Lesson 5f | Nuclear Cardiology Seminars

An Overview of Cardiac Medications

The principal noninvasive therapeutic approach in the treatment of heart disease is by patent medicines. Cardiac drugs are usually categorized by their pharmacologic action within the body.

Antilipemic Agents (lipid-lowering agents) are prescribed for patients who have hyperlipidemia and are also used for prevention of cardiovascular disease. There are four classes of lipid-lowering agents: resins, statins, fibrates, and miscellaneous (includes fish oil and niacin).

Antidysrhythmic Agents are drugs given to prevent and/ or control atrial and ventricular arrhythmias. They may counterac those factors that contribute to the development of arrhythmias and/ or altering the electrophysiologic properties of the heart. Lidocaine is one of the most commonly used antidysrhythmic drugs, suppressing ectopic pacemakers in the heart and management of ventricular tachycardia. Others include procainamide, quinidine, phenytoin, and propranolol.

Antianginal Agents are effective in alleviating chest pain and decreasing the risk of ventricular fibrillation in the early post-MI patient. These agents treat a wide range of conditions, including hypertension, myocardial ischemia, arrhythmias, and congestive heart failure. Three classes of antianginal agents are used to treat stable and unstable angina:

Beta-adrenergic blockers- The effects of Beta-adrenergic blockers on the patient with ischemic heart disease include decreased heart rate, oxygen demand, myocardial contractility, afterload and exercise-induced vasoconstriction; and increased diastolic perfusion. Commonly prescribed beta blockers include: Propranolol, Metoprolol,Timolol, Acebuterol, Labetalol, Sotalol, Pindolol, Nadolol.
Calcium channel blockers- Muscle contracts in response to a rise in intracellular levels of calcium. Calcium channel blockers prevent the influx of calcium ions through specialized cell membrane channels of the myocardium and vascular smooth muscle. By blocking calcium influx, calcium channel blockers relax arterial smooth muscle. Cardiac muscle and coronary vessels dilate, increasing myocardial perfusion and collateral flow, reducing blood pressure. The oxygen demand on the heart decreases while the oxygen supply increases. These agents decrease heart rate by slowing conduction in the SA and AV nodes and also reduce myocardial contractility. Calcium channel blockers include: Verapamil, Amlodipine, Dilitazem, Nifedipine, Nicardipin, Bepridil.
Nitrates- Nitrates are among the oldest cardiac medications and are effective for patients with angina. Nitrates dilate large arteries and veins (capacitance vessels). In patients with angina, relief is achieved primarily as a result of venous dilation. Venodilation reduces cardiac preload, which in turn reduces ventricular filling pressures and volumes, decreases ventricular wall stress, and ultimately reduces oxygen demand of the myocardium. Nitroglycerin is perhaps the most well-known and frequently prescribed nitrate.

Antifailure agents
Congestive heart failure (CHF) is a syndrome of tissue congestion and edema that develops when the heart fails to maintain adequate circulation of blood. Right-sided failure typically leads to congestion in the lungs (pulmonary edema), impairing oxygen transfer at the alveolus. Left-sided failure causes congestion in the peripheral circulation. CHF usually indicates that the extent of the infarction is great, and the patient’s prognosis is serious.

The primary goal of medical therapy for CHF is to improve the performance of the heart using diuretics, ACE inhibitors, conventional vasodilators, vasosuppressors, and inotropic agents. Additional medical treatments correct systemic metabolic abnormalities (acidosis and hypoxemia), and to prevent or control arrhythmias.

Diuretics
enhance the excretion of sodium and water from the body. They decrease blood
pressure by reducing fluid volumes and total peripheral resistance, which is
the basis for their use in patients with hypertension. The types of
diuretics used in the treatment of CHF and hypertension include loop
diuretics, thiazide diuretics, and potassium-sparing diuretics.
ACE Inhibitors (angiotensin-converting enzyme)
have been shown to reduce morbidity and mortality following an MI with reduced ejection
fraction. ACE inhibitors block the conversion of angiotensin I to
angiotensin II, thereby causing vasodilation. These agents are commonly used
to improve left ventricular function and reduce the progression of CHF. They
are also first-line therapy in the treatment of hypertension. Examples of
drugs in this class include captopril, enalapril, and lisinopril.
Inotropic Agents. Inotropic refers to an effect on the force of myocardial contraction, whereas chronotropic refers to an effect on heart rate. The positive inotropic agents listed below are used to increase the force of contraction of the failing ventricle.-Digitalis(digoxin) increases the force of myocardial contraction. Additionally, digitalis stimulates the vagus nerve, resulting in slower conduction of impulses at the SA and AV nodes and decreasing heart rate. Digitalis is indicated for treating atrial and ventricular arrhythmias, managing CHF, and preventing tachycardia in patients about to undergo open-heart surgery.-Isoproterenol produces both positive inotropic and chronotropic effects. Used for heart failure patients, it increases stroke volume, cardiac output, cardiac work, and coronary flow.
By virtue of increasing myocardial oxygen demand, this drug may induce ischemia and/or infarction.-Dobutamine A positive inotropic and mild chronotropic agent used in the treatment of heart failure. Administration of dobutamine produces an increase in cardiac output and stroke volume with minimal changes in heart rate. In addition, dobutamine produces a decrease in systemic vascular resistance and mild arrhythmogenic effects
Vasopressors or vasoconstrictors contract arterial smooth muscle. Vasoconstriction raises
blood pressure and ensures perfusion of tissues. In the CCU, vasopressors may be administered to patients in shock, when perfusion of critical organs such as the brain and heart is threatened.

Antithrombotic Agents Cardiac patients can develop clots or thrombi in a number of ways. Atrial fibrillation, for example, can result in pooling of blood in the cardiac chambers, precipitating thrombus formation. The vascular damage characteristic of ischemic heart disease can also lead to thrombi. Mural thrombi may form during a MI. Once formed, thrombi can lyse within the vessel and can become lodged in the coronary or cerebral vasculature.

As a drug class, antithrombotic agents include platelet inhibitors, anticoagulants, and thrombolytic agents. They are indicated for the treatment of thromboembolic disorders. Patients receiving antithrombotics should be aggressively monitored to ensure that the proper dose is being administered.

Platelet inhibitors
Perhaps the most well-known yet misunderstood platelet inhibitor is aspirin. Aspirin, administered either alone or with beta blockers, has been used in patients with stable angina to reduce the risk of new or recurring MI, to prevent closure of bypass grafts, and to prevent restenosis of vessels postangioplasty.
Anticoagulants
are used in MI patients to decrease the possibility of extension of coronary thrombi, to prevent development of mural thrombi, and to decrease the likelihood of venous thromboembolism. Heparin and Warfarin are used by physicians to treat thromboembolic disorders. Heparin prevents coagulation by: inhibiting the conversion of prothrombin to thrombin, preventing thrombin from acting as a catalyst in converting fibrinogen into fibrin, and preventing aggregation of platelets. Heparin increases the clotting time of blood by disrupting the clotting process in proportion to the availability of the patient’s clotting factors and the dose of the drug administered.
Thrombolytic agents are also referred to as fibrinolytic agents. Thrombolytic therapy is indicated for lysis of intracoronary thrombi in the early stages of an acute MI. Tissue plasminogen activator (tPA), urokinase, and streptokinase are common thrombolytic agents. It is recommended that these agents be administered within 4 to 6 hours after the onset of pain, since permanent myocardial necrosis may occur if coronary perfusion has not been restored within that time.

Antihypertensive Agents Hypertension is a leading risk factor for heart disease and stroke. In some patients, blood pressure can be controlled by weight reduction, sodium restriction, and exercise. However, medical therapy is needed in many cases. In addition to lowering blood pressure, the other concomitant risk factors for CAD and stroke (eg, high cholesterol, smoking) must be controlled.

Many different classes of drugs are used to treat hypertension. Physicians may prescribe diuretics, beta blockers, calcium channel blockers, vasodilators, or ACE inhibitors. Drug therapy should be individualized to the patient’s blood pressure and presence of other risk factors.