A 63-year-old woman with an arteriovenous fistula is experiencing heart failure symptoms. What cardiovascular finding is expected?

In a patient with an arteriovenous fistula, blood is shunted from the arterial system directly into the venous system, bypassing the capillary beds. This results in a significant increase in blood flow returning to the heart, which can lead to a compensatory increase in cardiac output as the heart works to manage the increased volume of blood.

As the heart experiences this increased preload, it responds by increasing stroke volume initially, and thus the overall cardiac output rises. This mechanism is particularly relevant in this scenario, especially considering the patient is experiencing heart failure symptoms. The heart, although compromised, attempts to accommodate the increased workload and volume through enhanced output. Therefore, the expectation of increased resting cardiac output aligns with the pathophysiology of arteriovenous fistulas and the physiological adaptations seen in heart failure.

In contrast, the other choices do not reflect the expected changes in this situation. Decreased arterial oxygen saturation and decreased mixed venous oxygen saturation are generally observed in conditions causing low cardiac output or severe hypoxia, which isn’t the primary concern here. Lastly, while decreased stroke volume may occur in severe heart failure, the initial response to the increased volume load from the arteriovenous fistula would typically be an increase, not