Review Question - QID 100660

This patient with a bruit over the site of a prior penetrating trauma has an arteriovenous shunt. Such a shunt results in increased venous return and is a potential cause of high-output heart failure.

Penetrating trauma may lead to formation of a fistula (a direct connection between the high pressure arterial system and low pressure venous system). Fistula formation has the effect of decreasing peripheral resistance because blood traveling through the arteriovenous shunt does not pass through the capillary bed. This decrease in peripheral resistance leads to compensatory sympathetic stimulation of the heart with an increase in contractility, heart rate, and stroke volume initially. These changes collectively result in increased venous return to the heart, which may lead to heart failure due to volume overload. As a result, overtime, the heart becomes strained and is no longer able to pump blood efficiently.

Incorrect Answers:
Answer 1: Arteriovenous shunting leads to increased sympathetic output secondary to decreased peripheral resistance.
Answer 2: Arteriovenous shunting causes decreased, not increased, peripheral resistance.
Answer 4: Arteriovenous shunting causes increased contractility due to sympathetic stimulation initially in arteriovenous shunting but as it becomes chronic, the heart fails to pump sufficient blood to meet the body's demands (contractility decreases eventually).
Answer 5: Increased pulmonary resistance is not the primary cause of heart failure symptoms in this patient, who is suffering from LV volume overload; arteriovenous shunting in the lungs may cause decreased pulmonary resistance.