I don't know about the 5500, but on the 5000 there were a couple of round RS-232 connectors on the back.
At least one of those was intended (I believe) for connection to a modem. So some sort of file transfer protocol must have been available to transmit the (presumably) ECG data.
Although much "fun" could no doubt be had in trying to recreate a printed output from such a (serial) data stream, surely it would be better to spend whatever time is available in fixing the initial problem with the built-in thermal printer?
What problems are you experiencing? Still the same