Keywords
deep vein thrombosis - mechanical thrombectomy - ClotTriever - postthrombotic syndrome
Introduction
Lower extremity deep vein thrombosis (DVT) can be a cause of significant morbidity,
with acute symptoms often progressing to postthrombotic syndrome (PTS), which is sequala
of chronic venous insufficiency developing after DVT. To prevent clot propagation
in acute DVT, the first line of therapy remains therapeutic anticoagulation.[1] Anticoagulation alone, however, does not lead to active thrombus removal, and long-standing
thrombus within the veins can lead to venous hypertension, valve incompetence, and
inflammatory reaction to the thrombus. This is thought to be the mechanism for the
development of PTS, and therefore, thrombus removal is advocated in selected patients
to provide symptomatic relief and reduce the incidence of PTS.[2] A multitude of endovascular thrombectomy devices are available that vary in rates
of technical success and may be limited by need for thrombolytics. The ClotTriever
system is a large-bore suction thrombectomy platform designed for thrombus removal
without the need for concomitant thrombolytics. Although there is robust data on catheter-directed
thrombolysis in acute DVT management, there is relative paucity of safety and efficacy
data on purely mechanical thrombectomy without the use of lytics. The purpose of this
study is to provide a preliminary single-center experience in utilization of the ClotTriever
mechanical thrombectomy (Inari Medical Inc, Irvine, California, United States) system
in acute (< 14 days) and subacute (14–28 days) DVT.
Materials and Methods
Institutional board review approval was obtained for this retrospective study.
Patient Population
Retrospective chart review was performed for all patients who underwent DVT thrombectomy
using the ClotTriever system from 9/2018 to 7/2020 (from device availability to time
of study) at a single academic medical center. Data recorded included age, gender,
etiology, laterality of DVT, acuity of DVT (acute <14 days, subacute 14–28 days, chronic
>28 days of clinical symptoms), fluoroscopy time, perioperative parameters, type of
anesthesia, concomitant usage of thrombolytics and/or stents. Technical success was
defined as adequate thrombus evacuation leading to restoration of antegrade flow determined
on postprocedural venography without the use of adjunct thrombectomy devices. Follow-up
time period was recorded, Doppler ultrasounds/venograms (if reintervention was required)
were reviewed, and Villalta scores recorded. Postthrombotic changes were defined as
sonographic signs of decreased venous diameter, intraluminal material, wall thickening,
or synechiae/webbing/bands.
Technical Details
The ClotTriever system includes two components: a proprietary 13F sheath and the thrombectomy
device. The system is advanced over a 0.035-inch wire. The sheath features a self-expanding
nitinol funnel at its tip. The catheter comprises a nitinol coring element at its
leading edge, and a braided thrombus collection bag at its trailing edge ([Fig. 1]).
Fig. 1 The ClotTriever system comprising the thrombectomy device (A) and proprietary 13F sheath (B).
All procedures were performed in the interventional radiology suite with moderate
sedation or general anesthesia by board certified interventional radiologists with
average 3.8 years of postfellowship experience in interventional management of venous
disease. Patients were anticoagulated prior to and during the procedure, and heparin
administration was guided by intraoperative measurement of activated clotting time
(target >250). The vein was accessed using a standard micropuncture set under ultrasound
guidance. Initial venogram was performed using 5F sheath and catheter to determine
the clot burden. A 0.035 inch wire was advanced through the occluded venous segment
into the internal jugular vein or subclavian vein. The 5F sheath was then upsized
and exchanged for 13F ClotTriever sheath with deployment of the funnel. The catheter
was introduced through the sheath and advanced superiorly into the inferior vena cava
(IVC), with the nitinol coring element cranial to the occluded venous segment. The
coring element and collection bag was deployed and the system retracted caudally under
fluoroscopic guidance until the coring element reached the funnel tip of the sheath.
The collection bag was then closed and catheter removed. All clot was then removed
from the collection bag prior to reinsertion for a second pass. Repeat venogram was
performed via the sheath to document resolution of clot burden, and additional interventions
(venoplasty or stenting) were performed per operator preference ([Figs. 2] and [3]).
Fig. 2 A 40-year-old patient with acute left lower extremity deep venous thrombosis. Fluoroscopic
and digital subtraction venographic images obtained with patient in prone position
and access via the left popliteal vein. Initial DSV (A) showing acute thrombus within the iliofemoral segment, with opacification of collaterals.
Subsequent fluoroscopic image (B) showing the ClotTriever device deployed over the wire within the iliofemoral segment.
DSV after three passes of ClotTriever (C) showing restoration of in-line flow. (D) Stent placed in the iliac venous segment at the site of May–Thurner lesion. DSV,
digital subtraction venogram.
Fig. 3 A 80-year-old patient with myelofibrosis presenting with acute left lower extremity
deep vein thrombosis. Fluoroscopic and digital subtraction venographic images before
(A, B) and after (C, D) mechanical thrombectomy and stent placement. Fluoroscopic image (E) showing the ClotTriever device deployed over the wire within the iliofemoral vein.
Acute thrombus (F) extracted from the thrombotic veins.
Data Analysis
All data was stored and analyzed in Excel 2016 (Microsoft Corp, Redmond, Washington,
United States). Two sample t-test was used to compare groups and p-value of <0.05 was considered significant.
Results
Ten patients were included in the study ([Table 1]), with 6/10 female (60%), mean age 54.6 years (range: 24–80). The mean (±standard
deviation) fluoroscopy time was 34.01 (±15) minutes and dose-area product of 67.48
(±34.9) Gy*cm2. Eight patients presented with acute iliofemoral DVT, one patient with subacute iliofemoral
DVT, and one patient with subacute IVC thrombosis. The popliteal and femoral veins
were accessed in 9/10 and 1/10 patients, respectively. Only one patient required concomitant
intraprocedural thrombolytic administration, and four patients underwent same-session
venous stent placement. Restoration of antegrade flow was achieved in all patients
and technical success was achieved in 90% patients without any procedure-related adverse
events. There was no significant difference in pre- and postoperative hemoglobin (10.38
vs. 10.08, p = 0.78) and creatinine (0.87 vs. 0.86, p = 0.95). Reintervention within 30 days was required in two (20%) patients at 12 and
13 days, both using the AngioJet rheolytic pharmacomechanical thrombectomy system.[3] No patient required intensive care unit (ICU) stay and mean postprocedure hospital
length of stay was 2.3 days. Follow-up imaging was available for 9 patients, with
a mean follow-up interval (defined as date of procedure to date of most recent ultrasound/venogram)
of 230 days (range: 48–569). Five (of 9) patients had no evidence of recurrent DVT.
Four (of 9) patients had chronic postthrombotic changes in femoropopliteal veins that
did not require further intervention and only one patient had clinical signs and symptoms
of mild PTS (Villalta score 11). Mean follow-up Villalta score of patients was 3.
Table 1
Characteristics of patients who underwent mechanical thrombectomy using ClotTriever
system
|
Age/gender
|
Contributing etiology
|
Segments
|
Lytics
|
Stent
|
Technical success
|
Postop LOS
|
Most recent follow-up
|
Reintervention
|
|
41/M
|
May–Thurner
|
Left iliofemoral
|
No
|
Yes (CIV)
|
Yes
|
6
|
386
|
No
|
|
44/F
|
Liposarcoma
|
IVC
|
No
|
No
|
Yes
|
2
|
NA
|
|
|
74/F
|
Idiopathic
|
Left iliofemoral
|
No
|
No
|
Yes
|
1
|
569
|
No
|
|
50/F
|
May–Thurner
|
Left iliofemoral
|
No
|
No
|
Yes
|
2
|
450
|
Yes, 427 days, venoplasty
|
|
64/M
|
May–Thurner
|
Left iliofemoral
|
No
|
Yes (CIV, CFV)
|
Yes
|
2
|
91
|
Yes, 12 days, AngioJet
|
|
49/F
|
TKR
|
Left iliofemoral
|
No
|
No
|
Yes
|
1
|
246
|
No
|
|
24/M
|
IVC atresia
|
Left iliofemoral
|
Yes
|
No
|
No
|
1
|
48
|
Yes, 13 days, AngioJet
|
|
77/F
|
Myelofibrosis
|
Left iliofemoral
|
No
|
Yes (CIV, CFV)
|
Yes
|
4
|
84
|
No
|
|
43/M
|
COVID-19
|
Right iliofemoral
|
No
|
No
|
Yes
|
1
|
99
|
No
|
|
80/F
|
Myelofibrosis, May–Thurner
|
Left iliofemoral
|
No
|
Yes (CIV, CFV)
|
Yes
|
3
|
98
|
No
|
Abbreviations: CFV, common femoral vein; CIV, common iliac vein; COVID-19, coronavirus
disease 2019; IVC, inferior vena cava; LOS, length of stay; TKR, total knee replacement.
Discussion
The ClotTriever is an over-the-wire mechanical thrombectomy system designed to core
and extract thrombus off the venous wall. It has the ability to capture and remove
large clot burden from large caliber vessels in a single session. The device obviates
the need for thrombolytics, thereby eliminating ICU stay, which is a major advantage
of this device. Although thrombolytics are effective in removing thrombus, they are
associated with higher incidence of bleeding. Although the incidence of thrombolytic-related
bleeding in endovascular procedures was as low as 1.7% in the ATTRACT trial,[4] the rate of adverse bleeding due to lytics is commonly reported to be between 3
and 5%.
The present study showed high technical success and safety in all patients ([Table 1]). Only one patient required concomitant use of lytics, which was intraprocedural
on operator preference. Two patients with May–Thurner anatomy and IVC atresia, respectively,
required reintervention due to persistent clinical symptoms, and both were accomplished
using AngioJet. The technical results from present study are similar to those reported
by Benarroch-Gampel et al, who also reported high technical success and low reintervention
rates with the ClotTriever device.[5] In addition to mitigating thrombolytic use, the device also has potential financial
benefits. It avoids the cost of thrombolytic drugs (tissue plasminogen activator),
ICU stay, and potential repeat intervention after removal of thrombus. These benefits
do come at the expense of increased fluoroscopy time and dose. The mean fluoroscopy
time and dose-area product in the present study were 34.01 minutes and of 67.48 Gy*cm2, respectively, which are higher than those reported by Lim et al for lower extremity
DVT thrombolysis, the median fluoroscopy time and dose-area product in this study
being 16.35 minutes and 9.2 Gycm[2], respectively.[6] However, it must be noted that in the present series, four patients underwent concomitant
stenting; the mean fluoroscopy time for stented patients was 41.15 and for nonstented
cases was 29.36 minutes.
There are several limitations to this study. First, the retrospective nature of the
study and lack of control group prevent comparisons and control for extraneous factors
affecting outcomes. Second, patient selection for the ClotTriever system is not uniform
among the practitioners and is largely based upon operator's choice. Third, there
are limitations of the device itself, that is, large access size (13F) and relatively
contraindicated via the internal jugular vein approach (to avoid nitinol coring element
and collection bag passing through the heart). Finally, the small sample size is a
limiting factor in generalizing these results, while being cognizant that this is
a real-world nonindustry-sponsored study.
In conclusion, in this early real-world experience, the ClotTriever mechanical venous
thrombectomy system appears to have a high efficacy in the removal of thrombus from
lower extremities in a single-session setting, and may obviate the need for thrombolytic
therapy with low reintervention rates and short postprocedure hospital stay. Future
large-scale studies should be performed to further establish the role of this system
in patients with DVT and candidates for thrombectomy.
