Pathophysiology of congestive heart failure.

Congestive heart failure is a syndrome common in the United States, especially in elderly patients. The most common etiology is coronary artery disease. A number of general factors contribute to the heart failure syndrome, including loss of muscle, decreased myocardial contractility, pressure or volume overload, or restricted filling. All of these factors may play a role in a given patient as, for example, with coronary artery disease. Although systolic dysfunction with a reduced ejection fraction is the most common heart failure syndrome, up to 40% of patients may have a relatively preserved ejection fraction with diastolic dysfunction. As the heart begins to fail, a number of compensatory mechanisms are activated. These include increased heart rate, the Frank-Starling mechanism, increased catecholamines, activation of the renin-angiotensin system, and release of atrial natriuretic peptides. Although these mechanisms are initially helpful to the cardiovascular system, they frequently overshoot, initiating a vicious cycle. For example, with a decrease in cardiac output, there is a reflex increase in systemic vascular resistance in order to maintain perfusion pressure. This increase in resistance, however, acts as a load on the left ventricle and further reduces cardiac output. The best evidence for the existence of this vicious cycle is the beneficial change in hemodynamics produced by vasodilator drugs and the ACE inhibitors. Thus, an understanding of pathophysiology allows for the selection of rational therapy. An unresolved problem in heart failure patients is how best to reduce the high incidence of sudden death, which is one of the major challenges for the future.