Most patients with heart failure (HF) have systolic dysfunction with a low or normal cardiac output and elevated systemic vascular resistance and/or diastolic dysfunction in which an increase in ventricular stiffness impairs ventricular filling during diastole. In rare circumstances, the cardiac output is elevated and calculated systemic vascular resistance is very low.
High-output HF is characterized by an elevated resting cardiac index beyond the normal range of 2.5 to 4.0 L/min per m2. Ineffective blood volume and pressure, chronic activation of the sympathetic nervous system and renin-angiotensin-aldosterone axis, increased serum vasopressin (antidiuretic hormone) concentrations, and chronic volume overload gradually cause ventricular enlargement, remodeling, and HF.
As will be described in this topic review, a number of conditions lead to an obligatory increase in cardiac output, which can be associated with HF in some patients. However, these conditions are rarely the sole cause of HF; in most such patients, the high cardiac output provokes HF in the setting of reduced ventricular reserve from some underlying cardiac problem. Thus, the presence of high-output HF should prompt a search for another underlying cardiovascular problem.
Several characteristic findings are usually seen on physical examination in patients with high-output HF. The heart rate is typically between 85 and 105 beats per minute, but it may be higher with some causes, eg, thyrotoxicosis. Examination of the systemic veins may reveal a cervical venous hum, heard best over the deep internal jugular veins, particularly on the right side. Less often, a venous hum may be appreciated over the femoral veins.
Examination of the arteries may display signs related to increased left ventricular stroke volume. The pulse is usually bounding with a quick upstroke, and the pulse pressure is typically wide. Pistol-shot sounds may be auscultated over the femoral arteries, and a systolic bruit may be heard over the carotid arteries. Although these findings may be seen in other cardiac conditions, such as aortic regurgitation or patent ductus arteriosus, in the absence of these conditions, these signs are highly suggestive of elevated left ventricular stroke volume due to a hyperdynamic state.