Congestive Heart Failure

Compiled by

Eric Brandt, B.Sc. Pharm

(References available on request)

Definition

Congestive Heart Failure (CHF) , also termed Heart Failure (HF) by definition is the inability of the heart to pump the blood required by metabolizing tissues or its ability to do so only from an abnormally elevated filling pressure.

Physiology

The result is organ hypoperfusion and inadequate tissue oxygen delivery as well as pulmonary and venous congestion.

The heart tries to compensate for this in a variety of ways: increased including increased left ventricular volume (dilatation) and mass (hypertrophy), increased systemic vascular resistance secondary to enhanced activity of the sympathetic nervous system and elevated levels of catecholamines and activation of renin-angiotensin and vasopressin systems.

Causes

Hypertension and coronary artery disease are the most frequent causes of CHF. Other causes include, pulmonary embolism, heart attack, abnormality of heart muscle, abnormal valve function, and disease of the tissue surrounding the heart. Additionally, severe anemia, highly overactive thyroid and beriberi can also lead to heart failure.

Symptoms

Patients usually present with difficult breathing except in the upright position, fatigue, labored or difficult breathing, and/or peripheral edema. A chest X-ray can reveal an enlarged heart and abnormal distribution of blood vessels in the lung.

There are some medical conditions that can mimic the symptoms of heart failure. These include chronic bronchitis, emphysema, and asthma. Peripheral edema can be caused also by liver disease, or kidney disease.

Treatment

Treatment is aimed at relieving symptoms, removing precipitating factors, and control of underlying cardiac disease.

Nonpharmacologic measures

1. Restriction of physical activity and bed rest reduce the work on the heart and oxygen consumption. Exercise should be guided by specially trained personnel.

2. Weight loss in obese patients will reduce systemic vascular resistance and will also reduce demands on the heart.

3. Sodium restriction and limits on water consumption may improve volume overload

4. Administering oxygen will improve oxygen delivery to tissues, relieve shortness of breath

5. Quitting smoking is important in optimizing the oxygen carrying capacity of blood and will reduce the risk of heart coronary artery disease.

Pharmacologic measures

Drugs used to treat the symptoms of heart failure are often used in combination because people suffering from heart failure often have more than one problem.

These drugs include: diuretics, angiotensin converting enzyme inhibitors (ACE), vasodilators, digoxin, beta blockers and anti-arrhthmics.

ACE INHIBITORS - Angiotensin-converting enzyme (ACE) inhibitors interfere with formation of angiotensin II, an important vasoconstrictor in patients with heart failure, and inhibit the metabolism of the vasodilator bradykinin. Many ACE inhibitors are available for clinical use; despite differences in pharmacokinetics and tissue binding properties, available data suggest that they are all about equally effective. ACE inhibitors can improve symptoms and exercise tolerance in patients with heart failure, sometimes within days, but more commonly with a delay of four to twelve weeks. These drugs slow the progression of heart failure and can prolong survival in patients with impaired left ventricular function, whether or not they have symptoms of heart failure. The optimal dosage of ACE inhibitors needed to slow progression and reduce mortality remains undefined, but most controlled trials have used doses such as 50 mg three times a day of captopril (Capoten), 10 mg twice a day of enalapril (Vasotec) or 5 mg twice a day of ramipril (Altace), which may cause hypotension in patients with heart failure, especially if they are also taking a diuretic. Starting with lower doses and increasing gradually may be helpful.

Adverse Effects - The most common adverse effects of ACE inhibitors are related to suppression of angiotensin II (hypotension and renal insufficiency or increases in concentrations of endogenous kinins (cough and angioneurotic edema). Those related to angiotensin II suppression can often be ameliorated by decreasing the dose of diuretic taken concurrently. Those related to kinins may be relieved by replacing the ACE inhibitor with an angiotensin II receptor antagonist such as losartan (Cozaar), which acts mainly on the renin-angiotensin system.

DIURETICS - Most patients with heart failure have fluid retention and require diuretics. By increasing renal excretion of sodium and water, diuretics relieve symptoms of heart failure but do not stop progression of the underlying disease, and their effect on survival is unknown. Loop diuretics that act on the loop of Henle, such as furosemide (Lasix, and others), bumetanide (Bumex, and others) or torsemide (Demadex) are more effective than thiazide diuretics such as chlorothiazide (Diuril, and others), which act on the distal tubule. Patients resistant to an oral diuretic may respond to intravenous administration or to concurrent use of two diuretics with different sites of action.

Adverse Effects - The most common adverse effect of diuretic therapy is potassium depletion, which can be decreased or prevented by taking oral potassium supplements or by concurrent use of either an ACE inhibitor or a potassium-sparing diuretic such as spironolactone (Aldactone, and others), amiloride (Midamor, and others) or triamterene (Dyrenium).

Use of both an ACE inhibitor and a potassium-sparing diuretic can produce a dangerous level of hyperkalemia.

DIGITALIS - Digoxin (Lanoxin, and others) can decrease the symptoms of heart failure, increase exercise tolerance, and decrease the frequency of hospitalization. The clinical benefits of digoxin may be due to its positive inotropic effects and/or suppression of increased neurohormonal activity. The unpublished results of a large long-term study indicate that digoxin has neither a beneficial nor an adverse effect on survival (JJ Ferguson, Circulation, 94:3,July 1, 1996).

Dosage and Adverse Effects - The optimal dosage of digoxin is not clear. Clinical studies have often used a daily dosage of 0.25 to 0.50 mg, but many clinicians prescribe 0.125 to 0.25mg daily. The most common adverse effects of digitalis glycosides are conduction disturbances and cardiac arrhythmias; nausea, vomiting, confusion and visual disturbances can occur. Hypokalemia or renal insufficiency increases the risk of digitalis toxicity.

VASODILATORS - Concurrent use of two vasodilators, hydralazine (Apresoline) and isosorbide dinitrate, dilates both arterial resistance and venous capacitance vessels, decreasing both afterload and preload in the failing heart. In patients already taking digitalis and diuretics, this combination had less benefit on mortality than use of an ACE inhibitor. Concurrent use of hydralazine and isosorbide dinitrate produces frequent adverse effects, especially headache, gastrointestinal disturbances, palpitations and nasal congestion. Neither hydralazine nor isosorbide dinitrate, alone or in combination, is approved for treatment of heart failure by the FDA.

BETA-BLOCKERS - Even though short-term use of beta-blockers can decrease the contractility of the heart, blocking the effects of the sympathetic nervous system can produce long-term clinical benefits in patients both with and without coronary artery disease as the cause of heart failure. Controlled trials have shown that metoprolol (Lopressor, and others), bisoprolol (Zebeta) or carvedilol (recently approved in Canada) added to conventional therapy may slow progression of heart failure and decrease the frequency of hospitalization

Dosage and Adverse Effects - Beta-blockers should be used in heart failure with great caution, starting with low doses and observing patients closely for hypotension and worsening failure, which may occur during the first two to four weeks of treatment. As with ACE inhibitors, the occurrence of early circulatory instability does not preclude the possibility of long-term benefit. Dosage should be increased gradually over several weeks until therapeutic doses are reached; full clinical benefits may not occur for one to three months.

OTHER DRUGS - Calcium Channel Blockers - Although calcium channel blockers dilate arterial resistance vessels, in some studies use of these drugs, including sustained-release formulations, has made heart failure worse. In one long-term study of more than 1,000 patients with severe heart failure, amlodipine (Norvasc) did not increase morbidity or mortality and decreased cardiac events in patients with nonischemic cardiomyopathy

Amiodarone - In one report, low doses of the antiarrhythmic drug amiodarone (Cordarone) decreased mortality in patients with heart failure, but this benefit was not confirmed in a second trial. In general, antiarrhythmic agents can make heart failure worse and cause proarrhythmic effects.

CONCLUSION - Patients with heart failure due to left ventricular dysfunction should take an ACE inhibitor. Most patients also require a diuretic to relieve fluid retention, and use of digoxin can decrease symptoms. The addition of a beta-blocker may slow the progression of heart failure in some patients.