High output cardiac failure refers to a state of cardiac failure that is associated with a higher than normal cardiac output which is still not sufficient for body tissue demands.
Patients can present with a number of symptoms of varying degrees which include tachycardia, elevated pulse pressure, hyperkinetic precordium, and jugular venous distension.
There are three major mechanisms of high output heart failure:
- large extracardiac left-to-right shunt
- overstimulation of the body metabolism
- severe reduction of the blood's capacity to carry oxygen and nutrients; i.e. severe anemia
There are several conditions that can predispose to this situation:
- arteriovenous malformations
- arteriovenous shunting without a distinct malformation 2
- other conditions that can lead to high output states
The most common etiology in the United States is morbid obesity, which decreases systemic vascular resistance through several distinct mechanisms;
- adipokine mediated shunting of flow through their local vascular beds
- exuberant elaboration of capillary beds within the adipose tissue by similar mediators
- displacement of the cardiac axis by the mass effect of adipose tissue, which may decrease the efficiency of cardiac work
- subsequent activation of renin-angiotensin-aldosterone system due to decreased perfusion of the kidneys
- salt and water retention increases plasma volume and cardiac work
The hemodynamic milieu of the heart failure syndrome is present, despite a normal to hyperdynamic ejection fraction, with elevated left sided filling pressures (E/e' > 15), right sided pressure overload (measured right ventricular systolic pressure (RVSP) >42 mmHg) and cardiac indices typically above 3.5 liters per minute per square kilogram. Other common features include increased left ventricular end diastolic diameters, with subnormal end systolic diameters. An elevated heart rate is also commonly present.
The single finding with the best ROC curve is the right ventricular systolic pressure; as measured by Doppler, an RVSP over 42 mmHg has demonstrated a 92% sensitivity and 100% specificity (in a study group with abnormally elevated cardiac indices) 5.
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