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.
Intra‐aortic balloon pump (IABP).
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).
Durable (long‐term) mechanical circulatory support
These devices are indicated in patients with NYHA stage IV progressive heart failure unresponsive to medical therapies.
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.
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.
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.
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.
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.
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).
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
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
Severe peripheral vascular disease Irreversible neurologic disease
Moderate to severe aortic insufficiency Moderate to severe aortic stenosis Left ventricular thrombus Recent stroke Aortic abnormalities Contraindication to anticoagulation
Hemolysis Pump migration Aortic valve injury Tamponade due to LV perforation Aortic insufficiency Ventricular arrhythmia
Disorders of pulmonary artery wallprecluding placement Severe stenosis or regurgitation of tricuspidor pulmonary valve Thrombus in the right atrium or vena cava Contraindication to anticoagulation
Hemolysis Pump migration Tricuspid/pulmonic valve injury Tamponade due to RV perforation Tricuspid/pulmonic insufficiency Ventricular arrhythmia
Severe aortic insufficiency Unwitnessed cardiac arrest Disseminated malignancy Not LVAD, heart, or lung transplant candidate Contraindication to anticoagulation
Thrombosis of circuit Upper body hypoxia due to incomplete retrograde oxygenation LV dilation Systemic gas embolism
Intermediate‐term mechanical circulatory support devices
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.
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).
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.
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
Contraindication to anticoagulation
Thromboembolic events Air embolism
Ventricular septal defect Moderate to severe aortic insufficiency Contraindication to anticoagulation
Cannula migration Tamponade due to perforation Thromboembolism Air embolism during cannula insertion Interatrial 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.
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.
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
Calculated value (estimatedfrom power and speed) Directly proportional to power ↑Power = ↑ flow estimate ↓Power = ↓ flow estimate
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
Directly measured by system controller
HW: 4–6 watts HMII: 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 is set by medical team Individualized for each patient based on echo optimization, as well as clinical markers including BP and symptoms
HW: 2600–3200 rpm HMII: 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)
Stenting of outflow graft obstruction Pump replacement
GI bleeding (20% within 1 year) Epistaxis
AC related Acquired von Willebrand factor deficiency GI angiodysplasias and arteriovenous malfunctions
Colonoscopy and/or endoscopy If no source, consider tagged RBC scan
Hold AC and antiplatelets for hemodynamically significant bleeding Possible reversal of AC if INR elevated and clinically unstable bleed Monitor 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/neck Evaluate for signs of pump thrombosis CTA of LVAD
Neurosurgery and neurology consultation Possible discontinuation/reversal of AC in the setting of intracranial bleed Possible use of mechanical thrombectomy for large vessel occlusion
Thromboembolic (5% within 1 year)
Subtherapeutic INR Hypercoaguable state
May present with power spikes, high flow alarms, cardioembolic events, pigment nephropathy, cola colored urine Heart failure symptoms
Trend daily LDH (3× upper limit of normal) Plasma‐free Hb Urinalysis: hemoglobinuria Echo RAMP study CTA of LVAD
AC protocols: bivalirudin, heparin Thrombolysis in select cases Surgical VAD exchange Inotropic support in heart failure IVF with diuresis if evidence of hemglobinuria
Infection (includes device‐related infection such as infectious endocarditis, mediastinitis, bacteremia)
Fevers/chills, etc. Discharge and/or pain from driveline site
Microbiology Driveline site C/S, blood culture, Imaging: CT chest and abdomen scan for deep infection
ID consult Appropriate antibiotics Occasionally surgical debridement
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).
CardioWest is approved as a bridge to transplant device in transplant eligible patients at risk of imminent death from biventricular failure.
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.
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