From the Guidelines
Demand ischemia should be managed by optimizing cardiac oxygen balance, which includes controlling tachycardia with beta-blockers, managing hypertension, correcting anemia, providing supplemental oxygen, and addressing fever. This approach is based on the principle of modifying the balance between myocardial oxygen supply and demand, as highlighted in the guidelines for the management of patients with unstable angina/non-st-elevation myocardial infarction 1. The management of demand ischemia focuses on treating the underlying cause while optimizing cardiac oxygen balance.
- Controlling tachycardia with beta-blockers (metoprolol 25-100mg twice daily) is essential to reduce myocardial oxygen demand.
- Managing hypertension with medications like amlodipine (5-10mg daily) is also crucial to reduce myocardial oxygen demand.
- Correcting anemia with blood transfusions to maintain hemoglobin above 7-8 g/dL is necessary to improve oxygen delivery to the myocardium.
- Providing supplemental oxygen to maintain saturation above 94% is vital to ensure adequate oxygen supply to the myocardium.
- Addressing fever with antipyretics like acetaminophen (650mg every 6 hours) is important to reduce myocardial oxygen demand. Unlike typical heart attacks, cardiac catheterization is often unnecessary unless standard treatments fail. Demand ischemia occurs because physiological stressors like sepsis, respiratory failure, or severe anemia increase the heart's workload while simultaneously reducing oxygen delivery, creating an imbalance that damages heart muscle even with normal coronary arteries, as described in the guidelines for the management of patients with unstable angina/non-st-elevation myocardial infarction 1. Prompt recognition and addressing the underlying cause are essential for preventing further cardiac damage. The use of nitrates, such as nitroglycerin, can also be beneficial in managing demand ischemia, as they reduce myocardial oxygen demand and improve myocardial oxygen supply 1.
From the Research
Demand Ischemia
Demand ischemia occurs when the heart's oxygen demand exceeds its oxygen supply. This can be caused by various factors, including:
- Increased heart rate, which increases the heart's oxygen demand 2
- Increased contractility, which also increases oxygen demand
- Decreased oxygen supply, which can be caused by coronary artery disease or other conditions that reduce blood flow to the heart
Reducing Demand Ischemia
Several strategies can help reduce demand ischemia, including:
- Beta-blockers, which reduce heart rate and contractility, thereby decreasing oxygen demand 3, 2
- Calcium channel blockers, which can help reduce heart rate and contractility, as well as improve blood flow to the heart 3, 4
- Reducing heart rate, which can be achieved through pharmacologic interventions such as beta-blockers, and is associated with decreased cardiovascular and all-cause mortality 2
Pathophysiology of Demand Ischemia
Demand ischemia is characterized by an imbalance between myocardial oxygen supply and demand, causing cardiac dysfunction, arrhythmias, myocardial infarction, and sudden death 5. The coronary circulation matches blood flow with oxygen requirements by coordinating the resistances within microvasculature, where the endothelium plays an important role by liberating several vasodilator substances 5. Impaired endothelial regulation is involved in the pathogenesis of a wide variety of cardiovascular diseases and therefore is an important therapeutic target 5.