My response is regarding general coding/modifier guidelines as I know practically nothing about cardiovascular procedures.
Modifier -51. Basically, this modifier tells the carrier - "pay me 50% less for this because another procedure was primary". Carriers will add this on when processing the claim. I don't advise using this modifier at all when coding. In fact, CMS had issued guidance several years ago specifically stating NOT to use -51 and their system will auto append.
The main reason being if you add -51 to an incorrect procedure, you will wind up with an underpayment. With Medicare, it's rather straightforward to determine which procedure will pay more, but with commercial carriers, not all payment contracts are based on RVUs so you might bill:
CPT12 $2000. Carrier's allowed amount $600
CPT34-51 $1500. Carrier's allowed amount $800
If you billed with no modifier, carrier would pay $800 plus 50% of $600. $800 + $300 = $1100
If you billed as above, carrier would pay $600 plus 50% of $800. $600 + $400 = $1000
Additionally, in your thrombectomy coding, 37185 is an add on code, so -51 should NEVER be applied to an add on code.
Regarding bilateral procedures. 37184 is permitted to be billed bilaterally. If you use any online coding software, it should indicate whether a code may be billed bilaterally. I THINK it may also be in the CPT book, but I rarely use paper books anymore. CMS also provides the information, but in a less readable/accessible format. Depending on your carrier, bilateral may be billed:
37184-50
- OR -
37184 -LT
37184 -RT
I know I have one carrier that will only accept the second way and deny claims billed the first way. Most carriers will accept either way, but may advise one over the other.
Running 37184/37185, there is no NCCI edit. Same for 37221/37224. As I've never coded CV, I cannot provide any other guidance than the NCCI edits. Don't forget some private payors may have edits above and beyond NCCI edits.