Mechanical circulatory support (MCS) devices allow us to offload myocardial work from the heart, and for the purposes of this post, the left ventricle (LV). Referring to my previous post on the work of breathing, we can extrapolate the same pressure-volume (PV) loop integral to represent work, except in this case, the volume we’re referring to is the stroke volume (LV end diastolic volume – LV end systolic volume) and the pressure is the left ventricular pressure during the cardiac cycle.
I’ve drawn four loops in the the diagram above illustrating how the native heart’s PV loop compares to percutaneous cardiopulmonary bypass (CPB, an example would be extracorporeal membrane oxygenation), intraluminal axial devices (like an Impella), and the TandemHeart.
It’s clear that if one were to look at the area enclosed by the PV-loop (the integral) of the TandemHeart (shaded in purpose) vs the native heart function, the former encompasses much less area. This translates to a significant decrease in LV work by using the TandemHeart. Compare this to the other devices as well.
Many factors will change these PV loops including volume status, inotropic/vasopressor support, the amount of support, and a combination of devices (ie, using Impella with ECMO). Nevertheless, it’s important to consider how MCS devices facilitate the reduction in myocardial work.
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