Abstract
The purpose of this study was to investigate the frequency and characteristics of silent myocardial ischemia in patients with proven ischemic heart disease using ambulatory ECG monitoring, and to clarify possible mechanisms for the absence of symptoms during these attacks. A total of 182 patients, including 78 patients with stable effort angina (EA), 12 with unstable angina (UA), and 92 with prior myocardial infarction (MI), were examined. During daily activities, 43% and 56% of all transient ST-segment depression observed was asymptomatic in patients with EA and MI, respectively. In addition, 74% of all ischemic episodes were asymptomatic in patients with UA. In patients with EA, 35% exhibited both symptomatic and asymptomatic attacks, and the duration and magnitude of ST-segment depression were greater for symptomatic attacks than for asymptomatic attacks. On the other hand, in patients with MI, 55% had only asymptomatic attacks. When asymptomatic episodes in patients who had only asymptomatic attacks were compared with symptomatic episodes in patients who had only symptomatic attacks, asymptomatic episodes tended to be associated with a greater magnitude of ST depression. They were also significantly longer in duration than the symptomatic episodes. All patients with UA had both symptomatic and asymptomatic episodes, and the magnitude and duration were significantly greater during the former. These results lead us to conclude that: (1) silent myocardial ischemia is observed frequently in patients with EA and MI during daily activities. In particular, patients with MI tend to have more severe silent ischemia. (2) In patients with EA and UA, the severity of ischemia is a fundamental factor in determining the presence or absence of pain during an ischemic attack. (3) In patients with MI, the occurrence of silent myocardial ischemia probably depends upon alteration in the pain threshold or perception.
