A 51-year-old male presents with recurrent chest pain on exertion. He is diagnosed with angina pectoris. When he asks what causes the pain, how should the nurse respond? The pain occurs when

Choice A reason: Cardiac output has not fallen below normal levels. Cardiac output is the amount of blood pumped by the heart per minute. It is affected by the heart rate and the stroke volume. Angina pectoris does not directly affect the cardiac output, but it can reduce the stroke volume due to impaired ventricular filling. Choice B reason: The vagus nerve is not stimulated. The vagus nerve is a cranial nerve that innervates the heart and other organs. It is part of the parasympathetic nervous system, which slows down the heart rate and lowers the blood pressure. Angina pectoris does not activate the vagus nerve, but it can trigger the sympathetic nervous system, which increases the heart rate and blood pressure. Choice C reason: Myocardial stretch has not exceeded the upper limits. Myocardial stretch is the degree of tension or load on the cardiac muscle fibers. It is determined by the end-diastolic volume, which is the amount of blood in the ventricle at the end of relaxation. Angina pectoris does not cause excessive myocardial stretch, but it can impair the myocardial contractility due to ischemia. Choice D reason: The myocardial oxygen supply has fallen below demand. This is the main cause of angina pectoris. It occurs when the coronary arteries, which supply blood and oxygen to the heart muscle, are narrowed or blocked by atherosclerosis or spasm. This creates an imbalance between the oxygen demand of the heart, which increases during exertion, and the oxygen supply, which is reduced by the obstruction.