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Original Contribution
Directional Coronary Atherotomy — Experimental Use of Single-Blade Cutting Balloon
September 2006
Drug-eluting stent (DES) implantation has been shown to considerably reduce the occurrence of restenosis compared to other modalities of percutaneous coronary intervention (PCI) such as plain old balloon angioplasty (POBA), bare metal stent (BMS) implantation, directional coronary atherectomy (DCA), rotational atherectomy and others.
However, restenosis still occurs in about 4% to 10% of cases according to the lesion complexity.1–4 The predictors of post-sirolimus-eluting stent (SES) restenosis are similar to those following POBA or BMS implantation, and include treatment of small vessel size, ostial lesions, diffuse lesions or diabetes.5 These characteristics may prevent adequate expansion or apposition of the stent, impeding the antiproliferative action of the drug. In these lesions, some modification of the plaque prior to stenting may be required.
A conventional Cutting Balloon (Boston Scientific Corp., Natick, Massachusetts), with its 3 or 4 tiny blades (atherotomes) configured at equal intervals along the surface of the balloon, achieves plaque modification with less injury to the vessel wall than a conventional PTCA balloon,6 and has been shown to be useful for the treatment of de novo lesions or in-stent-restenosis (ISR).7–9 Cutting balloon therapy before BMS stent implantation has also been shown to be beneficial in acute procedural results10 and at follow up, with a reduced incidence of ISR.11 However, care must be taken to avoid procedural complications. Although the complex lesion types such as eccentric or calcified lesions are at enhanced risk of coronary rupture,12 no currently available devices can effectively modify plaque in these lesions.
As a potential solution to this problem, we developed a single-blade Cutting Balloon (SBC) and report here on its experimental use in an animal trial, and on its potential usefulness in humans.
Methods
Device materials. The SBC is an over-the-wire type catheter with a single blade attached to the surface of a noncompliant balloon (Figure 1). The blade is 10 mm in length and runs along the same side and axis as the balloon inflation port. The polysulfone balloon shaft is 3.6 Fr proximal and 2.7 Fr distal and is compatible with a 6 Fr guiding catheter. The working height and width of the blade are identical to those used for the current Cutting Balloon, namely 0.005–0.006 inches in height and 0.003 inches thick.
Single-blade Cutting Balloon procedure. A guiding catheter with side holes is necessary, as the side holes serve as an intravascular ultrasound (IVUS) landmark to identify the plaque location. Before inserting the guiding catheter in the patient, the relative position of the side holes to the proximal catheter portion (guiding catheter hub) was checked. Then we marked the position of the side holes on the hub by scratching with a needle so that once the catheter is engaged in the coronary artery, the orientation or position of the side holes can be determined. Then, after crossing the lesion with a guidewire, an IVUS interrogation is performed. For this we used the CVIS imaging system (Sunnyvale, California), in which the transducer moves inside the catheter so that we could be sure of the position of the side holes relative to the lesion during pullback. From the IVUS images obtained during pullback, we ascertained the position of the lesion part to be cut in relation to the side holes, noting how many degrees clockwise or counter-clockwise the lesion was from the side holes. We then determined the orientation of the blade from the IVUS images and the position of the hub. If, for example, the lesion is at 180° clockwise from the side holes, the orientation of the blade (which is the same as that of the inflation port) will also be at 180° clockwise from the hub mark (Figure 2). Finally, taking care to keep the blade at the correct angle and orientation, we inserted the SBC into the guiding catheter, as the blade is not radiopaque and its position can therefore not be verified on fluoroscopy. A long guidewire or an extension wire is required at this time, as the SBC is an over-the-wire device. We then advanced the SBC fully along the guiding catheter and up to the lesion, while maintaining the orientation of the blade and side holes.
Animal study protocol. Angioplasty was performed on 5 lesions in 4 female Landrace Large Yorkshire-Berkshire pigs, including 3 bifurcation lesions. Lesion locations were in the left anterior descending artery (LAD) in 2 cases, the left circumflex artery (LCx) in 1 case, and the right coronary artery (RCA) in 2 cases. All procedures and care of the animals were in strict accordance with the National Research Council guidelines. On the day of the procedure, the animals were put to sleep using an intramuscular injection of 2 mg/kg azaperone, 0.05 mg/kg atropine and 12.5 mg/kg ketamine, after which they were intubated and kept anesthetized with 0.05 mg/kg/minute oxygen and 0.5%/kg/minute sevoflurane. The right femoral or right common carotid artery approach with an 8 Fr sheath was used for all procedures, and the SBC was advanced and dilated in the coronary artery exactly as described above. SBC inflation pressure was 6–8 atm for 60 seconds and IVUS was performed before and after SBC dilatation. The results recorded on VHS video. The KBT with 2 SBCs were also done on the 3 bifurcation lesions. After these procedures, all animals were euthanized and their hearts removed and preserved in 10% formaldehyde. We subsequently dissected the tissue of the relevant myocardial territory of the arteries that underwent angioplasty and did H&E and elastic staining of the sections.
Results
There were no device delivery failures. The 5 lesions were successfully dilated, and no complications, including coronary perforation or dissection, occurred. Angiographic images of a case are shown in Figure 3.
We were also able to confirm with IVUS that the atherotome or blade was successfully and correctly oriented in each case (Figure 2). In the lesions in which we performed KBT, none of the balloons ruptured from contact with each other, and all bifurcations were successfully dilated (Figure 4). Tissue pathology revealed focal injury to the vessel wall, but did not extend to the adventitia (Figure 5).
Discussion
In this small animal study we were able to show the feasibility and safety of PCI using a SBC in native coronary artery lesions, including bifurcation lesions. Inflation of the SBC resulted in focal injury to the vessel wall and did not extend to the adventitia.
In the pre-DES era, the Cutting Balloon was shown to be useful in the treatment of de novo lesions or in-stent restenosis (ISR). One study found that cutting balloon angioplasty was superior to POBA or BMS stent implantation in small (13 A lower restenosis rate in small-branch ostial lesions of native coronary arteries was also found with cutting balloon therapy compared to stenting alone (41% vs. 63%; p = 0.05).7 We previously showed that cutting balloon angioplasty has a lower rate of ISR compared with POBA (39% vs. 58%).9
Cutting balloon therapy before BMS stenting has also been shown to be beneficial for acute procedural results2 and at follow up, with a reduced incidence of ISR (4% vs. 21%; p = 0.09). It did not, however, reach statistical significance in this small study.11
Since their introduction, DES have had a major impact on the treatment of ischemic heart disease. The restenosis rate reported for DES in a number of trials since their introduction1,14 is by far lower than restenosis rates associated with previous devices.
However, in complex lesions and certain patient subsets, restenosis rates are still significant. Reported ISR rates are approximately 8–10% in small vessels (4 and 25% in diabetic patients with small vessels.16 Continued effort should therefore be made to reduce this rate. Restenosis following stenting correlates with post-stent minimum stent area (MSA) and strut distribution.17–19 In diabetic subjects and small-vessel lesions, the prevalence of eccentric plaques can prevent sufficient MSA or cause uneven expansion of the stent struts. In order to further reduce the restenosis rate in these lesions, some form of plaque modification to prepare the lesion prior to stenting may be necessary to ensure full and even expansion of the stent. The problem is that no existing device is suitable for this kind of small-reference eccentric lesion. Conventional PTCA alone does not modify the plaque sufficiently. Directional coronary atherectomy (DCA) is a useful modality for eccentric plaques, but its use is limited to smaller vessel sizes. Rotational atherectomy can modify plaque in smaller vessels than DCA can, but depending on lesion morphology and especially in very eccentric lesions, coronary perforation is a real risk.
There have been several reports detailing the usefulness of the conventional Cutting Balloon in calcified lesions or in small vessels,7,20–22 and we have previously reported that those kinds of plaque morphologies are an independent predictor of coronary perforation for conventional cutting balloon angioplasty.12 As conventional cutting balloons have 3 or 4 atherotomes attached along the balloon, we can speculate that perforation may occur when the blade incises a part of the lesion where the plaque volume is slight, or when in a lesion containing calcium, the Cutting Balloon causes excessive injury to the vessel wall on the opposite side.
The SBC we used in this study was designed to overcome the drawbacks of the conventional device as much as possible. Our experimental procedures show that this catheter can be delivered to distal sites in porcine coronary arteries. The reduced number of blades also means that the new device is more flexible than its conventional counterpart, and we were able to incise plaques exactly where intended, even in very distal locations. This SBC may permit accurate plaque modification in lesions inaccessible to any existing device, and the combined use of this SBC and DES may be expected to further reduce the restenosis rate in these key lesion subsets.
The SBC can also be used for KBT, which is not the case with the conventional Cutting Balloon. The fact that the conventional device results in little plaque shift makes it a useful tool in bifurcation lesions,7 but its inability to perform the KBT leaves a large number of cases, in our experience, in which plaque cannot be adequately modified. With the SBC, as long as care is taken with the position of the blade, it may well be possible to simultaneously perform plaque modification in two branches in almost all bifurcation lesions. This device may constitute a useful advance in the treatment of bifurcation lesions, which remain problematic for PCI as a whole.
Besides, stents, particularly DES, are contraindicated in patients who are not suitable for antiplatelet therapy, such as those with bleeding risks or in whom an operation is planned. For such patients, the SBC could have an important role for achieving an effective percutaneous coronary treatment.
Study limitations. This study has a number of limitations. First, we used animal coronary arteries and not human ones, and the lesions were relatively simple and few in number. We can therefore not conclude that this device would perform exactly in the same way in complex lesions of human subjects. The device we used in this study behaved as we envisaged and with similar effect, but there is much room for improvement in terms of the flexibility of the catheter itself and its responsiveness to handling. These refinements would improve the ease and accuracy of the direction of the incision. An in vivo trial would then be required to confirm the safety and feasibility of the SCB in human subjects.
Acknowledgements. The authors wish to thank Drs. Yoshio Matsuno, Tetsuro Ohta, Hiroyuki Yoshitomi, Seiji Okada, Dr. Jean-François Surmely, Mr. Akira Hirano, Mr. Naritoshi Yano and Mr. Mark Green for their assistance.
References
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