From the Guidelines
Demand ischemia occurs when the heart's oxygen demand exceeds its supply, causing myocardial ischemia without coronary artery blockage, and is typically precipitated by conditions that increase myocardial oxygen requirements, such as fever, tachycardia, or thyrotoxicosis, as noted in the 2011 ACCF/AHA guidelines 1. This condition is characterized by an imbalance between myocardial oxygen supply and demand, and is not a specific disease, but rather a syndrome, analogous to hypertension, as described in the 2011 ACCF/AHA guidelines 1. The most common mechanisms involve an imbalance that is caused primarily by a reduction in oxygen supply to the myocardium, whereas demand ischemia is principally due to increased myocardial oxygen requirements, usually in the presence of a fixed, restricted oxygen supply.
Some of the key causes of demand ischemia include:
- Increased myocardial oxygen requirements, such as fever, tachycardia, or thyrotoxicosis
- Reduced coronary blood flow, such as hypotension
- Reduced myocardial oxygen delivery, such as anemia or hypoxemia These causes are not mutually exclusive, and demand ischemia can occur in patients with underlying coronary atherosclerotic narrowing that limits myocardial perfusion, as well as in patients with chronic stable angina, as noted in the 2011 ACCF/AHA guidelines 1.
Management of demand ischemia focuses on treating the underlying cause while optimizing oxygen supply and reducing demand. This includes:
- Correcting anemia with blood transfusions
- Managing hypotension with fluids or vasopressors
- Controlling tachyarrhythmias with beta-blockers
- Addressing hypertension with appropriate antihypertensives
- Providing supplemental oxygen to maintain saturation above 94% For patients with severe left ventricular hypertrophy, controlling blood pressure is essential, often requiring combination therapy with ACE inhibitors, calcium channel blockers, or diuretics, as these conditions can increase myocardial oxygen demand and exacerbate demand ischemia, as described in the 2011 ACCF/AHA guidelines 1.
From the FDA Drug Label
Myocardial oxygen consumption or demand (as measured by the pressure-rate product, tension-time index, and stroke-work index) is decreased and a more favorable supply-demand ratio can be achieved
- Demand ischemia is decreased by nitroglycerin, as it reduces myocardial oxygen consumption or demand.
- This is achieved through the relaxation of vascular smooth muscle, dilation of arterial and venous beds, and reduction of left ventricular end-diastolic pressure (preload) and peripheral vascular resistance (afterload) 2.
From the Research
Demand Ischemia
- Demand ischemia occurs when there is an imbalance between myocardial oxygen supply and demand, causing cardiac dysfunction, arrhythmias, myocardial infarction, and sudden death 3.
- Myocardial oxygen requirements rise with increases in heart rate, contractility, or left ventricular wall stress, while myocardial oxygen supply is determined by coronary artery flow and myocardial oxygen extraction 4.
- Various factors can contribute to demand ischemia, including:
- Increased heart rate
- Increased contractility
- Increased left ventricular wall stress
- Decreased coronary artery flow
- Decreased myocardial oxygen extraction
Treatment Options
- Anti-anginal medications, such as nitrates, beta-blockers, and calcium channel blockers, are the mainstay of anti-ischemic management and act to correct the balance between myocardial supply and demand by increasing coronary blood flow, reducing myocardial oxygen requirements, or both 4, 5.
- Beta-blockers reduce myocardial oxygen demand, improve flow toward ischemic regions, and have mild antiplatelet and antiarrhythmic effects, making them effective in chronic stable angina and unstable angina 5.
- Calcium channel blockers reduce myocardial oxygen demand and improve oxygen supply, making them effective in the treatment of chronic stable angina, vasospastic angina, and unstable angina 5.
Pathophysiology
- The pathophysiology of myocardial ischemia is characterized by an imbalance between myocardial oxygen supply and demand, causing cardiac dysfunction, arrhythmias, myocardial infarction, and sudden death 3.
- 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 3.
- Impaired endothelial regulation is involved in the pathogenesis of a wide variety of cardiovascular diseases and is an important therapeutic target 3.