Abstract
The Impella (Abiomed, Danvers, MA, USA) is a novel percutaneous heart pump device for left ventricular (LV) assistance; however, LV thrombus is a notable contraindication for this device. Contrast computed tomography assessment is useful for detecting LV thrombus and preventing thromboembolism in patients recommended for Impella use.
<Learning objective: The Impella (Abiomed, Danvers, MA, USA) is a heart pump device which aspirates blood from a left ventricular (LV) cavity and ejects it into an ascending aorta. Therefore, LV thrombus should be explored before the Impella insertion to prevent systemic embolism. Generally, echocardiography is the first choice to detect LV thrombus. Given limited diagnostic sensitivity for detecting LV thrombus in echocardiography, contrast computed tomography might be a useful strategy for the patient targeting Impella insertion.>
Keywords: Impella, Left ventricular thrombus, Contrast computed tomography, Echocardiography
Introduction
The Impella (Abiomed, Danvers, MA, USA) is a novel percutaneous heart pump device that is inserted into the left ventricular (LV) cavity via the aortic valve for providing LV assistance [1], [2]. The use of Impella has been reported in various situations including cardiogenic shock with ST-elevation myocardial infarction, cardiomyopathy-related heart failure, and fulminant myocarditis. Impella 2.5 and Impella CP are temporary ventricular assist devices (for hours to days) that are inserted by standard femoral artery puncture; Impella 5.0 is inserted by surgical cut down and can be used for days to weeks. Impella 5.0 is a more powerful device that is used as a part of a bridge-to-decision strategy for patients with advanced heart failure. One of the most common current management strategies for cardiogenic shock involves the use of Impella with extracorporeal membrane oxygenation (ECMO) [3]. Owing to the reduction of LV function and retrograde blood flow in the ascending aorta from the ECMO, LV unloading often decreases and end-diastolic pressure (EDP) elevations, which can cause LV thrombus [4]. To solve this severe complication, the Impella device has increasingly been used to reduce LVEDP. However, LV thrombus is a notable contraindication for using the Impella device because arterial thrombosis has been reported in 3.4% of cases of Impella use [5]; it is therefore important to evaluate the existence of LV thrombus beforehand. Detecting apical LV thrombus using only echocardiography has been reported to be often difficult [6]. We report three LV thrombus cases wherein deciding to use the Impella device was difficult. Among these, contrast computed tomography (CT) clearly detected LV thrombus in two cases, which helped prevent Impella device-induced thromboembolism.
Case series
Patient 1
A 60-year-old man with a history of surgery for severe aortic regurgitation with annuloaortic ectasia and severe mitral regurgitation was re-operated for an aortic vascular graft infection. An unexpected cardiopulmonary arrest occurred during surgery; an ECMO and intra-aortic balloon pump (IABP) were used at the same time. His postoperative cardiac function remained depressed. Furthermore, a hematoma was detected in the mediastinal wound, which required a reoperation for hemostasis and evacuation of hematoma. The pre-operative transthoracic echocardiogram (TTE) and peri-operative transesophageal echocardiogram (TEE) revealed a reduced ejection fraction (10%) with severe hypokinesis of the LV. Pre-operative and post-operative TEE failed to identify any LV thrombus. Hence, an Impella 5.0 device was inserted through the right femoral artery for LV assistance following a successful operation for hemostasis and evacuation of hematoma from the mediastinum wound (Fig. 1A). However, the flow rate of the Impella device decreased and the pressure of the purge solution increased immediately after insertion. The Impella catheter was removed and a new Impella catheter was inserted. However, the same phenomenon occurred. We confirmed that the first removed Impella catheter had a thrombus inside (Fig. 1B, yellow arrows). As a result, we completely removed the second Impella catheter to avoid secondary complications such as multiple thromboembolism. Unfortunately, the patient died owing to ventricular fibrillation on the third postoperative day.
Fig. 1.
A 60-year-old man (Patient 1) with reduced left ventricular ejection fraction and left ventricular (LV) thrombus. (A) An Impella device was inserted to the LV under fluoroscopy. (B) A thrombus (yellow arrows) was detected in the suction hole of the Impella device.
Patient 2
A 56-year-old woman with systemic lupus erythematosus was admitted to the local hospital with chest pain and nausea that had been persistent for two days. An electrocardiogram revealed QS pattern in the V1-4 leads and the bedside TTE revealed an ejection fraction of 20%, with severe hypokinesis of the broad anterior LV and an LV thrombus. She was diagnosed with sub-acute myocardial infarction and treated with heparin and warfarin. Sustained ventricular tachycardia (VT) was documented on the third hospital day. Coronary angiography revealed a total occlusion in the ostium of the left anterior descending artery. Percutaneous coronary intervention was performed and the coronary flow improved from thrombolysis in myocardial infarction grade flow 0 to 2. However, the sustained VT did not improve. Amiodarone was administered intravenously and an ECMO was inserted. Her hemodynamic state gradually deteriorated. Thereafter, she was transferred to our hospital to insert the Impella 5.0 device. A careful bedside TTE revealed no obvious LV thrombus (Fig. 2A and Video S1); however, we considered the possibility of LV thrombus because of the experience we had had with patient 1. Therefore, contrast CT was performed, which revealed an LV thrombus (Fig. 2B and Video S2, yellow arrows); for this reason, we declined to insert the Impella device. She was treated using ECMO and IABP without developing a thromboembolism.
Fig. 2.
(Top) A 56-year-old woman (Patient 2) with reduced left ventricular ejection fraction (LVEF) and left ventricular (LV) thrombus. (Bottom) A 31 year-old-man (Patient 3) with reduced LVEF and LV thrombus.
(A) Bedside echocardiography showed no obvious LV thrombus. (B) The contrast computed tomography (CT) revealed thrombus in LV apex (yellow arrows). (C) Bedside echocardiography revealed no obvious LV thrombus. (D) The contrast CT showed thrombus in LV apex (red arrows).
LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
Patient 3
A 31-year-old man without any significant medical history was admitted to the local hospital with cardio-pulmonary arrest. Emergency ECMO and IABP insertion were performed. Coronary angiography showed thrombus in both coronary arteries and thrombus aspiration was performed. On the fifth hospital day, the patient was able to withdraw from ECMO; however, he was dependent on intensive inotropic therapy because of a very low LV ejection fraction of 20%. Hence, to insert the Impella device as a bridge to LV assist device (LVAD) implantation, he was transferred to our hospital on the 65th hospital day. A bedside TTE showed no obvious LV thrombus (Fig. 2C and Video S3). However, the contrast CT showed an obvious thrombus in the apical LV (Fig. 2D and Video S4, red arrows). The patient was therefore directly operated with the LVAD.
Discussion
In each case, the LV thrombus was not confirmed with careful TTE before the Impella insertion. In patients 2 and 3, a contrast-enhanced CT scan was performed after echocardiography because of our prior experience with patient 1, confirming the presence of a thrombus in the LV. This is the first report wherein CT findings were utilized to defer or reverse Impella insertion, thereby avoiding potential multiple embolization. The Impella 5.0 is an intravascular micro axial blood pump that delivers up to 5.0 L/min of forward flow from the LV to the aorta [1], [2]. Therefore, in cases of LV thrombus, the Impella catheter may suck the thrombus and cause thrombotic occlusion of the catheter or multiple thromboembolism. Patients who are recommended for Impella insertion have a reduced LV function and are simultaneously considered at high risk for LV thrombus. Therefore, detecting the LV thrombus before Impella insertion is vital. Although conventional echocardiography has been used for detecting LV mural thrombus in routine clinical practice, a previous study reported that the sensitivity of conventional TTE for the detection of LV thrombus was low (23–33%). This is owing to the presence of noise and artifacts [6], [7]. In the cases reported by us, TTE failed to identify LV thrombus as it did not protrude in to the LV to reveal any crescent shape along the LV wall. TEE is reported to be superior, with a sensitivity of 40%, to TTE for the detection LV thrombus [7]. However, TEE requires sedation, which may result in hemodynamic instability. Contrast echocardiography is reported to further improve diagnostic performance (sensitivity, 61–100%) for thrombus detection [8], [9]. Based on this evidence, contrast-TTE or TEE may have been useful in our patients. The sensitivity of cardiac CT is reported as 94% [10], suggesting that cardiac CT assessment is useful in screening for LV thrombus prior to Impella insertion. The limitation is the difficulty in moving the patient to the CT room because critically ill patients use many devices such as ECMO, IABP, monitors, and infusions. However, once thromboembolism occurs, patients find themselves in a miserable situation often leading to death. Hence, wherever possible, contrast CT may be considered prior to Impella insertion in patients at high risk for thrombosis to prevent complications related to multiple and systemic thromboembolism.
In conclusion, our case series suggests that assessment using contrast CT is useful for detecting LV thrombus and beneficial for patients who are recommended for Impella device use to prevent thromboembolism.
Conflict of interest
The authors have no conflicts of interest.
Footnotes
Supplementary material related to this article can be found, in the online version, at https://doi.org/10.1016/j.jccase.2020.07.016.
Appendix A. Supplementary data
The following are Supplementary data to this article:
Echocardiography showing no obvious left ventricular thrombus in Patient 2.
The contrast computed tomography detecting left ventricular thrombus (yellow arrows) in Patient 2.
Echocardiography showing no obvious left ventricular thrombus in Patient 3.
The contrast computed tomography detecting left ventricular thrombus (red arrows) in Patient 3.
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Associated Data
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Supplementary Materials
Echocardiography showing no obvious left ventricular thrombus in Patient 2.
The contrast computed tomography detecting left ventricular thrombus (yellow arrows) in Patient 2.
Echocardiography showing no obvious left ventricular thrombus in Patient 3.
The contrast computed tomography detecting left ventricular thrombus (red arrows) in Patient 3.