This study is the first to evaluate the impact of Chocolate PTA balloon for vessel preparation with the DCB strategy compared to other conventional balloons. This study found that the Chocolate PTA balloon had less vessel dissection and sufficient expansion than the conventional balloon. A representative case is illustrated in Fig. 4.
In recent years, the development of DCB has resulted in favorable outcomes and has contributed greatly to revascularization without stent implantation. Tepe et al. (Tepe et al. 2015) demonstrated that DCB was associated with a higher primary patency at 12 months than conventional balloon angioplasty 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 a sufficient lumen area using uncoated balloon dilatation and to prevent flow-limiting dissection. To achieve successful EVT using the DCB strategy, balloon angioplasty must be optimized.
The frequency of severe angiographic dissection after pre-dilatation was 4.2% in the Chocolate PTA group and 25% in the conventional group (Fig. 2). In a previous study (Mustapha et al. 2018), the incidence of type C or higher dissection was 11.1%. Their findings were comparable to ours, although we could not compare them directly. 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 study (Fujihara et al. 2017) reported an incidence of severe dissection of 42%, with reference vessel diameter < 5 mm, lesion length > 15 cm, and CTO lesion as predictors. We observed no significant differences in the lesion characteristics of reference diameter, lesion length, and the ratio of CTO (Table 1). The effect of the Chocolate PTA balloon might have prevented the 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 (Spiliopoulos et al. 2019; Ward and Mena-Hurtado 2014). The Chocolate PTA balloon is a balloon constrained by a mounted nitinol structure surrounding it. This nitinol cage prevents vessel injury from torsional stress that causes dissections. It also prevents partial overdilation of the balloon, distributes the pressure on the vessel, and minimizes arterial wall stress on vessel.
Second, a previous study (Tan et al. 2018) demonstrated that long balloons covering CTO lesions have less dissection, suggesting the possibility of dissection at the balloon edge. We observed a shorter balloon length in the Chocolate PTA balloon group. However, fewer dissections and the Chocolate PTA balloon nitinol cage prevent longitudinal balloon elongation, which may reduce edge dissection.
Third, regarding preventing vascular dissection in balloon dilation, a previous study (Sugihara et al. 2020) performed super slow inflation that dilated the balloon slowly at a low pressure. In this study, the Chocolate PTA balloon uses the method of expansion in the Chocolate Bar registry (Mustapha et al. 2018), which “extends to half nominal in 30 s 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 (Sugihara et al. 2020), slower balloon inflation in the Chocolate PTA group than in the conventional group may be one of the factors that causes 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 (Fig. 2).
Predictors of bailout stents were CTO lesion, longer lesion length, and non-use of Chocolate PTA balloon (Table 4). In a previous study (Sirignano et al. 2018), using a Chocolate PTA balloon for vessel preparation before DCB, many complex lesions contained 65.5% CTO lesions and 21.4% of CTOs with a 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 (Schillinger et al. 2006; Laird et al. 2010). In addition, randomized controlled trials comparing DCB and POBA reported that the bailout stent rate was 7.3%–26.7% (Tepe et al. 2015; Zeller et al. 2015). Although direct comparisons could not be made, 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), had 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 in primary patency and freedom from TLR between the two groups (Fig. 4). This may be because if a severe dissection was achieved by pre-dilation, bail-out stenting did not make a significant difference between residual stenosis and severe incision on final angiography.
This study has several limitations. First, it was a small, retrospective, single-center study. Second, grouping according to the period may have included 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.
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