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NBME 21 Answers
A 63-year-old woman comes to the physician because ...
Increased resting cardiac output
"Immediately following creation, arteriovenous fistula (AVF) is associated with an increase in cardiac output (CO), achieved predominantly through a reduction in systemic vascular resistance, increased myocardial contractility, and an increase in stroke volume (SV) and heart rate. Over the following week, circulating blood volume increases in conjunction with increases in atrial and brain natriuretic peptides. These alterations are associated with early increases in left ventricular (LV) filling pressure with the potential for resultant impact on atrial and ventricular chamber dimensions and function." (PMID: 25258554)
There's also another study by Epstein from the 1950s looking at the effects of AVF's effect on CO in men (PMID: 13052718). Apparently, the increase in resting CO is a big problem because it can lead to high-output cardiac failure (LVH).
Jesus big92 you went in on the research lmao u must be MSTP
big92 you are right. that is why pagets disease pagets have high output cardiac failure because of the av shunts.
I believe there would be no decrease in O2 saturation because oxygenated blood (high pressure) is shunted into deoxygenated circuit. As long as the lungs can keep up, this should increase venous oxygenation on average.
ty both of you for this, was wondering the same thing
O2 sat won’t change b/c you’re not adding deoxygenated blood to the arterial side. You’re just taking arterial blood and putting it into venous blood. Same reason why L->R cardiac shunts don’t decrease O2 sat (while in contrast, a R->L shunt would).
just realized: the high pressure of the arterial system keeps out low-pressure venous blood in an AV fistula (probably obvious to most ppl but it was a eureka moment for me lol)
AV fistulas are one cause of high-output cardiac failure. This person presents with heart failure, but it is due to chronically increased resting CO.