Which statement correctly defines afterload and its determinants?

• A. Afterload is the LV’s load to eject blood; determinants include systemic vascular resistance and arterial impedance/arterial compliance.
• B. Afterload is the heart rate;
• C. Afterload is preload;
• D. Afterload is contractility.

Answer: (A)

Afterload is the left ventricle’s load to eject blood, meaning the pressure the ventricle must generate to open the aortic valve and push blood into the arterial system. The main determinants are systemic vascular resistance and arterial impedance/arterial compliance. Systemic vascular resistance reflects the overall friction the blood faces in the systemic circulation; higher resistance means the ventricle must work harder to reach the necessary pressure. Arterial impedance combines the resistive and elastic properties of the arterial tree, including wave reflections and how stiff the arteries are; increased impedance raises the pressure the ventricle must overcome at the start of ejection. Arterial compliance, or how stretchy the arteries are, also matters: stiffer arteries (lower compliance) raise systolic pressure for a given stroke volume, increasing afterload.

Heart rate is not the load the ventricle must overcome to eject blood. Preload refers to the filling pressure/volume before contraction, and contractility is the heart muscle’s intrinsic ability to generate force. These influence cardiac performance in other ways but do not define afterload.