Document Detail

Circadian variations in ischemic threshold and their relation to the occurrence of ischemic episodes.
MedLine Citation:
PMID:  8095188     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: The occurrence of ischemic episodes during daily activity has been reported to exhibit a bimodal circadian distribution, yet its relation to the ischemic threshold (heart rate at 1-mm ST segment depression) has not been explored. METHODS AND RESULTS: To determine whether the ischemic threshold during daily activity exhibits a circadian pattern that might relate to the frequency of occurrence of ischemic episodes, we studied the time of occurrence and the heart rate at onset of ischemia in 1,371 ischemic episodes recorded in 41 patients with stable coronary disease, positive exercise testing, and repeated ischemic episodes during ambulatory ECG monitoring (AEM). All patients had 7 days of AEM; 23 were off any anti-ischemic therapy, while 18 were on low dose of beta-blockers. The occurrence of ischemic episodes exhibited the typical bimodal circadian distribution with a prominent peak between 7:00 and 11:00 AM and a second less prominent peak between 6:00 and 9:00 PM. The threshold of myocardial ischemia exhibited a different single-peaked circadian distribution; it was lowest between 1:00 and 3:00 AM and highest between 10 AM and 1 PM. Time series analyses indicated a strong hour-by-hour trend of each of the two circadian distributions, whereas the two series cross-correlated maximally at a lag of zero hours (p < 0.01), indicating a complex interplay between myocardial oxygen demand and supply in determining the occurrence of ischemic episodes during daily activity. The morning increase in the frequency of ischemic episodes could not be attributed to a reduced threshold but rather to an increase in demand. The low threshold at night-time might probably indicate that the mechanism of ischemia during these hours is reduced coronary flow due to increased coronary tone. Secondary analyses for several predefined patients' subsets gave similar results. Patients who received low-dose beta-blockers maintained the bimodal circadian distribution of the occurrence of ischemic episodes, whereas the ischemic threshold exhibited a constant pattern with no circadian changes. CONCLUSIONS: Our results demonstrate that myocardial oxygen demand is a major determinant of daily ischemia, yet changes in the ischemic threshold that probably reflect dynamic changes in coronary tone play also an important role. The relative contribution of increased demand and decreased threshold to the genesis of ischemic episodes during daily activity can be assessed by AEM and may help to optimize medical therapy.
J Benhorin; S Banai; M Moriel; A Gavish; A Keren; S Stern; D Tzivoni
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Circulation     Volume:  87     ISSN:  0009-7322     ISO Abbreviation:  Circulation     Publication Date:  1993 Mar 
Date Detail:
Created Date:  1993-04-06     Completed Date:  1993-04-06     Revised Date:  2010-03-24    
Medline Journal Info:
Nlm Unique ID:  0147763     Medline TA:  Circulation     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  808-14     Citation Subset:  AIM; IM    
Heiden Department of Cardiology, Bikur Cholim Hospital, Jerusalem, Israel.
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MeSH Terms
Adrenergic beta-Antagonists / therapeutic use
Analysis of Variance
Circadian Rhythm*
Coronary Disease / drug therapy,  physiopathology*
Differential Threshold
Electrocardiography, Ambulatory
Heart Rate*
Middle Aged
Reg. No./Substance:
0/Adrenergic beta-Antagonists

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