance values for forearm ischemia and for electrical skin stimulation. These differences in sensitivity to pain may partly explain a higher incidence of painful ischemic episodes detected by ambulatory electrocardiographic monitoring during unrestricted daily life.