Believe it or not, heart failure is somewhat difficult to define. It is best thought of as a condition in which the heart cannot meet the demands of the peripheral circulation in all situations.
How is it diagnosed?
No single test is diagnostic for congestive heart failure. The diagnosis is usually not difficult to make and is based on an assessment of the history, physical examination, and chest x-ray. It is important to use these data to decide if the patient has left ventricular failure, right ventricular failure, or a combination of both, since the causes and treatments differ. Occasionally, it is necessary to call on more sophisticated testing to make the diagnosis.
What are the four determinants of cardiac output?
Afterload, preload, heart rate, and myocardial contractility.
Which of these is abnormal in heart failure?
Actually, all four are abnormal. In most cases of heart failure, the initial event is a decline in myocardial contractility from any one of a number of causes.
What happens to afterload?
In response to decreased peripheral perfusion caused by a decline in cardiac output, systemic vascular resistance rises. Although there are several mechanisms for this, the most important are a rise in circulating catecholamines and activation of the sympathetic nervous system. Initially, this rise in afterload helps to maintain organ perfusion. When .more advanced, it can become counterproductive and lead to a further reduction in cardiac output.