Early morning reduction in ischemic threshold in patients with unstable angina and significant coronary disease
1Unitat Coronària, Hospital General Vall d'Hebron, Barcelona, Spain.
Insights
Patients with unstable angina experience lower ischemic thresholds in the morning, increasing myocardial ischemia risk. This suggests reduced coronary vasodilator capacity or increased coronary tone may be responsible.
Area of Science:
- Cardiology
- Cardiovascular Physiology
Background:
- Patients with unstable angina and significant coronary stenosis exhibit a morning peak in myocardial ischemia.
- The mechanisms underlying this increased morning ischemia incidence in unstable angina patients are not fully understood, despite similar patterns observed in stable angina.
Purpose of the Study:
- To investigate if the morning peak of myocardial ischemia in unstable angina patients is linked to a reduced ischemic threshold.
- To explore the underlying mechanisms of increased morning ischemic episodes in unstable angina.
Main Methods:
- Assessed ischemic threshold using atrial pacing in 46 unstable angina patients with significant coronary stenosis (>70%).
- Measurements were taken in the early morning (7-8 AM) and early afternoon (12-1 PM).
- Evaluated ST segment shifts, heart rate, and diastolic blood pressure responses during pacing.
Main Results:
- A significantly lower ischemic threshold was observed in the morning (131 bpm) compared to the afternoon (139 bpm) in 34 patients with a positive pacing response (P < .001).
- Four patients experienced ST segment elevation during morning pacing, versus only one in the afternoon.
- Baseline heart rate and diastolic blood pressure were not significantly higher in the morning.
Conclusions:
- The morning reduction in ischemic threshold, independent of changes in heart rate or blood pressure, suggests impaired coronary vasodilation or heightened coronary tone.
- These factors may contribute to the increased incidence of myocardial ischemic events observed in the morning interval for unstable angina patients.
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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