Aimo, Alberto

Bianchi, Giacomo

Vergaro, Giuseppe

English

PubMed

Archivio della ricerca della Scuola Superiore Sant'Anna

J A C C : C A S E R E P O R T S V O L . 2 , N O . 1 0 , 2 0 2 0ª 2 0 2 0 T H E A U T H O R S . P U B L I S H E D B Y E L S E V I E R O N B E H A L F O F T H E A M E R I C A NC O L L E G E O F C A R D I O L O G Y F OU N D A T I O N . T H I S I S A N O P E N A C C E S S A R T I C L E U N D E RT H E C C B Y - N C - N D L I C E N S E ( h t t p : / / c r e a t i v e c o mm o n s . o r g / l i c e n s e s / b y - n c - n d / 4 . 0 / ) .EDITORIAL COMMENTIntegrated Imaging to InvestigateLow-Flow Alarms ofLeft Ventricular Assist Devices*Alberto Aimo, MD,a Giacomo Bianchi, MD, PHD,b Giuseppe Vergaro, MD, PHDa,cW ith the ongoing shortage of available or-gans for heart transplantation, mechani-cal circulatory support devices havebeen increasingly used to manage acute and chronicheart failure that is refractory to medical therapy (1).In particular, the introduction of left ventricular(LV) assist devices (LVADs) has revolutionized thisfield, by extending life as either a bridge to transplan-tation or a destination therapy (1). Although first-generation devices provided pulsatile flow, currentLVAD devices produce continuous flow and arefurther classified according to their impeller technol-ogy (i.e., axial or centrifugal). Normal componentsinclude the pump, inflow and outflow cannulas, adriveline, and an external controller. Clinical trialsand real-world experience have revealed the possibil-ity of many potentially life-threatening complications(2). These complications can be categorized as LVAD-specific and LVAD-associated complications, andmany of them can result in severe patient morbidityand mortality (2). LVAD-specific complicationsinclude device malfunctioning or failure, pumpthrombosis, and suction events, whereas LVAD-ISSN 2666-0849*Editorials published in JACC: Case Reports reflect the views of the au-thors and do not necessarily represent the views of JACC: Case Reports orthe American College of Cardiology.From the aInstitute of Life Sciences, Scuola Superiore Sant’Anna, Pisa,Italy; bDivision of Adult Cardiac Surgery, Fondazione Toscana GabrieleMonasterio, Massa, Italy; and the cDivision of Cardiology and Cardio-vascular Medicine, Fondazione Toscana Gabriele Monasterio, Pisa, Italy.The authors have reported that they have no relationships relevant to thecontents of this paper to disclose.The authors attest they are in compliance with human studies commit-tees and animal welfare regulations of the authors’ institutions and Foodand Drug Administration guidelines, including patient consent whereappropriate. For more information, visit the JACC: Case Reports authorinstructions page.associated complications include bleeding, cerebro-vascular events, infection, right ventricular failure,arrhythmias, and aortic regurgitation (2).The evaluation and management of patients withLVAD require a team-based approach, and consulta-tion with an LVAD specialist is recommended (3).LVAD dysfunction may be indicated by devicealarm systems sensing a low pump flow, possiblyassociated with LVAD power spikes, ventriculararrhythmias, or clinical evidence of pulmonarycongestion or tissue hypoperfusion. The first step inevaluating the patient with alarms reported by theLVAD controller is the assessment of clinical status, todetermine the treatment priority and the settingwhere the patient should be treated (i.e., medicaldepartment or intensive care unit).One of the complications that can generate a low-flow alarm is pump thrombosis. Thrombosis of thedevice can occur in any of its parts (inflow cannula,rotor, outflow cannula, and distal anastomosis zone)and recognizes different causes depending onthe zone. At the inflow level, thrombosis can bedetermined by inadequate myectomy at the time ofdevice implantation or by positioning against theinterventricular septum. At the impeller level, it isinfluenced by the design of the pump itself (axial vs.centrifugal, fully magnetic levitation vs. magneticrotation with blood displacement) and by operationalrotations per minute. At the outflow graft level,thrombosis can occur by twisting, kinking, or abextrinseco compression, as well as by fibrin plateletthrombosis.In suspected pump thrombosis, laboratory exami-nation is crucial because it can predict pump throm-bosis at an early stage, before machine alarms soundor imaging is obtained (4). Combining an elevatedlactate dehydrogenase (LDH) and plasma-freehttps://doi.org/10.1016/j.jaccas.2020.07.006CENTRAL ILLUSTRATION Main Causes of Low-Flow LVAD AlarmsAimo, A. et al. J Am Coll Cardiol Case Rep. 2020;2(10):1457–60.Main causes are reported, together with possible diagnostic imaging techniques. CT ¼ computed tomography; IVUS ¼ intravascular ultra-sound; LVAD ¼ left ventricular assist device; TEE ¼ transesophageal echocardiography; TTE ¼ transthoracic echocardiography.Aimo et al. J A C C : C A S E R E P O R T S , V O L . 2 , N O . 1 0 , 2 0 2 0Imaging and Alarms of Left Ventricular Assist Devices A U G U S T 2 0 2 0 : 1 4 5 7 – 6 01458hemoglobin reading with other common markers forhemolysis, such as reduced levels of hemoglobin,hematocrit, and haptoglobin and increased indirectbilirubin levels, is strongly suggestive of ongoinghemolysis from pump thrombosis.Multimodality imaging is then crucial to refine orrule out the pump thrombosis and its location. Chestradiography allows assessment of the position of theinflow cannula and the presence of pulmonarycongestion secondary to insufficient unloading (fromoutflow obstruction). Transthoracic echocardiogra-phy (TTE) is the primary imaging modality tofacilitate pre-LVAD management and for post-implantation monitoring because it is noninvasive,is widely available, and can be performed at thebedside (5). A comprehensive LVAD evaluation con-sists of standard TTE with a focus on biventricularsize and function, valvular function, velocities in theinflow and outflow conduits, contribution of thenative left ventricle and LVAD to systemic flow, pul-monary pressures, and evidence of LV recovery (5).Investigators have proposed performing baseline TTE2 weeks after implantation and then routinely every 3to 6 months and as clinically indicated (5). If echo-cardiographic evaluation is technically difficultdespite the use of a contrast agent, transesophagealechocardiography is usually performed when LVADdysfunction or other complications are suspected (5).Cardiac computed tomography (CT) angiographycan be used if there is persistent clinical concern forinflow-outflow graft thrombosis or malposition in thesetting of a nondiagnostic echocardiogram (6). CTangiography allows an accurate evaluation of LVADcannulas. Unlike echocardiography, CT angiographyis not limited by acoustic windows and lacks acousticshadowing. Furthermore, LVAD cannulas can beJ A C C : C A S E R E P O R T S , V O L . 2 , N O . 1 0 , 2 0 2 0 Aimo et al.A U G U S T 2 0 2 0 : 1 4 5 7 – 6 0 Imaging and Alarms of Left Ventricular Assist Devices1459interrogated from multiple views, thus permittingdirect visualization (6). The sensitivity and specificityof CT angiography to detect cannula thrombosis orinflow cannula malposition by using intraoperativefindings as the gold standard are as high as 85% and100%, respectively (7). Possible limitations of CTangiography are the need for radiation exposure andthe risk of nephrotoxicity from iodinated contrastagents (5). Additionally, when there is evidence ofoutflow graft lumen narrowing in the portion coveredby the bend relief, CT angiography does not allow theclinician to discriminate between intraluminalthrombosis and extrinsic compression by biodebrisbetween the bend relief and the outflow graft,although treatment of these 2 conditions is radicallydifferent (e.g., anticoagulation vs. percutaneousstenting within the graft) (8). Narrowing of theoutflow graft lumen is not a rare occurrence; it wasfound in 14% of patients in a recent case series (8).Apart from direct surgical revision of the device,luminal thrombosis and extrinsic compression can bedifferentiated by invasive graft examination withintravascular ultrasound (8).In this issue of JACC: Case Reports, Asawaeer et al.(9) reappraised the topics of LVAD complications andthe choice of imaging techniques for identification ofthese complications. They reported the case of a 66-year-old man who underwent HeartMate II (AbbottLaboratories, Abbott Park, Illinois) LVAD implanta-tion in 2013 for end-stage ischemic heart failure andwho recently presented with exertional dyspnea andlow-flow, high-power LVAD alarms. Laboratory ex-aminations showed an international normalized ratiolower than the therapeutic range and elevated LDHlevels, 2 findings that were compatible with (but byno means specific for) thrombotic events. Thisprompted the treating physicians to start anti-coagulation therapy with bivalirudin, which did notprevent further LDH elevation. Echocardiographyrevealed inflow and outflow velocities rangingaround the upper reference limit (2 m/s) (10). Thepatient underwent pump exchange through a leftsubcostal incision, but outflow cannula velocity roseto 3.5 m/s immediately after the exchange. At thispoint, CT angiography revealed an obstruction of theoutflow cannula secondary to kinking and twisting,which were apparently attributed to device replace-ment. Interestingly, evaluation of the explantedpump showed thrombosis of the inflow stator region,which was considered the original cause of the low-flow alarm (9).Asawaeer et al. (9) should be commended for pre-senting this interesting case and also for providing asimple diagnostic flowchart for the use of imagingtechniques to assess patients with low-flow alarms. Aschematic depiction of the main causes of low-flowLVAD alarms is provided in the Central Illustration.The first-line imaging examination is TTE, which maybe augmented by the use of ultrasound contrastagents or transesophageal echocardiographic evalua-tion. Echocardiography should allow the clinicianto evaluate cannula position, flow velocities, andbiventricular size and function. The CentralIllustration shows the following possibilities: malpo-sition of the inflow or outflow cannula, right ven-tricular dysfunction, indirect evidence of pumpmalfunctioning (increased LV size with reduced flowvelocities), pericardial tamponade, or inconclusivefindings (particularly increased flow velocities withan unclear mechanism). In the last case, problemswith the inflow or outflow cannulas (thrombosis,malpositioning, or kinking) can be readily detected byCT angiography. As stated earlier, CT angiographydoes not allow discrimination between intraluminalthrombosis and extrinsic compression of the outflowgraft. Therefore, intravascular ultrasound evaluationor direct surgical revision of the device is warranted.ADDRESS FOR CORRESPONDENCE: Dr. GiuseppeVergaro, Division of Cardiology and CardiovascularMedicine, Fondazione Toscana Gabriele Monasterio,Via Moruzzi, 1, 56124 Pisa, Italy. E-mail: vergaro@ftgm.it.RE F E RENCE S1. Kadakia S, Moore R, Ambur V, Toyoda Y. Currentstatus of the implantable LVAD. Gen Thorac Car-diovasc Surg 2016;64:501–8.2. Long B, Robertson J, Koyfman A, Brady W. Leftventricular assist devices and their complications:a review for emergency clinicians. Am J EmergMed 2019;37:1562–70.3. Cook JL, Colvin M, Francis GS, et al. Rec-ommendations for the use of mechanical circu-latory support: ambulatory and communitypatient care: a scientific statement from theAmerican Heart Association. Circulation 2017;13:e1145–58.4. Bartoli CR, Ghotra AS, Pachika AR, Birks EJ,McCants KC. Hematologic markers better predictleft ventricular assist device thrombosis thanechocardiography or pump parameters. ThoracCardiovasc Surg 2014;62:414–8.5. Estep JD, Stainback RF, Little SH, et al. The roleof echocardiography and other imaging modalitiesin patients with left ventricular assist devices.J Am Coll Cardiol Intv 2010;3:1049–64.6. Barac YD, Nevo A, Schroder JN, et al. LVADOutflow graft role in pump thrombosis. ASAIO J2020;66:128–31.7. Raman SV, Sahu A, Merchant AZ, et al. Nonin-vasive assessment of left ventricular assist deviceswith cardiovascular computed tomography andimpact on management. J Heart Lung Transplant2010;29:79–85.Aimo et al. J A C C : C A S E R E P O R T S , V O L . 2 , N O . 1 0 , 2 0 2 0Imaging and Alarms of Left Ventricular Assist Devices A U G U S T 2 0 2 0 : 1 4 5 7 – 6 014608. Trankle CR, Grizzard JD, Shah KB, et al. Leftventricular assist device outflow graft compres-sion: incidence, clinical associations and potentialetiologies. J Card Fail 2019;25:545–52.9. Asawaeer M, Kadir S, Albulushi A,Castleberry AW, Chatzizisis YS. Left ventricularassist device outflow cannula obstruction: impor-tance of multimodality imaging. J Am Coll CardiolCase Rep 2020;2:1454–6.10. Stainback RF, Estep JD, Agler DA, et al.Echocardiography in the management of patientswith left ventricular assist devices: recommenda-tions from the American Society of Echocardiog-raphy. J Am Soc Echocardiogr 2015;28:853–909.KEY WORDS cardiac assist devices,cardiomyopathy, computed tomography

Integrated Imaging to Investigate Low-Flow Alarms of Left Ventricular Assist Devices

Aimo A

Bianchi G

Vergaro G

Archivio della Ricerca - Università degli Studi di Siena

https://www.iris.sssup.it/bitstream/11382/567983/1/1-s2.0-S2666084920308743-main.pdf

Integrated Imaging to Investigate Low-Flow Alarms of Left Ventricular Assist Devices

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