What is afterload mismatch and how does it affect LV ejection during acute afterload changes?

• A. LV ejection is normal regardless of afterload.
• B. Afterload mismatch occurs when afterload is too low for LV pressure to exceed.
• C. Afterload mismatch occurs when afterload is too high for LV pressure to exceed; ejection is impaired, increasing ESV and reducing SV.
• D. LV ejection improves as afterload increases.

Answer: (C)

Afterload is the pressure the left ventricle must overcome to eject blood into the aorta. When afterload rises acutely beyond what the ventricle can generate during systole, the ventricle can’t push the blood out as effectively. This is afterload mismatch. Because ejection is limited, more blood remains in the ventricle at the end of systole, so the end-systolic volume increases and the stroke volume falls. The ejection fraction typically drops as a result. The other ideas don’t fit because ejection wouldn’t be normal when afterload is high, increasing afterload doesn’t improve ejection, and low afterload would make ejection easier rather than impaired.