This study is the first to evaluate the impact of Chocolate PTA balloon for vessel preparation with DCB strategy compared to other conventional balloons. This study found that Chocolate PTA balloon had less vessel dissection and sufficient expansion than conventional balloon vessel preparation.
In recent years, the development of DCB has resulted in favorable outcomes and has made a substantial contribution to revascularization without stent implantation. Tepe et al. demonstrated that compared with conventional balloon angioplasty, DCB was associated with higher primary patency at 12 months in a randomized controlled trial (82.2% vs. 52.4%, p<0.01). However, 7%–12% of patients require provisional stent implantation; therefore, the DCB strategy is essential to obtain sufficient lumen area using uncoated balloon dilatation and to prevent flow-limiting dissection. To achieve successful EVT using DCB strategy, balloon angioplasty must be optimized.
In this study, the frequency of severe angiographic dissection after pre-dilatation was 4.2% in the Chocolate PTA group and 25% in the conventional group (Figure 2). In a study on Chocolate PTA balloon, the incidence of type C or higher dissection was reported to be 11.1%. Although it was not possible to make a direct comparison, the results were comparable to those of this study. IVUS findings showed a similar minimum lumen area in both groups after pre-dilatation, but the incidence of dissection above 180° was lower in the Chocolate PTA balloon group (Table 3).
A previous report reported the incidence of severe dissection to be 42%, and its predictors were reference vessel diameter <5 mm, lesion length >15 cm, and CTO lesion. As shown in Table 1, there were no significant differences in the lesion characteristics of reference diameter, lesion length, and the ratio of CTO in this study. It is possible that the effect of the Chocolate PTA balloon could prevent the occurrence of severe dissection.
There are several reasons for this effect. First, Chocolate PTA balloon is a novel, semi-compliant balloon catheter aimed at less traumatic percutaneous transluminal angioplasty.[19,20] The concept of this technology is to deliver controlled dilatation of vessels, resulting in successful angioplasty without dissection. Chocolate PTA balloon is a balloon constrained by a mounted nitinol structure around it, which during inflation, forces the balloon to form several segmented ‘pillows’ and ‘grooves’ along the lesion. The formation of these pillows and grooves resembles a chocolate bar and thus its name. The manufacturers report the following mechanism of action: the balloon-confined inflation prevents ‘dog-boning’ inflation pattern and protects healthy vessel tissue, while simultaneous expansion of the nitinol cage with the balloon protects the vessel from traumatic torsional stress that usually causes dissections. Conversely, the ‘pillows’ contact the vessel wall and apply force to create small dissections, necessary for effective lesion dilatation, while the grooves minimize arterial wall stress and stop the dissections created by them from propagating.
Second, a previous study demonstrated that long balloons covering CTO lesions have less dissection, and this report points out the possibility of dissection at the balloon edge. In this study, the Chocolate PTA balloon group had a shorter balloon length. However, fewer dissections and Chocolate PTA balloon nitinol cage prevent longitudinal balloon elongation, which may reduce edge dissection.
Third, regarding the method of preventing vascular dissection in balloon dilation, a previous study performed super slow inflation that slowly dilated the balloon at low pressure. In this study, the Chocolate PTA balloon uses the method of expansion in the Chocolate Bar registry, which "extends to half nominal in 30 seconds and then increases to nominal pressure". Conversely, the conventional group raises the nominal pressure by approximately 10 s according to the decision of each operator. Although different from the protocol of super slow inflation, slower balloon inflation in the Chocolate PTA group than in the conventional group may be one of the factors that cause less severe dissection.
Another finding of our study is that the use of Chocolate PTA balloon may prevent bailout stents. The rate of bailout stenting in the Chocolate PTA balloon group was 2.1%, which was a low probability in the Chocolate PTA balloon group, considering that it was 15.9% in the conventional group (Figure 2).
Predictors of bailout stents were CTO lesion, longer lesion length, and non-use of Chocolate PTA balloon (Table 4). In a previous study using a Chocolate PTA balloon for vessel preparation before DCB, many complex lesions contained 65.5% CTO lesions and 21.4% of CTOs with lesion length >150 mm. However, the bailout stent rate was 9.5%. Randomized controlled trials comparing bare nitinol stents with plain old balloon angioplasty (POBA) reported a bailout stent frequency of up to 40% in the PTA group.[24,25] In addition, randomized controlled trials comparing DCB and POBA reported that the bailout stent rate was 7.3%–26.7%.[18,26] Although this is a different study and cannot be directly compared, the Chocolate PTA balloon group in this study, even in treating complex lesions (TASC-II C/D 42%, CTO 23%, PACSS 3/4 50%, and lesion length 134±98 mm), has a low rate of bailout stenting.
Relationship between vessel preparation by Chocolate PTA balloon and clinical outcomes
After six months, there were no significant differences between the two groups in the results for both primary patency and freedom from TLR. Our study demonstrated that Chocolate PTA balloon did not improve the primary patency. There is a possible reason for this finding. Because primary patency was investigated in patients with few severe dissections after balloon angioplasty after bailout stenting, it is likely that Chocolate PTA balloon improved immediate procedural success of DCB strategy but was not associated with maintaining the arteries in an open state if severe dissection was absent.
This study has several limitations. First, this study was retrospective and included a small number of patients. This study was conducted at a single facility, and the number of available participants was small. Second, grouping according to the period may include potential bias. Third, since there were few cases of bailout stents, the factor can only be investigated by univariate analysis. Thus, it is necessary to increase the number of events and perform a multivariate analysis. There is a need to increase this number. Finally, the observation period was only six months, and the long-term prognosis is unknown. Further investigation is required to clarify the long-term prognosis.