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Diagnosis and Treatment Strategies of Outflow Graft Obstruction in the Fully Magnetically Levitated Continuous-Flow centrifugal Left Ventricular Assist Device: A Multicenter Case Series

Wert, Leonhard*; Kaufmann, Friedrich*; Solowjowa, Natalia*; Dreysse, Stephan; Zimpfer, Daniel; Falk, Volkmar*,†,§,¶; Potapov, Evgenij V.*; Mulzer, Johanna*

Author Information
doi: 10.1097/MAT.0000000000001213

Abstract

Reports of pump thrombosis are less common for the HeartMate 3 (HM 3, Abbott, IL) than for other commercially available LVAD. However, blood flow obstructions of the inflow and especially of the outflow graft are likely to occur also with this device.1 A correct diagnosis is crucial for optimal treatment to ultimately avoid bail-out by (urgent) heart transplantation (HTx) or unwarranted pump exchange.2 We present six cases of outflow graft obstruction (OGO) other than twist of the outflow graft after 648–1,222 days on support under oral anticoagulation with Coumadin. We present detection principles and discuss treatment strategies.

Case 1

In 2016, a 64-year-old female patient with valvular heart disease underwent HM 3 implantation through left lateral thoracotomy with the outflow graft connected to the descending aorta. Twenty months later, she underwent transcatheter aortic valve implantation due to severe aortic regurgitation. Four weeks later (648 days on support), she presented with multiple low-flow alarms. Transthoracic echocardiography (TTE) showed left ventricular (LV) enlargement (left ventricular end diastolic diameter 56 mm). The computed tomography (CT) scan showed 50% OGO. Percutaneous angiography (PA) showed external cannula compression proximal of the LVAD outflow conduit. Interventional treatment was considered technically not possible. After performing re-thoracotomy in the sixth intercostal space, the bend relief made of a reinforced polytetrafluoroethylene (PTFE) graft was identified and opened, a hyaline thrombus was removed and pump flow returned to normal immediately (Figure 1). Ten days after surgery the patient was transferred to her local hospital. After 488 days of follow-up, she remains asymptomatic and the pump parameters are within a normal range.

Figure 1.
Figure 1.:
Intraoperative view to split polytetrafluoroethylene (PTFE) graft.

Case 2

A 70-year-old female patient with dilated cardiomyopathy (CMP) underwent implantation of a HM 3 through median sternotomy (MS) with the outflow graft connected to the ascending aorta. Nearly 3 years later (1,049 days on support), she reported recurrent low-flow alarms (2.5 L/min), high PI values. A ramp study demonstrated a consistently low flow. A CT scan revealed a filling defect consistent with thrombus material accumulated in the space between the graft and PTFE protector, causing severe OGO (Figure 2). The patient underwent PA (see Video 1a, Supplemental Digital Content 1, http://links.lww.com/ASAIO/A512 and Video 1b, Supplemental Digital Content 2, http://links.lww.com/ASAIO/A513, Figure 3, A and B) and was treated with two Smart Control Stents (C14080MV; 14/80 mm, 7 F). After the intervention, pump flow returned to normal and the patient was discharged home. After 50 days of follow-up, she remains asymptomatic and the pump parameters are within a normal range.

Figure 2.
Figure 2.:
CT scan showing OGO. OGO marked with blue arrow. CT, computed tomography; OGO, outflow graft obstruction.
Figure 3.
Figure 3.:
A: Pre-interventional percutaneous angiography. Outflow graft obstruction marked with blue arrow. B: Post-interventional percutaneous angiography. Former location of outflow graft obstruction marked with blue arrow.

Case 3

A 55-year-old male patient underwent implantation of an HM 3, similar to case 1. After 815 days on support, the patient presented at his local hospital with angina pectoris and dyspnea and was transferred to our institution. The CT scan showed 75% OGO. Left ventricular assist device flow was 5.6 L/min, the pulsatility index was >8. The patient was on oral anticoagulation [target international normalized ratio (INR) 2.5–3.0]. The patient underwent PA and two stents were implanted (Aortic BeGraft Stent, Bentley: 1 × 14/49 mm + 1 × 16/29 mm). Immediately after the intervention, the patient reported relief from clinical symptoms, but LVAD flow did not increase. After 136 days of follow-up, he remains asymptomatic and the pump parameters are within a normal range.

Case 4

A 37-year-old male patient with dilated CMP underwent HM 3 implantation via MS. After 1027 uneventful days on support, the asymptomatic patient was routinely admitted for evaluation for HTx. LVAD log files were completely normal. Surprisingly the CT scan showed significant OGO (minimal cross-sectional area 0.2–0.35 cm2). TTE showed LV enlargement (LV diameter of 66 mm). A subsequently performed PA confirmed the diagnosis, but showed no relevant gradient pressure across the outflow graft, so we opted for a “watchful waiting approach” and listing for HTx, and then discharged the patient. After 3 months of follow-up, all parameters were unchanged.

Case 5

A 67-year-old male patient underwent HM 3 implantation via MS. After 1,222 uneventful days on the support, he presented in a reduced general condition and slightly reduced pump flow from 4.6 to 4.1 L/min. The CT scan showed significant 70% OGO with a minimal cross-sectional area of 0.5 cm2. The treatment was similar to that described in cases 2 and 3. Pump flow increased to normal. After 6 weeks of follow-up all parameters are within a normal range.

Case 6

A 56-year-old female patient with ischemic CMP underwent HM 3 implantation via MS with outflow graft connection to the ascending aorta. After 911 days of stable outpatient condition, she presented with persistent low-flow alarms (pump flow 2.2 L/min, pulsatility index <2.4) in the emergency department with a therapeutic INR of 2.7 under oral anticoagulation and 100 mg/d aspirin antiplatelet therapy. Within 20 minutes, pump flow decreased to 1.4 L/min, the patient had to be defibrillated due to ventricular fibrillation she was intubated and external chest compressions performed. The CT scan showed 50% OGO and cranial CT showed multiple hypodense areas in the infra- and supratentorial region as consequence of an embolic induced ischemic stroke. After diagnostic imaging, a hemodynamic stabilization for a sufficient therapy of the OGO was not possible. Despite emergency treatment, the patient died on the same day.

Discussion

Obstruction of blood flow through the pump is a potentially life-threatening complication in patients treated with a LVAD.3 Nathan et al.4 report about patients with HeartWare or Heartmate II who developed OGO. Outflow graft obstruction is a rare but severe complication whose clinical presentation may be subtle.5 Recently thrombotic impingement between the outflow graft and bend relief in patients supported with HM 3 has resulted in pump exchange6 or high urgency HTx.3

Outflow graft obstruction is usually first detected when low-flow alarms occur7 or when clinical signs, for example, new-onset dyspnea or angina, occur. Therefore, CT scan and PA is recommended to identify and locate the cause of blood flow obstruction,1,7,8 since various treatment options of outflow graft twist exist.7 The incidence is low, in Berlin, five out of 150 patients supported with HM3 and one (case 6) out of 100 in Vienna (Table 1).

Table 1. - Characteristics of the Cases
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
Center Berlin Berlin Berlin Berlin Berlin Vienna
Sex Female Female Male Male Male Female
Age, years 64 70 55 37 67 56
Cardiac pathology Valvular CMP Dilated CMP Ischemic CMP Dilated CMP Dilated CMP Ischemic CMP
Surgical approach LLT, outflow graft connection to descending aorta LLT, outflow graft connection to ascending aorta LLT, outflow graft connection to descending aorta MS, outflow graft connection to ascending aorta MS, outflow graft connection to ascending aorta MS, outflow graft connection to ascending aorta
Days on support 648 1049 815 1027 1222 911
Therapy Rethoracotomy, PTFE graft spliced Two stents via PA Two stents via PA Watchful waiting Two stents via PA
*Therapy of OGO was not possible.
CMP, cardiomyopathy; LLT, left lateral thoracotomy; MS, median sternotomy; OGO, outflow graft obstruction; PA, percutaneous angiography; PTFE, polytetrafluoroethylene.

For OGO, treatment should be initiated in case of a low flow (fixed alarm <2.5 L/min) or related clinical symptoms. In all other cases, close monitoring is mandatory. Outflow graft obstruction discovered incidentally should be evaluated by investigation of the log files of the system parameters or pressure gradient measuring. A reduction of 25% may not be clinically relevant because it results in a remaining 1.52 cm2 cross-section of the OG. However, sudden decrease of pump flow (<1.5 L/min) with catastrophic result (case 6) may occur without previous signs. Unfortunately, the HM 3 does not offer adequate logging capacity. The limited memory of the HM 3 controller is insufficient for patient surveillance. Therefore, intervention—preferably stenting—should be considered in an early stage, even without relevant hemodynamic impairment.

Furthermore, the PTFE material of the outflow graft appears to have an impact on the development of OGO. Leakage of blood components through the outflow graft material which then become trapped in the impermeable PTFE bend relief leads to formation of an extravascular thrombus.6 Alnabelsi et al.6 outline that this thrombotic complication occurs despite therapeutic anticoagulation because of the intrinsic thrombogenicity of the extravascular space; they even recommend abandoning PTFE grafts. As a similar problem has been described for OGO in patients with an HVAD system, we have adapted the implantation technique at our institution and use a shorter (10 cm), longitudinally spliced piece of Gore-Tex graft, thus avoiding compression of the outflow graft by accumulating hyaline substance.2 We believe that a change of the outflow graft, making it non-permeable, or integration of bend relief into the outflow graft, thus circumventing the additional space between the grafts, will prevent extrinsic OGO in patients supported with HM 3.

References

1. Kaufmann F, Krabatsch T. Using medical imaging for the detection of adverse events (“incidents”) during the utilization of left ventricular assist devices in adult patients with advanced heart failure. Expert Rev Med Devices. 2016; 13:463–474
2. Potapov EV, Kaufmann F, Mueller M, Mulzer J, Starck C, Falk V. Avoidance of outflow graft extrinsic compression in polytetrafluoroethylene reinforcements of the bend relief component. J Heart Lung Transplant. 2019; 38:474–475
3. Duero Posada JG, Moayedi Y, Alhussein M, et al. Outflow graft occlusion of the heartmate 3 left ventricular assist device. Circ Heart Fail. 2017; 10:e004275
4. Nathan S, Ghotra AS, Rajagopal K, et al. Left ventricular assist device outflow graft obstruction: A case series. ASAIO J. 2020; 66:657–662
5. Pieri M, Scandroglio AM, Kukucka M, et al. Heart failure after 5 years on LVAD: Diagnosis and treatment of outflow graft obstruction. ASAIO J. 2017; 63:e1–e2
6. Alnabelsi T, Shafii AE, Gurley JC, Dulnuan K, Harris DD II, Guglin M. Left ventricular assist device outflow graft obstruction: A complication specific to polytetrafluoroethylene covering. A word of caution. ASAIO J. 2019; 65:e58–e62
7. Scandroglio AM, Kaufmann F, Pieri M, et al. Diagnosis and treatment algorithm for blood flow obstructions in patients with left ventricular assist device. J Am Coll Cardiol. 2016; 67:2758–2768
8. Grüger T, Kaufmann F, Dreysse S, Falk V, Krabatsch T, Potapov E. Late post-pump blood flow obstruction in a novel left ventricular assist device: The unusual case of a twisted outflow graft. J Thorac Cardiovasc Surg. 2018; 155:e33–e35
Keywords:

left ventricular assist device; HeartMate 3; outflow graft obstruction

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