Which aspect of the LV pressure-volume response to afterload is primarily independent of afterload?

• A. Systolic pressure generation.
• B. End-systolic pressure.
• C. End-systolic volume.
• D. Contractility as reflected by ESPVR slope.

Answer: (D)

When afterload changes, the pressure-volume loop shifts in ways that reflect both loading and the heart’s intrinsic performance. The end-systolic pressure-volume relationship (ESPVR) is a line whose slope, end-systolic elastance, reflects contractility. If the heart’s inotropic state stays the same, increasing or decreasing afterload moves the loop (changing end-systolic volume and the pressures needed to eject) but leaves the ESPVR slope largely unchanged. In other words, contractility—how strongly the heart can eject blood for a given end-systolic pressure—is the aspect that remains largely independent of afterload.

End-systolic volume tends to rise with higher afterload because the ventricle ejects less blood, so more remains at the end of systole. End-systolic pressure is influenced by the pressure the ventricle must overcome, i.e., afterload, and the heart’s contractility. Systolic pressure generation itself scales with afterload and contractility. So the element that truly reflects intrinsic myocardial performance and stays constant across afterload changes is the ESPVR slope representing contractility.