apparatus and method for accessing the wall of a body lumen while simultaneously providing zone isolation and fluid bypass capability , the apparatus comprising : an erectable proximal isolation barrier capable of making a sealing engagement with the wall of the body lumen ; an erectable distal isolation barrier capable of making a sealing engagement with the wall of the body lumen ; a bypass channel secured to , and extending between , the proximal isolation barrier and the distal isolation barrier , the bypass channel comprising a lumen communicating with the region proximal to the proximal isolation barrier and with the region distal to the distal isolation barrier ; and a working catheter passing through the proximal isolation barrier and terminating short of the distal isolation barrier , the working catheter providing a central lumen for providing access to the wall of the body lumen between the proximal isolation barrier and the distal isolation barrier .