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  • Title: Early morning reduction in ischemic threshold in patients with unstable angina and significant coronary disease.
    Author: Figueras J, Lidón RM.
    Journal: Circulation; 1995 Oct 01; 92(7):1737-42. PubMed ID: 7671355.
    Abstract:
    BACKGROUND: The objective of this study was to investigate in patients with unstable angina and significant coronary stenosis (> 70%) whether or not the morning peak of myocardial ischemia is associated with a reduction in the ischemic threshold. The morning increased incidence of ischemic episodes in stable angina appears to be attributable to a coincidence of several factors. Patients with unstable angina who remain at bed rest, however, also present a similar morning increased incidence of ischemia, but its mechanisms are not completely understood. METHODS AND RESULTS: The ischemic threshold was assessed by atrial pacing at 7 to 8 AM and at 12 to 1 PM in 46 patients. In the 34 with a positive pacing response (ST segment shift > 1.0 mm), ischemic threshold was lower at 7 to 8 AM than at 12 to 1 PM (131 +/- 16 versus 139 +/- 15 beats per minute, P < .001), whereas in the remaining 12 patients, the pacing response was negative. Moreover, 4 patients presented ST segment elevation during pacing in the morning but only 1 at noon and at a higher threshold. Baseline heart rate and diastolic blood pressure were higher at noon than in the morning (81 +/- 16 versus 76 +/- 13 beats per minute, P < .01, and 87 +/- 11 versus 82 +/- 10 mm Hg, P < .05). CONCLUSIONS: The morning lowering of ischemic threshold in the absence of increases in baseline blood pressure or heart rate suggests that a reduced coronary vasodilator capacity or an increased coronary tone may favor the increased incidence of ischemic events during this interval.
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