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An circulating enzyme released by mammalian kidneys that converts angiotensinogen to angiotensin-I. Because its activity ultimately leads to formation of angiotensin-II and aldosterone, this hormone plays a role in maintaining blood pressure.
Heart failure is a common, costly, disabling, and potentially deadly condition. In developed countries, around 2% of adults suffer from heart failure, but in those over the age of 65, this increases to 6–10%. Heart failure is the leading cause of hospitalization in people older than 65. In developed countries, the mean age of patients with heart failure is 75 years old. In developing countries, 2-3% percent of the population suffers from heart failure, but in those 70 to 80 years old, it occurs in 20-30%.
Heart failure affects close to five million people in the U.S. and each year close to 500,000 new cases are diagnosed. What is of more concern is that more than 50% of patients seek re-admission within six months after treatment and the average duration of hospital stay is six days.
What is CHF?
Heart failure is a global term for the physiological state in which cardiac output is insufficient in meeting the needs of the body and lungs. Often termed "congestive heart failure" or CHF, this is most commonly caused when cardiac output is low and the body becomes congested with fluid. It may also occur when the body's requirements for oxygen and nutrients are increased and the demand outstrips what the heart can provide.
Heart failure can result from any one, or combinations of, cardiomyopathies or problems within the heart muscle, and these problems can result in heart failure. Ischemic cardiomyopathy implies that the cause of muscle damage is coronary artery disease. Dilated cardiomyopathy implies that the muscle damage has resulted in enlargement of the heart. Hypertrophic cardiomyopathy involves enlargement and thickening of the heart muscle. Ultimately, acute decompensated heart failure can occur; a term used to describe episodes in which a patient can be characterized as having a change in heart failure signs and symptoms resulting in a need for urgent therapy or hospitalization.
Increased heart rate in CHF is stimulated by increased sympathetic activity in order to maintain cardiac output. Initially, this helps compensate for heart failure by maintaining blood pressure and perfusion, but it places further strain on the myocardium, increasing coronary perfusion requirements, which can lead to worsening of ischemic heart disease. Sympathetic activity may also cause potentially fatal arrhythmias.
Hypertrophy (an increase in physical size) of the myocardium also results as a compensatory mechanism when the terminally differentiated heart muscle fibers increase in size in an attempt to improve contractility. Ultimately, hypertrophy may contribute to the increased stiffness and decreased ability to relax during diastole. Ventricular hypertrophy will also contribute to the enlargement and spherical shape of the failing heart and may reduce stroke volume due to mechanical and contractile inefficiency.
Reduced perfusion (blood flow) to the kidneys stimulates the release of renin – an enzyme that catalyzes the production of the potent vasopressor angiotensin . Angiotensin and its metabolites cause further vasoconstriction, and stimulate increased secretion of the steroid aldosterone from the adrenal glands. This promotes salt and fluid retention at the kidneys, also increasing the blood volume.
The increased peripheral resistance and greater blood volume place further strain on the heart and accelerates the process of damage to the myocardium. Vasoconstriction and fluid retention produce an increased hydrostatic pressure in the capillaries. This shifts the balance of forces in favor of interstitial fluid formation as the increased pressure forces additional fluid out of the blood, into the tissue. This results in edema (fluid build-up) in the tissues.
In the U.S., HF is much higher in African Americans, Hispanics, Native Americans and recent immigrants from the eastern bloc countries like Russia. This high prevalence in these ethnic populations has been linked to high incidence of diabetes and hypertension. In many new immigrants to the U.S. the high prevalence of heart failure has largely been attributed to lack of preventive health care or substandard treatment. In tropical countries, the most common cause of HF is valvular heart disease or some type of cardiomyopathy. Moreover as underdeveloped countries become more affluent, there has also been an increase in diabetes, hypertension, and obesity which has resulted in heart failure.