Heart failure refers to the state when the heart is unable to pump blood at a rate commensurate with the metabolic requirements of tissues and/or can do so only from an abnormally elevated left ventricular (LV) end-diastolic volume.
Heart failure is most frequently caused by a defect in myocardial contraction. Insufficiency of the myocardial contraction may result from a primary abnormality in heart muscle, as occurs in the cardiomyopathies or myocarditis of any origin. Myocardial failure also may be caused by extramyocardial abnormalities such as coronary occlusion and long-standing excessive hemodynamic burden.
Occasionally heart failure is exhibited without any detectable abnormality of the myocardial function. In these patients, heart failure develops suddenly as a result of mechanical overload that exceeds heart functional capacity. It can result from an acute hypertensive crisis, rupture of an aortic valve cusp, or massive pulmonary embolism. Heart failure in the presence of the normal myocardial function also occurs in chronic conditions, such as tricuspid and/ or mitral stenosis, constrictive pericarditis without myocardial involvement, endocardial fibrosis, and concentric hypertrophy. In many patients with heart failure, particularly those with valvular or congenital heart disease, a combination of the impaired myocardial function and mechanical abnormality coexists. Heart failure should be distinguished from circulatory disorders in which low cardiac output results from abnormal venous return. Heart failure always causes circulatory failure, but the converse is not necessarily the case because various noncardiac conditions (e.g. hypovolemic shock, septic shock) can produce circulatory failure in the presence of the normal, modestly impaired, or even supranormal cardiac function. In these conditions, ejection fraction (ratio of stroke volume to end-diastolic volume) is normal, whereas heart failure, except diastolic form, manifests low ejection fraction.