If you are being asked to go deeper (beyond basic codes), rather than reinventing the wheel, you could try using ARTG* codes.
site ... try searching for electrocardiograph
for example. Note that you can save (export) search results to .xls.
Meanwhile, how about yet another code-base ... take a look at UNSPSC
** ... and try entering electrocardiograph
in the Code Name field.
* Australian Register of Therapeutic Goods
** United Nations Standard Products and Services Code
Note that UNSPSC is associated with GS1 (formerly the Uniform Code Council) - another one that has become popular. Yes; there's money
But UNSPSC is not too bad, as (at least) it uses an hierarchical (8-digit) structure.