CHAPTER 13Mechanical Circulatory Support
Natasha Pradhan, Tim Hinohara, and Umesh K. Gidwani
Icahn School of Medicine at Mount Sinai, New York, NY, USA
Overview of devices and indications
Mechanical circulatory support can be classified in terms of the duration of intended support.
Short‐term mechanical circulatory support
- These devices are used in patients with cardiogenic shock refractory to pharmacologic therapies.
- They are typically used for days, rather than weeks.
- Examples include:
- Intra‐aortic balloon pump (IABP).
- Impella® devices.
- Extracorporeal membrane oxygenation (ECMO).
Intermediate‐term mechanical circulatory support
- These devices are robust extracorporeal pumps that can be used for several weeks.
- They are usually employed emergently and serve as bridge to transplant or bridge to decision (BTD).
- Examples include:
- TandemHeart® device.
- CentriMag™ device.
Durable (long‐term) mechanical circulatory support
- These devices are indicated in patients with NYHA stage IV progressive heart failure unresponsive to medical therapies.
- Examples include:
- Left ventricular assist device (LVAD): indicated for predominant LV failure as bridge to transplant or destination therapy.
- Total artificial heart (TAH): indicated for biventricular failure as bridge to transplant.
Short‐term mechanical circulatory support devices
Intra‐aortic balloon pump
- While the IABP has been a mainstay in the management of cardiogenic shock, current evidence has cast doubt as to the efficacy of the IABP in cardiogenic shock. Larger studies are underway.
- The IABP consists of an elongated polyurethane balloon (35–40 mL) inserted percutaneously through the femoral artery. A pump is attached to the balloon that uses helium to inflate the balloon during diastole (closure of the aortic valve), and to deflate the balloon during systole (opening of the aortic valve).
- Ideal location: the balloon tip should be at the level of the carina (Figure 13.1), and the distal balloon end should lie above the renal arteries. If prolonged support is required, can consider axillary insertion to allow sitting upright and possible ambulation.
Indications
- Cardiogenic shock complicating acute ST elevation MI (ACC/AHA stage IIa/b).
- Refractory unstable angina.
- Mechanical complications of acute MI (papillary muscle rupture leading to mitral regurgitation (MR) or ventricular septal defect (VSD)).
- Support of high risk coronary intervention (such as percutaneous coronary intervention, coronary artery bypass graft).
- Refractory heart failure as a bridge to further therapy.
- Intractable ventricular arrhythmia as a bridge to further therapy.
- Intractable MI awaiting further therapy.
Contraindications
- Moderate or severe aortic insufficiency.
- Aortic dissection.
- Aortic aneurysm.
- Occlusion/severe stenosis of distal aorta.
Postulated mechanisms of action
- Increased (augmented) diastolic pressure → improved coronary perfusion → increased myocardial oxygen delivery.
- Increased mean arterial pressure (increased diastolic, decreased systolic) → improved systemic blood flow.
- Decreased afterload: deflation of the balloon creates a suction effect causing decreased end‐distolic blood pressure → reduced aortic pressure at the start of systolic ejection → decreased afterload → increased stroke volume, decreased myocardial oxygen demand, and improved systemic perfusion.
IABP pressure waveform
- Unassisted wave: the wave immediately before balloon inflation (Figure 13.2).
- Augmented wave: waveform that correlates with balloon inflation.
- Assisted wave: the wave immediately following the augmented wave is called the assisted wave (seen in 1:2 or higher ratios). Due to balloon inflation, the assisted end‐diastolic pressure is lower, thereby reducing afterload and ‘assisting’ ventricular contraction.
Complications
- Vascular complications during insertion or removal.
- Limb ischemia (3–20%).
- Balloon rupture (rare): indicated by blood in connecting tube. Managed by placing patient in Trendelenburg position and immediately removing balloon.
- Hemolysis and consumptive thrombocytopenia.
- Catheter‐related infection.
Impella intraluminal catheter‐based axial flow pump
- The Impella is a catheter‐based device that propels blood by a non‐pulsatile axial flow Archimedes‐screw pump.
- Once the Impella catheter is confirmed to be in the desired position, it is connected to an external controller system where the user can adjust the rotational speed to provide the desired flow rate.
Left ventricular Impella
- The Impella originally was designed to provide LV support.
- It is inserted into the femoral artery either percutaneously or surgically by femoral cut‐down and is advanced in a retrograde fashion so that the tip housing the pump sits in the left ventricle (Figure 13.3A).
- The pump pulls blood from the left ventricle through an inlet area near the tip and expels blood from the catheter into the ascending aorta distal to the aortic valve.
- The three available models displace increasing amounts of blood with progressively larger axial motor sizes:
- Impella 2.5: catheter diameter 9 Fr, 12 Fr pump motor, flow rate up to 2.5 L/min.
- Impella CP: catheter diameter 9 Fr, 14 Fr pump motor, flow rate up to 4.3 L/min.
- Impella 5.0/LD: catheter diameter 9 Fr, 21 Fr pump motor, flow rate up to 5 L/min.
Right ventricular Impella
- The Impella RP is designed to provide RV support; it comes in one size and provides flow rates greater than 4.0 L/min.
- The Impella RP is inserted via the femoral vein, into the right atrium, across the tricuspid and pulmonic valves, and into the pulmonary artery (Figure 13.3B).
- The motor which sits in the terminal IVC propels blood through the catheter and to the outlet opening near the tip of the catheter in the main pulmonary artery.
Indications
- During high risk percutaneous coronary intervention in hemodynamically stable patients with severe coronary artery disease.
- Treatment of cardiogenic shock occurring after myocardial infarction or open heart surgery.
- Impella RP is indicated for right heart failure refractory to conventional therapy.
Extracorporeal membrane oxygenation
- ECMO provides cardiopulmonary support similar to the cardiopulmonary bypass circuit used in cardiac surgery.
- Blood is drained from the vascular system, circulated outside of the body by a mechanical pump, oxygenated, and then reinfused into the circulation (Figure 13.4).
- There are two primary types of ECMO: veno‐venous (V‐V) and veno‐arterial (V‐A):
- V‐V ECMO helps only with oxygenation by oxygenating venous blood and returning it back to the venous circulation.
- V‐A ECMO provides both oxygenation and circulatory support. Venous blood is oxygenated and returned back into the arterial circulation, thereby bypassing both the lung and heart.
- Venous access is usually by cannulation of the internal jugular vein or femoral vein, while arterial access is through the femoral artery.
- Cannulas are inserted primarily by cardiothoracic surgeons at the bedside, catheterization lab, or operating room.
- An ECMO team is required, including a cardiologist, cardiothoracic surgeon, intensive care nurse, and perfusionist (specially trained respiratory therapist).
Indications
ECMO is deployed when conventional therapies have failed, risk of mortality is imminent, and the disease process is either reversible or there is a plan to bridge to VAD or organ transplant.
Indications for V‐V ECMO
- Acute respiratory distress syndrome.
- Provide lung rest in airway obstruction, pulmonary contusion, or smoke inhalation.
- Primary graft failure after lung transplantation.
- Bridge to lung transplant.
- Lung hyperinflation due to status asthmaticus.
- Pulmonary hemorrhage or massive hemoptysis.
Indications for V‐A ECMO
- Cardiogenic shock.
- Inability to wean from cardiopulmonary bypass after cardiac surgery.
- Primary graft failure after heart or heart–lung transplantation.
- Chronic cardiomyopathy as a bridge to VAD or heart transplantation.
- Peri‐procedural support for high risk percutaneous cardiac interventions.
Contraindications and complications
| Device | Contraindications | Complications |
| All devices | Severe peripheral vascular diseaseIrreversible neurologic disease | BleedingVascular injuryInfectionNeurologic injury |
| Impella LP/CP | Moderate to severe aortic insufficiencyModerate to severe aortic stenosisLeft ventricular thrombusRecent strokeAortic abnormalitiesContraindication to anticoagulation | HemolysisPump migrationAortic valve injuryTamponade due to LV perforationAortic insufficiencyVentricular arrhythmia |
| Impella RP | Disorders of pulmonary artery wallprecluding placementSevere stenosis or regurgitation of tricuspidor pulmonary valveThrombus in the right atrium or vena cavaContraindication to anticoagulation | HemolysisPump migrationTricuspid/pulmonic valve injuryTamponade due to RV perforationTricuspid/pulmonic insufficiencyVentricular arrhythmia |
| ECMO | Severe aortic insufficiencyUnwitnessed cardiac arrestDisseminated malignancyNot LVAD, heart, or lung transplant candidateContraindication to anticoagulation | Thrombosis of circuitUpper body hypoxia due to incomplete retrograde oxygenationLV dilationSystemic gas embolism |
Intermediate‐term mechanical circulatory support devices
TandemHeart
- The TandemHeart utilizes an extracorporeal continuous flow centrifugal pump that withdraws oxygenated blood from the left atrium and pumps it into the arterial circulation (Figure 13.5).
- One cannula is inserted into the femoral vein and another into the femoral artery.
- The left atrium is accessed through the venous system by trans‐septal puncture.
- Provides up to 4 L/min of blood flow.
- There are no randomized controlled data on the TandemHeart, which limits its more widespread use.
Indications
- Cardiogenic shock.
- Extracorporeal circulatory support for procedures lasting up to 6 hours and not requiring complete cardiopulmonary bypass (e.g. mitral valve reoperation, valvuloplasty, surgery of the vena cava).
CentriMag
- The CentriMag is a surgically implanted extracorporeal centrifugal pump that utilizes a magnetic rotor (Figure 13.6). It can provide support to either ventricle or both.
- For RV support, the cannulas are placed in the right atrium and pulmonary artery to bypass the right ventricle.
- For LV support, the cannulas are placed in the left atrium and aorta to bypass the left ventricle.
- It is possible to insert two CentriMag devices to provide biventricular support (as shown in Figure 13.6).
- Provides up to 10 L/min of blood flow.
Indications
- Cardiogenic shock with acute RV failure, approved for use for up to 30 days.
- Acute LV failure, approved for use for up to 6 hours while longer term options are considered.
Contraindications and complications
| Device | Contraindications | Complications |
| CentriMag | Contraindication to anticoagulation | Thromboembolic eventsAir embolism |
| TandemHeart | Ventricular septal defectModerate to severe aortic insufficiencyContraindication to anticoagulation | Cannula migrationTamponade due to perforationThromboembolismAir embolism during cannula insertionInteratrial shunt development |
Durable (long‐term) mechanical circulatory support devices
Left ventricular assist device
- A LVAD is a mechanical pump that works in parallel with the patient’s heart, used in the management of end‐stage cardiac failure that is refractory to advanced medical therapy.
Evolution of LVAD devices
- Historically, LVADs can be divided into first, second, and third generation devices.
- The first generation devices provided pulsatile flow and were bulky, noisy, and associated with high complication rates. However, they were evolutionary and led to the first continuous flow devices.
- The second generation devices were smaller and had an axial flow rotor powered by a battery connected to a small caliber driveline.
- The Thoratec HeartMate™ XVE and HeartMate II devices are in wide use in the USA and other countries. Blood flows through an inflow cannula from the apex of the left ventricle to the pump and returns back through an outflow cannula to the ascending aorta.
- The landmark REMATCH study (2001) demonstrated significant survival benefit in patients with end‐stage heart failure treated with a pulsatile HeartMate XVE LVAD versus optimal medical therapy (52% versus 25% survival at 1 year, P = 0.002) with an improved quality of life.
- Third generation devices are centrifugal pumps that are designed for long durability, compact size, and optimization of blood flow through the device to minimize the risk of thrombus formation and hemolysis.
- The HeartWare™ HVAD is a continuous flow centrifugal pump with the Impeller partly magnetically suspended and with no bearings.
- The Thoratec HeartMate III is a magnetically levitated centrifugal flow pump designed to minimize the risk of pump thrombosis.
- In the MOMENTUM trial (2018) comparing the HeartMate III with an axial flow pump in 366 patients with advanced heart failure, the centrifugal flow pump was superior to the axial flow pump with regard to the composite primary outcome (2 years free of disabling stroke or survival free of reoperation to replace or remove a malfunctioning device). Mortality rates and disabling stroke rates were similar in the two treatment groups.
Components
The LVAD receives blood from the left ventricle and returns it to the ascending aorta (Figure 13.7), with Figures 13.8 and 13.9 showing details of some of the components.
Indications
- Bridge to cardiac transplant.
- Destination therapy as long‐term assistance for patients who are ineligible for transplant (approximately 40% of implants).
- Bridge to recovery for potential reversible myocardial pathology.
Management of cardiac arrest in patients on mechanical circulatory support
- Step 1: call the VAD attending or fellow.
- Step 2: establish an arterial line. The most important step is establishing an accurate blood pressure with an arterial line.
- Step 3: begin chest compressions. While chest compressions run the risk of cannula dislodgment, it should be performed in cases where the mean arterial pressure is 0 (patient has actually lost perfusion, as opposed to situations with poor perfusion where an alternative means to restore this may be considered).
- Step 4: consider volume bolus and inotropes where appropriate.
Parameters used to monitor LVAD function
| Parameter | Definition | Range | Increase | Decrease |
| Flow | Calculated value (estimatedfrom power and speed)Directly proportional to power↑Power = ↑ flow estimate↓Power = ↓ flow estimate | 4–6 L/min | Abnormal increase in power may lead to a falsely elevated flow, i.e. increased drag on rotor due to pump thrombosis results in high power requirements and falsely elevated flow reading | |
| Power | Directly measured by system controller | HW: 4–6 wattsHMII: 5–8 watts | High power (trend is more important than transient spikes) may be due to development of thrombus. | Obstruction of outflow graft (kinking, stenosis, aortic anastomosis) |
| Speed | Speed is set by medical teamIndividualized for each patient based on echo optimization, as well as clinical markers including BP and symptoms | HW: 2600–3200 rpmHMII: 8600–9600 rpm | Pump programmed to avoid potential suction events by reducing speed | |
| Pulsatility index (PI) (displayed on HMII only) | Correlates with degree of native LV residual contractility(max flow – min flow/mean flow) | 3–6 | Increased LV contractility – exercise, ionotropes, myocardial recovery (rare):
|
Decreased LV contractility:
|
HMII, HeartMate II; HW, HeartWare.
LVAD troubleshooting
| Pulsatility index | Power | Flow | Fixed speed | |
| HeartMate IIHeartWare | 3–6N/A | 5–8 watt4–6 watt | 4–6 L/min4–6 L/min | 8600–9600 rpm2600–3200 rpm |
| Pump logistics | Echo findings | Diagnostic aids | Management options | |
| Right ventricular failure | Lower pulsatilityLower flowPossible suction events | RV dilation and dysfunctionSeptal bowing to right | Right heart catheterization (RHC) | DiureticsInotropesDigoxinPulmonary vasodilatorsEcho optimizationTemporary percutaneous support: Impella RP device, or right‐sided TandemHeart |
| Hypovolemia | Lower pulsatilitySuction eventsLower flow | Decompressed LV | Response to fluid challengeHypotensionOrthostatic vital signs | Intravenous fluid |
| Tamponade | Lower flowLower pulsatilitySuction events | Effusion or localized peri‐RV clotClear tamponade physiology rarely seen with VAD support | ExamRHCCT scanHypotension | Pericardial drainage/surgical exploration |
| Pump thrombus | Higher powerHigher flow estimation (falsely elevated)Lower pulsatility | Ramped speed studyDecreased LV unloadingDilated LVAortic vein (AoV) openingIncreased mitral regurgitation (MR) | Hemolysis labsLog file anlaysisRHCDevice auscultation (‘running rough’)LV angiography | Increased anticoagulationInotropic support if in heart failureThrombolysis (high risk of bleeding)Pump exchange surgery |
| Volume overload | Higher pulsatility (occasional) | RV dysfunction, tricuspid regurgitationDilated LV
|
Physical exam: volume overload, jugular venous pressure, ralesRHC | |
| Hypertension | Possible higher pulsatility (especially on VAD) | Non‐specific | Doppler blood pressure | Antihypertensive therapy |
| Pump or percutaneous lead failure | Not maintaining set speedVAD running irregularController alarms | Dilated LVPoor LV unloadingIncreased MRAoV opening | Device auscultationLog file analysisX‐ray of percutaneous lead | Percutaneous lead repairLVAD surgical replacement |
| Inflow/outflow obstruction | Higher/ lower powerHigher/ lower pulsatilityHigher/ lower flow | Ramped speed studyDilated LVPoor LV unloadingAoV openingIncreased MR | CT angiographyCXRFluoroscopyLV angiographyHemolysis labs | Stenting of outflow graft obstructionPump replacement |
LVAD‐related complications
| Complication | Details | Etiology/presentation | Investigations | Treatmentconsiderations |
| Bleeding | GI bleeding (20% within 1 year)Epistaxis | AC relatedAcquired von Willebrand factor deficiencyGI angiodysplasias and arteriovenous malfunctions | Colonoscopy and/or endoscopyIf no source, consider tagged RBC scan | Hold AC and antiplatelets for hemodynamically significant bleedingPossible reversal of AC if INR elevated and clinically unstable bleedMonitor device parameters closely while holding AC |
| CVA (10% within 1 year) | Hemorrhagic (5% within 1 year) | Presents with new focal neurolgic deficit, altered mental status | CTA head/neckEvaluate for signs of pump thrombosisCTA of LVAD | Neurosurgery and neurology consultationPossible discontinuation/reversal of AC in the setting of intracranial bleedPossible use of mechanical thrombectomy for large vessel occlusion |
| Thromboembolic (5% within 1 year) | Pump thrombosis | |||
| Device thrombosis | Subtherapeutic INRHypercoaguable state | May present with power spikes, high flow alarms, cardioembolic events, pigment nephropathy, cola colored urineHeart failure symptoms | Trend daily LDH (3× upper limit of normal)Plasma‐free HbUrinalysis: hemoglobinuriaEcho RAMP studyCTA of LVAD | AC protocols: bivalirudin, heparinThrombolysis in select casesSurgical VAD exchangeInotropic support in heart failureIVF with diuresis if evidence of hemglobinuria |
| Infection (includes device‐related infection such as infectious endocarditis, mediastinitis, bacteremia) | Driveline infection | Fevers/chills, etc.Discharge and/or pain from driveline site | MicrobiologyDriveline site C/S, blood culture,Imaging: CT chest and abdomen scan for deep infection | ID consultAppropriate antibioticsOccasionally surgical debridement |
| Pocket infection |
Total artificial heart
- A TAH is a durable mechanical circulatory support device that is used for patients with severe biventricular dysfunction or other structural abnormalities that make them poor candidates for LVAD implantation.
- Surgical implantation includes sternotomy, removal of both native ventricles and their associated atrioventricular valves, and implantation of the TAH by connecting each synthetic ventricle to the respective atria and great vessel.
- The TAH is connected to an external power source via a driveline similar to an LVAD.
- The device is composed of two polyurethane pneumatically powered ventricles, each with a single leaflet tilting disc valve.
- The most commonly used TAH device is the CardioWest™ TAH (Syncardia).
Indications
- CardioWest is approved as a bridge to transplant device in transplant eligible patients at risk of imminent death from biventricular failure.
Complications
- Surgical implantation complications most commonly include infection (72%), bleeding (42%), hepatic dysfunction (36%), and respiratory dysfunction (30%).
- Long‐term complications include driveline failure, systemic or driveline infections, thromboembolic events, and bleeding.
Reading list
- Aaronson KD, et al. Use of an intrapericardial, continuous‐flow, centrifugal pump in patients awaiting heart transplantation. Circulation 2012; 125(25):3191–200.
- Csepe TA, Kilic A. Advancements in mechanical circulatory support for patients in acute and chronic heart failure. J Thorac Dis 2017; 9(10):4070–83.
- Feldman D, et al. The 2013 International Society for Heart and Lung Transplantation Guidelines for mechanical circulatory support: executive summary. J Heart Lung Transplant 2013; 32(2):157–87.
- Naidu SS. Novel percutaneous cardiac assist devices: the science of and indications for hemodynamic support. Circulation 2011; 123(5):533–43.
- Rose EA, et al. Long‐term use of a left ventricular assist device. N Engl J Med 2001; 345(20):1435–43.
- Slaughter MS, et al. Clinical management of continuous‐flow left ventricular assist devices in advanced heart failure. J Heart Lung Transplant 2010; 29(Suppl 4):S1–39.
- Werdan K, Gielen S, Ebelt H, Hochman JS. Mechanical circulatory support in cardiogenic shock. Eur Heart J2014; 35(3):156–67.
Images
Figure 13.1 CXR demonstrating the tip of the IABP in the correct position (arrow).
Figure 13.2 Normal IABP pressure waveform.
Figure 13.3 (A) Left heart catheterization. Using femoral arterial access, the catheter has been guided into the left ventricle. (B) Right heart Impella inserted via the femoral vein.
Figure 13.4 Veno‐venous and veno‐arterial ECMO circuits.
Figure 13.5 TandemHeart assisting the left ventricle in pumping oxygenated blood.
Figure 13.6 CentriMag extracorporeal pump.
Figure 13.7 LVAD components.
Figure 13.8 HeartWare controller screen.
Figure 13.9 HeartMate II controller screen.
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