What causes silent myocardial ischemia?

Myocardial ischemia is an imbalance between consumption and production of adenosine triphosphate (ATP) that leads to ATP depletion and a cascade of biochemical events. Why some patients have pain during these events while others do not is unclear, but some studies indicate that a combination of pain threshold and magnitude of ischemia may be at work. Ischemia can occur during vigorous or daily activities or at rest and can be influenced by mental stress. It is most common in the morning hours, possibly because heart rate, blood pressure, and contractility rise rapidly in the morning and factors that increase coronary vessel tone and reduce blood flow also increase during these hours. The specific pathophysiology of an ischemic episode depends on whether the patient also has chronic stable coronary disease, variant angina, or unstable angina, not on whether the episode is silent or symptomatic.