This is the first report of our novel technique, named the “fracking technique (FT)”, to modify deep calcium with hydraulic pressure through an 18-gauge needle, which punctures calcifications to crack them, achieve greater acute luminal gain, increase vessel compliance, and restore vessel mobility, serving as a new versatile treatment option for patients.
The process of FT is as follows. First, a 6-Fr guiding sheath is percutaneously inserted to establish the crossover system from the contralateral CFA. A 5000-IU of unfractionated heparin was injected intra-arterially from the guiding sheath for systemic heparization. After a guidewire crosses calcified CFA lesion, a balloon dilatation sized by intravascular ultrasound (IVUS) measurement for the lesion is performed. If unacceptable procedure results, of which are residual stenosis > 30% on angiography and insufficient acute gain on IVUS, remain after the balloon angioplasty, an 18-gauge needle (Terumo, Japan) without a plastic outer sheath is inserted into a part of the calcification that shows inadequate expansion on angiography and/or IVUS. Alternatively, a larger needle hole is not recommended to use, as it may cause hydraulic pressure leakage from the gap between the needle hole and calcified plaque. The balloon dilation is maintained during the FT to compress the lesion to make it denser and prevent dissection, which might extensively spread during the FT. After needle insertion, a 3.0-ml lock syringe is sequentially attached to the needle to confirm the location of the needle tip inside the plaque by injecting saline from the syringe. As the needle tip reaches dense areas of calcification and the plunger of the syringe cannot be pushed further, the location of the “fracking point” is determined. A balloon indeflator with a half concentration of contrast agent is connected to the needle, and the pressure of the indeflator is gradually increased in the area of dense calcification under angiography until a sudden drop in the pressure occurs, which indicates cracking of the calcification. This process is “fracking”. Fracking is repeatedly performed at several fracking points in calcified plaques until the fracking points cannot be detected anymore or a sufficient MLA is obtained. The contrast agent in the indeflator sometimes flows from the fracking point into the vessel lumen, which indicates that the deep calcification has been cracked and connected to the lumen. Often time the calcifications are cracked by less than 10-atm (atm) of pressure; however, a few severely calcified plaques may require up to 30-atm from our experiences. After fracking, dilatation using the previous balloon is performed to further compress the calcification, which has a network of grains, pores, and cracks due to fracking, this process also serves to stop bleeding at the fracking points. Usually, hemostasis can be achieved in less than 5 min. Finally, when IVUS demonstrates that a larger or the targeted MLA has been achieved, the procedure is finished. The typical process of the FT is shown in the supplementary material (Supplementary Movie 1).
Additional file 1: Supplementary Movie 1. The typical process of the fracking technique.
Here, we present the two representative cases of treatment with the FT. Case 1 involved an 81-year-old female with diabetes mellitus who presented with claudication in her right calf. A 6-Fr guiding sheath was inserted into the left CFA via a contralateral approach. Quantitative vessel analysis (QVA) demonstrated 94% stenosis with eccentric calcification, which occupied from the middle to distal part of the right CFA. A 0.014-in. guidewire passed through the lesion, and IVUS revealed eccentric calcification with an MLA of 6.2-mm2 (3.9 × 2.2-mm) (Fig. 1A). After dilation with a 6.0 × 20-mm cutting balloon, QVA showed 24% residual stenosis. However, the MLA (10.7-mm2; 6.3 × 2.1-mm) was not acceptable (Fig. 1B). The percutaneous direct needle puncture of calcified plaque (PIERCE) technique was attempted to modify the calcification (Ichihashi et al. 2014), and a 7.0 × 40-mm noncompliant balloon was used to dilate the lesion with maximal pressure. IVUS showed an improvement in MLA (17.1-mm2; 6.8 × 2.9-mm) (Fig. 1C). To further expand the MLA, the FT was implemented to modify the eccentric calcification, which could not be satisfactorily compressed with the conventional balloon angioplasty. After fracking was repeated at three locations at up to 8-atm, QVA showed significant improvement of the residual stenosis to 16% and an MLA of 27.1-mm2 (7.6 × 4.2-mm) (Fig. 1D). Finally, a satisfactory result was achieved without complications.
Case 2 involved a 72-year-old male undergoing hemodialysis who presented with ischemic pain in his right limbs at rest. Angiography revealed severe stenosis with eccentric calcification in the distal CFA. The QVA and MLA on IVUS before and after dilation with a 7.0 × 40-mm noncompliant balloon was 96% and 10.0-mm2, 42% and 13.1-mm2, respectively (Fig. 2A, B). The MLA showed a slight improvement of 15.9-mm2 after PIERCE technique (Fig. 2C). To achieve the greater acute luminal gain, the FT was attempted at two locations at up to 5-atm, yielding a larger MLA of 28.9-mm2 without complications (Fig. 2D). ABI was normalized after the procedure, and these patients had lack of hematoma damage to CFA and absence of downstream trash embolization in perioperative period. Furthermore, restenosis caused by neointimal hyperplasia occurrence has not been detected for 2 years follow-up period.
