In patients with coronary artery disease, what can lead to myocardial ischemia during increased activity?

Myocardial ischemia during increased physical activity in patients with coronary artery disease is primarily due to increased oxygen demand. During periods of exertion, the heart works harder to meet the metabolic requirements of the body. This increased workload leads to heightened demand for oxygen by the myocardium (heart muscle) to support its activity.

In individuals with coronary artery disease, the coronary arteries are often narrowed or obstructed due to atherosclerosis, which impairs the ability of these vessels to adequately supply blood (and thereby oxygen) to the heart muscle during times of increased demand. As a result, the heart may not receive sufficient oxygen, leading to ischemia, which can result in angina or even myocardial infarction (heart attack) in severe cases.

In contrast, factors such as decreased metabolic rates would generally reduce oxygen demand, improving the balance between supply and demand rather than causing ischemia. Improved blood supply would also alleviate ischemia rather than contribute to it. While increased blood pressure can increase the workload on the heart, the primary concern in the context of coronary artery disease during increased activity is the mismatch between increased oxygen demand and the heart's ability to supply that oxygen.