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Myocardial ischemia during daily activities: the importance of increased myocardial oxygen demand
A Hinderliter1, P Miller, E Bragdon
1Department of Medicine, University of North Carolina, Chapel Hill 27599-7075.
Insights
Increased myocardial oxygen demand during daily activities can cause myocardial ischemia in patients with coronary artery disease. This ischemia, detected by electrocardiogram (ECG) ST segment depression, often occurs without chest pain.
Area of Science:
- Cardiology
- Clinical Medicine
- Exercise Physiology
Background:
- Coronary artery disease (CAD) frequently leads to myocardial ischemia.
- Myocardial ischemia can occur during daily activities due to increased myocardial oxygen demand.
- Exercise-induced ST segment depression is a marker for significant coronary artery disease.
Purpose of the Study:
- To evaluate the role of increased myocardial oxygen demand in causing myocardial ischemia during daily activities.
- To assess the relationship between ambulatory ischemia and exercise-induced ischemia in CAD patients.
Main Methods:
- Ambulatory electrocardiographic (ECG) monitoring for ST segment shifts during daily activities.
- Symptom-limited bicycle exercise testing with continuous ECG monitoring.
- Analysis of 50 patients with coronary artery disease and exercise-induced ST segment depression.
Main Results:
- 31 out of 50 patients experienced ST depression during daily activities.
- Ambulatory ST depression episodes were rarely accompanied by angina (6%).
- Ischemia during daily activities correlated with earlier ST depression during exercise and lower exercise heart rates.
Conclusions:
- Increased myocardial oxygen demand during daily activities is a significant factor in myocardial ischemia in CAD patients.
- Ambulatory ischemia detection is valuable, as it often occurs without symptoms.
- Exercise testing parameters can predict the likelihood of ischemia during daily activities.
Abstract:
The role of increased myocardial oxygen demand in the pathophysiology of myocardial ischemia occurring during daily activities was evaluated in 50 patients with coronary artery disease and exercise-induced ST segment depression. Each patient underwent ambulatory electrocardiographic (ECG) monitoring for ST segment shifts during normal daily activities and symptom-limited bicycle exercise testing with continuous ECG monitoring. All 50 patients had ST depression greater than or equal to 0.1 mV during exercise. A total of 241 episodes of ST depression were noted in the ambulatory setting in 31 patients; only 6% of these were accompanied by angina pectoris. Significant (0.1 mV) ST depression during ambulatory monitoring was preceded by a mean increase in heart rate of 27 +/- 12 beats/min. Patients with ischemia during daily activities developed ST depression earlier during exercise (7.9 +/- 4.4 vs. 14.2 +/- 6.4 min, p less than 0.001) and tended to have significant ECG changes at a lower exercise heart rate and rate-pressure product than did those without ST depression during ambulatory monitoring. In the 31 patients with ischemia during daily activities, the mean heart rate associated with ST depression in the ambulatory setting was closely correlated with the heart rate precipitating ECG changes during exercise testing (r = 0.74, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)