In our study, the SwiftNINJA® steerable microcatheter was used for superselective angiography and embolization procedures. Target vessels were selected successfully in all cases and there were no adverse events reported. The device was found to be intuitive to use and a steep learning curve was not encountered. No guidewires were needed to cannulate most vessels. Even when selecting small and tortuous vessels, adequate steerability was achieved and the device tracked appropriately when used with a guidewire.
We found statistically significant improvements in time to target vessel selection which were most pronounced when cannulating high difficulty (HD) vessels. Vessels such as prostatic arteries and superior vesicular arteries are typically difficult and time consuming to cannulate and benefit the most from use of a SM that can better navigate tortuous vessels with variable anatomy. While no adverse events were noted in either group, fewer microcatheter exchanges and decreased time to vessel would be expected to be associated with a decrease in intraoperative complications such as vascular spasms and arterial dissection. Median total procedure time was found to be 37.5 min lower in the SM group, and 55 min lower in the high-difficulty subgroup. The time spent physically performing fluoroscopy and selecting the target vessel is one component of this. Further, less time with microcatheter and wire exchanges, angiography in different obliquities, and reviewing prior angiography and/or cross-sectional imaging studies to assess best approaches to vasculature may also have led to a significant decrease in overall procedure times. The increased throughput allowed by shorter procedure times and cost savings from the use of fewer microcatheters and guidewires may offset the higher cost of steerable microcatheters. Analysis of the cost-effectiveness of steerable microcatheters is a topic for future research.
After correcting DAP for BMI using a logarithmic transformation, SM use was associated with significantly lower DAP. In addition, when examining the high-difficulty subgroup, even uncorrected DAP was found to be significantly lower in the SM group. This suggests that decreased TTVS and procedure times is accompanied by a radiation safety benefit. A larger study would be beneficial for further evaluation. The volume of contrast used was also found to be lower with SM use, although only in the high difficulty subgroup. This can potentially impact nephrotoxicity, particularly in patients with borderline renal function.
The SM was used successfully in four prostatic artery embolization (PAE) procedures in patients with benign prostatic hyperplasia (BPH) experiencing lower urinary tract symptoms (LUTS). The PErFecTED technique was utilized (proximal embolization first, then followed by distal/central embolization), and bilateral embolization was successful in all four cases (Carnevale et al. 2014). The median time to advance the microcatheter from the internal iliac artery to the prostatic artery was 10.5 s. This is notable as PAE is considered to be a challenging procedure as prostatic artery anatomy is often variable, tortuous, and angulated. Further, as intra-prostatic collaterals require coil embolization in up to 20% of PAE cases, the ability to select and embolize these collaterals to prevent non-target embolization is important (Bhatia et al. 2018; Moreira 2017). The SM was able to be advanced into distal prostatic arterial vasculature bilaterally in each case, despite its 2.4F size. In addition, when needed, the SM can be placed into distal branch vasculature to allow for appropriate coil embolization (Fig. 5).
While the SM can be used as a bailout option during cases with more complex anatomy after extensive attempts with various pre-shaped microcatheters and microwires have failed, its use prior to opening multiple other devices has advantages in procedural efficiency, radiation exposure, and overall cost. The SM has a higher unit cost compared to fixed-shaped microcatheters; however, overall cost of use is relative. If the higher up front cost of the steerable microcatheter avoids the use of several lower cost microcatheters and microwires during a procedure, the per-case expenditure may be reduced. In addition, decreasing procedure times can allow for increased procedural efficiency and increased throughput in the angiography suite, with higher overall procedural volumes in a given period of time. The cost per minute to run and staff a procedure room is not insignificant, but does vary between institutions. Additional studies may be beneficial to further study this cost relationship.
Our study has multiple limitations. Case selection was non-randomized. In addition, the SM group was evaluated prospectively, while the CM group was evaluated retrospectively. When calculating TTVS in the control group, 120 s was subtracted from the time available based on time-stamps and other staff documentation to allow for initial time to prep the microcatheter and wire. This was chosen based on calculating the time it takes for the operator and staff to select and prep the equipment based on our experience, and over-estimated the prep time with the goal of minimizing risk of artificially higher TTVS in CM group based on prep time. Selection bias and interpretation bias can exist, given that a single operator performed all procedures. However, the cases assigned to the SM group appear to be more complex than those assigned to the CM group. In three cases, steerable microcatheters were only used after vessel cannulation had failed with conventional microcatheters. Cases in the SM group more often targeted two vessels while those in the CM group more often targeted just one. Also, there were more high-difficulty (HD) vessels in the SM group, including four bilateral PAE. However, additional studies at multiple institutions and with multiple operators would be beneficial for further investigation. In addition, no radial access cases were included as the steerable microcatheter currently is 125-cm in length, limiting its use from this access.