A method for re-transmission in a multiple-input multiple-output communication system, the method comprising: performing spatial mapping of one or more retransmitted data streams and one or more newly transmitted data streams, wherein the spatial mapping comprises switching bits between the re-transmission data streams and the new transmission data streams. The distal tip of the first elongated member is engaged with the distal tip of the second elongated member at the first location, and, upon engagement, the distal tip of the first elongated member is advanced to a second location via the second elongated member as the second elongation member is advanced to the second location. An amplitude of the cardiac signal following delivery of the pacing pulse may be referenced using the baseline amplitude.