Stress Testing questions

This scenario has been presented to me recently by the Nursing Staff in our Heart Center: On occasion when a stress test isn't completed due to issues such as BP readings, it is discovered the patient cant walk on a treadmill safely, heart rhythm problems etc., charges are not entered however, the tech portion or nurse portion has been started. The nurse has 1 hour of their time scheduled for an EST; if the test isn't completed, they still have had 1/2 hour of their time used getting the patient ready with obtaining history baseline, VS/baseline rhythms, etc. Wondering if this should be billed or not; if so, what portion? Is it appropriate to bill 99211-99213 or bill for the stress test (93015 for example) with a 52 modifier indicating a reduced service as the physician has to sign off either way? As the patient is obviously aware that the stress test wasn't completed due to any of the circumstances mentioned previously, they need to be made aware that they MAY still have a copay/coinsurance/deductible if it applies to their contract.

Also, if it is discovered there is an equipment problem, test is cancelled and no charges are created.

Any input is greatly appreciated.