In recent years, a number of authors have clearly documented a circadian rhythm in the timing of cardiovascular morbidity and mortality. Several studies have shown that the major acute cardiovascular disorders, transient myocardial ischemia, acute myocardial infarction, sudden cardiac death, and stroke, occur more frequently within the interval from 6 am to 12 noon and reach their lowest incidence during the night (midnight to 6 am). buy levaquin online
Various reports on ambulatory ischemia monitoring have demonstrated a predominance of ischemic activity in the mornings. Using 24-hour Holter monitoring to detect transient myocardial ischemia in 32 patients with chronic stable angina, Rocco and associates established a significant circadian variation in the incidence of transient ischemic events: 39 percent of such episodes occurred between 6 am and 12 noon. Furthermore, an even stronger relationship was found when the occurrence of ischemic ST segment depressions (with or without symptoms) was corrected for the time of awakening and arising. The maximal incidence of transient myocardial ischemia was observed during the first four hours after waking and peak ischemic activity occurred one to two hours after rising.
The same authors found no difference in the incidence of painful ischemic attacks (15 percent overall), activity level, threshold heart rate, ischemic threshold, or the duration of attacks at different times of the day. They found, however, that heart rates within the “ischemic range” were more common in the morning, and that the likelihood of developing ischemic ST depression once these rates were exceeded was significantly higher in the morning. The ratio of total ischemic time to the total threshold time was 26 percent in the morning and only 15 percent in the evening.
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