INTRODUCTION — Short-term mechanical circulatory assist (support) devices are designed to provide hemodynamic support for a wide range of clinical conditions, ranging from prophylactic insertion for high-risk invasive coronary artery procedures to the management of cardiogenic shock, acute decompensated heart failure, or cardiopulmonary arrest. Each of these devices provides circulatory support by performing work for a failing left or right ventricle or both.
There are four major (arbitrary) categories of circulatory assist devices: intraaortic balloon pumps (IABP), non-IABP percutaneous mechanical circulatory assist devices (image 1), extracorporeal membrane oxygenator pumps, and nonpercutaneous centrifugal pumps, which are used for cardiopulmonary bypass. These devices are often inserted in the catheterization laboratory but in some cases, such as an IABP, they can be inserted in the intensive care unit.
A description of short-term mechanical circulatory assist devices will be reviewed here. The role for intermediate- and long-term mechanical circulatory devices as "bridges" to transplantation or as replacement therapy for failing hearts is discussed separately. (See "Treatment of advanced heart failure with a durable mechanical circulatory support device".)
MECHANISM OF BENEFIT — While each device discussed below has a different design and operation, the following parameters of circulatory function are improved by all devices (the degree of improvement varies between devices and patients [1]):
●End-organ perfusion
●Reduction in intracardiac filling pressures
●Reduction in left ventricular volumes, wall stress, and myocardial oxygen consumption
●Augmentation of coronary perfusion
Consequent to improvement in these parameters, the following clinical parameters may be improved:
●Prevention or amelioration of cardiogenic shock
●Reduction in pulmonary congestion
●Reduction in manifestations of myocardial ischemia
●Reduction in infarct size
IABP — The intraaortic balloon pump (IABP) is the most commonly used mechanical support device, and it is the device interventional cardiologists are most familiar with. It is inserted easily and rapidly, is the least expensive of all the devices, and does not require continuous monitoring by technical support personnel. However, it is limited in that it is capable of generating only modest hemodynamic support and myocardial protection. In addition, clinical trials of patients with cardiogenic shock have not shown an improvement in mortality with IABP use. IABP use is discussed separately. (See "Intraaortic balloon pump counterpulsation" and "Prognosis and treatment of cardiogenic shock complicating acute myocardial infarction", section on 'Intraaortic balloon pump'.)
NON-IABP PERCUTANEOUS CIRCULATORY DEVICES — The major limitations of the intraaortic balloon pump (IABP), discussed directly above, formed the basis for the development of other percutaneous mechanical circulatory devices. Compared with the IABP, they provide greater improvement in hemodynamic parameters. Similar to IABP, there is no evidence to suggest they improve clinical outcomes such as mortality. (See "Prognosis and treatment of cardiogenic shock complicating acute myocardial infarction", section on 'Other mechanical devices'.)
These devices, relative to IABP, cost more, take longer to insert, and have a higher complication rate (ie, bleeding, hemolysis, limb ischemia).
Differing names are used: percutaneous ventricular support devices, percutaneous mechanical circulatory assist devices, percutaneous mechanical circulatory support devices, and percutaneous ventricular assist devices (VADs). In addition, their hemodynamic effects differ (table 1).
Indications — Percutaneous mechanical circulatory support may be considered in the following clinical situations [1]:
●Very high-risk percutaneous coronary intervention, including those with complex coronary artery disease involving a large territory and severe left ventricular dysfunction (ejection fraction <35 percent) or recent decompensated heart failure [1].
●Acute myocardial infarction complicated by acute ischemic mitral regurgitation or ventricular septal rupture and cardiogenic shock. (See "Prognosis and treatment of cardiogenic shock complicating acute myocardial infarction", section on 'Other mechanical devices' and "Acute myocardial infarction: Mechanical complications", section on 'Management' and "Acute myocardial infarction: Mechanical complications", section on 'Management'.) (Related Pathway(s): Acute decompensated heart failure: Management of patients with cardiogenic shock.)
●Advanced right- and/or left-sided heart failure during the period of stabilization of a critically ill patient while making decisions about longer-term support ("bridge-to-a-bridge"). (See "Treatment of acute decompensated heart failure: Specific therapies", section on 'Mechanical cardiac support'.)
●Support during high-risk percutaneous valve procedures.
●Support for patients referred for electrophysiologic procedures who have severe underlying left ventricular dysfunction and who may not tolerate sustained ventricular arrhythmias during the procedure.
●Patients with medically refractory (particularly ventricular) arrhythmias associated with ischemia. (See "Electrical storm and incessant ventricular tachycardia" and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis".)
●Acute cardiac allograft failure or post-transplant right ventricular failure. (See "Heart transplantation in adults: Graft dysfunction".)
Contraindications — Some of these devices are contraindicated in the following clinical conditions:
●Aortic regurgitation or metallic aortic valve
●Aortic aneurysm or dissection
●Severe aortic or peripheral artery disease
●Left ventricular or left atrial thrombi
●Bleeding diathesis
●Uncontrolled sepsis
Contraindications may apply to some but not other devices.
Short-term left ventricular assist devices — Left ventricular assist devices (LVAD) pump blood from the left ventricle or left atrium to the aorta.
Left ventricle to aorta — The axial flow pump works on the principle of an Archimedes screw. The inflow is placed retrogradely across the aortic valve into the left ventricle. A pump revolving at high speeds draws blood out of the left ventricle and ejects it proximally into the ascending aorta. A device that uses this principle is the Impella micro-axial flow device (figure 1), which is a miniature impeller pump located within a catheter. The Impella System is available in different sizes (versions 2.5, CP and 5.0), where the smaller device can be placed percutaneously but only provides half the support of the larger device that is placed surgically.
Impella was designed for either surgical placement using a graft in the ascending aorta or subclavian artery, or for percutaneous placement via the femoral artery [2,3]. In a study of 24 patients who received a surgically-implanted Impella device for post-cardiotomy failure, mortality was 54 percent, comparable to that seen in a cohort of high-risk patients supported with an IABP [2].
The PROTECT II trial was designed to compare outcomes in over 600 symptomatic patients with complex three-vessel or unprotected left main coronary artery disease and severely depressed left ventricular function (left ventricular ejection fraction ≤35 percent) who were to be randomly assigned to an Impella (version 2.5) or an IABP [4]. The trial was stopped for futility at 69 percent (n = 448) of planned enrollment. There was no significant difference in the primary end point of major adverse events at 30 days (35.1 versus 40.1 percent, respectively).
On per-protocol analysis, Impella use was associated with a reduction in the composite end point (major adverse cardiovascular events) at 90 days (51.0 versus 40.0 percent, p = 0.023), driven mostly by a reduction in the need for repeat revascularization (8.1 versus 3.7 percent, p = 0.06). There appeared to be effect modification by rotational atherectomy use, such that patients not undergoing this procedure had a significant reduction with Impella in major adverse event rate at 30 (p = 0.01) and 90 days (p = 0.003), as compared with IABP. It remains to be seen whether the two other Impella pumps that provide greater flow (3 to 5 L/min) will provide further improvement outcomes.
Intravascular microaxial LVAD and IABP have also been compared in patients with acute MI and cardiogenic shock [5-8] (see "Prognosis and treatment of cardiogenic shock complicating acute myocardial infarction", section on 'Hemodynamic support'). These studies have found no mortality advantage to microaxial LVAD and a higher rate of bleeding. The following two studies are representative:
●One small (n = 48) randomized trial and one large observational study found no significant difference in mortality at 30 days between the two devices [6].
●In a 2020 propensity-matched, registry-based retrospective cohort study of over 28,000 patients with acute MI and cardiogenic shock in the American College or Cardiology's National Cardiovascular Data Registry, 1680 propensity-matched pairs were identified [5]. The rate of in-hospital death or bleeding at 30 days was higher with intravascular microaxial LVAD (45.0 versus 34.1 percent; absolute risk difference, 10.9 percentage points, 95% CI 7.6-14.2 and 31.3 versus 16.0 percent; absolute risk difference 15.4 percentage points, 95% CI 12.5-18.2, respectively).
These data are limited by small numbers or unmeasured confounding. Larger randomized trials in this population are needed.
Moderate degrees of hemolysis and thrombocytopenia have been reported with this device [3]. (See "Management of long-term mechanical circulatory support devices", section on 'Bleeding'.)
Left-atrium-to-aorta assist device — The TandemHeart (figure 2), a centrifugal pump that contains a spinning impeller, is a percutaneous left-atrium-to-aorta assist device, with a venous catheter inserted into the left atrium by transseptal puncture and an arterial cannula inserted into the iliofemoral arterial system [9]. Blood is pumped from the left atrium to the iliofemoral system and is used in patients with very poor left ventricular function. The device is approved for use by the United States Food and Drug administration for six hours of support and by the European Commission for up to 30 days.
In its standard configuration (left atrium to iliofemoral artery), adequate right ventricular function is necessary for optimal performance of the TandemHeart. Circuits have been placed in a right-atrium-to-iliofemoral-artery system configuration with an interposed oxygenator to provide a circuity similar (albeit with lesser peak flow) to extracorporeal membrane oxygenation (ECMO).
Left ventricular assist device outcomes — The role of these continuous flow left ventricular assist devices for short-term stabilization until recovery of jeopardized myocardium or as a bridge to definite surgical treatment was evaluated in 18 patients with cardiogenic shock due to a myocardial infarction [10]. After a mean of four days of assistance, cardiac index improved from 1.7 to 2.4 L/min/m2, and there was a significant increase in mean blood pressure and reduction in pulmonary artery, pulmonary capillary wedge, and central venous pressures.
A subsequent randomized trial compared the TandemHeart device with an IABP in 41 patients with cardiogenic shock after an acute myocardial infarction [11]. Although hemodynamic and metabolic parameters were more effectively reversed with the VAD, complications such as severe bleeding and acute limb ischemia were more common, and there was no difference in 30-day mortality (VAD 43 percent versus balloon pump 45 percent).
An observational study evaluated outcomes in 117 patients with severe refractory cardiogenic shock treated with percutaneous VAD for an average of 5.8 days [12]. Severe refractory cardiogenic shock was defined as a systolic blood pressure of <90 mmHg, a cardiac index of <2.0 L/min/m2, and evidence of end-organ failure despite pressor/IABP support (82 percent had received an IABP). Fifty-six (48 percent) patients underwent cardiopulmonary resuscitation immediately before or at the time of implantation. Eighty patients had coronary artery disease (five with acute ST-elevation myocardial infarction), and 37 patients had nonischemic cardiomyopathy. The cardiac index improved from the median of 0.52 to 3.0 L/min/m2 following VAD implantation. Mortality was 40.2 percent at 30 days and 45.3 percent at six months.
Right ventricular assist devices — Two right ventricular assist devices bypass a failing right ventricle by pumping blood from the vena cava (VC) to the pulmonary arteries. The Impella RP Catheter provides up to 5.0 L/min of flow. It is indicated for providing temporary right ventricular support for up to 14 days in patients with a body surface area ≥1.5 m2 who develop acute right heart failure or decompensation following left ventricular assist device implantation, myocardial infarction, heart transplant, or open-heart surgery. Contraindications include biventricular failure, in which case it can be used in conjunction with a left ventricular support device, or respiratory failure where patients are likely to be better served with ECMO (table 1) [13]. This pump delivers blood from the inlet area, which sits in the IVC, through the cannula to the outlet opening near the tip of the catheter in the pulmonary artery (PA). The pump can be inserted through a standard catheterization procedure via the femoral vein.
The TandemHeart pump, coupled with the Protek Duo catheter, can be inserted into the right internal jugular vein with an outlet cannula in the main PA and connected to an oxygenator. This allows for an right atrium-to-PA cannulation that provides right ventricular support and oxygenation. When using internal jugular or femoral venous access with a catheter placed in the SVC or IVC, respectively, and another in the right atrium, oxygenation can be provided without right ventricular support (table 1).
The CentriMag device is also used for right ventricular support, often in conjunction with a left ventricular assist device, when the left ventricular assist device implantation is complicated by right ventricular failure. (See 'Extracorporeal membrane oxygenation' below.)
EXTRACORPOREAL MEMBRANE OXYGENATION — An extracorporeal membrane oxygenation (ECMO) device is a cardiopulmonary support system that, in addition to helping to move blood forward, removes carbon dioxide from and adds oxygen to venous blood using an artificial membrane lung. When placed in its standard venoarterial configuration (right-atrium-to-the-iliofemoral-artery system), the pulmonary circulation is bypassed and oxygenated blood returns to the patient via an arterial or venous route. With veno-venous bypass, ECMO is effective primarily as a therapeutic option for patients with severe respiratory failure. With venoarterial bypass, an extracorporeal pump is employed to support systemic perfusion, thus providing a hemodynamic support option in patients with circulatory and respiratory failure. A MagLev centrifugal pump in combination with long-term oxygenators (CentriMag plus Maquet Quadrox or the Maquet CardioHelp) provides full cardiopulmonary support (including hemodynamic support and oxygenation of venous blood) analogous to that provided by bypass during cardiac surgery. The ECMO systems involve placement in the central arterial and venous circulation of large bore catheters that allow positioning of cannulae in the aorta and right atrium. Blood from the venous catheter is pumped through a heat exchanger and oxygenator and then returned to the systemic arterial circulation via the arterial cannula. The ECMO systems can be used for support for up to 30 days. ECMO can also be placed in a venovenous configuration where deoxygenated blood is drawn from the superior vena cava/inferior vena cava and right atrium to the ECMO pump, and fully oxygenated blood is then returned through the tricuspid valve to the lungs (table 1). This circuit requires intact right ventricular function. (See "Extracorporeal membrane oxygenation (ECMO) in adults".)
These ECMO systems can be initiated through percutaneous cannulation or central cannulation (in the operating room). They can be used in patients with or undergoing:
●Acute hemodynamic deterioration such as cardiogenic shock and cardiopulmonary arrest with severe pulmonary congestion. (See "Prognosis and treatment of cardiogenic shock complicating acute myocardial infarction".)
●High-risk percutaneous coronary intervention.
●Fulminant myocarditis presenting with cardiogenic shock [14].
●Post-cardiotomy circulatory failure.
●COVID-19. (See "COVID-19: Extracorporeal membrane oxygenation (ECMO)".)
ECMO is contraindicated in the following clinical conditions:
●Significant aortic regurgitation
●Severe peripheral artery disease
●Bleeding diathesis
●Recent cerebrovascular accident or head trauma
●Uncontrolled sepsis
ECMO is discussed in detail in other topics. (See "Extracorporeal membrane oxygenation (ECMO) in adults".)
In contrast to left-ventricle-to-aorta pumps that unload the left ventricle, ECMO and left-atrium-to-iliofemoral system pumps produce a significant load on the left ventricle. With compromised left ventricular function, this load can reduce left ventricular ejection fraction substantially, causing in some cases complete closure of the aortic valve and an increase in left ventricular filling pressures and/or pulmonary edema or pulmonary hemorrhage. As such, ECMO has been combined with an axial flow pump, referred to as "ECPELLA," to unload and decompress the left ventricle in this setting. Whether this circuit provides an effect that allows the heart to recover and avoid an otherwise necessary durable ventricular assist device or death remains to be shown. In August, 2020, the U S Food and Drug Administration issued an emergency use authorization for left-sided Impella heart pumps as a tool to provide unloading therapy for COVID-19 patients undergoing ECMO.
NONPERCUTANEOUS CENTRIFUGAL PUMPS — External centrifugal pumps use rotating cones or impellers to generate energy that is recovered in the form of pressure flow work. There are presently two centrifugal pumps available for very short-term use (less than six hours): the Bio-Medicus (Bio-Medicus Inc, Minneapolis, Minnesota) and the Sarns (Sarns/3M Ann Arbor, Michigan). They are used primarily for cardiopulmonary bypass during open heart cases and thus are not placed percutaneously. They cause too much hemolysis to permit long-term use. (See "Management of cardiopulmonary bypass", section on 'General principles'.)
There are currently two magnetically-levitated implantable centrifugal pumps approved by the United States Food and Drug Administration (FDA) for ventricular assistance: Thoratec CentriMag and TandemHeart (see 'Left ventricle to aorta' above). One example of their use is right ventricular support at the time of left ventricular assist device placement. The Maquet Rotaflow is also magnetically levitated and can be used long or short term but is FDA-approved only for use in cardiopulmonary bypass during open-heart procedures. The magnetic levitated pumps cause less trauma, less heat generation, and are standard of care for short-term ventricular assist device support. They can be implanted for long periods of time (up to four months). They have the capability of supporting patients who cannot be weaned from cardiopulmonary bypass, those in cardiogenic shock, or who are awaiting cardiac transplantation. The pumps are versatile and can be used as a right ventricular assist device, left ventricular assist device, or biventricular support.
Insertion of centrifugal pumps, especially for long-term use, generally requires a sternotomy. The right and/or left atrium can be cannulated by using simple purse string sutures. The aorta and/or the pulmonary artery are cannulated by using standard cardiopulmonary bypass aorta cannulae placed through a purse string suture. For long-term use, sewn grafts to the aorta or pulmonary artery are preferred. With appropriate cannulae, these devices can also be placed percutaneously in the catheterization laboratory as described above.
Centrifugal pumps have several important caveats:
●Flow is nonpulsatile, which may be reflected in poor microcirculation perfusion and reduced end-organ function (eg, renal dysfunction).
●The magnetically-levitated devices are generally well tolerated and cause a minimal amount of hemolysis and generalized inflammatory response. The devices themselves perform well; most of the complications occur due to the method of cannulation, whether percutaneous or open.
●An important potential complication of these devices is clot formation. The main source of problematic clots is at the tips of the cannulae and not the devices themselves. These clots can lead to arterial embolization or inflow occlusion. Patients with centrifugal pumps should be maintained on continuous intravenous heparin anticoagulation, which is started as soon as the initial bleeding subsides and continued until device removal. The activated partial thromboplastin time is maintained between 150 and 200 seconds but can be reduced if flows are maintained and if bleeding increases.
Outcomes — In a report from the Society for Thoracic Surgery, the outcomes of 5735 patients who had percutaneous assist devices implanted after cardiac surgery over a 10-year period from 1995 to 2004 were evaluated [15]. Survival to hospital discharge improved from 38.5 to 59.1 percent with a reduction in stroke, renal failure, and bleeding.
More current information comes from a study of outcomes of Medicare (United States) beneficiaries who received ventricular assist device support within 30 days of open-heart surgery between 2000 and 2006 [16]. Among 1467 post-cardiotomy patients, 34 percent were discharged alive with a device. Of those patients discharged alive, 48 percent were readmitted within six months and 77 percent were alive at one year. Overall, one-year survival was 31 percent in the post-cardiotomy group. At one year, 4 percent had undergone heart transplantation, 9 percent had a device removed, and 24 percent were alive with a device.
The above two studies identified predictors of poor outcome:
●Preoperative need for dialysis and performing ventricular assist device implantation as an urgent salvage procedure or reoperation, myocardial infarction, aortic stenosis, female sex, race, peripheral vascular disease, New York heart Association Class IV heart failure, cardiogenic shock, left main coronary artery disease, and valve procedures [15].
●Low hospital implantation volumes, peripheral artery disease, valvular heart disease, and geographic region [16].
IMPLICATIONS OF SHORT-TERM MECHANICAL CIRCULATORY SUPPORT ON THE NEW UNOS HEART TRANSPLANT ALLOCATION POLICY — In the fall of 2018, a new heart allocation policy went into effect. This schema (table 2) [17] gives high priority to patients supported with short-term mechanical circulatory support, either extracorporeal membrane oxygenation (ECMO; Tier 1.i), intraaortic balloon pump (IABP; Tier 2.i ), or acute percutaneous endovascular circulatory support device (Tier 2.ii). All of these need hemodynamic justification after 14 days given the lower one-year survival of heart transplant patients after support with ECMO [18]. A retrospective analysis of the French National Heart Transplant Registry (CRISTAL) of 80 patients supported by venous arterial ECMO prior to heart transplant had a 52.2 percent one-year survival post-heart transplant compared with 75.5 percent in 866 patients not supported by ECMO [19]. Given these results, it is doubtful that Tier 1.i will often be used for bridging transplant. Tiers 2.i and 2.ii (IABP and percutaneous endovascular hemodynamic support) will be utilized to keep patients alive until transplant and facilitate transplantation. This will likely result in increased utilization of short-term mechanical circulatory support. The new system was implemented in October 2018. Outcome information will be available in mid-2019. (See "Heart transplantation in adults: Donor selection and organ allocation", section on 'Allocation'.)
SUMMARY
●Short-term mechanical circulatory assist devices improve cardiovascular hemodynamics by assisting a failing left or right ventricle or both. However, with the exception of those devices used during open-heart surgery, they have not been shown to improve mortality. (See 'IABP' above.)
●These devices are broadly categorized as follows: intraaortic balloon pump (IABP), non-IABP percutaneous mechanical circulatory assist devices, extracorporeal membrane oxygenator pumps, and nonpercutaneous centrifugal pumps. (See 'IABP' above and 'Non-IABP percutaneous circulatory devices' above and 'Extracorporeal membrane oxygenation' above and 'Nonpercutaneous centrifugal pumps' above.)
●Percutaneous cardiopulmonary support devices are commonly used in the following circumstances (see 'Indications' above):
•Myocardial infarction complicated by cardiogenic shock
•High-risk percutaneous coronary artery interventions
•Fulminant myocarditis presenting with cardiogenic shock
•Advanced heart failure with cardiogenic shock as a "bridge-to-a-bridge"
●Important contraindications exist for each device type (see 'Extracorporeal membrane oxygenation' above and 'Contraindications' above).
ACKNOWLEDGEMENTS — The UpToDate editorial staff acknowledges Julian M Aroesty, MD, and Duane Pinto, MD, MPH, who contributed to earlier versions of this topic review.
