Introduction The development of new revascularization devices has significantly improved recanalization rates and time to reperfusion. A direct aspiration first-pass (ADAPT) technique for stroke thrombectomy was recently shown to be an effective and rapid way to achieve revascularization. The technique focuses on engaging and removing a clot without the use of a separator or retriever by relying on the force and aspiration generated by the catheter. We sought to compare the physical and fluid dynamic properties (force and aspiration) of commercially available catheters to determine the most effective catheter for the ADAPT technique.
Methods Benchtop models were employed to compare aspiration for each catheter by submersing the catheter into a graduated cylinder and aspirating water. The volume of fluid aspirated and flow rates were calculated. Force of aspiration at the tip of each catheter was measured using a vacuum pressure gauge while the catheter was attached to a standard aspiration pump. Force was then calculated.
Results The Penumbra 5MAX ACE catheter had the greatest aspiration rate of all the catheters at 245 mL/min. The Penumbra 5 MAX catheter aspirated 212 mL/min, followed by the Navien 058 and DAC 057 with 198 mL/min and 197 mL/min, respectively. The Penumbra 5MAX ACE generated the greatest tip force (18.25 g) and the 5MAX had the least amount of force (14.77 g).
Conclusions The physical and fluid dynamic properties of currently available catheters suggest that the 5MAX ACE is the optimal catheter to use in direct aspiration for stroke therapy.
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In the USA approximately 800 000 people experience a stroke annually, of which 610 000 are first occurrences.1 Among all strokes, around 87% are diagnosed as ischemic while the remaining are attributed to intracerebral (10%) or subarachnoid (3%) hemorrhages.1 Stroke accounts for one in 18 deaths in the USA, resulting in 135 952 deaths per year.1 Current treatment options in the USA for acute ischemic stroke (AIS) are limited to intravenous thrombolytic agents, such as recombinant tissue plasminogen activator, or chemical and mechanical thrombolysis. However, even with attempts to increase public awareness and reduce the time from stroke onset to intervention, at most only 3% of the patients presenting with stroke each year are treated by these therapies, resulting in a significant unmet medical need for this disease.2 ,3
Interim analysis of a prospective natural history study in a stroke cohort eligible for but untreated by endovascular therapy found that spontaneous recanalization to Thrombolysis In Cerebral Infarction (TICI) 2a–3 was only seen in 12%.4 At 90 days, 20% achieved functional independence while 40% died. The results showed that stroke is a devastating disease with nearly 80% of patients dying or suffering long-term disabilities if untreated. When compared with the FIRST natural history cohort, the intra-arterially treated group in the IMS III study had higher recanalization and functional independence rates and lower mortality.5 ,6
The development of new revascularization devices has significantly improved recanalization rates and time to recanalization. A direct aspiration first-pass (ADAPT) technique for stroke thrombectomy was recently shown to achieve a higher quality of thrombectomy in a multicenter series.7–10 This technique focuses on engaging and removing the clot with the force and aspiration generated by the catheter without the use of additional devices such as a separator or retriever. We sought to characterize the physical and fluid dynamic properties (force and aspiration) as well as flexible zone transitions of commercially available catheters to determine the most effective catheter for the ADAPT technique.
Catheters currently used as part of standard endovascular stroke treatment were tested, including the 5MAX ACE (Penumbra, Alameda, California, USA) and 5MAX (Penumbra). In addition, two devices designed as intermediate guide catheters, the DAC 057 (Stryker, Fremont, California, USA) and the Navien 058 (Covidien, Irvine, California, USA), which although not aspiration catheters designed for use in AIS have an end-hole size similar to the 5MAX, were analyzed. The results comparing the 5MAX ACE, 5MAX, DAC 057, and the Navien 058 catheters are reported.
Catheter tip pressure testing
The force of aspiration at the tip of each catheter was measured and compared. The catheter tip pressure was measured using a vacuum pressure gauge while the catheter was attached to a commercially available aspiration pump (Penumbra MAX Aspiration Pump) set to −29 Hg and commercially available tubing (Penumbra). The force was then calculated using the following formula: 1
Flow rate testing
Benchtop models were employed to compare catheter flow rates. The aspiration pump was set to aspirate at −29 Hg. The aspiration catheter was immersed in a graduated cylinder and room temperature water was aspirated for 20 s.11 The total volume of fluid aspirated over 20 s was measured and the volume flow rate was then calculated (mL/min).
Effective flow lumen calculations
‘Effective flow lumen’ is a term used to describe the flow rate of a tapered catheter compared with another catheter with a unidimensional lumen. The Poiseuille and ‘resistors in series’ equations were used to determine the equivalent unidimensional lumen that would possess the same flow rate as the 5MAX ACE and 5MAX tapered lumen catheters and empirically measured flow rates using the pump and water.
The 5MAX ACE has a distal inner lumen of 0.060 inch and a proximal inner lumen of 0.068 inch; the 5MAX has a distal inner lumen of 0.054 inch and a proximal inner lumen of 0.064 inch; the Navien 058 and DAC 057 are unidimensional lumen catheters with an inner lumen of 0.058 inch and 0.057 inch, respectively. The methods and calculations used to determine the effective flow lumen values for the 5MAX and 5MAX ACE are shown below.
ΔP=pressure drop, Q=volumetric flow rate, R=resistance to flow, μ=dynamic viscosity, L=length of tube, π=constant pi, and d=inner diameter of tube.
Resistors in series 4
The total resistance is equivalent to the sum of all resistance in series.
Catheter tip force evaluation
The Penumbra 5MAX ACE generated the greatest tip force (18.25 g), the Penumbra 5MAX had the least amount of force (14.77 g), while the Navien 058 and DAC 057 exerted forces of 17.03 g and 16.48 g, respectively (table 1).
Flow rate evaluation
The 5MAX ACE catheter had the highest aspiration rate of all the catheters tested (245±1.7 mL/min), followed by the 5MAX, Navien 058, and DAC 057 catheters with aspiration rates of 212±1.7mL/min, 198±3.0 mL/min, and 197±1.7 mL/min, respectively (N=3 for each device; table 2). Using an analysis of variance with the Tukey test to compare the rate distribution, the ACE and 5MAX had significantly different flow rates and both catheters aspirated significantly faster than the Navien 058 and DAC 057 catheters (F value=18.79, df=11, p<0.001).
Effective flow lumen calculations
Using the methodology outlined above, the 5MAX ACE was found to have an effective flow lumen equivalent to a unidimensional lumen catheter with an inner diameter of 0.066 inch, the 5MAX had a flow lumen equivalent to a unidimensional lumen catheter with an inner diameter of 0.062 inch; both exceeded the Navien 058 and DAC 057 catheters which had effective flow lumens equivalent to unidimensional lumens of 0.058 inch and 0.057 inch, respectively (table 2).
The recently described ADAPT technique used direct aspiration with a large-bore catheter for vessel revascularization of patients with AIS at six institutions.7 ,10 TICI 3 recanalization was attained in 65% and 61% of cases, respectively, as quickly as 7 min after arterial puncture. The underlying rationale of the ADAPT technique was originally thought to be based on clogging of the catheter tip, but current understanding now suggests there may be a spectrum of variables that contribute to the technique. One end of the spectrum is catheter tip corking. In these instances, the major parameters are aspiration flow rate and catheter tip force. The aspiration flow rate serves to pull the clot into the catheter in a dynamic sense—that is, ensuring the catheter is corked sufficiently. Tip force is the static force that the catheter tip imparts on the thrombus when the thrombus is corked at the catheter tip. It is governed by F=P/A, where A=(π/4)×d2, where d is the internal diameter of the catheter. For a given input pressure (P), the catheter with the largest tip internal diameter will therefore have the greatest tip force. The other end of the spectrum is clot ingestion which is being seen more often with the use of the newer 5MAX ACE catheter. Simply stated, the system flow rate pulls the clot into the catheter lumen through the tubing and into the pump canister.
In this study of aspiration catheters used in stroke thrombectomy, catheter tip force, aspiration flow rate, and effective flow lumen were evaluated to determine the optimal catheter for application of the ADAPT technique. Tip force was found to be highest with the 5MAX ACE, the catheter with the largest internal diameter, which is consistent with theoretical derivations. In addition to greater tip force, empirical flow rate analysis demonstrated a difference in flow rate during aspiration through the four catheters studied, with the 5MAX ACE producing the highest flow rate, followed by the 5MAX, Navien 058, and DAC 057 catheters. Mathematical modeling suggests that the aspiration efficiency of the 5MAX ACE has been increased by enlarging the distal and proximal lumen compared with that of the 5MAX. The increased flow rate of the 5MAX over the Navien 058 catheter was due to the large 0.064 inch proximal internal diameter of the 5MAX, which leads to a lower overall resistance compared with the unidimensional lumen of the Navien 058. This hypothesis was confirmed in the subsequent effective flow lumen calculations for the 5MAX and 5MAX ACE catheters. The study showed that, due to its larger lumen, the 5MAX ACE catheter outperformed the three other catheters evaluated.
The physical and fluid dynamic properties of catheters currently available suggest that the 5MAX ACE is the optimal catheter to employ for direct aspiration in stroke therapy. The recent commercial release of the 5MAX ACE has shown an evolution of the ADAPT technique (which was initially developed with the 5MAX catheter) also to perform intact clot removal. Effective flow lumen calculations elucidate the mathematical basis underpinning tapered catheter technology versus unidimensional lumen manufacturing methods. Mathematically, the tapered lumen technology, as is seen with the 5MAX, allows for increased aspiration efficiency compared with conventional neurovascular catheters that may have larger distal end-holes but unidimensional lumens.
Use of the ADAPT technique to directly engage and remove the thrombus is thought to minimize embolization to new territory, which has been linked with worse patient outcomes. Stent retrievers with proximal aspiration demonstrated a new embolus rate of 5.7%.12 In the multicenter ADAPT study (N=100), no cases of emboli to new territories were noted, with 90-day modified Rankin scale scores of 0–2 in 40%.10
The limitations of this study include the small number of repetitions for each test performed and lack of assessment in a clinical setting. In addition, the Poiseuille equation is based on several assumptions: flow through a circular tube of constant cross-section substantially longer than its diameter; incompressible and Newtonian fluid; and laminar flow. In other words, the authors acknowledge the effective flow lumen calculations as approximations.
Technology continues to play a pivotal role in the field of endovascular ischemic stroke treatment. Improvements in devices and methodologies will continue to move the field forward. The ACE catheter represents the newest catheter technology. When considering the ADAPT technique, it allows for more powerful and efficient thrombectomy which may translate into improved patient outcome.
Contributors Both authors contributed equally to the conception and design of the work as well as drafting and revising the manuscript and both gave final approval of the version published and are equally accountable for all aspects of the work.
Competing interests MFS is a consultant with Penumbra and Covidien. YCH is a consultant with Covidien.
Provenance and peer review Not commissioned; externally peer reviewed.