A nurse is providing education to a client who has been experiencing unstable angina. What is the nurse's best explanation of this condition?

A. "A coronary vessel has become completely plugged and is unable to deliver blood to your heart." This describes a myocardial infarction, not unstable angina. In unstable angina, the artery is narrowed but not entirely blocked. B. "The pain is caused by a spasm of a blood vessel, not just from the vessel narrowing." This better describes variant (Prinzmetal’s) angina, which involves coronary vasospasm rather than plaque-induced ischemia. C. "There is serious narrowing of a coronary artery causing a reduction in oxygen to the heart." This accurately explains unstable angina, which occurs due to significant plaque buildup or rupture leading to transient, reduced coronary blood flow and oxygen delivery. D. "Your body's response to a lack of oxygen in the heart muscle is causing the pain you are feeling." While accurate in stating that the pain is due to a lack of oxygen (ischemia), this explanation is applicable to any type of angina or even a heart attack. It does not provide the specific nuance of unstable angina.