Action

The heart receives its blood supply and oxygen from the coronary arteries. These small arteries are often plugged or damaged when the patient has angina or a heart attack. Blood may also be cut off from the coronary arteries if there is coronary vasospasm. Blockage or spasm causes cardiac angina when the heart muscle is without oxygen. Currently there are three major classes of drugs used in the medical management of angina. Nitrates (both short and long acting), β-blockers, and calcium channel blockers. Some other vasodilating agents (agents to open up the vessels) are used for increasing circulation in peripheral vascular disease. (Information about the use of beta blockers in treating angina by decreasing the oxygen demands of the heart and calcium channel blockers that may relieve angina by dilating the coronary vessels and reducing the work load of the heart can be found in the discussion of antihypertensives and diuretics in the fifth section of this chapter.)

Uses

Rapid-acting nitrates (such as amyl nitrite, sublingual nitroglycerin, and sublingual or chewable isosorbide dinitrate) are used mostly to relieve pain in acute angina. The long-acting nitrates and topical, transdermal, transmucosal, and oral sustained-release nitroglycerin products are used to prevent or treat anginal attacks when they are likely to occur (for example, with exercise) and to reduce the severity and frequency of anginal attacks. They are also used to reduce the work of the heart in cases of MI and in chronic heart failure; and for relief of gallbladder, gastrointestinal (GI), urethral, and bronchial smooth muscle pain.

It is not always clear if it is safe to use nitroglycerin in patients with acute MIs. When it is used in patients with recent MIs, the transdermal patch systems work best, but patients must be closely evaluated. Intravenous (IV) nitroglycerin is used to control severe angina in an acute MI and also to control acute pain during procedures on the heart, such as cardiac catheterization. This IV nitroglycerin requires careful monitoring of the patient in a cardiac care or critical care unit due to the possibility the medicine may cause a severe drop in blood pressure.

Peripheral vasodilating agents are used to treat pain in the legs caused by problems such as intermittent claudication, arteriosclerosis obliterans, Raynaud’s disease, nocturnal leg cramps, and vasospasm caused by blood clots.

Adverse Reactions

There are many common adverse reactions to nitrates, including flushing, postural hypotension (low blood pressure when a person suddenly stands up), tachycardia (rapid heartbeat), confusion, dizziness, fainting, headache, light-headedness, vertigo (feeling of dizziness or spinning), weakness, drug rash, localized pruritus (itching), local burning in the mouth, nausea, and vomiting.

Some of these cardiac preparations contain tartrazine, a chemical that may cause an allergic type of reaction with symptoms similar to asthma. Patients who are allergic to aspirin have a greater chance of reacting to tartrazine.

When nitrate products are used, high doses may cause violent headaches. All nitrates should be given with care to patients with a recent history of stroke or cerebrovascular accident, because these conditions cause widening of the cerebral arteries.

Peripheral vasodilating agents may cause dizziness, headache, weakness, tachycardia, flushing, postural hypotension, dysrhythmias, confusion, severe rash, nervousness, tingling, and sweating. Some side effects disappear within a few weeks if they are mild and if the patient can keep taking the medication.

Drug Interactions

Nitrates increase the effects of atropine-like drugs and tricyclic antidepressants and decrease the effects of all choline-like drugs. The action of anticholinergic drugs and antihistamines may be made stronger. Nitrates should not be taken at the same time as prazosin because of the possibility of a significant interaction. Taking alcohol, beta blockers, antihypertensives, narcotics, and vasodilators with nitrates and nitrites (especially amyl nitrite) may produce severe hypotension (low blood pressure) and cardiac collapse. Nitrates may antagonize (interfere with) the vasopressor actions of sympathomimetic drugs. A cold environment or the use of tobacco reduces the action of nitroglycerin.

The action of peripheral vasodilating agents is stronger if used with antihypertensives and alcohol and may cause hypotension.

Nursing Implications and Patient Teaching

Action

Uses

The cause of the dysrhythmia will determine which drug will be most effective in correcting it. The two basic actions within the heart that cause dysrhythmias are: (1) increased sensitivity of electrical cells in the heart, resulting in irregular or early ectopic beats (the cell fires before it should); and (2) electrical activity moving through abnormal conduction pathways (the trigger that causes the cell to fire does not always work properly). For example, a block of the sinus or AV node pacemakers force the heart to use a different pathway than usual. The amount of medication that can be given for these dysrhythmic drugs has a very small range. If too much is given, the dose may be toxic and add to the problems of the heart.

There are now many dysrhythmic drugs on the market. Only a few of the most commonly used drugs are described here. Two drugs that are often used to treat rapid and irregular dysrhythmias are quinidine and procainamide. These drugs are chemically different, but both act to quiet the myocardial cells and make them less excitable and less likely to fire. This not only decreases the heart rate but also stops some of the extra or irregular beats. These drugs were once the mainstay of dysrhythmia therapy but new drugs now have less significant side effects.

Bretylium is another drug that used to be in greater use to slow the conduction rate of the electrical impulse in the ventricular muscle. This drug also acts to slow the release of norepinephrine, a powerful chemical in the cardiac cells, so the heart muscle beats more slowly.

Disopyramide slows the depolarization of the cardiac cells. Depolarization is the movement of electrolytes into and out of the cell as it gets ready to send another electrical message. Under the influence of disopyramide, the heart rate is slowed because each cell is slower in recovering from sending the message to the next cell (the reloading time takes longer).

Lidocaine IV is a drug that was formerly widely used. The electrical impulse sent to the cardiac muscle must be of certain strength, or it cannot pass along the conducting nerve fibers. Lidocaine increases the strength of the impulse. A drug that affects the rate of rhythmic movements, such as the heartbeat, is called a chronotropic drug. A dromotropic drug influences the velocity (speed) of the passage of an electrical impulse in nerve or cardiac muscle fibers.

A diseased heart may have many electrical impulses trying to move at the same time, but some impulses are very weak. By increasing the strength the impulse must reach before it may be conducted, many weak impulses will be screened out, and the overall heart rate will be slower.

Adenosine is a powerful drug that slows the conduction through the AV node and decreases how rapidly the SA node will fire. An IV injection to end serious atrial tachycardia may cause the heart to stop beating for several seconds when a very rapid heartbeat is changed to normal (normal sinus rhythm). Although this drug has only a 10-second half-life, this pause in the heart beat is very upsetting for patients, who often refuse to take it more than once. Some institutions may use benzodiazepines at the same time to help the patients relax during this procedure.

Digoxin is used primarily to treat heart failure but also plays a role in treating fast dysrhythmias such as atrial fibrillation or tachycardia. It slows the heart rate by slowing how fast the SA node fires and slowing conduction through the AV node. It also strengthens the contraction of the heart. Toxic levels of this medication also cause dysrhythmias. (See cardiotonics in a later section.) Other drugs that affect heart activity are the beta-adrenergic blockers, of which propranolol (Inderal) and metoprolol (Lopressor) are the most well known. Drugs in this category act very much like quinidine, but they also decrease the response of the heart muscle to epinephrine and norepinephrine (other chemical neurotransmitters) by blocking the stimulation of the heart’s beta receptors. (Again, the reloading of the cell is affected.)

It is clear that many of the antidysrhythmic drugs are so powerful that they should only be used in critical care units where the patient may be closely monitored. Some of these drugs are given as an IV injection followed by an IV solution filled with the medication. As the patient’s condition becomes more stable, some drugs may be changed to other antidysrhythmic drugs that are better for long-term therapy.

Adverse Reactions

Most drugs given to control dysrhythmias may also cause other dysrhythmias. All patients receiving these drugs should have their heart carefully monitored by ECG for any change.

Quinidine is an older drug that is still in use in some hospitals and parts of the world, although it has many adverse effects. It may cause cardiac dysrhy­thmias, hypotension, diarrhea, tinnitus, headache, vertigo, confusion, delirium, disturbances in vision, and abdominal pain. Toxic effects are called cinchonism, and the patient will complain of tinnitus, light-headedness, headache, fever, vertigo, nausea, vomiting, and dizziness. The first time the patient takes the medicine, a test dose should be given to check for quinidine syncope—a condition in which the body reacts to quinidine by reducing blood flow to the brain, producing syncope (light-headedness and fainting), loss of consciousness, and sometimes death.

Drug Interactions

Quinidine’s effect is increased by potassium and is reduced by hypokalemia. Verapamil actions are stronger when used at the same time as digitalis and beta blockers. Beta blockers have many interactions with other drugs, and the nurse should read about every other drug the patient is taking when a beta blocker is prescribed.

Nursing Implications and Patient Teaching