65. Durable Support – Mechanical Circulatory Support- Clinical Scenarios

Clauden Louis, MD, Daniel Ryan Ziazadeh, MD, Igor Gosev, MD

Concept

  • Identifying LVAD malfunctions, common errors and troubleshooting techniques
  • Post-operative concerns (right heart post procedure, pump pocket infection)

Terms

Bridge to Transplant (BTT): Refers to implantation of a VAD or TAH to support patient until orthotopic heart transplantation

Bridge to Decision (BTD): Refers to implantation of a VAD or TAH to support patient while undergoing work-up for possible transplantation or alternative mechanical circulatory support strategy

Destination Therapy (DT): Refers to implantation of a VAD or TAH as a definitive device for end-stage heart failure.

Durable Support (Long Term MCS)

Ventricular assist devices take over the function of the damaged ventricle in order to re-establish normal hemodynamics and end-organ blood flow. Unloading of the native heart and correcting the underlying cause of myopathy can optimize conditions for cardiac recovery.  While some patients may overcome the initial injury and sequelae of acute cardiogenic shock, those without evidence of meaningful myocardial recovery should be considered for durable support either as bridge to transplantation or destination therapy. While heart transplantation remains the most successful and desirable long-term option, organ scarcity prevents ~50% of patients on the waitlist from receiving an organ. Waitlist mortalities are institution dependent but range from 15-47% at one year. Some patients are also not candidates for transplantation making durable mechanical support devices important in maximizing survival and minimizing morbidity. 

Like short term devices, they can support the right, left or both ventricles. They can be implanted through a full median sternotomy, mini upper hemi-sternotomy, or bilateral thoracotomies. For LV support, an inflow cannula is attached to the LV apex and the outflow cannula is tunneled and anastomosed to the ascending aorta, thereby bypassing the LVOT and the aortic valve. For RV support, the inflow cannula is attached to the RA or RV while the outflow cannula terminates in the pulmonary artery.

Thoratec pVAD/IVAD

The Thoratec pVAD was one of the 1st generation durable support devices available. Similar to its use in acute shock, it is indicated for use as bridge to transplantation (BTT) and bridge to recovery (BTR) and can provide uni or biventricular support. Similarly, the IVAD functions in the same manner of the pVAD, but its smaller size makes it suitable for intracorporeal support. It has also been approved for BTT and BTR. For more information, see above.

Novacor

The Novacor LVAD was another 1st generation pulsatile, intracorporeal device that was designed for durable cardiac support. It was the first VAD to provide more than four years of continuous circulatory support without pump replacement. With over 20 years of clinical use, primary device failure has remained rare with no deaths attributed to its failure. The INTREPID trial studied its feasibility as a device for BTT with a remarkable 78% survival to transplantation, which led to its approval for BTT in 1998. It shares similarities to the original HeartMate I, with an electric, dual pusher plate and pump housing constructed of polyurethane with inflow and outflow grafts containing porcine bioprosthetic valves. It featured the same external drive line system and portable power pack used in current LVADs. The device required systemic anticoagulation to prevent thromboembolism with target INR of 3.0 to 3.5.

HeartMate IITM, Abbott, IL, USA

Axial flow LVAD designed for durable cardiac support. The REMATCH trial was groundbreaking and demonstrated for the first time that a durable device (the pulsatile HeartMate XVE) could have a dramatic survival advantage (53% vs 25%) at one year compared to maximum medical therapy. As technology evolved, the second-generation HeartMate II offered advantages given its smaller, continuous axial flow design. It featured an inflow and outflow cannula without valves and eliminated the reservoir necessary in pulsatile pumps. It was approved for BTT after a study demonstrated that 42% of heart transplant candidates supported via HeartMate II underwent HT within the 6 months of support, with an overall 1-year survival of 68%. In the landmark HEARTMATE II trial, the HeartMate II significantly improved the probability of survival free from stroke and device failure at 2 years as compared with the HeartMate XVE. To date, more HeartMate II’s have been implanted than any other device. 

HeartWare®, Medtronic, MN, USA

Heartware also known as (HVAD) is a continuous flow centrifugal left ventricular assist device. As a small pump it allows for the intrapericardial implantation as well as lesser invasive approaches and particularly suitable for the bride-to-transplant cohort.

Advance BTT Trial was a multi-center (30), 140-patient, prospective trial designed to evaluate the HVAD® System as a bridge to heart transplantation for patients with end-stage heart failure. Endurance DT trial was a prospective, randomized, multi-center, non-inferiority clinical trial to evaluate the use of the HVAD® System in advanced heart failure patients for destination therapeutics.

HeartMate 3TM, Abbott, IL, USA

Centrifugal flow LVAD designed for durable cardiac support. Landmark clinical trial that sought to answer the question of whether a new magnetically levitated centrifugal pump (HM3) was both non-inferior and superior to an axial flow pump (HM II) regarding reoperation for device malfunction or disabling stroke at six months after implantation. Previous trials including REMATCH and HEARTMATE II demonstrated that in patients with advanced heart failure refractory to medical management, left ventricular assist device (LVAD) placement was effective in providing temporary support as a bridge to heart transplantation and improved survival and quality of life in patients who were not eligible for transplantation (destination therapy).

Each subsequent iteration of LVAD technology has improved, beginning with first generation axial flow pump to the second-generation centrifugal flow pump, which lead to fewer mechanical failures and strokes. However, the second generation was particularly susceptible to pump thrombosis that often necessitate emergent reoperation. The HM3 improved on the first axial flow design by including a magnetically levitate pump with wider blood flow channels and asynchronous pulsatility. The MOMENTUM 3 final analysis at two years demonstrated a 14.6% absolute reduction in pump thrombosis rates in HM3 vs HM II, which coincided with a 15.4% absolute reduction in reoperation rates for device malfunction. The study met its primary endpoint of 12% absolute increase in patients implanted with HM3 who were alive and free of disabling stroke or reoperation to replace or remove a malfunctioning device at 2 years.

Chief Complaint

“A 55-year-old male with severe non-ischemic cardiomyopathy (NICM) and end stage systolic and diastolic congestive heart failure presents to the heart failure clinic with worsening symptoms and is found to have NYHA Class 4 symptoms and Stage D failure. After being presented in multidisciplinary heart failure conference, he is planned for LVAD implantation as destination therapy for INTERMACS Profile 4. Discuss your pre-operative workup.” 

Evaluation of patients for destination therapy VAD therapy should include a complete and systematic workup equivalent to evaluation for cardiac transplantation. This workup includes:

  • Cardiac Catheterization (LHC + RHC) depending on presence of previous imaging and renal function
  • Echo Complete TTE or TEE if imaging limited
  • CT Chest – Non-contrast
  • CTA Coronary Protocol with 3D Reconstruction if greater than 6 months from prior CABG
  • Draw surveillance blood cultures, obtain MRSA swab up to 72 hours pre-op
    • UA with Reflex obtained only in symptomatic patients
  • ID consultation should be obtained for any patient currently on antibiotics
  • Remove and replace old central lines to minimize line related infections
  • Operative notes from prior Cardiac Surgery should be obtained and reviewed
  • Psychosocial evaluation is necessary whether for bridge-to-transplant or destination therapy

Medication Guideline:

  • Hold SQ heparin products 48 hours pre-implant;
  • Hold IV anticoagulation drips 6 hours pre-implant
  • Consider stopping Amiodarone if clinically indicated
  • Primary sternotomy INR < 2.0 / Redo stereotomy INR < 1.5
  • Anti-platelet
    • Stop clopidogrel (Plavix) 5 days priors to surgery
    • Stop ticagrelor (Brilinta) 7 days prior to surgery
    • Bridging agents to be determined on case by case basis
  • Hold oral heart failure agents 72 hours preoperatively:
    • ACEI/ARBs cause vasoplegia intraoperatively
    • Hold long acting beta blockers (Carvedilol/Bisoprolol/Toprol XL)

Operative Steps

Describe the operative procedure for LVAD implantation:

The patient is brought in the operating room and placed in supine position.  He is placed under general anesthesia with care to monitor very closely hemodynamics. The patient is prepped and draped in the appropriate fashion for open heart surgery although it is important to avoid a belly button towel.  Appropriate invasive monitoring lines are placed including arterial line, PA catheter and a TEE probe.   

A standard sternotomy incision is performed. Alternatively, for bilateral minimally invasive thoracotomy (left 5th interspace at the inframammary crease and right 2nd parasternal interspace).  The retractor placed, pericardium opened, stay sutures placed. Full dose IV heparin is given to the patient to maintain an ACT of greater than 480 seconds.  Standard aorto-right atrial cannulation is performed, and cardiopulmonary bypass is initiated. Normothermia is maintained and cardioplegic arrest is avoided.

A circular ventriculotomy is made in the left ventricular apex.  The LV is inspected for thrombus. Obstructing trabeculations removed and sewing ring secured to the left ventricle with interrupted pledgeted sutures (using the core then saw technique).  (Alternatively, one can saw then core.)  Also, the sutures can be placed in the LV apex prior to making the ventriculotomy.  The outflow graft is connected to the LVAD and the anti-rotation clip is placed to lock the graft from rotating.  The pump is then connected to the sewing ring and locked in place.  The bend relief is then secured in place and the outflow graft inspected for twisting.

The driveline is then tunneled to the premarked location and connected to the controller.  The outflow graft is measured and cut to the appropriate length with a 60-degree bevel.  A partially occluding clamp is placed on the right side of the ascending aorta and longitudinal aortotomy performed.  The outflow graft is then anastomosed to the aorta with prolene suture.  The graft is clamped, the aorta is unclamped and the graft deaired typically by sticking it multiple times with a small (24-26g) needle.

The patient is placed in steep Trendelenburg position and aggressively de-aired with a venting needle in the outflow graft. Flow is gradually increased on the LVAD and weaned the patient off bypass successfully on the first attempt without problems.  Right ventricular function is assessed.  Post-implant evaluation by TEE evaluates for PFO and septum midline positioning with the LVAD at appropriate RPM.  

Protamine is started. The bypass cannulas removed. Hemostasis acquired.  Chest tubes placed and multiple layers of suture in the skin and liquid adhesive applied. The driveline exit site closed with suture and then anchored with prolene suture.  The driveline exit site was covered with dry gauze and occlusive dressing.

“What is your anticoagulation strategy for Continuous Flow LVADs post operatively?”

  • The goal is to prevent thromboembolism and minimize bleeding. Start heparin drip when bleeding <50 cc/hour and after the chest has been closed.  Our institution favors starting without a bolus and at a reduced dose (~10u/kg/hr).  Most of these patients have some level of end organ dysfunction and the initial PTTs can be quite high. 
  • Target INR should be between 2-3 once bleeding is no longer an immediate postoperative concern. Oral anticoagulation with VKA antagonist (Warfarin) is started.
  • Plavix can be restarted 48 hours post implant for patients with existing stent
  • Compared to previous pump devices, HM 3 LVAD has shown to be more resistant to pump thrombosis and tolerate less strict anticoagulation thus a standardized regimen does not exist currently

“What is your strategy for removing tubes and wires post operatively?”

  • Pleural and mediastinal tubes can be pulled while on heparin or warfarin
  • Temporary pacing wires should be pulled when INR<1.9
    • If on heparin, pause the heparin gtt for 2 hours immediately before and after wire removal
  • Some institutions do not routinely use epicardial pacing wires after LVAD placement.

Index scenario (additional information)

What if during your preoperative workup, the patient’s echocardiography reveals moderate to severe aortic valvular insufficiency.

Valvular regurgitation in the setting of LVAD placement poses a problem as this physiology compromises LVAD efficiency. In the setting of aortic regurgitation, the LVAD recirculates regurgitant blood decreasing cardiac output. Patients with aortic insufficiency experience a reduced survival versus patients without as noted by Topkara et al 2018. Consensus reports favor concurrent repair/replacement of aortic valve for aortic insufficiency greater than mild. Severe mitral and/or tricuspid regurgitation is a matter of debate although some find it reasonable on case by case bases dependent on patient risk factors and implantation status of destination versus bridge therapeutics.

Alternative Scenarios

Following uneventful LVAD placement, the patient was placed in steep Trendelenburg position and aggressively de-aired with a venting needle in the outflow graft. You gradually increase the flow on the LVAD and attempt to wean the patient off bypass. You notice there is an increase in right sided filling pressures, and you are unable to successfully wean from bypass. The anesthesia monitor shows the following values: CVP 24, PCWP 14, PA 40/17, and SvO2 45%. What is the next step in your management?

There is significant concern for RV failure. Start by evaluating the right ventricular function on post-implant TEE. Check for PFO and confirm the septum is midline.  It is estimated that RV failure occurs in 20-50% of patients after LVAD implantation, and it remains a common cause of instability, morbidity and mortality. Preoperative risk factors for post-LVAD RV failure include female gender, non-ischemic cardiomyopathy, and the need for preoperative support with mechanical ventilation, intra-aortic balloon pump, or temporary mechanical circulatory support.

Of note, patients without pulmonary hypertension are more likely to develop RV failure as these patients have inadequate RV contractility to overcome an acute increase in pulmonary vascular resistance (PVR).  Strategies for dealing with post-LVAD RV issues include pulmonary vasodilators (inhaled nitric oxide or veletri) and/or the addition of a lusitrope (milrinone).  Finally, if the patient remains in significant RV failure, mechanical circulatory support options (ECMO vs. RVAD) can be employed. 

Index scenario (additional information)

After an uneventful post-operative recovery, the patient is seen in clinic six weeks later where he is found to have blood pressures with MAP 120-130 mmHg. He does not have significant peripheral edema or LVAD alarms or concerns. How would you optimize his hemodynamics?

The goal of LVAD therapy is to utilize the pump to unload the left ventricle, by setting the speed such that it will provide a pulse pressure of 10-20mmHg. Pharmacologic therapy is used to decrease afterload and blood pressure, which optimizes pump flow. Non-invasive blood pressure cuffs alone are inaccurate as there is no pulsatile flow. A doppler probe should be used to accurately obtain blood pressure measurements.

Hypertension:

MAP should be between 70-80 mmHg with Doppler assistance. MAP <90mmHg may be acceptable based on the clinical situation. When a peripheral pulse is palpable, the target systolic BP is ~120 mmHg. It is reasonable to decrease systolic targets to 110 mmHg in asymptomatic patients.

Index scenario (additional information)

Patient has done well with his left ventricular assist device (LVAD) now s/p 12 months since implantation. He currently takes ASA 325mg and Warfarin with INR goal between 2-3. He now presents with a 5-day history of worsening malaise and fatigue. He describes recurrent bowel movements which have progressively darkened in color. His examination is concerning for sinus tachycardia and blood pressure with MAP 60 with intermittent suction events. His hematocrit is now 18. What is the concern and next step in the management of this patient?

The patient’s presentation is concerning for a gastrointestinal bleed, which is a common complication after LVAD implantation. The bleeding is thought to be caused by altered blood flow patterns from continuous flow. Loss of pulsatile perfusion is implicated in intestinal hyperperfusion, distention of the submucosal venous plexus, and acquired von Willebrand factor deficiencies.

Evaluation of the patient should begin with a full history and physical exam. Evaluate and auscultate the LVAD to check for any suction or PI events. Obtain a CMP, CBC, and PT/INR to ensure the patient’s anticoagulation is not supratheraptuic. In the setting of life-threatening GI bleed, anticoagulation should be held and the patient should be started on IV Protonix. Gastroenterology should be consulted for endoscopic evaluation. Due to alterations in blood flow, patients will often have evidence of angiodysplasia and arteriovenous malformations. After correcting any underlying coagulopathy, a significant portion of LVAD patient with GI bleed will self-resolve. Should these patients remain refractory, an upper and lower endoscopy should be performed to cauterize or clip any active bleed.

If patients are intolerant to anticoagulation secondary to recurrent life-threatening GI bleeds, then antiplatelet and anticoagulation may need to be held indefinitely. A risk/benefit discussion should be had given increase risk for pump thrombosis and exchange. New data has shown that cessation of anticoagulation for bleeding in HM3 is safe.

Reversal for Elevated INR:

  • FFP for INR reversal for urgent procedures
  • INR trend for elective procedures
  • Factor 4 prothrombin (K-centra) for life threatening bleeding per attending and institution

GIB Readmit:

For patients with recurrent GIB concerning for AVM, more aggressive therapeutics can be added for each occurrence. Danazol has been shown to decrease GI bleed rehospitalization and pRBC transfusion

  • 1st GIB: Resume warfarin and anti-platelet agent once H/H is stable following conservative therapy
  • 2nd GIB: Start danazol low dose twice daily in addition to warfarin and anti-platelet agent
  • 3rd GIB: Increase danazol to medium dosing twice daily, hold anti-platelet agents and consider lowering INR goal.

Index scenario (additional information)

After holding anticoagulation for 3 months, your patient returns to clinic without recurrent GI bleeding. On routine physical, your patient appears to be slightly jaundiced. Routine labs demonstrate elevated indirect bilirubin, mildly elevated LDH, and anemia. What is the likely cause of your patient’s findings?

Hemolysis is a common complication of LVAD therapy and is associated with device malfunction. In severe cases, thrombosis can occur, and the device may need to be exchanged.  The etiology of hemolysis is unclear but thought to be a result of destruction of red blood cells secondary to mechanical shear stress, flow acceleration, and abnormal blood device interactions.

INTERMACS further stratifies hemolysis as major and minor.

  • Minor Hemolysis:  A serum lactate dehydrogenase (LDH) level greater than 2.5x normal after the first 72 hours post-implant in the absence of clinical symptoms or findings of hemolysis or abnormal pump function.
  • Major Hemolysis:  A serum LDH level greater than 2.5x normal after the first 72 hours post-implant and associated with clinical symptoms or findings of hemolysis or abnormal pump function.
  • Hemoglobinuria
  • Anemia
  • Hyperbilirubinemia (total bilirubin > 2)
  • Pump malfunction and/or abnormal pump parameters

Guideline:

  • LDH should be monitored monthly
  • For patients with minor hemolysis, defined as a LDH >2.5x normal:
  • Optimize pump speed and blood pressure
  • Evaluate patient volume status, consider decrease diuretics
  • Review of INRs for time in therapeutic range
  • If above criteria controlled, consider INR goal adjustment to 3-3.5, continue current anti-platelet dosing
  • For patients with major hemolysis or new onset heart failure symptoms obtain:
    • LDH, CBC, INR, CMP
    • VAD interrogation for alarms, PI events, power spikes
    • TTE or TEE with RAMP to check pump function
    • Consider CTA with 3d reconstruction if ECHO is unremarkable
    • Ensure optimal anticoagulation
  • CXR for evidence of pulmonary edema.
  • Blood cultures to rule out bacteremia

  Treatment Guideline

  • Optimize fluid status based on patient exam and renal function
  • Optimize pump speed with RAMP ECHO and/or right heart catheterization
  • If patient have findings of hemolysis in the presence of therapeutic INR, add unfractionated Heparin
    • Continue warfarin if INR <3.
    • When aPTT in therapeutic range, check Unfractionated Heparin and anti-Xa level. 
    • Monitor patients for internal bleeding while on high dose anticoagulation.
  • If hemodynamically unstable, utilize inotropes as required to maintain CI, organ perfusion

Treatment Options for Unresolved Hemolysis

  1. Consideration for UNOS listing upgrade and urgent transplantation
  2. Pump exchange if patient is a surgical candidate
  3. Pump explant for patients with positive LVAD wean study
  4. Consider thrombolytics in patients who are not surgical candidates

Potential Questions / Alternative Scenarios

Your patient is now 3 years s/p implantation and had been doing relatively well. He presents after 1 week of dyspnea on exertion, dark color urine over the past 48 hours. VAD interrogation demonstrates decreased pump flow and increased pump power over the last 72 hours. What is your concern and the next step in management?

The patient is presenting with signs and symptoms concerning for pump thrombosis. The incidence of continuous axial flow LVAD pump thrombosis during the first year after implantation in the current era is 5-12%.  Patients may present with pronounced heart failure symptoms such as increased shortness of breath, ascites, or extremity edema. Pump alarms may or may not sound.

The patient should be admitted to the hospital and lactate dehydrogenase levels, INR, ECHO, and CTA Chest should be obtained. The VAD coordinator should be called and the device should be thoroughly interrogated. An ECHO can support the diagnosis of pump thrombosis with findings of a dilated left ventricle, opening of the aortic valve with every heartbeat, and worsening mitral regurgitation. A pulsatile waveform would indicate increased ventricular ejection and decreased ventricular decompression by the pump. A right heart catheterization can also reveal elevated filling pressures and a low cardiac index.  CTA would show no contrast opacifying in the outflow graft and retrograde filling of the LVAD from the ascending aorta.

Medical therapy should be tailored to the patient’s heart failure symptoms with appropriate inotropes, diuresis, and oxygen.  It is important to arrest propagation of the clot with heparin gtt and to lyse it via intraventricular thrombolysis.  With timely diagnosis and adequate treatment most cases will resolve, but pump exchange must be considered if initial measures fail.

Several etiologies exist as to the cause such as pump position, pump migration and subtherapeutic anticoagulation. Bark pigment in the urine is an early sign of hemolysis and/or pump thrombosis.

LVAD thrombosis requires aggressive treatment and ultimately may require pump exchange. Transplant list priority is increased while with LVAD thrombosis. Is treated aggressively with medical therapy including IV antiplatelet therapy plus heparin or bivalirudin prior to consideration of LVAD exchange.

Adapted from:

Goldstein DJ, John R, Salerno C et al. Algorithm for the diagnosis and management of suspected pump thrombus. J Heart Lung Transplant 2013;32(7):667-670.

Potential questions/alternative scenarios

Workup confirms pump thrombosis and the patient is scheduled to undergo pump exchange. Immediately after redo-sternotomy, massive bleeding is noted at the xiphoid. What are the best next steps in management?

There is significant concern for outflow graft compromise. Immediately pack the chest, turn the device off, maximize inotropic support, maximize volume infusion, emergently establish femoral cardiopulmonary bypass, insert pump suckers, cool the patient to 18C, and initiate circulatory arrest.

Entrance into the outflow graft is a feared and dramatic complication of re-operation for LVAD explant. A rapid institution of a defined series of events will help to prevent death from exsanguination. Axial flow pumps do not have valves, therefore turning the device off allows for retrograde flow through the device. Ejection of the native heart will create forward flow through the aorta, but also retrograde flow through the outflow graft. A concerted effort by anesthesia to improve forward flow (by maximizing inotropes and administering volume) will improve mean arterial pressure but will also impose a fair amount of afterload on the pulmonary circulation by acutely increasing LVEDP. Turning the device off and administering inotropes is the first step, but only a temporary solution. Since the graft is presumably adherent to the chest wall, packing the chest and binding it together with perforating towel clips may reduce the blood loss. Groin bypass is rapidly established, and the patient cooled towards 18C. The safest method is to cool for a full twenty minutes and arrest the circulation. The outflow graft must be identified and clamped on both sides of the graftotomy, since there is bidirectional flow. If the sternum is almost completely divided there is inclination to go after the graft without circulatory arrest. The problem with this intervention is the possibility of widening the aperture and exsanguinations before definitive control is obtained. A short period of circulatory arrest is generally well tolerated, and the patient may be rewarmed after control of the graft is obtained. The downside is the increased likelihood of pulmonary congestion from the acute increase in LVEDP.

Suggested readings

  1. Bhatia, A, Juricek, C, Uriel et al: Increased Risk of Bleeding in Left Ventricular Assist Device Patients Treated with Enoxaprin as Bridge to Therapeutic INR. Asaio J. 2017 May.
  2. Jennings, Shullo et al: Assessing Anticoagulation Practice Patterns in Patients on Durable MCS Devices: An International Survey. Asaio J. 2016 Jan-Feb;62(1): 28-32.
  3. Saeed, Jorde et al: Antiplatelet Therapy and Adverse Hematologic Events during HMII support. CircHeartFailure 2016;9.
  4. Momentum 3 Medical Management Working Group Recommendations. Chairs: Uriel, Horstmanshof, Naka. 1-20-2017.
  5. HeartMate II Left Ventricular Assist System Instructions for Use: Thoratec Corporation, 2014.
  6. HeartMate III Left Ventricular Assist System Instructions for Use: Thoratec Corporation, 2015
  7. HeartWare Left Ventricular Assist System Instructions for Use: HeartWare Corporation, 2014.
  8. Bennett MK, Adatya S. Blood pressure management in mechanical circulatory support. J Thorac Dis 2015;7(12):2125-2128.
  9. Nir Uriel (University of Chicago), Douglas Horstmanshof (Integris Baptist Medical Center), Yoshifumi Naka (Columbia University). MOMENTUM 3 Medical Management Working Group Recommendations 1/20/2017]
  10. Maltais S, Kilic A, Nathan S, Keebler M, Emani S, Ransom J et al. Prevention of HeartMate II pump thrombosis through clinical management: The prevent multi-center study. J Heart Lung Transplant. 2016.
  11. Maltais S, Kilic A, et al. PREVENtion of HeartMate II Pump Thrombosis Through Clinical Management: The PREVENT multi-center study. J Heart Lung Transplant, 36 (2017) pp. 1-12.
  12. Intermacs Manual of Operations, Version 5.0. Adverse event definitions 2/4/16
  13. Katz J, Jensen B, Kirklin J, et al. A multicenter analysis of clinical hemolysis in patients supported with durable, long-term left ventricular assist device therapy. J Heart Lung Transplant, 34 (2015) pp. 701-709.  
  14. Kirklin JK, Naftel DC, Kormos RL, et al. Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) analysis of pump thrombosis in the HeartMate II left ventricular assist device. J Heart Lung Transplant 33 (2014), pp, 12-22.
  15. Whitson B, Eckman P, et al. Hemolysis, Pump Thrombus, and Neurologic Events in CFLVAD Recipients.  Ann Thorac Surgery 97 (2014), pp. 2097–103.
  16. Feldman D, et al.   The 2013 International Society for Heart and Lung Transplantation Guidelines for mechanical Circulatory Support: Executive Summary. J Heart Lung Transplant, 32 (2013), pp. 157-187.
  17. Goldstein DJ, John R, Salerno C et al. Algorithm for the diagnosis and management of suspected pump thrombus. J Heart Lung Transplant. 2013; 32:667-70.
  18. Schroder J, Milano C. Is is time to get more aggressive with aortic valve insufficiency during LVAD implantation? JACC 2018; 6(11):961-913
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