222:. Scar tissue does not contract, and it does not help the heart pump blood. This persistently stresses the heart and increases the workload of the lasting myocardium as measured by MVO2. Clinical research indicates that as the size of the myocardial scar increases, so does the likelihood of the patient to develop heart failure. Acute cardiac unloading decreases cardiac MVO2 and has been demonstrated to limit the amount of scar tissue that forms, thus preserving heart function after a heart attack.
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78:. 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.
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Current treatment paradigms for increasing cardiac output after the heart has been damaged often increase the stress placed on the heart and cause more damage leading to a progressive cycle into functional decompensation. Acute unloading removes the heart from this cycle by increasing cardiac output
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The pumping of blood is considered the workload of the heart and requires power expenditure. Acute cardiac unloading is any maneuver, therapy, or intervention that decreases the power expenditure of the ventricle while maintaining cardiac output. Oxygen consumption (MVO2) is a direct measure of the
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is the primary objective of therapeutic approaches treating these cardiac conditions. However, many therapies aimed at increasing cardiac output place further stress on the heart. In this way a well-document vicious cycle begins in which increased cardiac output is required, but in order to achieve
110:, current therapeutic approaches do not allow the heart to rest and recover. The workload of the heart (pumping blood) is never uncoupled from heart function. Acute cardiac unloading is able to functionally uncouple the heart from cardiac output, allowing the heart to rest and recover from damage.
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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
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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
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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.
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Under conditions of mechanical support, mean aortic pressure (MAP) is maintained independent of native ventricular function, and ventricular and aortic pressures become uncoupled.
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Burkhoff D., Dickstein M. HARVI: Cardiovascular
Physiology & Hemodynamics. Part I. Basic Physiological Concepts (Version 2.0.0) . 2012. Updated 2014. Available at:
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As the level of support increases, aortic pressure is maintained independent of ventricular function. Perfusion pressure is uncoupled from heart function (1-4).
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Minicucci MF, Azevedo PS, Polegato BF, Paiva SA, Zornoff LA. Heart failure after myocardial infarction: clinical implications and treatment.
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Early
Assistance With Left Ventricular Assist Device Limits Left Ventricular Remodeling After Acute Myocardial Infarction in a Swine Model.
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result in an impaired ability of the heart to pump blood. Without proper blood flow the person will ultimately die. Maintaining sufficient
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Burkhoff D. HARVI: Cardiovascular
Physiology & Hemodynamics. Part II. Advanced Physiological Concepts (Version 2.0.0) . Available at:
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Mechanically unloading the left ventricle before coronary reperfusion reduces left ventricular wall stress and myocardial infarct size.
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device can achieve this in two ways. First, the device is a continuous flow device. It directly aspirates blood from the
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Relationship
Between Infarct Size and Outcomes Following Primary PCI: Patient-Level Analysis From 10 Randomized Trials.
74:. This technique is being investigated as a therapeutic to aid after damage has occurred to the heart, such as after a
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this the heart must work harder. This exacerbated stress leads to poorer outcomes. With the exception of
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The pressure-volume area (PVA) is the total mechanical energy generated by ventricular contraction.
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D. S. Burkhoff, G.; Doshi, D., Uriel, N., Hemodynamics of
Mechanical Circulatory Support.
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Suga, H. Total mechanical energy of a ventricle model and cardiac oxygen consumption.
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is any maneuver, therapy, or intervention that decreases the power expenditure of the
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218:. The dead heart muscle is replaced by non-contractile fibrotic tissue, forming the
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total energy requirements of the heart, including the energy needed to pump blood.
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and results in a left-shift and loss of the normal isovolumic contraction line.
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Murry, C. E. & Lee, R. T. Development biology. Turnover after the fallout.
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that is outside of the loop is the potential energy (PE) that resides in the
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a portion of muscle is permanently lost. The heart has a limited innate
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151:) used to actively pump blood every beat, measured in mmHg·mL (aka, a
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ability to replace dead muscle with new, functional muscle
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ESPVR and EDPVR are dynamic properties of the myocardium.
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https://itunes.apple.com/gb/app/harvi/id568196279?mt¼8
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app/harvi/id568196279?mt¼8. Accessed
October 2, 2015.
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66:and limits the hemodynamic forces that lead to
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262:Journal of the American College of Cardiology
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284:The American Journal of Physiology
144:Pressure-volume (PV) loop analysis
85:(commonly called a heart attack),
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396:10.1161/CIRCULATIONAHA.112.000029
159:The remaining area bound by the
210:When the heart is damaged by a
155: ). This is known as the
70:after insult or injury to the
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314:https://itunes.apple.com/gb/
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368:10.1016/j.jacc.2016.01.069
91:peripartum cardiomyopathy
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31:through mechanical means.
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99:takotsubo cardiomyopathy
81:Cardiac traumas such as
338:10.1126/science.1172255
60:Acute cardiac unloading
19:Acute cardiac unloading
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108:cardiopulmonary bypass
68:ventricular remodeling
212:myocardial infarction
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198:Myocardial infarction
187:. This decreases the
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83:myocardial infarction
240:Clinical Cardiology.
149:pressure-volume work
267:, 2663-2674 (2015).
242:2011;34(7):410-414.
440:Cardiac procedures
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421:10.1111/aor.12541
413:Artificial organs
157:stroke work (SW).
114:Power expenditure
95:cardiogenic shock
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390:, 328-336,
385:Circulation
87:myocarditis
226:References
42:cardiology
332:, 47-48,
183:into the
181:ventricle
64:ventricle
38:Specialty
434:Category
407:Sun, X.
423:(2015).
370:(2016).
340:(2009).
327:Science
189:preload
177:Impella
89:,
409:et al.
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381:et al.
351:et al.
185:aorta
165:EDPVR
161:ESPVR
153:joule
72:heart
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163:and
131:MVO2
417:doi
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