Which maternal cardiac condition is classified as preload dependent?

The classification of aortic stenosis as a preload-dependent maternal cardiac condition is based on the dynamics of blood flow and the heart's function. In conditions that are preload dependent, the heart relies on the volume of blood filling the ventricles (preload) to maintain adequate cardiac output.

In aortic stenosis, the narrowed aortic valve impedes outflow from the left ventricle, resulting in an increased pressure gradient across the valve. This situation necessitates the heart to have adequate volume to function effectively, especially during times of increased demand, such as in pregnancy when blood volume increases. If preload is low in patients with aortic stenosis, it can impair cardiac output, potentially leading to symptoms of heart failure or compromise in perfusion.

Other conditions listed have different hemodynamic profiles. For instance, mitral regurgitation may not be as strictly preload dependent, as the regurgitant flow can occur despite varying preload levels. Likewise, conditions such as pulmonary stenosis and ventricular septal defect demonstrate different reliance on preload due to their unique mechanisms of blood flow and pressure regulation across the valves and septa.

Understanding the preload dependency in aortic stenosis underscores the importance of careful monitoring and management of fluid status in pregnant patients