Are you hoping for an off-the-shelf solution? If so, I should imagine that each manufacturer can sell you one of its own (that probably only works with its own products).
Otherwise LabChart and LabView come to mind.
If you thinking of a "home-grown" solution (and why not), then you shall need to establish what data is available from each machine you wish to include.
As you probably know, there have been a number of attempts at standardising ECG data formats:- SCP-ECG, DICOM-ECG, and HL7 aECG for example.
I'll leave you to look up those on the web for yourself!
Meanwhile, data capture is a interesting topic ... and this one would make a very nice project (for students,
et al).
Lastly, "medical" file formats can be tricky ... just take a look at those mentioned
here.