INTRODUCTION

Since Andreas Grüntzig’s first published series of angioplasty cases there has been an exponential rise in the complexity of coronary artery disease deemed treatable by percutaneous revascularisation. This has been enabled by the equally rapid change in the technology and number of devices available to the cardiologist. The principal driving force behind all these developments have been to conquer the two areas that have limited the application of PTCA, now affectionately known as POBA (plain old balloon angioplasty) namely acute vessel closure/coronary dissection and restenosis. Coronary artery stenting has addressed to a significant extent these two Achilles’ heels of POBA but has its own drawbacks with the problem of in-stent restenosis that has not been entirely resolved even in the DES era.

POBA³ increases luminal size by controlled barotrauma causing plaque rupture and vessel wall expansion. It is established that while the final angiographic result of POBA is related to the extent and force of balloon dilatation it is the extent of vessel wall trauma that determines acute vessel closure and also initiates the mechanism that when exaggerated leads to restenosis. Part of the difficulty is that the balloon frequently exerts its maximal force on the more normal parts of the vessel wall causing stretching which is prone to early recoil and damaging normal endothelium rather than cracking more organised fibrous plaque.

The Barath cutting balloon¹ was designed specifically to address the problems of barotrauma-related complications of POBA. The device is a non-compliant balloon which when expanded has three or four longitudinally mounted microtomes on the external surface. The balloon material is folded to shield the blades and protect the vessel wall as the catheter is passed to and from the lesion. When the balloon is expanded at the site of a coronary lesion the blades produce controlled incisions into plaque rather than a random dissection. This allows the balloon barotrauma pressure to be evenly distributed and force to be applied to plaque at least as effectively as to normal parts of the vessel wall. The reduction in hoop stress and lower pressures used to achieve an angiographically acceptable result (maximum of 6–8 atmospheres) are the main factors put forward as being likely to reduce both acute complications and restenosis.

Intravascular ultrasound (IVUS) studies have demonstrated that the different mechanism of lesion dilation with CBA achieves similar luminal dimensions to POBA but with larger plaque reduction and less vessel expansion in noncalcified lesions.² In contrast in calcified lesions CBA achieves larger lumen gain than POBA with similar proportional effects on plaque compression and vessel expansion. The virtual absence of vessel recoil would appear to be a significant factor in reducing the restenosis rates.

PRACTICAL POINTS

The Flextome Cutting Balloon (Boston Scientific, US) is the latest incarnation of the original Barath design (Fig. 16.1) and is sized from 2.0 to 4.0 mm in quarter sizes. The deflated profile is from 0.041 to 0.046”, the atherotome lengths are either 6, 10 or 15 mm and the distal shaft is 3.2 F (Fig. 16.2). The changes to balloon material and the incorporation of flex points every 5 mm for the 10 and 15 mm atherotomes has improved flexibility although its ability to cross areas of excessive tortuosity is inevitably inferior to the performance of modern compliant balloons. As with many interventional devices there are relative indications and contraindications, which are varied, in everyday use. Clear contraindications to its use are extensive vessel calcification and visible intraluminal thrombus. In practical terms excessive tortuosity and long lesions present difficulties though repeated inflations of the shorter balloon can achieve a good result. If there is difficulty crossing a lesion predilatation with a small balloon to allow passage of the cutting balloon is accepted practice. Once positioned across the lesion inflation should be undertaken slowly to reach 6 atmospheres at 30 seconds and inflation maintained for up to 2 minutes provided patients can tolerate this. The slow unfolding of the microtomes prevents vessel damage and allows the movement of the artery to assist incision. It is important to allow full deflation to ensure involution of the microtomes prior to withdrawing the balloon. If full expansion is not achieved up to 8 atmospheres pressure may be applied. The balloon/artery ratio should be 1.2:1 and in practical terms this means using one-quarter size more than the normal vessel segment. The final appearance may be ‘stent-like’ but up to a 30% residual stenosis is counted as an acceptable result and it is well observed that further positive remodelling takes place after initial dilatation such that follow-up angiograms not infrequently look better than the final result. Small controlled linear dissections are not uncommon and provided there is no change in the appearance over 5–10 minutes, acute vessel closure is extremely unlikely.³ As stenting is undertaken in 90% lesions acute closure is not a clinical issue and small linear dissection may allow better stent expansion.

Figure 16.1 Flextome Cutting Balloon (Boston Scientific).

Figure 16.2 Flextome Cutting Balloon dimensions.

CLINICAL DATA

The hypothesis that controlled ‘surgical’ expansion using CBA would induce less vessel wall injury and reduce neointimal hyperplasia was explored by the CUBA investigators.⁴ This study examined the clinical effectiveness as a primary treatment in 304 patients randomised to CBA or POBA and demonstrated that restenosis rates were significantly lower at six months in the CBA arm (CBA 30% vs POBA 42%; p=0.03). These promising early findings, however, were not confirmed by the pivotal multi-center Global trial,⁵ which randomised 1,238 patents to either CBA or POBA. The study was limited to simple A/B1 lesions and used a single CBA inflation at a balloon artery ratio of 1.1:1. Restenosis rates were identical in the two groups (CBA 31.4% vs POBA 30.4%; p=0.75) with significantly more coronary perforations in the CBA group (CBA 5 vs POBA 0; p=0.03).

The results of the Global trial combined with the widespread use of coronary stenting has, therefore, confined CBA as a primary interventional procedure to a variety of specific areas. These are principally in small vessel coronary disease, resistant or ostial lesions and as a treatment of the burgeoning problem of in-stent restenosis. There is, however, increasing interest in the use of CBA in vessel preparation prior to stent implantation as a method of providing optimal stent deployment.

SMALL VESSEL PTCA

The CAPAS study randomised 232 patients (248 type B or C lesions) with a reference vessel diameters of <3 mm to CBA or POBA.⁶ The success rate was high with a stent implant rate of 6% in CBA and 11% in POBA. Angiographic follow-up was 95% complete and showed a significant reduction in restenosis after CBA (22% vs 41%; p <0.01). Although there was a reduction in TVR after CBA this did not reach statistical significance (22% vs 29%). A further randomised trial by Ergene and colleagues⁷ although small, confirmed similar findings with a restenosis rate significantly lower after CBA (27% vs 47%; p <0.05) and observed significantly fewer dissections after CBA. Iijima et al.⁸