High Output Cardiac Failure

Congestive heart failure describes a syndrome with complex and variable symptoms and signs, including dyspnea, increased fatigability, tachypnea, tachycardia, pulmonary rales, and peripheral edema. Although this syndrome usually is associated with low cardiac output, it may occur in a number of so-called high output states, when the cardiac output is normal or greater than normal. A high output state may occur in chronic severe anemia, large arteriovenous fistula or multiple small arteriovenous shunts as in Paget's bone disease, some forms of severe hepatic or renal disorders, and acutely in septic shock. The syndrome of systemic congestion in a high output state is traditionally referred to as high output heart failure. However, the term is a misnomer because the heart in these conditions is normal, capable of generating very high cardiac output. The underlying problem in high output failure is a decrease in the systemic vascular resistance that threatens the arterial blood pressure and causes activation of neurohormones, resulting in an increase in salt and water retention by the kidney. Many of the high output states are curable conditions, and because they are associated with decreased peripheral vascular resistance, the use of vasodilator therapy for treatment of congestion may aggravate the problem. There are other clinically important issues in high output failure that have received little attention in the current medical literature. This article reviews the available data on high output cardiac failure with particular emphasis on the underlying mechanisms and treatment.