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.