page_title: Acute cardiac unloading
section_title: MVO2
hierarchical_section_title: Acute cardiac unloading / Power expenditure / MVO2
caption_attribution_description: English: Cardiac Pressure-Volume area plot.
context_page_description: Acute cardiac unloading is any maneuver, therapy, or intervention that decreases the power expenditure of the ventricle and limits the hemodynamic forces that lead to ventricular remodeling after insult or injury to the heart. This technique is being investigated as a therapeutic to aid after damage has occurred to the heart, such as after a heart attack. The theory behind this approach is that by simultaneously limiting the oxygen demand and maximizing oxygen delivery to the heart after damage has occurred, the heart is more fully able to recover. This is primarily achieved by using temporary minimally invasive mechanical circulatory support to supplant the pumping of blood by the heart. Using mechanical support decreases the workload of the heart, or unloads it.
  Cardiac traumas such as myocardial infarction, myocarditis, peripartum cardiomyopathy, cardiogenic shock, and takotsubo cardiomyopathy result in an impaired ability of the heart to pump blood. Without proper blood flow the person will ultimately die. Maintaining sufficient cardiac output is the primary objective of therapeutic approaches treating these cardiac conditions.
context_section_description: Pressure-volume (PV) loop analysis provides a framework for understanding how acute cardiac unloading reduces MVO2 in the heart. The PV loop characterizes the events occurring during a single cardiac cycle (a single heartbeat). The total area bound by the PV loop is the mechanical energy (pressure-volume work) used to actively pump blood every beat, measured in mmHg·mL (aka, a joule ). This is known as the stroke work (SW). The remaining area bound by the ESPVR and EDPVR that is outside of the loop is the potential energy (PE) that resides in the myofilaments that was not transduced into the work of pumping blood. The sum of these two areas (PE + SW) is known as the pressure-volume area (PVA). PVA is a first order approximation of MVO2.
  Acute cardiac unloading decreases the workload of and the oxygen demand of the heart.  This can be visualized as an overall decrease in the PVA of the PV loop. Mechanical unloading of the heart by a percutaneous ventricular support device such as the Impella device can achieve this in two ways. First, the device is a continuous flow device. It directly aspirates blood from the ventricle into the aorta. This decreases the preload and results in a left-shift and loss of the normal isovolumic contraction line.
  Under conditions of mechanical support, mean aortic pressure (MAP) is maintained independent of native ventricular function, and ventricular and aortic pressures become uncoupled.
caption: The pressure-volume area (PVA) is the total mechanical energy generated by ventricular contraction.
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