EFFECT OF LOW-GRADE CONDUCTIVE HEATING ON VASCULAR COMPLIANCE DURING IN-VITRO BALLOON ANGIOPLASTY

Radiofrequency-powered, thermal balloon angioplasty is a new technique that enhances luminal dilatation with less dissection than convention al angioplasty. The purpose of this study was to assess the effect of radiofrequency heating of balloon fluid on the pressure-volume mechani cs of in vitro balloon angioplasty and to determine the histologic bas is for thermal-induced compliance changes. In vitro, radiofrequency-po wered, thermal balloon angioplasty was performed on 46 paired iliac se gments freshly harvested from 23 nonatherosclerotic pigs. Balloon infl ations at 60 degrees C were compared to room temperature inflations in paired arterial segments. Intraballoon pressure and volume were recor ded during each inflation as volume infusion increased pressure over a 0 to 10 atm range. Pressure-volume compliance curves were plotted for all dilatations. Six segments were stained to assess the histologic a bnormalities associated with thermal compliance changes. Radiofrequenc y heating acutely shifted the pressure-volume curves rightward in 20 o f 23 iliac segments compared to nonheated controls. This increase in c ompliance persisted after heating and exceeded the maximum compliance shift caused by multiple nonheated inflations in a subset of arterial segments. Histologically, heated segments showed increased thinning an d compression of the arterial wall, increased medial cell necrosis and altered elastic tissue fibers compared to nonheated specimens. In con clusion, radiofrequency heating of intraballoon fluid to 60 degrees C acutely increases vascular compliance during in vitro balloon angiopla sty of nonatherosclerotic iliac arteries. The increased compliance per sists after heating and can be greater than the compliance shifts indu ced by multiple conventional dilatations. Arterial wall thinning and i rreversible alteration of elastic tissue fibers probably account for t hermal compliance changes.