Silent myocardial ischemia during ambulatory electrocardiographic monitoring in patients with effort angina.

The frequency and characteristics of asymptomatic ischemic attacks were investigated in 39 patients with effort angina. During 24 hour Holter monitoring, 32 of the 39 patients displayed one or more episodes of ischemic ST depression. Eight patients had attacks (n = 25) always accompanied by pain; 9 patients had only asymptomatic ischemic episodes (n = 40) and 15 patients had both symptomatic (n = 29) and asymptomatic attacks (n = 76). In the 15 patients exhibiting both symptomatic and asymptomatic attacks, mean duration of symptomatic episodes was longer (probability [p] less than 0.001) and mean maximal ST depression was greater (p less than 0.001). When patients exhibiting only symptomatic episodes were compared with those exhibiting only asymptomatic attacks, differences were not significant. All symptomatic and asymptomatic attacks during Holter monitoring were correlated with the results of stress testing: patients experiencing a delayed response to pain after the onset of St ischemic depression during stress testing had a higher ratio of asymptomatic to symptomatic attacks during Holter monitoring compared with those patients reporting pain before or at the moment of the appearance of ischemic electrocardiographic features during stress testing. It is concluded that: 1) asymptomatic episodes of ischemia are more frequent than symptomatic episodes in patients with effort angina; 2) in the same patient, the severity of ischemia is generally a fundamental factor in determining the presence or absence of pain during an ischemic attack; and 3) differences among patients with respect to predominance of symptomatic or asymptomatic attacks probably depend on individual factors.