Indications for Ventricular Assist Devices (VAD) (Modified from Circulation, 2009) [MEDLINE]

• Body Surface Area >1.5 m2
• Continued Need for Intravenous Inotropic Therapy Limited by Symptomatic Hypotension, Worsening Renal Function, or Worsening Pulmonary Congestion
• Failure to Respond to Optimal Medical Management for >60 of the Last 90 Days
• Life Expectancy <2 yrs
• Left Ventricular (LV) Ejection Fraction ≤25%
• New York Heart Association (NYHA) Functional Class IV Symptoms
• Progressive Cardiac Cachexia
• Recurrent Symptomatic Sustained Ventricular Tachycardia or Ventricular Fibrillation in the Presence of an Untreatable Arrhythmogenic Substrate
• Refractory Cardiogenic Shock or Cardiac Failure: without potential for recovery
  • Either Ischemic/Dilated Cardiomyopathy or Restrictive/Hypertrophic Cardiomyopathy
    • For Ischemic/Dilated Cardiomyopathy: ejection fraction <25% or cardiac index <2.2 L/min per m2
    • Data Suggest that the 1-Year Survival for LVAD Implantation in Ischemic/Dilated Cardiomyopathy vs Restrictive/Hypertrophic Cardiomyopathy are Comprarable
• Threshold Levels: these are not required for bridge to transplantation, but are considered for later heart transplantation
  • Peak Oxygen Consumption ≤12 mL/kg/min with Cardiac Limitation
  • 6-Minute Walk Distance <300 m (see 6-Minute Walk Test, [[6-Minute Walk Test]])
• Unmanageable Angina Unresponsive to Therapy or Revascularization

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Clinical Scenarios in Which Ventricular Assist Devices (VAD) May Be Used

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Relative Contraindications to Ventricular Assist Device (VAD) (Modified from Circulation, 2009) [MEDLINE]

• Age >65 y/o: unless minimal or no other clinical risk factors
• Chronic Kidney Disease (CKD) with Cr >3 mg/dL (see Chronic Kidney Disease, [[Chronic Kidney Disease]])
• Malnutrition (BMI <21 kg/m2 in Males/BMI <19 kg/m2 in Females)
• Mechanical Ventilation (see Mechanical Ventilation-General, [[Mechanical Ventilation-General]])
• Morbid Obesity (BMI >40 kg/m2) (see Obesity, [[Obesity]])
• Moderate-Severe Aortic Insufficiency (see Aortic Insufficiency, [[Aortic Insufficiency]])
• Severe Mitral Stenosis (see Mitral Stenosis, [[Mitral Stenosis]])
• Uncorrectable Mitral Regurgitation (see Mitral Regurgitation, [[Mitral Regurgitation]])

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Contraindications to Ventricular Assist Device (VAD) (Modified from Circulation, 2009) [MEDLINE]

• Active Systemic Infection/Major Chronic Risk for Infection
• Abdominal Aortic Aneurysm (AAA) ≥5 cm (see Abdominal Aortic Aneurysm, [[Abdominal Aortic Aneurysm]])
• Biventricular Heart Failure in Patient >65 y/o
• Contraindication to Anticoagulation
• Fixed Portal Hypertension
• Fixed Pulmonary Hypertension
• Heparin-Induced Thrombocytopenia (HIT) (see Heparin-Induced Thrombocytopenia, [[Heparin-Induced Thrombocytopenia]])
• High Surgical Risk for Successful Implantation
• Impending Hepatic Failure
• Impending Renal Failure
• Multiorgan Failure
• Neurologic Deficits Which May Impair the Ability to Manage the Device
• Potentially Reversible Cause of Heart Failure
• Recent/Evolving Stroke (see Ischemic Cerebrovascular Accident, [[Ischemic Cerebrovascular Accident]])
• Severe Pulmonary Disease (FEV1 <1L)
• Significant Psychiatric Illness or Lack of Social Support Which May Impair the Ability to Manage Device
• Terminal Condition
  • Cirrhosis/End-Stage Liver Disease (see Cirrhosis, [[Cirrhosis]])
  • Metastatic Cancer

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Physiology

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Technique

Anticoagulation/Anti-Platelet Agents

• Required for LVAD

Ventricular Assist Device (VAD) Parameters

Device Parameters to Set

• Pump Speed (RPM) is the Only Parameter Set by the Physician
  • For HeartMate II Device, Pump Speed Can Be Set Between 6k-15k RPM to Achieve Blood Flow Up to 10 L/min
  • Other Variables (Below) Which are Displayed by the Machine (Including Power, Flow, and Pulsatility) are Dependent on the Patient’s Underlying Physiology

Device Parameters to Monitor

• Pump Power: direct measurement of the number of watts required by the device to pump blood at the set RPM
  • Pump Power Generally Correlates Well with Blood Flow (with Some Exceptions, as Noted Here)
  • Etiology of Increased Pump Power Required
    • Pump Thrombosis
• Blood Flow: calculated based on the measured pump power and the the set pump speed
  • Blood Flow Depends on the Pump Speed and the Pressure Differential (Head Pressure) Across the Pump
    • At a Given Pump Speed, the Difference Between Mean Arterial Pressure (Afterload) and the Left Ventricular Chamber Pressure (Preload) Correlates Inversely with Blood Flow
      • Although the Greatest Determinant of Pump Differential Pressure is the LV Intracavitary Pressure, Increased Vascular Tone (Afterload) Can Also Decrease Blood Flow
    • During Exercise
      • Systemic Vascular Resistance (Afterload) Decreases, Resulting in a Decreased Pump Differential During Systole
      • Blood Flow Will Therefore, Increase, Even at a Given Pump Speed
  • Calculated Blood Flow May Underestimate Cardiac Output, Since it Does not Account for Blood Ejected by the Native LV Across the Aortic Valve
  • Device-Specific Considerations
    • For HeartMate II Devices, Calculated Flows are Inaccurate with Pump Speeds ≤8000 RPM
    • For HeartWare Devices, Blood Viscosity Significantly Impacts Flow: consequently, hematocrit is integrated into its algorithm
  • Etiology of Decreased Blood Flow
    • Arrhythmia
      • Address by Treating Arrhythmia
    • Hypovolemia/Hemorrhage (see Hypovolemic Shock, [[Hypovolemic Shock]] and Hemorrhagic Shock, [[Hemorrhagic Shock]])
      • Address with Intravenous Fluids/Packed Red Blood Cells
  • Etiology of Increased Blood Flow
    • Vasodilation
      • Address by Decreasing Vasodilator Dosage
    • Sepsis (see Sepsis, [[Sepsis]])
      • Address by Treating Sepsis with Vasopressors, etc
• Pulsatility Index (PI): mathematical difference between the maximal and minimal flows divided by the average flow per cardiac cycle
  • Normal PI: 3.5-5.5
  • PI is Largely Dependent on the Intrinsic LV Performance and Preload
  • Device-Specific Considerations
    • When the HeartMate II Detects a Abrupt Decrease in PI, it Automatically Decreases the Pump Speed to the Lower Limit Pump Speed Set by the Operator (Which Serves to Ameliorate the Suction Event)
    • HeartWare Device Does Not Mathematically Calculate the Pulstatility (But Flow and Pulsatility is Shown Graphically on the Display
  • Etiology of Decreased PI
    • Decreased LV Contractility
      • Address by Adding Inotropic Support
    • Excessive Pump Speed
      • Address by Decreasing Pump Speed
    • Hypovolemia/Hemorrhage (see Hypovolemic Shock, [[Hypovolemic Shock]] and Hemorrhagic Shock, [[Hemorrhagic Shock]])
      • Address with Intravenous Fluids/Packed Red Blood Cellls
    • Outflow Cannula Obstruction
  • Etiology of Increased PI
    • Percutaneous Lead Damage
      • Assess VAD Components
    • Recovery of Left Ventricular Function

Other Problems

• Suction Event: defined as the VAD pulling out more blood than the LV can supply
  • Clinical Features of Suction Event
    • Collapse of Ventricular Cavity Around Device Inflow
    • Shift of the Intraventricular Septum and Partial Obstruction of the LV Outflow Cannula
    • Contact Between the Cannula and the LV Wall Can Trigger Ventricular Tachycardia
    • Sudden Decrease in PI (Since Pump Flow Decreases)
      • May Be Associated with Low Flows, Low PI, or Alarms
  • Etiology of Suction Event
    • Ventricular Tachycardia (VT): due to a decrease in LV preload
      • Address by Treating Arrhythmia
    • Excessive Unloading of Ventricle by the VAD
      • Lower Pump Speed
    • Hypovolemia (see Hypovolemic Shock, [[Hypovolemic Shock]]): most common etiology
      • Address with Intravenous Fluids

Physical Exam Findings

• Absence of Peripheral Pulses: due to continuous flow VAD

Blood Pressure Management

General Comments

• MAP is Usually Maintained at 70-90 mm Hg
  • Assuming Adequate Intracavitary Volume, Increasing Pump Speed Will Increase Mean Arterial Pressure and Diastolic Blood Pressure (without Changing the Systolic Blood Pressure)
  • Excessive Blood Pressure is Associated with Neurologic Events, Hemorrhage, and Decreased Blood Flow

Blood Pressure Measurement

• Non-Invasive Blood Pressure Cuff
  • Unreliable and Values Usually Underestimate the Mean Arterial Pressure (MAP) and Systolic Blood Pressure (SBP)
  • Occlusion Pressures Obtained by Doppler at the Brachial Artery Usually Correlate Well with Invasive Arterial Blood Pressure Measurements
    • This Measurement Reflects the Mean Arterial Pressure, But Not the Systolic Blood Pressure
• Arterial Line (see Arterial Line, [[Arterial Line]])
  • Usually Required in the Immediate Post-Operative Period, During Shock, and to Assesss Device Function

Pulse Oximetry (see Pulse Oximetry, [[Pulse Oximetry]])

• Disadvantages
  • Pulse Oximetry May Be Unreliable in the Setting of Minimal/Absent Pulse

Echocargiogram (see Echocargiogram, [[Echocargiogram]])

• Clinical Utility
  • Echocardiogram May Be Used to Assess Septal Position and Chamber Size (Both of Which May Guide Pump Speed Adjustments)
  • Echocardiogram May Be Used to Assess Aortic Valve Opening to Determine the Contribution of Native Cardiac Function to Overall Output

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Adverse Effects/Complications

General Comments

• Complications Requiring Hospitalization are Common with VAD’s
  • Dcereasing Frequency of Complications Occurs within the First 6 mo of Implantation, with Subsequent Stabilization (J Am Coll Cardiol, 2013) [MEDLINE]
  • Most Common Adverse Effects/Complications (J Am Coll Cardiol, 2013) [MEDLINE]
    • Arrhythmia
    • Congestive Heart Failure
    • Hemorrhage
    • Infection
    • Thrombosis

Cardiovascular Adverse Effects/Complications

Left Ventricular Thrombus/Thromboembolic Complications

• Epidemiology: occurs in 10-16% of cases
  • Rate of Pump Thrombosis with HeartMate II Has Recently Been Noted to Increase from 2.2% to 8.4% (NEJM, 2014) [MEDLINE]
    • Median Time from Implantation to Thrombosis Decreased from 18.6 mo to 2.7 mo
    • Pump Thrombosis was Presaged by an Increase in LDH within the Weeks Before Diagnosis
    • Pump Thrombosis was Managed by Either Pump Replacement or Heart Transplantation
    • Mortality Rate Among Patients with Pump Thrombosis Who Did Not Undergo Pump Replacement or Heart Transplantation was 48.2% in the 6 mo After Pump Thrombosis
• Risk Factors for Pump Thrombosis
  • Declining Renal Function
  • Development of Thrombus or Myocardial Infarction Before Device Implantation
  • Large Stature
  • Left Atrial Cannulation
  • Less Severe Ventricular Dysfunction
  • Marked LDH Elevation 1 mo Post-Implantation
  • Post-Implantation Hemorrhage
  • Recent Implantation: risk of thrombosis appears to be highest within the first 6 mo
  • Younger Age
• Diagnosis
  • Echocardiogram (see Echocardiogram, [[Echocardiogram]]): useful to detect pump thrombosis
  • Cardiac CT (see Cardiac Computed Tomography, [[Cardiac Computed Tomography]]): may be more reliable means of detecting pump thrombosis (sensitivity = 85%, specificity = 100%)
• Clinical
  • Evidence of Increased Hemolysis (Manifested by Increased LDH): may be an early harbinger of pump thrombosis
  • Evidence of Increased Pump Power Utilization: may be an early harbinger of pump thrombosis
  • Evidence of Worsened Heart Failure Symptoms
  • Systemic Embolization
• Treatment
  • Heparin Anticoagulation in Anticipation of LVAD Explantation/Reimplantation (see Heparin, [[Heparin]]): commonly used strategy with the lowest mortality rate (around 5%)
  • Lepirudin (XXXX) (see Lepirudin, [[Lepirudin]])
  • Thrombolytics: has been described, but has very high mortality rate (up to 50%)

Right Ventricular Dysfunction After Left Ventricular Assist Device (LVAD) Implantation

• Epidemiology
  • Definition of RV Dysfunction: need for right ventricular support (pharmacologic or mechanical) for >14 days after LVAD implantation
  • RV Dysfunction iOccurs in 20-30% of Patients Receiving LVAD’s (Cardiovasc Surg, 2000) [MEDLINE]
  • RV Dysfunction After Implantation Predicts Poorer LVAD Outcome
• Pre-Operative Risk Factors (Mayo Clin Proc, 2016) [MEDLINE]
  • Anemia (see Anemia, [[Anemia]])
  • Echocardiographic Indicators of Right Ventricular Dysfunction
  • Elevated Filling Pressures
  • Hepatic Dysfunction
  • Renal Dysfunction
  • Requirement for Intra-Aortic Balloon Pump Support (IABP)
• Physiologic Mechanisms of RV Dysfunction After LVAD Placement
  • Altered Interventricular Balance
  • Excessive Right Ventricular Preload
  • Leftward Shift of Intraventricular Septum
  • Perioperative Fluctuations in Pulmonary Vascular Resistance
  • Preoperative RV Dysfunction and Pulmonary Hypertension: preexisting RV dysfunction increases the susceptibility of the RV to further decline after LVAD implantation
  • RV Ischemia: although the RV is generally less susceptible to ischemia than the LV (due to less myocardial mass and a more favorable oxygen supple/demand ratio)
• Considerations: however, since preexisting RV dysfunction can be managed, it is not an absolute contraindication to LVAD implantation

Ventricular Arrhythmias

• Epidemiology
  • Incidence of Arrhythmias is Highest in the First Month After Implantation
• Physiologic Mechanisms
  • Cannula Malposition: may occur months after implantation due to migration of the device associated with change in body weight or development of scar tissue
  • Contact Between the Cannula and the Ventricular Septum During Hypovolemia, RV Failure, or Small Ventricular Size
  • Creation of Reentrant Circuit by Placement of the LVAD Cannula
  • Mechanical Irritation of the Left Ventricle
• Clinical
  • Ventricular Fibrillation (VF) (see Ventricular Fibrillation, [[Ventricular Fibrillation]])
  • Ventricular Tachycardia (VT) (see Ventricular Tachycardia, [[Ventricular Tachycardia]])
• Treatment
  • First, Decrease the LVAD Speed to Allow for Increased Ventricular Filling: this may shift the cannula away from the ventricular wall
  • Treat Hypovolemia with Intravenous Fluids
  • Antiarrhythmics
    • Amiodarone (Cordarone) (see Amiodarone, [[Amiodarone]]): first-line agent
    • β-Blockers (see β-Adrenergic Receptor Antagonists, [[β-Adrenergic Receptor Antagonists]]): first-line agents
    • Mexilitene (XXXX) (see Mexilitene, [[Mexilitene]]): for refractory VT

Gastrointestinal Adverse Effects/Complications

Gastrointestinal Hemorrhage (see Gastrointestinal Hemorrhage, [[Gastrointestinal Hemorrhage]])

• Epidemiology
  • Continuous-Flow LVAD: bleeding rate is 63 per 100 patient-years (ASAIO J, 2010) [MEDLINE]
    • Increased Bleeding Risk May Be Due to Acquired Von Willebrand Syndrome Secondary to Cleavage of Large Von Willebrand Factor Multimers into Smaller Multimers in the Pump: smaller multimers are cleared more readily, leading to lower levels of Von Willebrand factor
  • Pulsatile-Flow LVAD: bleeding rate is 6.8 per 100 patient-years (ASAIO J, 2010) [MEDLINE]
  • Specific Etiologies of Gastrointestinal Hemorrhage
    • Arteriovenous Malformation
    • Gastroesophageal Reflux with Erosions
    • Gastrostromy/Feeding Tube
    • Polyp
• Physiology
  • Anticoagulation
  • Effect of Pump on Von Willebrand Factor: as noted above

Hematologic Adverse Effects/Complications

Hemolysis (see Hemolytic Anemia, [[Hemolytic Anemia]])

• Epidemiology: occurs in most patients (although is generally not severe)

Hemorrhage

• Epidemiology
  • Hemorrhage is the Most Common Complication of VAD Implantation
    • Early Bleeding Requiring Repeat Surgery Occurs in 26% of Cases
  • Most Common Sites of Early Hemorrhage
    • Chest Wall Hemorrhage
    • Gastrointestinal Hemorrhage (see Gastrointestinal Hemorrhage, [[Gastrointestinal Hemorrhage]])
    • Mediastinal Hemorrhage: most common early site of hemorrhage
    • Pleural Space
  • Most Common Sites of Hemorrhage >30 Days After Implantation
    • Epistaxis (see Epistaxis, [[Epistaxis]])
    • Gastrointestinal Hemorrhage (see Gastrointestinal Hemorrhage, [[Gastrointestinal Hemorrhage]])
    • Intracranial Hemorrhage
    • Mediastinal Hemorrhage
    • Pleural Space
• Treatment
  • Use Only Leukoreduced, Irradiated Blood Products in Patients Being Considered for Future Cardiac Transplantation

Thrombocytopenia (see Thrombocytopenia, [[Thrombocytopenia]])

• Epidemiology: occurs in 7% of cases

Infectious Adverse Effects/Complications

Infection (see Sepsis, [[Sepsis]])

• Epidemiology
  • Infection Occurs in 50% of Cases
  • Infection is the Second Most Common Cause of Death (After Heart Failure) in Patients with VAD’s
• Mechanisms
  • Presence of Foreign Body
  • Impairment of T-Cell Function
• Prevention: continuous antimicrobial treatment before/during/after transplantation was associated with fewer relapses compared to a limited course of antibiotics
• Prognosis
  • Infection May Be Fatal
  • However, Infection Does Not Preclude Transplantation

Neurologic Adverse Effects/Complications

Intracranial Hemorrhage

• Epidemiology
  • Risk Factors
    • High LVAD Flow Rates
    • Hypertension (MAP >90 mm Hg)
• Clinical
  • Hemorrhagic Conversion of Ischemic Cerebrovascular Accident (CVA) (see Ischemic Cerebrovascular Accident, [[Ischemic Cerebrovascular Accident]])
  • Intracerebral Hemorrhage (see Intracerebral Hemorrhage, [[Intracerebral Hemorrhage]])
  • Subarachnoid Hemorrhage (SAH) (see Subarachnoid Hemorrhage, [[Subarachnoid Hemorrhage]])
  • Subdural Hematoma (SDH) (see Subdural Hematoma, [[Subdural Hematoma]])

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Prognosis

Risk Factors for Mortality After Ventricular Assist Devices (VAD) Implantation (Modified from Circulation, 2009) [MEDLINE]

• Platelet Count ≤148k: risk score = 7
• Serum Albumin ≤3.3 g/dL: risk score = 5
• INR >1.1: risk score = 4
• Vasodilator Therapy: risk score = 4
• PA Mean ≤25 mm Hg: risk score = 3
• AST >45 IU/mL: risk score = 2
• Hct ≤34%: risk score = 2
• BUN >51 U/dL: risk score = 2
• No Intravenous Inotropes: risk score = 2

Destination Therapy Risk Score

• Low Risk: score 0-8
• Medium-High Risk: score 9-19
• Very High Risk: score >19

Risk Factors for Mortality After Left Ventricular Assist Devices (LVAD) Implantation (J Heart Lung Transplant, 2014) [MEDLINE]

• Older Age
• Female Sex
• Higher BMI
• High BUN and Creatinine
  • Baseline Creatinine Predicts Survival After LVAD
• History of Dialysis
• History of Stroke
• Hypoalbuminemia
• Implantation for Destination Therapy
• Lower Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) Class
• Previous Cardiac Surgery
• Signs of Right-Sided Heart Dysfunction (High Central Venous Pressure, Elevated Bilirubin, Ascites, or Concurrent RVAD)

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References

• Postoperative acute refractory right ventricular failure: incidence, pathogenesis, management and prognosis. Cardiovasc Surg 2000, 8(1):1-9 [MEDLINE]
• REMATCH Trial. Long-term use of a left ventricular assist device for end-stage heart failure. N Engl J Med. 2001;345(20):1435 [MEDLINE]
• Use of a continuous-flow device in patients awaiting heart transplantation. N Engl J Med 2007; 357:885.
• Chronic mechanical circulatory support for inotrope-dependent heart failure patients who are not transplant candidates: results of the INTrEPID Trial. J Am Coll Cardiol 2007; 50:741
• Use of continuous-flow device in patients awaiting heart transplantation.  N Engl J Med  2007;357:885–896 [MEDLINE]
• Advanced heart failure treated with continuous-flow left ventricular assist device. N Engl J Med 2009; 361:2241.
• Extended mechanical circulatory support with a continuous-flow rotary left ventricular assist device. J Am Coll Cardiol 2009; 54:312
• Evaluation for a ventricular assist device: selecting the appropriate candidate.  Circulation 2009;119:2225–2232 [MEDLINE]
• Heartmate II axial-flow left ventricular assist system: management, clinical review and personal experience. J Cardiovasc Med (Hagerstown). 2009 Oct;10(10):765-71. doi: 10.2459/JCM.0b013e32832d495e [MEDLINE]
• Comparative analysis of von Willebrand factor profiles in pulsatile and continuous left ventricular assist device recipients. ASAIO J. 2010;56(5): 441-445 [MEDLINE]
• Right ventricular failure—a continuing problem in patients with left ventricular assist device support.  J Cardiovasc Transl Res 2010;3:604–611 [MEDLINE]
• Management of right ventricular failure in the era of ventricular assist device therapy.  Curr Heart Fail Rep  2011;8:65-71 [MEDLINE]
• Who needs an RVAD in addition to an LVAD?  Cardiol Clin.  2011;29:599–605 [MEDLINE]
• Survival after biventricular assist device implantation: an analysis of the Interagency Registry for Mechanically Assisted Circulatory Support database. J Heart Lung Transplant. 2011 Aug;30(8):862-9. Epub 2011 May 31 [MEDLINE]
• Results of the post-U.S. Food and Drug Administration-approval study with a continuous flow left ventricular assist device as a bridge to heart transplantation: a prospective study using the INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support). J Am Coll Cardiol 2011; 57:1890
• Multicenter evaluation of an intrapericardial left ventricular assist system. J Am Coll Cardiol 2011; 57:1375.
• Use of an intrapericardial, continuous-flow, centrifugal pump in patients awaiting heart transplantation. Circulation 2012; 125:3191.
• Outcomes in advanced heart failure patients with left ventricular assist devices for destination therapy. Circ Heart Fail 2012; 5:241

• Magnitude and time course of changes induced by continuous-flow left ventricular assist device unloading in chronic heart failure: insights into cardiac recovery. J Am Coll Cardiol. 2013;61(19):1985 [MEDLINE]

• Readmissions after implantation of axial ow left ventricular assist device. J Am Coll Cardiol 2013; 61:153–163 [MEDLINE]

• Unexpected abrupt increase in left ventricular assist device thrombosis. N Engl J Med. 2014;370:33–40. doi: 10.1056/NEJMoa1313385. Epub 2013 Nov 27 [MEDLINE]

• Left ventricular assist device management in the ICU. Crit Care Med. 2014 Jan;42(1):158-68. doi: 10.1097/01.ccm.0000435675.91305.76 [MEDLINE]
• Pump thrombosis-A riddle wrapped in a mystery inside an enigma. Ann Cardiothorac Surg. 2014 Sep;3(5):450-71. doi: 10.3978/j.issn.2225-319X.2014.09.10 [MEDLINE]
• A simplified echocardiographic technique for detecting continuous-flow left ventricular assist device malfunction due to pump thrombosis. J Heart Lung Transplant. 2014 Jun;33(6):575-86. doi: 10.1016/j.healun.2014.01.865. Epub 2014 Jan 28 [MEDLINE]
• Sixth INTERMACS annual report: a 10,000-patient database. J Heart Lung Transplant. 2014 Jun;33(6):555-64. Epub 2014 Apr 21 [MEDLINE]
• Current Status of Left Ventricular Assist Device Therapy. Mayo Clin Proc. 2016 Jul;91(7):927-40. doi: 10.1016/j.mayocp.2016.05.002 [MEDLINE]