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Wednesday, September 27, 2017

Heart Failure: Definition, Epidemiology, Causes, Prognosis, NYHA Classification

Today at The Health and Disease Blog we will discuss about Heart Failure. Heart failure, often called congestive heart failure (CHF) or congestive cardiac failure (CCF), is a common, usually progressive condition with a poor prognosis. Because many patients present without signs or symptoms of volume overload, the term “heart failure” is preferred over the older term “congestive heart failure.”

    Definition of Heart Failure

    Heart Failure is a complex clinical syndrome that results from any structural or functional impairment of ventricular filling or ejection of blood, which impairs the ability of the heart to function as a pump to support a physiological circulation which in turn leads to the cardinal clinical symptoms of dyspnea (breathlessness) and fatigue and signs of heart failure, namely edema and rales (an abnormal rattling sound heard when examining unhealthy lungs with a stethoscope).

    Basically what it means is that the heart is unable to pump blood at a rate sufficient to meet the metabolic demands of the tissues or can do so only at an elevated ventricular filling pressure.
    In mild to moderate forms of heart failure, cardiac output is normal at rest and only becomes impaired when the metabolic demand increases during exercise or some other form of stress.

    Epidemiology of Heart Failure

    Heart Failure (HF) is a burgeoning problem worldwide, with more than 26 million people affected.

    It is most common in the elderly.

    The overall prevalence of heart failure in the adult population in developed countries is 2%.

    Heart failure prevalence follows an exponential pattern, rising with age. The prevalence of heart failure rises from 1% in those aged 50-59 years to over 10% in those aged 80-89 years. The overall prevalence of heart failure is thought to be increasing, in part because current therapies for cardiac disorders, such as myocardial infarction (MI), valvular heart disease, and arrhythmias, are allowing patients to survive longer.

    In Scotland, the prevalence of heart failure is high at 7.1 in 1000, increasing with age to 90.1 in 1000 among people over 85 years. In the UK, overall incidence is about 2 in 1000. In North America and Europe, the lifetime risk of developing heart failure is approximately one in five for a 40-year-old.

    Although the relative incidence of heart failure is lower in women than in men, women constitute at least one-half the cases of heart failure because of their longer life expectancy.

    Very little is known about the prevalence or risk of developing heart failure in emerging nations because of the lack of population-based studies in those countries.

    The prognosis of heart failure has improved over the past 10 years with evidence-based therapy, but the mortality rate remains high and approximately 50% of patients are dead at 5 years mostly due to either pump failure or malignant ventricular arrhythmias.

    Heart failure accounts for 5% of admissions to hospital medical wards. The cost of managing heart failure exceeds £1 billion per year in the UK where most patients admitted to hospital with heart failure are more than 70 years old. They remain hospitalized for a week or more and may be left with chronic disability.

    Heart failure is the common end stage of many forms of chronic heart disease, often developing insidiously from the cumulative effects of chronic work overload (e.g., in valve disease or hypertension) or ischemic heart disease (e.g., following myocardial infarction with heart damage). However, acute hemodynamic stresses, such as fluid overload, abrupt valvular dysfunction, or myocardial infarction, can all precipitate sudden heart failure.

    Coronary artery disease and myocardial infarction is the most common cause of heart failure in Western countries.

    Rheumatic heart disease remains a major cause of heart failure in Africa and Asia, especially in the young.

    Hypertension is an important cause of heart failure in the African and African-American populations. Chagas’ disease is still a major cause of heart failure in South America.

    Anemia is a frequent concomitant factor in heart failure in many developing nations. As developing nations undergo socioeconomic development, the epidemiology of heart failure is becoming similar to that of Western Europe and North America, with coronary artery diseases emerging as the single most common cause of heart failure.

    Although the contribution of diabetes mellitus to heart failure is not well understood, diabetes accelerates atherosclerosis and often is associated with hypertension.

    Causes of Heart Failure

    Heart failure was once thought to arise primarily in the setting of a depressed left ventricular (LV) ejection fraction (EF). However, epidemiological studies have shown that approximately one-half of patients who develop heart failure have a normal or preserved ejection fraction (EF ≥50%). Accordingly, the historical terms “systolic” and “diastolic” heart failure have been abandoned, and heart failure patients are now broadly categorized into heart failure with a reduced ejection fraction (HFrEF- formerly systolic failure) or heart failure with a preserved ejection fraction (HRpEF- formerly diastolic failure).

    Although the etiology of heart failure in patients with a preserved ejection fraction differs from that of patients with depressed ejection fraction, there is considerable overlap between the etiologies of these two conditions.

    In industrialized countries, coronary artery disease (CAD) has become the predominant cause in men and women and is responsible for 60-75% of cases of heart failure. Hypertension contributes to the development of heart failure in 75% of patients, including most patients with coronary artery disease. Both coronary artery disease and hypertension interact to augment the risk of heart failure, as does diabetes mellitus.

    In 20-30% of the cases of heart failure with a depressed ejection fraction, the exact etiologic basis is not known. These patients are referred to as having nonischemic, dilated, or idiopathic cardiomyopathy if the cause is unknown.

    Prior viral infection or toxin exposure (for example, alcoholic or chemotherapeutic) also may lead to a dilated cardiomyopathy. Moreover, it is becoming increasingly clear that a large number of cases of dilated cardiomyopathy are secondary to specific genetic defects, most notably those in the cytoskeleton.

    Most forms of familial dilated cardiomyopathy are inherited in an autosomal dominant fashion. Mutations of genes that encode cytoskeletal proteins (desmin, cardiac myosin, vinculin) and nuclear membrane proteins (laminin) have been identified thus far. Dilated cardiomyopathy also is associated with Duchenne’s, Becker’s, and limb-girdle muscular dystrophies.

    Conditions that lead to a high cardiac output (for example, arteriovenous fistula, anemia) are seldom responsible for the development of heart failure in a normal heart. However, in the presence of underlying structural heart disease, these conditions can lead to overt heart failure.

    Table: Etiologies of Heart Failure
    Depressed Ejection Fraction (<40%)
    Coronary artery disease:

    • Myocardial infarction*
    • Myocardial ischemia*
    Nonischemic dilated cardiomyopathy:

    • Familial/genetic disorders
    • Infiltrative disorders*
    Chronic pressure overload:

    • Hypertension*
    • Obstructive valvular disease
    Toxic/drug-induced damage:

    • Metabolic disorder*
    • Viral
    Chronic volume overload:

    • Regurgitant valvular disease
    • Intracardiac (left-to-right) shunting
    • Extracardiac shunting
    Chagas’ disease
    Chronic lung disease:

    • Cor pulmonale
    • Pulmonary vascular disorders
    Disorders of rate and rhythm:

    • Chronic bradyarrhythmias
    • Chronic tachyarrhythmias
    Preserved Ejection Fraction (>40–50%)
    Pathologic hypertrophy:

    • Primary (hypertrophic cardiomyopathies)
    • Secondary (hypertension)
    Restrictive cardiomyopathy:

    • Infiltrative disorders (amyloidosis, sarcoidosis)
    • Storage diseases (hemochromatosis)
    Aging Endomyocardial disorders
    High-Output States
    Metabolic disorders:

    • Thyrotoxicosis
    Nutritional disorders:

    • Beriberi
    Excessive blood flow requirements:

    • Systemic arteriovenous shunting
    • Chronic anemia
    * Indicates conditions that can also lead to heart failure with a preserved ejection fraction.

    Prognosis of Heart Failure

    Despite many recent advances in the evaluation and management of heart failure, the development of symptomatic heart failure still carries a poor prognosis.

    Although the outlook depends, to some extent, on the underlying cause of the problem, community-based studies indicate that 30-40% of patients die within 1 year of diagnosis and 60-70% die within 5 years, mainly from worsening heart failure or as a sudden event (probably because of a malignant ventricular arrhythmia).

    Although it is difficult to predict prognosis in an individual, patients with symptoms at rest (New York Heart Association [NYHA] class IV) have a 30-70% annual mortality rate, whereas patients with symptoms with moderate activity (NYHA class II) have an annual mortality rate of 5-10%. Thus, functional status is an important predictor of patient outcome.

    New York Heart Association Classification of Heart Failure

    Functional Capacity Objective Assessment
    Class I No limitation. Patients with cardiac disease but without resulting limitation of physical activity. Ordinary physical activity does not cause undue fatigue, palpitations, dyspnea, or anginal pain. Asymptomatic left ventricular dysfunction.
    Class II Mild limitation. Patients with cardiac disease resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain. Symptomatically ‘mild’ heart failure.
    Class III Marked limitation. Patients with cardiac disease resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary activity causes fatigue, palpitation, dyspnea, or anginal pain. Symptomatically ‘moderate’ heart failure.
    Class IV Patients with cardiac disease resulting in inability to carry on any physical activity without discomfort. Symptoms of heart failure or the anginal syndrome may be present even at rest. If any physical activity is undertaken, discomfort is increased. Symptomatically ‘severe’ heart failure.

    That's all for today!
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