Type of drug, and drug transfer

Limus drugs are cytostatic, while paclitaxel is a cytotoxic drug, which means it essentially induces smooth muscle cell death and has potential for toxicity. Clinical data from randomized clinical trials of DCBs are primarily based on studies of PCB putatively related to their favorable pharmacokinetic properties. ^1,2 It is not clear whether the effect of vessel remodeling is exclusive for paclitaxel or whether it can also be seen with sirolimus or biolimus A9. In our case, an adequate drug transfer of paclitaxel after a short transit time of 45 seconds potentially could contribute to the late lumen enlargement (LLE).

Dissection

The degree of lesion expansion will be associated with the extent of dissection. Some studies demonstrated the relationship between non-flow limiting larger dissection during PCB treatment and the LLG or enlargement. ³ The mechanism might be explained by vessel growth (expansive remodeling) induced by a direct exposure to paclitaxel delivered into the adventitia and/or plaque regression induced by an intensive lipid-lowering therapy. In this case, flap type dissection extending to the media was observed; the maximum dissection arc was 153 degrees, and the total dissection volume was 13.8 mm3 (Figure 2A).

Figure 2 Extent of the barotrauma following DCB treatment. (A) Precise quantification of dissection volume derived from cross-sectional slices with a thickness of 100 microns. (B) OCT deep learning analysis using OctPlus software (Pulse, Shanghai). (C) Wall shear stress derived from the fusion of OCT and angiography. DCB= drug-coated balloon; OCT= optical coherence tomography 

Tissue composition

The tissue composition of the target lesion must have implication on the site of fracture, the extent of dehiscence of the intima from the media and adventitia, on the drug transfer at the time of the procedure, and later on the process of late lumen loss (LLL) or LLG. In this case, the tissue components of vessel wall plaque within the target lesion were identified by OCT deep learning (OctPlus, Pulse, Shanghai). ⁴ The distribution of fibrous, lipid, calcium plaque, and macrophage/ crystal-cholesterol were 89.5%, 3.7%, 6.4%, and 0.6% (Figure 2B). The fact that fibrous plaque is predominant in this lesion may have been associated with greater dissection, adequate drug transfer and subsequent favorable outcomes.

Wall shear stress

Figure 2C shows a great heterogeneity of high and low shear stress derived from the fusion of OCT and angiography in a Computational Fluid analysis based on the Navier Stoke and Quemada equations after finite element analysis. ⁵ In the dissected area low shear stress dominates and is associated with high viscosity prone to thrombosis. This pattern of shear stress is at total variance with the homogeneous profile usually seen after a well deployed stent implantation. Further investigations are warranted to understand the favorable or unfavorable impact of shear stress on outcome.

Post procedural physiological assessment

Although QFR >0.91 after stent implantation could predict a favorable vessel-oriented composite endpoint, only scarce evidence of prognostic value of QFR post procedure exists in patients treated with DCB. ⁶ In our case, the QFR gradually increased: 0.80 at procedure, 0.91 at post procedure, and 0.93 at 6-month follow-up.

In conclusion, the determinant of favourable outcomes following DCB treatment are multifactorial. Previous studies as well as our case report illustrate the numerous potential factors affecting outcomes after DCB treatment, and their positive and/or negative impact, as well as their complex interplay, need further study