A Comparison of Interventional Guidewires in a Canine Model

Introduction

Guidewires are a fundamental component of any cardiac and vascular interventional procedure. These interventions may include coronary angioplasty, carotid stenting, endovascular aortic aneurysm repair (EVAR), superficial femoral artery (SFA) stenting, and inferior vena cava (IVC) filter placement. Numerous options exist for the guidewire available to interventionalists and surgeons. These guidewires vary in design and physical properties, and thus are not identical in their capabilities. While there have been evaluations of individual guidewires,^1–9 there have not been formal in vivo studies on the differences among these wires. A prior study, completed at our institution,¹⁰ used a bench model to compare the ability to select a vessel, torqueability, the ability to cross a lesion and the hape memory capability of three commercially available guidewires. The results demonstrated that guidewires are not equivalent in their physical characteristics and capabilities, in specific situations. Our study further examined the characteristics of commonly used guidewires in an animal model.

Methods

This study was approved and performed in accordance with the guidelines of the Institutional Animal Care and Use Committee (IACUC) at Montefiore Medical Center. The animal model used for this experiment was a large mongrel hound (Marshall Farms, New Rose, New York).

Guidewires. Three commercially available hydrophilic guidewires were tested in this study. These included the angled 0.035 inch diameter hydrophilic coated Glidewire (Terumo, Somerset, New Jersey), the ZIPwire (Boston Scientific, Natick, Massachusetts), and the HiWire (Cook, Indianapolis, Illinois). The same three guidewires were used and maintained in normal saline throughout the study.

Animal model. Prior to operative anesthesia, the canine received 0.04 mg/kg atropine intramuscularly (IM) and 0.05 mg/kg IM acepromazine. Pre-emptive analgesia was administered using a fentanyl patch (75 ug/hr), applied 24 hours prior to operation. Peripheral intravenous access was placed in a forefoot vein for hydration and medication administration. Prophylactic antibiotics (cefazolin 10 mg/kg) were given intravenously. The canine was then anesthetized using intravenous thiopental (7 mg/kg) induction, intubated, and maintained under anesthesia with 1.5–2.0% inhalant isofluorane.¹¹

The right groin region was shaved, prepped, and draped in a surgical fashion. A femoral cutdown was performed to expose the right femoral artery. Access to the artery was achieved using a standard 18-gauge arterial puncture needle and a 6 Fr sheath (Terumo). The animal was then systemically heparinized (100 ug/kg BW).

A 5 Fr pigtail (Cook) catheter was inserted and an initial angiogram was obtained of the native aorta and bilateral lower extremity vessels.¹²

Vessel selection. A 5Fr angiographic catheter (Soft-Vu Omniflush catheter, AngioDynamics, Queensbury, New York) was used to access the contralateral iliac artery and an angiogram of the left lower extremity was performed. A 5 Fr angled catheter (Slip-Cath Beacon Tip KMP catheter, Cook) was then advanced to the contralateral femoral artery and a left lower extremity angiogram was obtained. The catheter was then advanced into a branch vessel of the femoral artery at 10 cm from the aortic bifurcation (total distance = 21 cm). The angled catheter was then advanced 8 cm within this vessel and secured in place (total distance = 30 cm). Test points A, B, and C were then chosen and designated as test sites.

Point A was a branch vessel 3cm from the tip of the positioned angled catheter (total distance 33 cm; 3 mm diameter). Point B was a branch vessel 10 cm distal into Point A (total distance 43 cm; 2 mm diameter). Point C was a branch vessel 11 cm distal into Point A (total distance = 44 cm; 2 mm diameter).

Next, a singly-blinded operator attempted to cross each branch point in succession, with the endpoint as the time needed to select each vessel within five min (300 sec). Prior to the start of the study, an assistant removed the individual wires from their sheaths and soaked in saline. The assistant to the operator was not blinded to the identity of the wires and kept track of the wires. A trial was considered a failure if a vessel was not able to be selected within the allotted time.

Torqueability. During the initial trial of each guidewire, the operator advanced the wire tip to test point B (total distance = 43 cm). Using a torque device, the operator rotated the guidewire until one completerotation was achieved. The degree of rotation on the torque device required to achieve the rotation was recorded. The purpose of this test was to determine the amount of rotation needed at the distal shaft of a wire to generate enough torque to cause the wire tip to complete a 360 degree rotation. The fewer degrees of rotation needed to generate more torque allows a wire to better maneuver and select vessels.

Animal care post-study. Upon completion of the trials, the animal was euthanized under general anesthesia with 100 mg/kg of 40 mEq of KCl and bilateral pneumothoraces created by a scalpel.

Statistical analysis. Statistical analysis was performed using the SPSS statistical package (SPSS, Chicago, Illinois). Average times were calculated for each guidewire at each test point. Paired sample t-tests were used to calculate mean differences among guidewires. Standard errors were included for each comparison.

Results

Vessel selection. Point A. The average time needed to selectively cannulate Point A with Guidewire 1 (Glidewire) was 34 sec (standard error [SE] = 5.3 sec). Guidewire 2 (ZIPwire) averaged 253 sec (SE = 47.0 sec), with four trials stopped after the maximum time allotted was reached (four failures). Guidewire 3 (HiWire) averaged 63 sec (SE = 15 sec).

Point B. At Point B, guidewires 1, 2, and 3 averaged 162 sec (SE = 56 sec), 300 sec (SE = 0 sec), and 221 sec (SE = 48.4 sec), respectively. At Point B, guidewire 1 had two trials stopped after the maximum time allotted was reached (two failures), while guidewire 2 reached the maximum allotted time of 5 min on all five trials (five failures). Guidewire 3 reached the maximum time on three trials (three failures).

Point C. At Point C, guidewire 1 required an average of 93 sec (SE = 22 sec), while guidewire 2 averaged 274 sec (SE = 26.0 sec) and guidewire 3 averaged 215 sec (SE = 39.7 sec). At this branch point, guidewire 2 had four trials stopped after the allotted time (four failures) while guidewire 3 had one trial stopped after the time allotted (one failure). Guidewire 1 did not have any failures in selecting Point C.

At Point A, the mean difference between guidewires 1 and 2 was –219 sec (SE = 45.7; p = 0.009). Compared with guidewire 3, guidewire 1 showed a mean difference of –29.2 sec (SE = 17.5; p = 0.17). Guidewires 2 and 3 demonstrated a mean difference of +190 sec (SE = 37.7; p = 0.007).

At Point B, guidewire 1 exhibited a mean difference of –138 sec (SE = 56.4; p = 0.071) when compared with guidewire 2. Wires 1 and 3 demonstrated a mean difference of –59.2 sec (SE = 81.6; p = 0.504) at this branch point, while wires 2 and 3 revealed a mean difference of +79 sec (SE = 48.4; p = 0.178).

At Point C, guidewires 1 and 2 demonstrated a mean difference of –181 sec (SE = 44.4; p = 0.015), while wires 1 and 3 revealed a mean difference of –122 sec (SE = 56.6; p = 0.097). Guidewires 2 and 3 demonstrated a mean difference of +58.6 sec (SE = 34.7; p = 0.167).

Torqueability results. After being maintained in saline throughout this study, the ability to torque the guidewires was evaluated. At branch point B (total distance 43 cm), guidewire 1 (Glidewire) required 30 degrees of rotation to achieve one complete turn of the wire. Guidewire 3 (HiWire) required 170 degrees of rotation to achieve the same result. Guidewire 2 (ZIPwire) was not able to complete this task due to excessive resistance when attempting to advance the guidewire to branch point B.

Discussion

At all three branch points tested, Guidewire 1 (Glidewire) averaged less time to select the vessels than guidewire 2 (ZIPwire) or guidewire 3 (HiWire). At Point A, the Glidewire demonstrated a statistically significant average time of 219 fewer sec needed to select this vessel than the ZIPwire. The true mean difference is likely larger, given that four of the trials to cannulate with the ZIPwire were stopped after the maximum time allotted (5 min) was reached. At this most proximal point, the Glidewire required an average of 29.2 fewer sec than the HiWire (p > 0.05). When comparing the HiWire and ZIPwire, the HiWire required a statistically significant average of 190 fewer sec than the ZIPwire to select branch point A.

At Point B, the Glidewire required an average of 138 fewer sec than the ZIPwire to select this vessel. Although this value did not reach statistical significance (p = 0.071), it is important to note the ZIPwire failed all trials at this point and attempt to select this vessel were stopped at the maximum amount of time allotted. Thus, the artificial time limit of 5 min masks the true average time of the ZIPwire at Point B. The Glidewire required 59.2 fewer sec than the HiWire in selecting this vessel, but this number was not statistically significant.

At Point C, the Glidewire needed an average of 181 fewer sec than the ZIPwire to select this vessel (p < 0.05), with the Glidewire completing all trials within the allotted time, while the ZIPwire failed 80% of the trials at this branch point. Similar to Point B, the true mean difference is likely to be larger if no artificial time limits had been imposed in this experiment. The HiWire required an average of 122 more sec than the Glidewire to select this vessel (p = 0.097), with the HiWire failing 20% of the trials. The ZIPwire and HiWire exhibited a mean difference of 58.6 sec, with the two wires failing a combined 50% of the trials.

When using the ZIPwire, there was increasing resistance to wire advancement in successive trials. In attempting the fifth trial, it was determined that the ZIPwire could not be feasibly advanced to the test point and the trial was aborted. This difficulty was not encountered with the Glidewire nor HiWire and is likely due to the inherent lubricity of the guidewires. All three guidewires had been exposed to air and soaked in saline for the same amount of time.

The ability to control the direction of a guidewire at a given distance is an important factor in performing interventions in distal vessels. The Glidewire demonstrated a minimal amount of rotation required less than 45 degrees of rotation of the torque device to achieve a complete turn of the guidewire, while the HiWire required nearly 180 degrees of rotation to achieve a complete turn. The inability of the ZIPwire to complete this task is also likely related to its lack of lubricity, relative to the other guidewires.

Limitations of this study included the use of one animal and its native vessels to perform all trials. Variations among guidewires may be masked or unmasked by the inherent characteristics of this canine’s vessels. However, the introduction of multiple canines and variable vasculature would limit our ability to accurately compare the guidewires. The artificial ceiling of five min allowed per trial also masked the true time certain guidewires may have needed to access a vessel. Further trials can be conducted with longer time limits.

The differences among the guidewires’ capabilities to select vessels might be explained by the physical characteristics of each guidewire. Studies have shown that the Glidewire has a more gradual increase in outer diameter when compared to the ZIPwire and HiWire.

In this table, the ZIPwire had the largest tip outer diameter while the Glidewire had the smallest. This differencemay account for the easier ability of the Glidewire to select vessels than other guidewires. Likewise, the shaft stiffness of the standard wires demonstrates a more gradual increase in stiffness in the Glidewire, which allows for increased steerability and control of the tip, with a decreased possibility of wire buckling. Only the standard wires were used in this investigation.

The stiffness of the Glidewire, ZIPwire and HiWire was measured 2–18 cm from the tip of each wire. Each wire was fixed on a platform with a 1-inch gap left open for the measurement to take place. The amount of force (measured in gram-force) needed to depress the wire by 2 mm was measured up to a total of 10 mm in 5 mm/min increments. The gram-force was measured to determine the stiffness of each guidewire, with stiffer wires requiring more pressure to depress the wire.

Conclusion

There exist differences in performance among guidewires examined in an animal model. Our results indicate that the Glidewire is the most efficient guidewire at selecting distal vessels and maintaining functionality over time.