ABSTRACT: Objective. We sought to clarify the mechanisms of backup force for right coronary artery intervention.
Background. Backup force of a guiding catheter is important for successful percutaneous coronary intervention (PCI); however, little attention has been given to its mechanism.
Methods and Results. Backup force of guiding catheters was measured in an arterial tree model. Judkins R, Amplatz L and Ikari R had greater backup force in the transfemoral intervention (TFI) than the transradial intervention (TRI). The primary attachment site of the catheter was the aortic arch in TFI, but it was the brachiocephalic artery in right TRI. This may be a major reason for the different backup force because generation of backup force is governed by the mechanics of the catheter at the attachment site. The Amplatz L and Ikari R had stronger backup force than the Judkins R both in TFI and in TRI because a slight backward motion of the catheter due to device advancement changed the primary attachment site to the reverse side of the aorta or sinus of Valsalva. The primary attachment site of the Ikari L at the power position was the reverse side of the aorta both in TFI and TRI, which was different from other catheters.
Conclusions. The primary attachment site of the catheter had great impact on the backup force in right coronary interventions. An understanding of the mechanism by which the guiding catheter works in TRI and TFI may help in choosing an appropriate approach site.
J INVASIVE CARDIOL 2009;21:570–574
Key words: Percutaneous coronary intervention, Judkins catheter,
Ikari catheter
There is no doubt that backup force of a guiding catheter is important for successful percutaneous coronary intervention (PCI). However, there have been few studies that address the mechanics of guiding catheters, while there have been many reports on treatment devices. Therefore, our understanding regarding this issue is not based on scientific research, but stems only from the opinions of experienced individuals.
In a prior study,1 we evaluated the mechanics of backup force generation for the left coronary artery. In this study, we evaluated the backup force mechanism for the right coronary artery.
Materials and Methods
Aortic model and measurement of backup force. The method for in-vitro measurement of backup force was reported in detail in a previous study.1 In brief, an arterial tree was constructed of polyvinyl chloride tubes. The outer and the inner diameters of the tubes (outer/inner) representing the vessels were: 36 mm/30 mm for the aorta, 10 mm/8 mm from the start of the radial artery to the aorta, and 6 mm/4 mm at the coronary artery. The structure of the arterial tree is three-dimensional.
The aortic model was filled with water at 37°C. A guide catheter was inserted into the model of the coronary artery via either the right radial or the femoral artery approach. A 0.014 inch Runthrough floppy guidewire
(Terumo, Tokyo, Japan) was passed through the coronary artery to the second curve. A 1.5 x 20 mm Arashi balloon catheter
(Terumo, Japan) was pushed automatically at 5 mm/second by a motor drive with a push-pull gauge until the guiding catheter dislodged from the coronary ostium. The maximum resistance was considered to be the maximum backup force where the guide catheter could remain lodged in the working position.
Guide catheter. All guide catheters used in this study consisted of 6 Fr Heartrail shafts (Terumo, Japan). A Judkins right2 (Figure 1A), an Ikari left
3,4 (Figure 1B), an Amplatz L (Figure 1C) and an Ikari right (Figures 1D) were used. The shape of the Ikari L was similar to that of the Judkins R when a 0.035 inch guidewire was inserted (Figure 1E). In Figure 2, catheter shapes are shown during PCI with a Judkins R4 (Figure 2A), Ikari L3.5 (Figure 2B), Amplatz L1 (Figure 2C) and Ikari R1.5. Ikari L4 also looks like a Judkins R4 during PCI.
Statistical analysis. Data were expressed as mean ± standard deviation (SD). Analysis of variance (ANOVA) was used for comparison of means of the three groups. A
p-value (SAS Institute, Inc., Cary, North Carolina).
Results
Judkins R in transradial and transfemoral approaches. A Judkins R4 catheter was used in the aortic model via the trans-radial and transfemoral approaches (Figure 3). The primary attachment site was the outer aortic arch in the transfemoral approach (red line, Figure 3A), and the inner curvature of the aortic arch in the left transradial (red line, Figure 3B) and brachiocephalic arteries in the right transradial approach (red line, Figure 3C). Backup force was greater in the transfemoral approach (Figure 3D) because the primary attachment site at the aortic arch produced a force sufficient to pass through a coronary stenosis. In the right transradial approach, the catheter easily disengaged from the coronary ostium because the brachiocephalic artery is anatomically unfavorable to produce the required force compared with the aortic arch. Results using the left transradial approach were in between the three approaches.
Amplatz L in transradial and transfemoral approaches. An Amplatz L1 catheter was also used in the model. Similar to the Judkins R, the primary attachment site was the aortic arch in the transfemoral approach (red circle, Figure 4A) and the brachiocephalic artery in the transradial approach (red circle, Figure 4B). However, an attempt to produce a force sufficient to pass through a tight coronary lesion dislodged the catheter and caused it to attach on the reverse side of the ascending aorta or sinus of Valsalva both in the transradial and transfemoral approaches (black squares). Thus, the Amplatz L can generate greater backup force than the Judkins R both in the transradial and transfemoral approaches. Comparing the transfemoral and transradial approaches, backup force of Amplatz L in TFI is greater than that in TRI although the difference was smaller than Judkins R.
Ikari R in transradial and transfemoral approaches. An Ikari R1.5 catheter was also used in the model. The primary and secondary attachment sites were similar to the Amplatz L1 catheter. Thus, backup force was also similar to that of the Amplatz L1. Backup force of the Ikari R 1.5 in the transfemoral approach was greater than that in transradial approach. Compared with the other catheters, the Ikari R could generate greater backup force than the Judkins R, and a similar backup force to that of the Amplatz L.
Ikari L in transradial and transfemoral approaches. The Ikari L was originally invented as the guiding catheter for use in the left coronary artery. However, Youssef et al reported that the Ikari L is an excellent catheter for both right and left coronary interventions.
5 Thus, we used the Ikari L as the right coronary guiding catheter in this model. The primary attachment site was the aortic arch in the transfemoral approach, and the brachiocephalic artery in the transradial approach (Figures 6A and 6B). However, an attempt to produce a force sufficient to pass through a tight coronary lesion dislodged the catheter from the coronary ostium and caused it to attach on the reverse side of the ascending aorta in both the transradial and transfemoral approaches (black squares). If the catheter was pushed, it caused the catheter to attach on the reverse side of the aorta without any backward motion (Figure 6C). The angle between the catheter and the reverse side of the aorta was 90º (Figure 6D) in the power position.
Comparison of backup forces in transfemoral interventions. As shown in Figure 7, the backup forces of the Amplatz L, Ikari R and Ikari L are stronger than that of the Judkins R. The force produced by the Ikari L in the power position was a little stronger than that of the Amplatz L and Ikari R, but it was not significantly different.
Comparison of backup force in the transradial approach. As shown in Figure 8, the backup forces of the Amplatz L and Ikari R were stronger than the Judkins R. In the power position, the Ikari L generated significantly greater backup force than the Amplatz L, Ikari R or Judkins R. In these experiments, the strongest backup force was produced by the Ikari L in the power position via the transradial approach. As shown in Figure 8, the Ikari L completely attached on the reverse side of the aorta and the catheter reached the coronary ostium. To the contrary, the Amplatz L and the Ikari R can attach on the reverse side of the aorta, but the catheter is turned away from the coronary ostium.
Discussion
A PCI operator will sometimes have difficulty with catheter selection due to arterial tortuosity, an anomaly of the coronary ostial takeoff, a dilated aorta, and so forth. As of yet, there is no clear idea of the precise mechanics involved in guiding catheters — even in normal anatomy — which would help operators make the appropriate device selection. This study may be the first step in analyzing guiding catheter mechanics in the right coronary artery in normal subjects.
In our prior study,
1 we focused on left coronary artery interventions. The study showed that there were two important factors contributing to the generation of backup force: 1) size of the guiding catheter, and 2) shape of the guiding catheter. In terms of catheter shape, two factors are important: 1) the angle between the catheter and the reverse side of the aorta (θ), and 2) frictional force (λ) in proportion to the attaching area. The hypothesis was shown to fit the following formula:
Fmax = k (cos θ' + λ) / cos θ
(k = constant determined by catheter size, θ' = upside angle between the catheter and aorta,
θ = downside angle between the catheter and aorta, λ = frictional force)
This formula answered a number of unexplained common observations such as the greater backup force of the Judkins L in TFI compared to TRI, the greater backup force of deep engagement of a guiding catheter, the greater backup force of the Judkins L 3.5 versus the Judkins L4 in TRI, and the adequate backup force of the Ikari L in TRI.
This study focused on right coronary artery interventions. We were unable to derive a formula for the right coronary artery as we did for the left coronary artery because the primary attachment site varies with each catheter, with each approach site, and with backward motion. We were, however, able to determine that the primary attachment site had the greatest impact on backup force because it is the supporting point for generating the required force to pass a device through a tight lesion. Considering the physics involved, the supporting point is important in determining the force at the point of application. The differences in supporting points could explain such findings as a weaker backup force with the Judkins R in TRI.
The Amplatz L has been used for the right coronary artery to achieve a strong backup force. Due to the long distal tip, the Amplatz L can attach to the reverse side of the aorta or the sinus of Valsalva with slight backward motion during the advancement of the device. Change of the supporting point is the main reason for the strong backup force of the Amplatz L in the right coronary artery. Thus, the Amplatz L can generate greater backup force than the Judkins R not only in TFI, but in TRI as well.
The Ikari R has a long distal tip similar to the Amplatz L. It can generate similar backup force to that of the Amplatz L because of similar mechanics. However, there are two differences between the Ikari R and Amplatz L: 1) the absence of a distal angle in the Ikari R makes it safe when trying to avoid deep insertion unlike the Amplatz L, which sometimes complicates deep insertion when the catheter is pulled out. The brachiocephalic angle of the Ikari R makes it possible to control the direction of the distal tip. In this case, pushing causes it to move upward and pulling causes it to move downward.
The Ikari L was originally invented as the guiding catheter for use in the left coronary artery. However, it is easy to engage in the right coronary artery as well because the Ikari L looks like a Judkins R catheter if a 0.035 inch guidewire is inserted (Figure 1E). The primary attachment site of the Ikari L was clearly different from other catheters such as the Judkins R, Amplatz L or Ikari R. This explains why the Ikari L generates a stronger backup force in right coronary artery interventions in TRI as well as in TFI. The Ikari L completely attached on the reverse side of the aorta and catheter reached the coronary ostium, as shown in Figure 8. To the contrary, the Amplatz L and the Ikari R can attach on the reverse side of the aorta, but the catheter faces away from the coronary ostium, which explains why the Ikari L has the strongest backup force in the right coronary artery.
Youssef et al reported a 98.1% rate of engagement success using the Ikari L3.5 in the right coronary artery, a 97.6% rate of device success and a 0.48% rate of coronary dissection in 621 cases.
5 The authors also mentioned the existence of a learning curve because coronary dissection occurred only in initial cases, with no dissection in the latter half of the cases.
TRI is more convenient for patients than TFI because of a lower risk of bleeding, shorter hospital stays and a lower frequency of pain reported by the patients.
6–10 Recently, complex PCI has become possible in TRI.
11–15 However, TRI has not been widely performed, likely because of the incorrect notion of weak backup support of guiding catheters in TRI. Scientific analyses showed that backup force is determined by the mechanics of the catheter, not by the approach site.
1 The only benefit with TFI is the ability to use a large guiding catheter such as 8 Fr size that can generate stronger backup force than a smaller guiding catheter. However, an understanding of the mechanism of backup force proves useful when performing PCI with a 6 Fr or smaller guiding catheter. Since a small-sized guiding catheter has a lower access-site complication rate,
16 there is no reason to choose TFI as the preferred approach. Furthermore, the use of a 90 cm long sheath can increase the backup force in real-world patients for right coronary artery angioplasty. An understanding of the mechanism by which the guide catheter works in TRI and TFI may lead to the choice of TRI as the preferred approach.
Study limitations. Because this was an in-vitro study, the results may not be identical to an
in-vivo situation in the human coronary artery. This study proposes a backup mechanism hypothesis. A more accurate hypothesis may exist. Coronary dissection caused by a guiding catheter is another significant problem. This study focused on backup force, but did not include the mechanism of coronary dissection. Furthermore, this study mainly focused on the differences between the right transradial and transfemoral approaches, and we only studied the left transradial approach with the Judkins R catheter.
Conclusion
In conclusion, the major factor that determines the backup force of a guiding catheter for the right coronary artery is the primary attachment site.
Acknowledgments. We would like to thank Mr. Takeshi Kawai, Mr. Masaki Sekino and Mr. Ayumu Takagi for their help with the in-vitro experiment.
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