Methods
Fresh (5 days non frozen) chicken breasts (Voltigeurs Farm, Drummondville, Qc, Canada) were placed and fixed to a rubber mat, in a water tank (wet lab) filled with an isotonic saline solution maintained at 37ºC. Medtronic SelectSecure 3830-69 cm pacemaker leads were screwed (by clockwise turning the lead until it reaches the desired location -left bundle branch lead implanters know how easily the 3830 lead advances just by screwing it into the septum-) with the proximal ring at least 5mm deep in the flesh. A Stockert EP Shuttle generator and a Thermocool SF NAV Bi-Directional Catheter (BNI35FJCT) from Biosense Webster were used to deliver RF energy for one minute at each iteration. Each 50 watts (W) power setting RF delivery was repeated at least once in another breast.
Three variations of a test were done. In the first variation (method A), the Biosense RF catheter touched the proximal ends of the pacemaker lead (sequentially distal tip and proximal ring) which was used to deliver the RF energy (direct fashion), the current passes from the RF catheter to the 3830 lead by having their ends touch together, and temperature rises on the interface where both catheters touch, and on the distal end of the 3830 lead which touches the flesh. The power was set at 50W, temperature was set but not limited at 70ºC, and a long metal string at the bottom of the water tank acted as the return patch. Power variations of this method were done at 10W, 5W, 2W and 1W.
In the second variation (method B), the Biosense RF catheter delivered the energy immersed freely in the solution of the tank (not in contact with the chicken breast) and the pacemaker lead was used as the return patch (sequentially attaching the metal string to the proximal and distal ends). The power was set at 50W, power variations of this method were done with 5W for the proximal end and 1W at the distal end.
In the third variation (method C), the Biosense RF catheter delivered the energy by touching the breast surface at one centimeter of the 3830 lead, screwed perpendicular to the RF catheter (see picture 2), and this 3830 lead was used as the return patch. The power was set at 50W.
Chicken breasts were used to test this concept since RF lesions turned promptly white, easily differentiable from raw chicken (non reported tests showed that after around 10-20 seconds of RF delivery the flesh turned white).
One chicken breast was prepared with RF applications at 50W, 10W, 5W, using A, B and C methods with a new 3830 lead for histologic examination.
To report the results, each lesion was cut in its middle, following the pacemaker lead long axis. A high-quality picture was obtained and digitized (24.1Mpx with a NIKON D5200 camera and a AF-S DX VR Nikkor 18-55mm f/3.5-5.6G II lens). Lesion surface area was then measured using the SketchAndCalc software (https://www.sketchandcalc.com). Each lesion surface area was averaged for the same kind of iteration and expressed as cm2.