Laser induced shockwave for calcium fracture and increasing coronary artery compliance

Percutaneous coronary intervention (PCI) for improving calcified coronary artery compliance remains a challenge and is associated with high rates of complications and adverse outcomes. In addition to traditional rotational atherectomy devices for improving coronary artery compliance, recently, electric discharge plasma mediated shockwave therapy has been introduced to cause calcium fracture and improve coronary compliance. However, this intervention has cardiac pacing limitations. Laser lithotripsy is commonly utilized to fracture kidney stones. High powered laser pulses are transmitted via small diameter optical fibers (200-400 μm core diameter) to the stone surface, where they induce fracture. We implemented a novel catheter device that utilizes indocyanine green (ICG) filled balloon to produce calcium fractures. At 2mg/mL, ICG has greater than 5x higher absorption coefficient (256cm^-1, 755nm) than water at 2.1 μm, a typical target of holmium lasers (~40cm^-1, 2.1μm) during lithotripsy. To demonstrate the feasibility of laser induced calcium fracture a balloon catheter device (2mm outer diameter un-inflated, 1 meter long) was constructed with a fiber port coupled to alexandrite lasers (755nm) and a balloon port to fill biocompatible ICG in front of the fiber. Different temporal pulse regimes (millisecond to sub-nanosecond) were explored inducing shockwaves pressure amplitudes higher than 50 atm sufficient to cause fracture in coronary artery phantoms made from Ultracal 30® material. This approach does not require cardiac pacing and can markedly improve arterial vessel compliance during stent deployment.