Heart Failure - Introduction
Skip to: Pathophysiology of Heart Failure
Heart failure is the inability of the heart to supply adequate blood flow and therefore oxygen delivery to peripheral tissues and organs. Under perfusion of organs leads to reduced exercise capacity, fatigue, and shortness of breath. It can also lead to organ dysfunction (e.g., renal failure) in some patients.
What is the incidence of heart failure and its prognosis?
It is estimated that there are more than 15 million new cases of heart failure each year worldwide. There are more than 600,000 new cases of heart failure diagnosed each year in the USA, and ten times that number of Americans currently in heart failure. The numbers are rapidly increasing because of the aging population. Heart failure is the leading cause of hospitalization of patients over 65 years in age.
Despite many new advances in drug therapy and cardiac assist devices, the prognosis for chronic heart failure remains very poor. One year mortality figures are 50-60% for patients diagnosed with severe failure, 15-30% in mild to moderate failure, and about 10% in mild or asymptomatic failure.
What are the causes of heart failure?
Causes of Heart Failure
- Myocardial infarction
- Coronary artery disease
- Chronic hypertension
- Valve disease
- Idiopathic cardiomyopathy
- Viral or bacterial cardiomyopathy
- Congenital heart disease
- Thyroid disease
- Septic shock
Heart failure is a clinical syndrome caused by disease or other abnormal conditions in the body. Heart failure can be caused by factors originating from within the heart (i.e., intrinsic disease or pathology) or from external factors that place excessive demands upon the heart. Intrinsic disease includes conditions such as dilated cardiomyopathy and hypertrophic cardiomyopathy. External factors that can lead to heart failure include long-term, uncontrolled hypertension, increased stroke volume (volume load; arterial-venous shunts), hormonal disorders such as hyperthyroidism, and pregnancy.
Acute heart failure develops rapidly and can be immediately life threatening because the heart does not have time to undergo compensatory adaptations. Acute failure (hours/days) may result from cardiopulmonary by-pass surgery, acute infection (sepsis), acute myocardial infarction, valve dysfunction, severe arrhythmias, etc. Acute heart failure can often be managed successfully by pharmacological or surgical interventions.
Chronic heart failure is a long-term condition (months/years) that is associated with the heart undergoing adaptive responses (e.g., dilation, hypertrophy) to a precipitating cause. These adaptive responses, however, can be deleterious in the long-term and lead to a worsening condition.
The number one cause of heart failure is coronary artery disease (CAD). CAD reduces coronary blood flow and oxygen delivery to the myocardium. This leads to myocardial hypoxia and impaired function. Another common cause of heart failure is myocardial infarction, which is the final and often fatal culmination of CAD. Infarcted tissue does not contribute to the generation of mechanical activity so overall cardiac performance is diminished. Furthermore, non-infarcted regions must compensate for the loss of function and this extra burden can precipitate changes that lead to failure. Valvular disease and congenital defects place increased demands upon the heart that can precipitate failure. Cardiomyopathies, of known origin (e.g., bacterial or viral) or idiopathic (unknown origin), can lead to failure. Myocarditis can have a similar effect. Arrhythmias such as severe bradycardia or tachycardia can also precipitate failure.