Ischemic heart disease occurs simply when the oxygen demand by the heart exceeds the supply (Figure 14–1). Angina is the primary symptom of ischemic heart disease.
Ischemic heart disease comes about when one, or more, of the factors that determine oxygen demand by the heart exceeds the blood/oxygen supply to the heart muscle.
To reduce myocardial oxygen demand β-blockers (see Chapters 10 and 13) can be used to decrease heart rate and contractility. Calcium channel blockers (see Chapter 12), particularly verapamil, diltiazem, and amlodipine, reduce systemic vascular resistance, improve coronary and myocardial blood flow, and decrease myocardial contractility. Nitrates (below) will produce venous dilation, which will decrease preload and decrease oxygen demand by the heart. β-Blockers are effective in exertional angina and improving survival in patients who have had a myocardial infarction. Finally, antiplatelet drugs (see Chapter 16), such as aspirin, will prevent thrombus formation in the coronary arteries. Lipid-lowering drugs (see Chapter 17) have been shown to reduce the risk of heart attacks in patients with coronary artery disease.
Unstable angina is treated with nitroglycerin, antiplatelet, and anticoagulant drugs. Finally, acute myocardial infarction is treated with thrombolytic agents (see Chapter 16). Recent guidelines have direct reversible P2Y12 receptor antagonists (ticagrelor and prasugrel) as the primary choice for acute coronary syndrome, which includes myocardial infarction.
These drugs are sources of nitric oxide (NO), which produces relaxation of vascular smooth muscle leading to vasodilation. The organic nitrates preferentially dilate veins and conductive arteries. The beneficial effect of nitroglycerin appears to come primarily from the reduction in cardiac oxygen demand. The increase in cyclic guanosine monophosphate (cGMP) that results will inhibit platelet function.
Nitroglycerin is administered under the tongue (sublingually) for rapid onset and to avoid first-pass metabolism.
Hopefully you remember what first-pass metabolism is! Repeated or continuous exposure leads to tolerance. Headache is common and tells the patient that the nitroglycerin is still active. Orthostatic hypotension and tachycardia can also occur.
Heart failure occurs when the heart can no longer pump enough blood to meet the demands of the body. Heart failure is a clinical syndrome that represents the final common pathway of multiple cardiac diseases. The most common cause is ischemic heart disease. Other causes include chronic arterial hypertension (HTN), valvular diseases, cardiomyopathies, viral infections and toxins.
Patients with a left ventricular ejection fraction (LVEF) ≤ 40% are considered to have heart failure with reduced ejection fraction (HFrEF). Patients with an LVEF ≥ 50% and symptoms of heart failure are considered to have heart failure ...