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Case Reports

Late HeartMate 3 Thrombosis

Pienta, Michael J.*; Knott, Kevin*; Bitar, Abbas; Haft, Jonathan W.*

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doi: 10.1097/MAT.0000000000001479
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Abstract

The HeartMate 3 (HM3) ventricular assist device (Abbott Laboratories, Abbott Park, IL) is a fully magnetically levitated centrifugal continuous flow pump, which has been designed with no mechanical bearings, wide blood-flow clearance, and an intrinsic artificial pulse to reduce the risk of thrombosis. Prior studies have demonstrated no pump thrombosis at 6 months and a 1.4% incidence of suspected or confirmed pump thrombosis at 2 years.1,2 Outflow graft occlusion via twist or compression has been the predominant mechanism, along with ingestion of ventricular thrombus.3–5 Here, we report on a patient with late HM3 pump thrombosis unrelated to outflow graft twist or clot ingestion.

Case Report

A 22-year-old man with end-stage heart failure due to left ventricular noncompaction cardiomyopathy underwent HM3 implantation via median sternotomy in December 2017 as bridge to transplant. He was discharged on postoperative day 15 after a relatively unremarkable postoperative course with a therapeutic international normalized ratio (INR) and aspirin 325 mg daily. Over the first 2 years after implantation, the patient was admitted to the hospital several times for volume overload as well as a methicillin-sensitive Staphylococcus aureus driveline infection, which resolved with IV cefazolin. The patient was removed from the transplant list due to medication noncompliance and obesity.

At 27 months after implantation, the patient noted low-flow alarms, which were initially self-managed with increased oral fluid intake. The patient presented for evaluation after 1 week of symptoms with persistent low-flow alarms, shortness of breath, and 15 pound weight gain. On admission, the patient was hypotensive with lactate elevated to 2.7 mmol/L. Lactate dehydrogenase (LDH) was 356 IU/L, within the patient’s previous baseline range, and INR was 4.9. In the year before presentation, INR ranged from 1.4 to 7.9 (Figure 1), with time in therapeutic range 58.1%. Echocardiography demonstrated that the left ventricle was full with regular opening of the aortic valve. Chest radiograph demonstrated appropriate positioning of the device. The patient had no hematuria or jaundice. Review of the device log demonstrated an acute drop in calculated average flow from 5 L/min to less than 3 L/min at 6,000 RPM and decrease in motor power from 5.0 watts to 4.1 watts approximately 1 week before presentation, with stable pulsatility index (Figure 2). CT scan was concerning for possible thrombus in the proximal outflow cannula, with no evidence of graft kinking or twisting (Figure 3).

F1
Figure 1.:
INR range 1 year before pump thrombosis admission. INR, international normalized ratio.
F2
Figure 2.:
Log file of HeartMate 3 from the week before admission.
F3
Figure 3.:
Possible thrombus in the proximal outflow graft.

Based on the abrupt and persistent drop in flow, the suggestion of outflow clot on CT, and the historical experience of late outflow graft obstruction in patients supported with the HM3, the patient underwent urgent redo sternotomy with a plan for outflow graft replacement. The bend relief was removed and the outflow graft was inspected, however, no twist, kink, or obstruction was apparent. At that point, the decision was made to proceed with HM3 pump exchange. Examination of the device demonstrated a large thrombus in the distal inflow cannula (Figure 4). There was no obstruction of the lumen of the outflow graft. The new HM3 device was secured using the original apical cuff. The new outflow graft was sutured end-to-end to the distal portion of the previous outflow graft. Subcutaneous heparin was started on postoperative day 1. Postoperatively, the patient developed atrial fibrillation requiring cardioversion. Otherwise, he recovered well with HM3 flow averaging 4.8 L/min at 5,800 rpm. The patient was discharged on postoperative day 15 and remains well.

F4
Figure 4.:
Photograph of the explanted HeartMate III pump, showing chronic adherent thrombus within the distal portion of the inflow cannula.

Discussion

We present a case of late HM3 pump thrombosis. Previous reports have highlighted HM3 thrombosis in the early postimplantation period or from ingested intraventricular thrombus.5,6 Other reports have highlighted outflow graft occlusion and graft twisting.3,4 In this case, thrombus accumulated at the distal segment of the inflow cannula over two years after implantation without occlusion of the outflow graft. The pump was well positioned on preoperative imaging and intraoperative inspection. On inspection, the thrombus also did not appear to be embolic given its planar appearance. On retrospective review of the preoperative CT, it is likely that the “thrombus” in the outflow graft was extraluminal from proteinaceous material typically seen between the outflow graft and the bend relief, as no thrombus was present on intraoperative inspection. The device was returned to the manufacturer for diagnostic evaluation and functioned as intended.

Here, pump thrombosis was associated with decreased pump power without significant LDH elevation. This stands in contrast to previous devices in which thrombosis was associated with increased power and significantly elevated LDH. Although the patient had episodes of subtherapeutic INR in the year before admission, the patient’s time in therapeutic range for INR was similar to previously published reports in continuous flow LVADs.7 The optimal anticoagulation strategy for HM3 devices has not been determined; however, lower levels of anticoagulation (INR 1.5–1.9) have been evaluated without an increase in thromboembolic complications.8 It is unclear if this episode of pump thrombosis is related to inadequate anticoagulation. Given the dietary influence on the therapeutic action of warfarin anticoagulation, it is expected that there will inevitably be some degree of deviation from therapeutic range.

Previous studies have demonstrated that HM3 thrombosis will be a rare event. Diagnosis of de novo pump thrombosis will require a high index of suspicion and exclusion of other known causes of low flow. New onset low flow despite adequate ventricular filling should prompt CT and echocardiographic evaluation. In the absence of outflow graft obstruction, pump thrombosis should be suspected.

Conclusion

This is the first reported case of late HM3 thrombosis unrelated to outflow graft obstruction. This case report demonstrates that although pump thrombosis in HM3 devices is uncommon, it can occur without a clear inciting event and should be considered in HM3 patients presenting with low flow.

References

1. Mehra MR, Naka Y, Uriel N, et al.: A fully magnetically levitated circulatory pump for advanced heart failure. N Engl J Med 376: 440–450, 2017.
2. Mehra MR, Uriel N, Naka Y, et al.; MOMENTUM 3 Investigators: A fully magnetically levitated left ventricular assist device—final report. N Engl J Med 380: 1618–1627, 2019.
3. 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 155: e33–e35, 2018.
4. Duero Posada JG, Moayedi Y, Alhussein M, et al.: Outflow graft occlusion of the HeartMate 3 left ventricular assist device. Circ Heart Fail 10: e004275, 2017.
5. Klotz S, Karluss A, Stock S, Frydrychowicz A, Sievers HH: HeartMate III left ventricular assist device thrombosis triggered by an automatic implantable cardioverter-defibrillator shock. Ann Thorac Surg 104: e421–e424, 2017.
6. Rubio AC, Buggey J, Nijst P, et al.: ACUTE PUMP THROMBOSIS IN A HEARTMATE III. J Am College Cardiol 75: 3365, 2020.
7. Henderson JB, Iyer P, Coniglio AC: Predictors of warfarin time in therapeutic range after continuous-flow left ventricular assist device. Pharmacotherapy 39: 1030–1035, 2019.
8. Netuka I, Ivák P, Tučanová Z, et al.: Evaluation of low-intensity anti-coagulation with a fully magnetically levitated centrifugal-flow circulatory pump—the MAGENTUM 1 study. J Heart Lung Transplant 37: 579–586, 2018.
Keywords:

HeartMate3; HM3; LVAD; pump thrombosis; heart assist devices

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