From the Guidelines
Nitroglycerin improves coronary perfusion primarily through vasodilation of coronary blood vessels, as evidenced by the most recent and highest quality study 1. When administered, nitroglycerin is converted to nitric oxide in the body, which relaxes vascular smooth muscle by increasing cyclic guanosine monophosphate (cGMP) levels. This vasodilation has several beneficial effects on coronary perfusion, including:
- Dilation of both epicardial coronary arteries and collateral vessels, increasing blood flow to ischemic myocardium
- Reduction of preload by dilating venous capacitance vessels, which decreases ventricular filling pressures and wall tension, thereby reducing myocardial oxygen demand
- Decrease of afterload through arterial dilation, further reducing cardiac workload These combined effects create a more favorable oxygen supply-demand balance in the heart. Nitroglycerin is typically administered sublingually (0.3-0.6 mg) for acute angina, as an intravenous infusion (starting at 5-10 mcg/min) for unstable angina or acute coronary syndromes, or as a transdermal patch (0.2-0.8 mg/hr) for prophylaxis, as recommended by the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1. Side effects may include headache, hypotension, and reflex tachycardia, so blood pressure monitoring is essential during administration. It is also important to note that nitrates should not be administered to patients with hypotension or to those who received a phosphodiesterase inhibitor, and should be used with caution in patients with right ventricular infarction, as stated in the 2014 AHA/ACC guideline 1. The use of nitroglycerin should not preclude the use of other anti-ischemic therapies with proven benefits, such as beta blockers, as recommended by the ACC/AHA guidelines 1. Overall, the benefits of nitroglycerin in improving coronary perfusion and reducing myocardial oxygen demand make it a valuable treatment option for patients with acute coronary syndromes, as supported by the evidence from the 2014 AHA/ACC guideline 1.
From the FDA Drug Label
The principal pharmacological action of Nitroglycerin Injection is relaxation of vascular smooth muscle and consequent dilatation of peripheral arteries and veins, especially the latter... Dilatation of the coronary arteries also occurs Effective coronary perfusion pressure is usually maintained, but can be compromised if blood pressure falls excessively, or increased heart rate decreases diastolic filling time. Coronary perfusion pressure was usually, but not always, maintained
- Nitroglycerin has a dilating effect on coronary arteries.
- Coronary perfusion pressure is usually maintained, but can be compromised in certain situations, such as excessive blood pressure falls or increased heart rate.
- The overall effect of nitroglycerin on coronary perfusion is to generally maintain or potentially increase it due to the dilation of coronary arteries, but this can be influenced by various factors, including blood pressure and heart rate changes 2, 3.
From the Research
Effect of Nitroglycerin on Coronary Perfusion
- Nitroglycerin has been shown to exert its primary vasodilatory effect on epicardial conductance vessels, which can lead to an increase in blood flow to poststenotic zones of ischemia 4.
- Studies have demonstrated that nitroglycerin can increase blood flow to ischemic myocardium, with a significant increase in the proportion of blood flow to ischemic zones 4, 5.
- The effect of nitroglycerin on coronary perfusion can vary depending on the method of administration, with intracoronary infusion potentially producing a coronary steal, while intravenous infusion may improve endocardial perfusion via indirect hemodynamic actions 6.
- Nitroglycerin has been shown to selectively dilate coronary arterial microvessels greater than 200 microns, which can alter the distribution of microvascular resistance without altering overall resistance 7.
- The use of nitroglycerin can also lead to an increase in the end/epi ratio in ischemic myocardium, indicating an improvement in endocardial perfusion 8.
Key Findings
- Nitroglycerin increases blood flow to ischemic myocardium 4, 5.
- Intravenous infusion of nitroglycerin may improve endocardial perfusion via indirect hemodynamic actions 6.
- Nitroglycerin selectively dilates coronary arterial microvessels greater than 200 microns 7.
- Nitroglycerin can increase the end/epi ratio in ischemic myocardium, indicating an improvement in endocardial perfusion 8.