Abstract
Mechanical circulatory support devices (MCS), namely percutaneous ventricular assist devices (pVAD) are temporarily introduced to support circulation in hemodynamically compromised patients and also during mid to high risk coronary artery procedures. Their multiple responsibilities include maintaining an adequate systemic blood pressure and cardiac output to provide satisfactory end-organ perfusion in unloading of the failing ventricle, and to temporary lower myocardial contractility while reducing myocardial oxygen demand supporting favorable ventricular remodeling. To timely and quantitatively assess hemodynamics during pVAD circulatory support post-cardiogenic shock or acute myocardial infarction (MI), pressure-volume (PV) measurements are becoming progressively more appreciated as they can longitudinally evaluate the status of the support. Hemodynamically, importance of constant circulatory interrogations by PV during pVAD support lies in its capacity to “fine-tune” the device for a specific patient to work in synergy with the ailing organ. In this review basic characteristics of a diagnostic value of pressure-volume during pVAD hemodynamic support will be discussed fostering conversation about the necessity of e.g. combining pump flow with load-independent indices creating indexes that can be used to further characterize pump unloading in relation to innate cardiac contractility during axial or centrifugal flow support. Additionally, discussion about central hemodynamics during different flow support will be provided evaluating pVADs to assess its ability to work in synergy and to anticipate potential difficulties that might occur during the procedure. Brief description of recent efforts to combine PV exam with pump flow during circulatory support using pVAD and the concept of pressure-volume area (PVA) and myocardial oxygen consumption (mVO2) during unloading will be also discussed.
Highlights
Mechanical circulatory support devices (MCS), namely percutaneous ventricular assist devices are temporarily introduced to support circulation in hemodynamically compromised patients and during mid to high risk coronary artery procedures
Placement of PV catheter is done centrally into the left ventricular (LV) or right ventricular (RV) chamber, while secondary pressure-only catheter is restricted to the areas close to e.g. the aortic valve
In some instances percutaneous ventricular assist devices (pVAD) device might need to be placed in advance to limit intravascular interactions, in case of e.g. intra-aortic balloon pump (IABP), percutaneous placement of PV catheter might not be possible
Summary
The aortic blood pressure along the left ventricular pressure and volume were measured using commercially available control unit from (Transonic, Inc.) allowing real-time assessment of left ventricular volume in addition to the aortic pressure. Function of deployed balloon at that location is to create similar counter pulsation as it is made by native physiological impedance to blood flow of vascular branching points ensuring partial blood return towards the aortic valve This pVAD uses the mechanism of balloon inflation during diastole to create a temporary increase of aortic blood pressure. Other hemodynamic related limitations of IABCP include its dependence on inner mechanical and electrical cardiac timing at balloon inflation/deflation triggered from electrocardiogram or from aortic pressure wave tracings.[2] When the aortic pressure wave intensity analysis was performed, during switched on balloon autoregulation, systolic unloading measured by tension time index (TTI) was decreased. Recent development uses subendocardial viability ratio (SEVR),[5] as a useful parameter coming from the ratio between diastolic pressure-time index (DPTI), an estimate of myocardial oxygen supply using coronary driving pressure in diastole and diastolic time and systolic pressure-time index (SPTI), an estimate of myocardial oxygen consumption-mVO2.6 Overall, to improve the ventricular unloading while supporting contractility of failing myocardium using counter pulsation, empirical hemodynamic study using PV and central/peripheral pressures combined with pump flow interrogation is necessary to determine whether the deployment of several smaller counter pulsating balloon(s) of a different size(s) at branching point location(s) might be more desirable
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