Mechanical Circulatory Support
Anju Bhardwaj
Alexis Shafii
Andrew Civitello
Ajith Nair
INTRODUCTION
Heart failure (HF) is a syndrome that affects over 6.5 million individuals in the United States. Despite significant advances in medical therapy, it remains a leading cause of death with a 5-year mortality of greater than 50%.1 Patients with HF refractory to medical therapy may qualify for advanced therapies including heart transplantation or implantation of mechanical circulatory support devices. Although heart transplantation is considered a definitive therapy for patients with advanced HF, its use is limited by a paucity of organs, prolonged wait times, and stringent selection criteria. With improvements in technology and the advent of smaller, durable continuous flow pumps, the use of implantable left ventricular assist devices (LVADs) has emerged as an effective and viable option.
Over the last decade, most patients treated with an implantable LVAD received continuous flow devices that have smaller profiles and a single moving impeller/rotor. Three pumps have been approved by the US Food and Drug Administration (FDA): the HeartMate II axial flow pump (Abbott Laboratories, Abbott Park, IL, USA); the HeartWare centrifugal pump ventricular assist device system (Medtronic, St. Paul, MN, USA); and the HeartMate III magnetically levitated centrifugal pumps (St. Jude Medical, Pleasanton, CA, USA). See Figure 78.1A-C.
 FIGURE 78.1 HeartMate II, HeartWare ventricular assist device (HVAD), and HeartMate III. (A) HeartMate II axial flow pump. (B) HVAD centrifugal flow pump and ventricular assist device system. (C) HeartMate III: magnetically levitated centrifugal pump. (A, HeartMate II is a trademark of Abbott or its related companies. Reproduced with permission of Abbott, © 2021. All rights reserved.; B, Reproduced with permission of Medtronic, Inc.; C, HeartMate 3 is a trademark of Abbott or its related companies. Reproduced with permission of Abbott, © 2021. All rights reserved.) |
These pumps are driven electrically by a percutaneous driveline that is connected to a small controller and an external energy source with either replaceable batteries or a direct alternating current power source. The LVAD unloads the heart and pumps blood from the left ventricle to the ascending aorta.
INDICATIONS
Candidate Selection
Four major indications for LVAD implantation are discussed here. These pumps were initially used for shorter periods of time as a “bridge to transplantation” to ensure survival of patients until a donor organ became available.2 The landmark REMATCH (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure) trial demonstrated that pulsatile LVADs were associated with a survival benefit and could be used as “destination therapy” with improved quality of life in patients on guideline-directed medical therapy who were not deemed candidates for transplant.3 Continuous flow LVADs subsequently demonstrated improved survival and freedom from device complications compared to pulsatile LVADs.4
Patients with acute hemodynamic instability in whom candidacy of transplant cannot be evaluated until after LVAD
implantation are deemed as “bridge to decision.” These patients may have relative contraindications or comorbidities—like renal dysfunction, pulmonary hypertension, or obesity—that may be reversible after prolonged hemodynamic support.5 Finally, “bride to recovery” is used in patients with potentially reversible myocardial dysfunction, such as fulminant myocarditis or peripartum cardiomyopathy, where LVAD support may function as a bridge to myocardial recovery.6
implantation are deemed as “bridge to decision.” These patients may have relative contraindications or comorbidities—like renal dysfunction, pulmonary hypertension, or obesity—that may be reversible after prolonged hemodynamic support.5 Finally, “bride to recovery” is used in patients with potentially reversible myocardial dysfunction, such as fulminant myocarditis or peripartum cardiomyopathy, where LVAD support may function as a bridge to myocardial recovery.6
Criteria for LVAD implantation are based on inclusion and exclusion criteria from clinical LVAD trials and are listed in Table 78.1. LVAD implantation is considered reasonable in patients with stage D HF who are advanced to medical and device-based therapies.
The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profiles for advanced HF are listed in Table 78.2 and may aid in identification of patients likely to benefit from mechanical support devices.7 LVAD implantation can be considered in selected INTERMACS profile 1 to 2 patients, in all INTERMACS profile 3 patients, and in severely symptomatic INTERMACS profile 4 to 7 patients after a frank, well-informed discussion with the patient regarding risk of adverse events versus benefits of better functional status and survival.7,8,9
Rigorous evaluation is required to assess candidacy for LVAD therapy. Major considerations include clinical necessity (assessed by patient’s clinical and functional status and hemodynamic studies), presence of absolute and relative contraindications as mentioned in Table 78.3, and psychosocial factors and patient goals of care. LVAD is still an evolving therapy fraught with complications, which makes ideal candidate selection imperative to maximize its benefit.
TABLE 78.1 Indications For Mechanical Circulatory Support | |
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PREIMPLANTATION CONSIDERATIONS: VALVE DISEASE AND PULMONARY HYPERTENSION
Aortic Valve Disease
Significant aortic regurgitation requires concomitant aortic valve repair or replacement with LVAD placement as regurgitant flows can diminish the hemodynamic support.10 Another strategy to address aortic regurgitation involves oversewing the aortic valve. Patients with oversewn valves are completely LVAD dependent, and pump dysfunction can be fatal. Mechanical aortic valves are associated with high risk of thrombosis and may necessitate valve replacement with a bioprosthetic valve or placement of a patch on top of the mechanical valve to mitigate the risk of valvular thrombosis and thromboembolism.11,12 Aortic stenosis does not warrant any intervention as systemic flow occurs through the device and bypasses the aortic valve.
Mitral Valve Disease
Functional mitral regurgitation does not routinely require intervention, as unloading of the ventricle by the LVAD leads to a reduction in regurgitation.13,14 Transcatheter edge-to-edge mitral valve repair has been performed for persistent mitral regurgitation despite LVAD support.15 Moderate-to-severe mitral stenosis may compromise left ventricular filling, reduce LVAD flows, and require prosthetic valve replacement. Both mechanical and bioprosthetic mitral valves are not associated with increased risk of thrombosis following LVAD insertion.16
Tricuspid Valve Regurgitation
Right ventricular failure is a major cause of morbidity and mortality after LVAD implantation. Tricuspid regurgitation may exacerbate right ventricular failure, and valve repair may
decrease the risk of postoperative right ventricular failure.17 As LVADs generally lead to an improvement in tricuspid regurgitation via reductions in pulmonary pressures and right ventricular dimension,18 valve repair may be considered for isolated cases of severe tricuspid regurgitation during LVAD implant.19
decrease the risk of postoperative right ventricular failure.17 As LVADs generally lead to an improvement in tricuspid regurgitation via reductions in pulmonary pressures and right ventricular dimension,18 valve repair may be considered for isolated cases of severe tricuspid regurgitation during LVAD implant.19
TABLE 78.3 Absolute and Relative Contraindications to Left Ventricular Assist Devices | |||||||||||||||||||||||
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Pulmonary Hypertension
In patients with advanced HF, pulmonary hypertension is primarily the consequence of left heart disease. In this setting, the mean pulmonary arterial (PA) pressure is greater than or equal to 20 mm Hg and mean pulmonary capillary wedge pressure (PCWP) is greater than or equal to 15 mm Hg.20 Combined precapillary and postcapillary pulmonary hypertension is characterized by a pulmonary vascular resistance (PVR) greater than or equal to 3 Wood units, and the transpulmonary gradient (mean PA pressure—PCWP) is greater than 12 mm Hg. Patients with fixed and elevated PVR are not candidates for heart transplant because of the high risk of posttransplantation right ventricular failure.21 Patients bridged with an LVAD may show improvement in PVR after LVAD over 3 to 6 months, thus altering their transplant eligibility.22,23,24
OTHER PREIMPLANTATION CONSIDERATIONS: PATIENT COMORBIDITIES
Renal Dysfunction
Renal dysfunction in advanced HF may be multifactorial. Cardiorenal syndrome related to low cardiac output and increased venous congestion generally improves after LVAD support, whereas intrinsic kidney disease related to chronic poor perfusion, hypertension, or diabetes mellitus may result in persistent and progressive renal failure.25
Renal dysfunction is associated with poor outcomes post-LVAD, and end-stage renal disease requiring dialysis is an absolute contraindication for LVAD because of high short-term mortality.26,27 However, there is no clear consensus on a glomerular filtration rate below which an LVAD would not be considered. Postoperative renal dysfunction may result from massive fluid shifts, acute blood loss, arrhythmias, and use of vasoactive medications, and transient renal replacement therapy may be required.28
Hepatic Dysfunction
Hepatic dysfunction is associated with increased mortality and morbidity in HF; it is usually attributed to ischemic hepatitis because of decreased hepatic blood flow, congestive hepatopathy related to increased hepatic venous pressures, and cardiac cirrhosis because of chronic right ventricular dysfunction.29 Elevated liver enzymes and bilirubin are associated with worse post-LVAD outcomes, and a liver biopsy may be required to exclude noncardiac causes of liver dysfunction prior to LVAD implantation. Hepatic dysfunction associated with HF has been shown to improve after LVAD implantation.25
Obesity
Morbid obesity is associated with worse outcomes post-LVAD implantation because of increased risk of device-related infections and thromboembolism.30 A body mass index greater than or equal to 35 kg/m2 is considered a contraindication for heart transplantation, but weight loss may reverse this eligibility. Bariatric surgery is an efficacious weight loss modality, and concomitant gastric sleeve during LVAD implantation has been performed with success.31
Age, Malnutrition, and Debilitation
Advanced age is associated with mortality and prolonged hospitalizations post-LVAD implant, but it should not be used as a criterion to exclude LVAD therapy.32 Carefully selected elderly
patients can have excellent outcomes. Rather than age alone, frailty may be a better surrogate to assess candidacy.33
patients can have excellent outcomes. Rather than age alone, frailty may be a better surrogate to assess candidacy.33
Psychosocial Considerations
Given the complexity of care associated with LVAD therapy, each patient should have a thorough psychosocial and behavioral evaluation before implantation. Compliance, self-care, and psychosocial and behavioral assessment are critical to ascertain appropriate management and support strategies for the patient. Factors evaluated for heart transplant can be followed for LVAD implantation as well.35
SURGICAL IMPLANTATION TECHNIQUE
LVAD implantation is performed by insertion of an inflow cannula into the left ventricular apex and attaching an outflow graft to the ascending aorta. A sewing ring that is sutured to the myocardial surface secures the inflow cannula in place and the myocardial tissue inside the sewing ring is removed with a coring knife. The typical location of the inflow cannula is slightly anterior to the left ventricular apex and 1 to 2 cm lateral to the left anterior descending coronary artery. Intraoperative transesophageal echocardiography (TEE) can facilitate pinpointing the proper insertion location of the inflow cannula, which is aligned with the long axis of the mitral valve inlet and is parallel to the intraventricular septum. The HeartMate II pump requires the creation of a preperitoneal pocket in the abdominal wall, but this device is no longer utilized as newer generation centrifugal pumps are entirely intrapericardial. Once the inflow cannula of the LVAD has been secured to the sewing ring, the outflow graft can then be directed to the ascending aorta. The outflow graft is attached to the mid-ascending aorta in an end-to-side fashion with a beveled angle directing blood toward the aortic arch. The outflow graft length must be carefully approximated as excessive length can lead to kinking and a short graft may be at risk for occlusion and bleeding.32 The device driveline is then tunneled with a lance through the rectus abdominis muscle and subcutaneous tissue to an exit site on the upper abdominal wall, where it is connected to the device controller module.
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