Percutaneous Circulatory Support: Intra-Aortic Balloon Counterpulsation, Impella, Tandem Heart, and Extracorporeal Bypass
Carlos D. Davila, MD
Michele Esposito, MD
Navin K. Kapur, MD
INTRODUCTION
The use of percutaneous acute mechanical circulatory support (AMCS) has steadily grown in the last decade. Currently, the main indications for AMCS include (1) high-risk percutaneous coronary and electrophysiological interventions, (2) cardiogenic shock (CS) due to myocardial infarction and myocarditis, (3) postcardiotomy shock, and (4) refractory chronic heart failure as a bridge to durable mechanical support or heart transplantation. Large randomized clinical trials proving benefits of these therapies are scarce. Guidelines and consensus statements addressing proper patient selection, timing of implantation, device choice, and postimplantation protocol are beginning to emerge. Optimization of clinical outcomes in this field requires a critical understanding of the different types of hemodynamic support provided by available devices and their applicability in a particular clinical scenario including best practices to monitor, wean, and optimize each device postimplantation. In this chapter we will review the mechanics of several AMCS devices, specifically discuss the hemodynamic effects of these devices, and review current data available, evaluating their clinical utility.
LVAD AND AMCS
In 2001, the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial demonstrated that durable, surgically implanted, left ventricular assist devices (LVADs) improved survival in patients with end-stage heart failure compared with medical therapy alone1. Moreover, in 2009 continuous flow LVADs (CF-LVADs) showed significantly improved 2-year survival compared with pulsatile LVADS. Since then, the use of permanent CF-LVADs has grown exponentially to more than 2500 implants per year.3 Consistent with this observation, several recent reports have identified increasing use of AMCS in the setting of CS. A recent analysis of the Nationwide Inpatient Sample from the Healthcare Cost and Utilization Project identified a 1511% increase in the use of AMCS devices and no significant change in intra-aortic balloon pump (IABP) use from 2007 to 2011 compared with
2004 to 2007, especially in the setting of high-risk interventions and CS with higher-than-normal-risk profiles for surgically implanted LVADs as a bridge to recovery (BTR) (FIGURE 17.1).2,4 Despite increasing use of AMCS devices, an analysis of the National Cardiovascular Data Registry CathPCI-participating hospitals from 2009 to 2013 identified that the probability of non-IABP AMCS device use for CS was <5% for 1/2 of the hospitals and >20% in less than 1/10th of these hospitals.4
2004 to 2007, especially in the setting of high-risk interventions and CS with higher-than-normal-risk profiles for surgically implanted LVADs as a bridge to recovery (BTR) (FIGURE 17.1).2,4 Despite increasing use of AMCS devices, an analysis of the National Cardiovascular Data Registry CathPCI-participating hospitals from 2009 to 2013 identified that the probability of non-IABP AMCS device use for CS was <5% for 1/2 of the hospitals and >20% in less than 1/10th of these hospitals.4
 FIGURE 17.1 Trends in the use of percutaneously delivered AMCS devices.2 PCPS, percutaneous cardiopulmonary support. Reproduced with permission from Stretch R, Sauer CM, Yuh DD, Bonde P. National trends in the utilization of short-term mechanical circulatory support: incidence, outcomes, and cost analysis. J Am Coll Cardiol. 2014;64:1407-1415. |
Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS)
See FIGURE 17.2 for trends.
 FIGURE 17.2 Trends in the use of surgically implanted durable MCS.5 A, The number of LVADs being implanted as part of a BTR strategy or as a rescue therapy has significantly declined over the past decade. This shift in LVAD use away from unstable, high-risk INTERMACS profiles is partly driven by data showing increased mortality after LVAD implantation for INTERMACS profiles 1 and 2 after the age of 65 years and the increasing availability of AMCS devices, which include short-term, percutaneously inserted devices without the need for cardiac surgery. B, The predicted 1 year mortality after LVAD implantation is highest among the sickest patients defined as INTERMACS Levels 1 and 2. Reproduced with permission from Kirklin JK, Naftel DC, Kormos RL, et al. Fifth INTERMACS annual report: risk factor analysis from more than 6000 mechanical circulatory support patients. J Heart Lung Transplant. 2013;32:141-156. |
AMCS Indications and Complications
See Tables 17.1 and 17.2.
TABLE 17.1 Suggested Indications for AMCS6 | ||||||||||||
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TABLE 17.2 Potential Complications Associated with AMCS Devices | ||||||||||||
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THERAPEUTIC OBJECTIVES
 FIGURE 17.3 The acute hemodynamic support equation. BNP, brain natriuretic peptide; EDV, end diastolic volume; MAP, mean arterial pressure. |
The main therapeutic objectives of acute percutaneous mechanical support are to provide adequate circulation to vital organs, augment coronary perfusion, improve ventricular unloading, and reduce myocardial oxygen demand (FIGURE 17.3). These parameters can be estimated using certain surrogates as shown in FIGURE 17.3. Different mechanical circulatory support (MCS) devices are available, and each of them addresses the hemodynamic equation in different degrees. Thus it is of paramount importance to understand the hemodynamics and the initial goal of MCS based on specific clinical scenarios (high-risk percutaneous intervention vs CS). The ideal MCS device would target all elements of the hemodynamic equation and prove to be safe and easy to use in the acute setting.
Mechanical Circulatory Support Systems (MCS)
MCS systems can be classified based on anatomical support provided, mechanism of action, flow pattern, and localization after percutaneous delivery (FIGURE 17.4A).
Four primary AMCS device platforms are currently used in clinical practice for left ventricular (LV) hemodynamic support (FIGURE 17.4B) and can be broadly categorized as pulsatile and continuous flow systems. These devices include (1) the IABP, (2) centrifugally driven left atrial-to-femoral artery bypass (TandemHeart; TandemLife Inc), (3) centrifugally driven venoarterial extracorporeal membrane oxygenation (VA-ECMO), and (4) micro-axial flow catheters (Impella; Abiomed Inc and Percutaneous Heart Pump [PHP]; St Jude Inc). At present, the PHP device is approved for clinical use in Europe but is under active investigation in the United States.
Right ventricular AMCS (RV-AMCS) device options include VA-ECMO, the TandemHeart centrifugal flow pump (TandemLife, Pittsburgh, PA), and the axial-flow Impella RP catheter (Abiomed Inc, Danvers, MA) (FIGURE 17.4C). RV-AMCS devices can be categorized according to their mechanism of action as either RA-PA (right atrium-pulmonary artery) drainage or RA-PA bypass systems. VA-ECMO is a RA-PA drainage system that oxygenates and displaces blood from the RA and/or PA into the arterial circulation. The Impella RP and the TandemHeart RVAD are RA-PA bypass systems that displace blood from the RA into the PA, thereby bypassing the failing RV.
 FIGURE 17.4 Options for MCS. |
CF-AMCS
 FIGURE 17.5 The pressure-flow (HQ) curve. |
Flow through all (nonpulsatile) CF-AMCS devices is directly related to rotations per minute (RPM) of the impeller and indirectly related to pressure at the inlet and outlet of the impeller (FIGURE 17.5).7 For this reason, preload and afterload are major determinants of AMCS device function. This pressure gradient (Pin-Pout) varies during systole and diastole. The relationship between pressure and flow is best described using an HQ curve, where H is defined as the pressure head (Pin-Pout) and Q is defined as device flow. Each device has a specific HQ curve signature. Axial-flow pumps tend to have a steeper HQ slope, whereas centrifugal flow pumps have a flatter HQ slope.8
For the TandemHeart, Impella, and PHP devices, the pressure head (H) includes LV pressure and aortic pressure. For patients without decompensated heart failure or aortic valve disease (ie, undergoing high-risk PCI), peak aortic and LV end systolic pressures are matched and at peak systole (ie, AoSP – LVESP = 120 – 120 mm Hg) the estimated H is zero. Throughout diastole, aortic diastolic pressure (AoDP) ranges between 60 and 80 mm Hg and LV end diastolic pressure (LVEDP) is often below 20 mmHg. Therefore, the estimated H ranges between 40 to 60 mm Hg (AoDP – LVEDP) and 0 (AoSP – LVESP). Based on this principle, for a given RPM, continuous flow devices will provide higher flow at peak systole (H = 0) and lower flow in diastole (H = 40 – 60). In contrast, the patient with CS may have a substantially lower H during diastole with high LVEDP and low AoDP. For this reason, for a given RPM, continuous flow devices will provide higher flow at both peak systole and end diastole compared with patients without decompensated heart failure.
PV Loop
LV ejection fraction depends on preloading conditions, afterload, and intrinsic ventricular contractility. These parameters can be visually represented in the pressure-volume loop (PV loop) (FIGURE 17.6). Each loop represents a single cardiac cycle, where preload is related to end diastolic volume and pressure (A). End diastolic pressure volume relationship (EDPVR) relates to the passive filling of the LV during diastole; the slope of EDPVR is the reciprocal of compliance and is used to measure ventricular remodeling. During isovolumetric contraction phase (B) there is a rapid rise in ventricular pressure without change in volume; the rate of pressure increase is determined by the rate of contraction of the myocytes. The maximal rate of pressure change during this phase is termed dP/dtmax. When LV pressure exceeds the aortic
diastolic pressure, the ejection phase begins; during this phase the ventricular volume decreases as the LV pressure reaches peak systolic pressure and then begins to relax (C); the residual LV volume is the end systolic volume. The end systolic pressure volume relationship (ESPVR) is a valuable measure of ventricular systolic function for both clinical and experimental evaluations. Changes in ESPVR represent changes in contractility, whereas the slope measures end-systolic chamber stiffness. Systole is then followed by the isovolumetric relaxation (D) before the next cardiac cycle.
diastolic pressure, the ejection phase begins; during this phase the ventricular volume decreases as the LV pressure reaches peak systolic pressure and then begins to relax (C); the residual LV volume is the end systolic volume. The end systolic pressure volume relationship (ESPVR) is a valuable measure of ventricular systolic function for both clinical and experimental evaluations. Changes in ESPVR represent changes in contractility, whereas the slope measures end-systolic chamber stiffness. Systole is then followed by the isovolumetric relaxation (D) before the next cardiac cycle.
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