Heart and organs failure is characterized by an inability of the myocardium to deliver sufficient oxygenated blood to meet the needs of tissues during exercise or at rest. Because diagnostic criteria for this clinical syndrome remain ill defined, the actual prevalence is difficult to determine. Heart failure is estimated to affect 2 to 4.5 million persons in the United States. (1-3) The condition is more common in men than in women, and its prevalence increases with age (1.1 percent in persons 25 to 54 years of age, 3.7 percent in persons 55 to 64 years, and 4.5 percent in persons 65 to 74 years). (3) Heart failure is becoming increasingly common as the U.S. population ages and survival rates after acute myocardial infarction increase.

The annual direct medical cost of caring for patients with heart failure is estimated to exceed $10 billion. (4) Furthermore, heart failure is a progressive condition: once symptoms appear, subsequent morbidity and mortality are high. In patients with heart failure identified by careful screening, five-year survival rates are only 59 percent in men and 45 percent in women. (5)

This article focuses on the diagnosis of heart failure from an evidence-based perspective. A clinical review (6) published in this issue examines the treatment of heart failure and the prognosis for affected patients.

Pathophysiology of Heart Failure
Normal myocardial function requires sufficient nutrient-rich, toxin-free blood at rest and during exercise; sequential depolarization of the myocardium; normal myocardial contractility during systole and relaxation during diastole; normal intracardiac volume before contraction (preload); and limited resistance to the flow of blood out of the heart (afterload). The capacity of the heart to adapt to short-term changes in preload or afterload is remarkable, but sudden or sustained changes in preload (e.g., acute mitral regurgitation, excessive intravenous hydration), afterload (e.g., aortic stenosis, severe uncontrolled hypertension), or demand (e.g., increased demand because of severe anemia or hyperthyroidism) may lead to progressive failure of myocardial function. Asymptomatic dysfunction progresses steadily to overt heart failure.

Coronary artery disease accounts for nearly 70 percent of all cases of heart failure. (7) Less frequent causes include diabetes mellitus and valvular heart disease (Table 1). Heart failure also can be multifactorial. For example, the disease can result from acute myocardial infarction (loss of myocardial contractility) with papillary muscle dysfunction (increased preload) and acute pulmonary edema (hypoxemia).

Heart failure may be classified into six types based on the role of diastolic or systolic dysfunction (Table 2). Diastolic dysfunction is heart failure caused by compromised myocardial relaxation in the presence of normal myocardial contractility and ejection fraction. It is associated most commonly with coronary artery disease, hypertension, aging, and infiltrative cardiomyopathy. Systolic dysfunction is caused by impaired myocardial contractility and low ejection fraction. It is associated most often with coronary artery disease (especially myocardial infarction), idiopathic dilated cardiomyopa-thy, hypertension, and valvular disease.

The five types of heart failure resulting from systolic dysfunction include high output heart failure, low cardiac output syndrome, right heart failure, left heart failure, and biventricular failure. High output heart failure occurs when the demand for blood exceeds the capacity of an otherwise normal heart to meet the demand. This type of heart failure may occur in patients with severe anemia, arteriovenous malformations with shunting of blood, or hyperthyroidism. Patients with low cardiac output syndrome have fatigue and loss of lean muscle mass as their most prominent symptoms, but they also may have dyspnea, impaired renal function, or altered mental status. Right heart failure is characterized by peripheral edema, whereas left heart failure is characterized by pulmonary congestion. Both systemic and pulmonary congestion are present in patients with biventricular heart failure.

Although the symptoms, causes, prevalence, and epidemiology of the six different types of heart failure are somewhat different, there is substantial overlap, and types may coexist. Therefore, this review presents an approach to diagnosis that is appropriate regardless of the type or cause of heart failure.

Overview of Diagnosis

The spectrum of patients who may be suspected of having heart failure ranges from those who are asymptomatic but at high risk for heart failure (i.e., patients who abuse alcohol or have coronary artery disease, hypertension, diabetes mellitus, exposure to cardiotoxic drugs, or familial history of cardiomyopathy) to those with florid signs and symptoms of heart failure.

Guidelines from the American College of Cardiology and the American Heart Association (8) identify four stages in the progression of heart failure. Patients in stage A have no structural abnormalities but are at high risk for heart failure. In stage B, patients are asymptomatic but have structural heart disease. Patients in stage C have structural abnormalities and past or present heart failure. In stage D, patients have end-stage heart failure and require mechanical circulatory support, infusion of inotropic agents, cardiac transplantation, or hospice care.