This paper is the first time to disclose our novel technique, named the “Fracking technique (FT)”, to crack deep calcium with hydraulic pressure through 18-gauge needle which punctures into calcification, so as to obtain larger luminal gain, increase vessel compliance, then provide new versatile treatment options for patients.
The process of FT is described as below. Balloon dilatation with a precisely sized balloon for calcified CFA lesions is performed. If minimal lumen area (MLA) by intravascular ultrasound (IVUS) is suboptimal, FT is indicated. 18-gauge needle (Terumo, Japan) with plastic outer sheath removed is optimal tip size and strength chosen to insert into a part of calcification which is not expended adequately by angiography and/or IVUS. Any larger needle is not recommended because of hydraulic pressure leakage. The reason for keeping the balloon dilation during implementing FT is to compress the lesion to make it denser and prevent dissection which might unexpectedly spread with FT. After needle insertion, 3.0-ml lock syringe is sequentially attached to the back end of needle to check the location of needle tip with injecting saline from the syringe. As the needle tip reaches dense calcification, and plunger of syringe cannot be pushed further, the location of “fracking point” is determined. A balloon indeflator with a half concentration of contrast agent is connected to the back end of needle, and the pressure of indeflator is gradually applied for the dense calcification under angiography till sudden drop in the pressure which means cracks of calcification occurred. This process is “fracking”. During fracking, the needle and the indeflator must be kept connected by hand so that they are not dislodged by the force of pressure. Fracking is repeatedly performed in several fracking points in calcification until the fracking point cannot be detected anymore or sufficient MLA is obtained. The contrast agent in the indeflator sometimes flows from fracking point into the vessel lumen, which means that deep calcification is cracked and connects to the lumen. Most calcifications are cracked by less than 10 atmosphere (atm), a few severe calcium acquire up to 30 atm. After fracking, the dilatation using the previous balloon is performed to compress the calcification which has the network of grains, pores, and cracks due to fracking, and this ballooning also serves to stop bleeding via fracking points. Most of hemostasis takes less than five minutes. Finally, when IVUS demonstrates the larger or targeted MLA, then the procedure finished. The typical process of FT is in the additional file (Supplementary Movie 1).
In terms of limitations, FT can be performed with only CFA or lower arteries. Calcification on the dorsal side of artery is also difficult to be punctured with needle. The effect of FT depends on the volume and density of calcification. FT may be more effective for eccentric calcified lesions than for concentric calcification. Also, there is a learning curve to puncture the calcification being compressed with balloon without puncturing the balloon or damaging the artery.
Here are two cases treated with FT. Case 1 involved an 81-year-old female with diabetes mellitus presented with claudication in her right calf. A 6-Fr sheath was inserted into left CFA as contralateral approach. Quantitative vessel analysis (QVA) demonstrated 94% stenosis with the eccentric calcification which occupied the middle to distal part of right CFA. A 0.014-in. guidewire passed the lesion, and IVUS revealed the eccentric calcification with MLA (6.2mm2; 3.9x2.2mm) (Fig. 1A). After dilation with 6.0x20-mm balloon with blades, QVA showed 24% residual stenosis. However, MLA (10.7mm2; 6.3x2.1mm) was not acceptable (Fig. 1B). Percutaneous direct needle puncture of calcified plaque (PIERCE) technique was attempted to modify the calcification (S. Ichihashi. 2014), and 7.0x40-mm non-compliant balloon at highest pressure dilated the lesion. IVUS showed the unsatisfactory MLA (17.1mm2; 6.8x2.9) (Fig. 1C), therefore, FT was implemented to modify the eccentric calcification which could not be satisfactorily compressed with conventional intervention. After fracking was repeated three locations, with up to 8 atm, QVA and MLA improved significantly to 16%, 27.1mm2 (Fig. 1D), respectively. Finally, the satisfied result was obtained with no complications.
Case 2 involved a 72-year-old male undergoing hemodialysis presented with ischemic rest pain on his right limbs. Angiogram revealed the severe stenosis with eccentric calcification in distal CFA to proximal superficial femoral artery. MLA-IVUS before, after dilation with 7.0x40-mm non-compliant balloon, and after PIERCE technique resulted with 10.0mm2, 13.1mm2, and 15.9mm2, respectively (Fig. 2A, 2B, 2C). None of the results lived up to our expectation. Therefore, FT was attempted and cracked this lesion at 5 atm. A larger MLA of 28.9mm2 was achieved without complications (Fig. 2D). Notable point in our cases was that larger MLA was obtained even though IVUS demonstrated the shape of superficial calcification did not change (Fig. 2A-D). From these IVUS images, we assumed a low probability of distal embolization. These cases have no clinical events two years after FT.
The concept of FT which targets deep calcified plaque is the same as intravascular lithoplasty (IVL) (M. Brodmann. 2019). IVL uses pulsatile sonic pressure waves to modify from intimal till medial calcium. Conversely, FT cracks the calcification from outer parts into the middle. FT might have the potential to achieve larger MLA and provide clinical outcomes similar to IVL. Therefore, long-term comparison studies between two methods are necessary.