Mechanical circulatory support

Mechanical circulatory support (MCS) devices are used to manage refractory cardiogenic shock and congestive heart failure by improving systemic and coronary artery perfusion while reducing myocardial oxygen demand. MCS devices are categorized into temporary and long-term devices. Left ventricular assist devices (LVADs) are a type of long-term support that provide continuous blood flow through a surgically implanted pump connected to an external controller and power source. Since LVADs generate nonpulsatile flow, traditional vital signs such as pulse, blood pressure, and pulse oximetry may be inaccurate or absent, requiring the use of alternative measures (e.g., Doppler opening pressure). LVAD parameters are displayed on the LVAD controller and are used to assess for evidence of complications. LVAD-associated complications include infection, shock, pump thrombosis, and suction events.

Indications ^[1]

• Cardiogenic shock refractory to pharmacological management
• Congestive heart failure refractory to guideline-directed medical therapy
  • Bridging therapy to heart transplant or recovery
  • Destination therapy for advanced heart failure
• Prophylactic support during high-risk procedures, e.g.:
  • Thrombolysis for pulmonary embolism
  • Complex percutaneous coronary interventions

Goals ^[1]

• Improve systemic and coronary artery perfusion
• Reduce left ventricular filling pressures, left ventricular wall stress, and myocardial oxygen demand

Types of devices ^[1][2]

• Ventricular assist devices (VAD): electromechanical devices designed to augment cardiac output by assisting the function of the left ventricle (LVAD), right ventricle (RVAD), or both (BiVAD)
• Other mechanical support devices
  • Intra-aortic balloon pump (IABP)
  • Venoarterial extracorporeal membrane oxygenation (VA-ECMO)
  • Total artificial heart

Temporary mechanical circulatory support devices

Long-term mechanical circulatory support devices

Complications of MCS devices ^[2][5][9]

See also “LVAD-associated complications” for the diagnosis and management of complications in patients with an LVAD.

• Mechanical: device malfunction, migration, damage, or obstruction
• Infectious
  • Surgical site infection
  • Cardiac device infections
  • Intravascular catheter-related bloodstream infection
  • Endocarditis, pericarditis, mediastinitis
• Cardiovascular
  • Valvular injury (e.g., leading to aortic regurgitation)
  • Heart chamber perforation
  • Pericardial effusion and cardiac tamponade
  • Arrhythmias
  • Acute limb ischemia
• Hematologic
  • Anemia
  • Hemorrhage
  • Hemolysis
  • Thrombocytopenia
  • Thromboembolism
  • Pump thrombosis
• Neurological
  • Ischemic stroke
  • Hemorrhagic stroke

Left ventricular assist devices (LVADs) are mechanical devices that support left ventricular function in patients with end-stage heart failure. The term most commonly refers to intracorporeal LVADs, which provide continuous blood flow through a surgically implanted pump connected to an external controller and power source.

Mechanism ^[2]

• Inflow cannula: a tube that directs blood from the apex of the left ventricle into the pump
• Pump: an internal device implanted into the chest or abdomen that generates continuous blood flow
• Outflow cannula: a tube that directs blood from the pump into the ascending or descending aorta
• Driveline: a percutaneously inserted cable that connects the internal pump to the external controller and batteries
• Controller: an external device that monitors pump function, displays parameters (e.g., pump speed, output), and shows battery life and alarms

LVAD parameters ^[2][7][10]

Overview

LVAD parameters are displayed on the LVAD controller.

• Speed (revolutions per minute)
  • The only manually adjustable parameter that is set by a heart failure physician
  • Determines the rate at which the pump spins to propel blood into the outflow cannula
• Power (watts)
  • Measured power consumption
  • Determined by pump speed and flow rate
• Flow (liters per minute)
  • Approximates cardiac output
  • Affected by pump parameters (e.g., speed, power) and patient parameters (e.g., blood volume, preload, afterload)
• Pulsatility index (dimensionless)
  • Measured differential flow across the LVAD in systole and diastole
  • Determined by the pulsatile flow generated by native heart

Causes of abnormal LVAD parameters ^[2][9][11]

• Power
  • High: pump thrombosis
  • Low: device or battery problem
• Flow
  • High: low systemic vascular resistance (e.g., due to sepsis, anaphylaxis)
  • Low
    • Hypovolemic shock
    • Hemorrhagic shock
    • Cardiogenic shock (e.g., arrhythmia, right-sided heart failure, pump malfunction)
    • Obstructive shock (e.g., pulmonary embolism, cardiac tamponade)
    • Hypertensive emergency
    • Suction event
• Pulsatility index
  • High
    • Device or driveline damage
    • Improvement in native left ventricular function
  • Low
    • Excess pump speed
    • Hypovolemia
    • Decline in native left ventricular function

Vital signs in patients with LVADs ^[9][12]

Traditional pulse, blood pressure, and pulse oximetry measures are inaccurate or absent in patients with LVAD due to continuous blood flow.

• Pulse: An absent pulse is a normal finding. ^[13]
• Blood pressure
  • Measure the Doppler opening pressure to approximate MAP.
    • Place a blood pressure cuff on the upper extremity.
    • Locate the brachial artery using a handheld Doppler.
    • Inflate the blood pressure cuff until the Doppler signal is lost.
    • Slowly deflate the blood pressure cuff until the signal returns.
    • Record the pressure at which the handheld Doppler signal returns as the MAP.
  • In critically ill patients, consider arterial line pressure monitoring.
  • Target MAP: 75–85 mm Hg ^[7]
• Oxygen saturation
  • Pulse oximetry is inaccurate because the pulse wave form is atypical.
  • Use ABG analysis to assess oxygenation as needed.

Approach to the emergency management of patients with LVADs ^[11][12][14]

• Perform ABCDE assessment and focused history and physical examination.
  • Measure the MAP using the Doppler opening pressure.
  • Assess volume status and perfusion.
  • Auscultate device hum.
• Perform LVAD assessment.
  • Determine the pump make and model, and assess positioning and connections.
  • Evaluate LVAD parameters.
• Contact VAD coordinator and consult cardiology.
• Consider urgent transfer to an LVAD center.
• Perform a FoCUS and obtain an ECG.
• Obtain additional diagnostics studies as indicated (e.g., coagulation studies, hemolysis studies).
• Manage any LVAD-associated complications.

Gastrointestinal bleeding ^[2][7][12]

GI bleeding in patients with an LVAD is most commonly an upper GI bleed or a small bowel bleed.

• Etiology: often multifactorial
  • Arteriovenous malformations and angiodysplasias
  • Acquired von Willebrand disease
  • Antithrombotic therapy
• Diagnosis: See “Initial evaluation of GI bleeding” and “Diagnosis of GI bleeding.”
• Management
  • Follow the stabilization steps and initial management of GI bleeding.
  • Provide hemostatic control of GI bleeding for ongoing or recent bleeding.
  • Given the risk of pump thrombosis, reserve anticoagulation reversal for refractory life-threatening bleeding. ^[9]

Infection ^[15][16]

Etiology

• VAD-specific infection: an infection involving any part of the VAD, e.g.:
  • Driveline infection
  • Pocket infection
  • Pump and/or cannula infection
• VAD-related infection: an infection that occurs as a complication of implantation surgery or VAD-specific infections, e.g.:
  • Infective endocarditis
  • Mediastinitis
  • Intravascular catheter-related bloodstream infection
• Non-VAD infection: an infection that is unrelated to the VAD (e.g., pneumonia)

Diagnosis

Follow a standardized approach for suspected infections in patients with LVADs because classic signs and symptoms may be subtle or absent. ^[15]

• Initial diagnostics
  • CBC, BMP, urinalysis, urine culture
  • Blood cultures from central and peripheral sites
  • Chest x-ray
• Advanced diagnostics
  • Sterile aspirate or swab of purulent drainage for bacterial and fungal cultures
  • CT or ultrasound to assess for deep space infections and/or abscess
  • TEE to assess for vegetations, abscess, turbulent flow, and/or cannula dehiscence
  • See also “Diagnostics for sepsis.”

Management

Manage infections in consultation with infectious diseases, LVAD team, and other specialists (e.g., cardiac surgery, critical care) as appropriate.

• Sepsis
  • Start empiric antibiotic therapy for sepsis with coverage for MRSA and Pseudomonas.
  • Begin septic shock management as for patients without LVADs. ^[11]
• VAD-specific and VAD-related infections
  • Base initial antibiotic therapy on local institutional guidelines and patient's prior culture results.
  • Consider surgical debridement, device explant, and/or long term suppressive antibiotic therapy.
• Non-VAD infection: Manage the underlying cause as in patients without LVADs. ^[12]

Hypotension and shock ^[2][12]

Hypotension in patients with an LVAD is defined as a MAP and/or Doppler opening pressure < 60 mm Hg. See also “Diagnostics in shock” and “Immediate hemodynamic support.” ^[12]

Hypovolemic shock and hemorrhagic shock

• Diagnosis
  • LVAD parameters: low flow, low pulsatility index
  • FoCUS: nondilated right ventricle, underfilled IVC
  • Other measurements: ↓ central venous pressure, ↓ mixed oxygen venous saturation
• Management
  • Hemorrhagic shock
    • Give blood products and obtain hemostatic control.
    • Due to the risk of pump thrombosis, consider anticoagulant reversal only for severe refractory bleeding.
  • Nonhemorrhagic hypovolemic shock
    • Provide IV fluid resuscitation.
    • Manage the underlying cause (e.g., antiemetics for vomiting, stop diuretics).

Cardiogenic shock and obstructive shock

• Etiology
  • LVAD: pump thrombosis, device malfunction, cannula obstruction
  • Cardiac: e.g., myocardical infarction, cardiac tamponade
  • Pulmonary: pulmonary embolism, pneumothorax
• Diagnosis
  • LVAD parameters: low flow, suction event
  • FoCUS: noncollapsing IVC, dilated right ventricle
  • ECG: to assess for acute coronary syndrome, arrhythmias, and conduction abnormalities
  • Other measurements: ↑ central venous pressure, ↓ mixed oxygen venous saturation
• Management
  • Manage the underlying cause.
  • See “Management of cardiogenic shock” and “Treatment” in “Obstructive shock.”

Distributive shock

• Diagnosis
  • LVAD parameters: high flow
  • FoCUS: collapsing IVC, nondilated right ventricle, hyperdynamic left ventricle
  • Other measurements: ↓ central venous pressure, normal or ↑ mixed oxygen venous saturation
• Management: Manage the underlying cause, e.g.:
  • Management of septic shock
  • Management of anaphylaxis
  • Management of adrenal crisis

Arrhythmia ^[2][7][12]

• Etiology
  • Supraventricular arrhythmias
  • Ventricular arrhythmias
  • Bradycardia
  • Suction event
• Diagnosis
  • ECG: to identify the type of arrhythmia
  • FoCUS: to assess for suction event
  • Cardiac implantable electronic device interrogation ^[11][12]
• Management
  • Management of tachycardia
    • Unstable patients: Perform electrical cardioversion or defibrillation with pads applied in an anterior-posterior placement away from the LVAD. ^[12]
    • Stable patients: Consider pharmacological cardioversion (e.g., with amiodarone).
  • Also see “Management of bradycardia” and “Suction event.”

Maintain a low threshold to obtain an ECG, as symptoms of arrhythmia in patients with LVAD may be mild or absent. ^[12]

Pump thrombosis ^[2][12]

Pump thrombosis is a potentially fatal LVAD complication.

• Etiology
  • Inadequate anticoagulation
  • Poorly controlled blood pressure
  • Inappropriately low pump flow
  • Cannula malposition or device malfunction
• Clinical features
  • Signs of shock
  • Signs of heart failure
  • Signs of hemolysis
• Diagnosis
  • LVAD parameters and alarms: high power, low or high flow
  • Laboratory signs of hemolysis
  • FoCUS: left ventricular dilatation, mitral regurgitation, frequent aortic valve opening
  • Chest x-ray: to assess positioning of cannulas and CXR findings in acute heart failure
  • CTA chest: to assess filling defect in the inflow or outflow canula
• Management
  • Provide adequate anticoagulation (e.g., unfractionated heparin, direct thrombin inhibitor)
  • Reserve fibrinolytic therapy for selected patients under expert guidance. ^[12]
  • May require device exchange or heart transplant

Suction event ^[2][11]

• Definition: obstruction of the LVAD inflow cannula by the left ventricular wall due to reduced left ventricular filling and increased negative pressure
• Etiology
  • Decreased left ventricular filling (e.g., due to hypovolemia, right-sided heart failure, cardiac tamponade)
  • Increased left ventricular unloading (e.g., due to excessive pump speed)
• Clinical features
  • Hypotension, shock, and/or signs of heart failure due to low LVAD flow
  • Arrhythmias due to myocardial irritation
• Diagnosis
  • LVAD parameters and alarms: low flow, inappropriately high pump speed
  • FoCUS: collapsed or underfilled left ventricle
• Management
  • Administer an IV fluid bolus to increase left ventricular filling.
  • Decrease pump speed to decrease left ventricular unloading.
  • Manage the underlying cause (e.g., decrease diuretic dose, perform pericardiocentesis).

Cardiac arrest ^[2][12][17]

Suspect cardiac arrest in any LVAD patient with sudden loss of consciousness.

• Diagnosis
  • Absence of precordial mechanical hum
  • Inability to obtain Doppler opening pressure
  • No cardiac activity on FoCUS
• Management: Follow the ACLS algorithm. ^[17]
  • Attempt to restart the LVAD if it is not functioning.
    • Ensure all LVAD connections are secure.
    • Ensure an adequate power source is connected.
    • Consider replacing the LVAD controller.
  • Perform chest compressions for any of the following: ^[17]
    • Non-functioning LVAD
    • MAP ≤ 50 mm Hg ^[17]
    • End-tidal CO₂ ≤ 20 mm Hg

Other complications

See “Complications of MCS devices.”