The main findings in our retrospective study were as follow: 1) As an OCT indicator for the reaction of guidewire bias, Dcmb and touch angle are two very valuable and convenient independent predictors of ROTA-related coronary intimal dissections; 2) The OCT catheter bias quadrant pre-ROTA was highly consistent with the quadrant where the ROTA-related coronary intimal dissection was present; 3) OCT catheters are always trapped beneath the ROTA-related dissection.
The operation of ROTA is accomplished by pushing a burr in and out of the calcified lesion along the special guide wire.16,17 Due to the principle of differential cutting and friction, it is generally believed that ROTA only ablate inelastic fibrocalcific plaques while sparing adjacent elastic tissue that deflects away from the ablating burr.18,19 However, the ROTA burrs may have ablative effect on the substance in contact.20–22 Guidewire bias position in an angled or tortuous coronary artery is inevitable: a divergence from the central axis of the vessel or the lumen and may result in ablation on the bias side of the coronary wall occurs, iatrogenic injury to intima or media may result and deeper cutting action could lead to more complications: such as dissection or even perforation).5,21,23
In our retrospective study, we analyzed for the first time the quantitative indicators that guide wire bias caused the motion path bias of ROTA burrs and further led to the occurrence of iatrogenic coronary dissection. Guidewire position bias in an angled or tortuous coronary artery is inevitable; a divergence from the central axis of the vessel or the lumen and may result in ablation on the bias side of the coronary wall. If bias to relatively normal coronary wall occurs, iatrogenic injury to intima or media may result and deeper cutting action could lead to more complications: such as dissection or even perforation).5,21,23 no quantitative data have been reported before. In this study, we used a novel method to analyze the distribution characteristics of coronary cross-sectional plaques, location of OCT catheters, and their relationship with the coronary dissection post-ROTA by IVI technique at 1mm intervals after manual co-registration pre-, post-ROTA and angiographic data. Although Dcmb and touch angle could predict ROTA-related dissection to the same extent, the simple and clinically feasible measurements were Dcmb and touch angle indicators, the cut-off value of Dcmb was 0.720mm which including the radius of the OCT catheter (0.45mm) and the thickness of the intima and part of the media and of touch angle was 98.2º.
Shoter Dcmb resulted in higher ratios of ROTA-related coronary intimal dissection. Small value Dcmb often indicates the OCT catheter is biased to and in contact with the coronary vessel wall.
Touch angle is another novel finding which indicates the closeness of OCT catheter contact with a coronary wall. The bigger the touch angle, the closer to contact; the presence of OCT catheter entrapment in the coronary wall (like a finger pressure sign) is often indicative of relatively soft vessel wall at the bias site (usually normal blood vessel segments rather than calcified lesions), as well as a strong compression force of OCT catheter against the vessel wall.
Sometimes media is not easy recognized at the bias site without a large plaque burden. Touch angle, which can be measured easily, is a good alternative index for avoiding ROTA-related complications (Figure 2).
The following four points must be understood when we use the guidewire bias idea to infer the point of view of ROTA bias:
1) Guidewire bias is the starting point but cannot be quantified and guided to optimize ROTA precisely.
2) Catheter bias can be quantified by IVI checking along a PCI guidewire of 0.014 inch, but IVI is a monorail system (not an over-the-wire system like ROTA), it may be similar to or consistent with the guidewire position.
3) A special ROTA wire (0.009 inch body and 0.014 inch tip) was replaced during ROTA operation which might affect guidewire bias by different support and compliance.
4) different positions between tip of the PCI guidewire and the ROTA wire, and the placement of the guide catheter may be changed, which may result in the inaccurate alignment between the ROTA burr movement route and the IVI catheter.
However, the condition of guidewire bias due to coronary anatomical characteristics (distortion and angulation, etc.) will not change. In most cases, IVI bias can reflect the uneven effect of ROTA, especially when the bias is in normal vascular segments, which easily lead to ROTA-related coronary dissections.
Our study showed that the quadrant of pre-ROTA OCT catheter bias was highly consistent (100%) with the location of ROTA-related dissections, which indicates position of the ROTA burr friction is closely associated with the position of the OCT catheter location highly.
However, wire bias could not be detected by angiography precisely unless IVI detection was performed, wire position appears to have been disturbed by the IVI catheter and the concept of wire bias may, upon further study be replaced by IVI catheter bias.
Another critical finding was that OCT catheter was always trapped beneath the intima (subintimal space) if ROTA-related dissection had occurred. This has potential clinical implications, as further replacement of a larger ROTA burr size may lead to further expansion and deepening of the dissection, and even perforation. So, the most important idea is to recognize ROTA-related dissection as early as possible and avoid further ROTA.24 Coronary dissection caused by ROTA must be treated seriously and should be discontinued ROTA procedure once detected, otherwise more serious complications such as inhabited flow or coronary perforation may occur.25 The sensitivity of angiographic ROTA-related coronary dissection was significantly lower than that of IVI detection, and even if the dissections were detected by angiography, it was not possible to determine whether the guidewire bias was beneath the dissections (subintimal space), so IVI-guided ROTA therapy was recommended to detect the ROTA-related dissection early and accurately.