CCTA after negative stress echo and negative perfusion scan?

[SpottedT]

58 year old female with long-standing hypertension (30 mg Benazepril daily). Wt, chol, lipids, glucose, etc. all good.  Last year, my primary referred me to a Cardio for a 24 hour Holter for palpitations. The cardiologists' comment on the ECG was "non specific ST and T wave changes."  This May, after resuming regular exercise (daily 2.4 mile walk uphill), following 8 weeks de-conditioning for sprained ankle, I experienced a first episode of extreme breathlessness, nausea, sweating, at peak.  My primary recommended a stress echo. She administered an ECG and said, "it's not abnormal but it's not normal."  The stress echo was normal, 7 Mets and 158 bpm, but I stopped it at 158bpm due to shortness of breath and sensation of throat tightening. The cardiologist's interpretation was normal with no wall motion abnormalities and no ECG suggestion of ischemia (some ST and T changes less than 1 mm, rapidly resolving). The Cardio said this could be equivocal, as throat tightening is an anginal equivalent.  I next had a Myocardial Spect Perfusion test and an Echocardiogram. The echo showed mild mitral and mild tricuspid regurgitation.  The perfusion scan was negative, at 99% of 159bmp, no perfusion abnormalities at rest or at peak. I did not experience throat tightening. I still occasionally experience throat tightening at peak exercise; on the inhale. The Cardio invited me to participate in a CCTA trial. Would a CCTA provide additional useful info?  Apparently, false stress echo negatives are due to: not achieving 85% target rate, balanced ischemia, left anterior circumflex stenosis.  Also, wall motion abnormalities occur later chronologically than perfusion abnormalities in the CAD cascade.  But what causes a falsely negative Myocardial perfusion scan?
CAn the CCTA show microvascular occlusion?   Given a negative stress echo and a negative perfusion scan, would a CCTA add useful information?  

[SpottedT]

Thank you for this reply.  

I erred in my question.   The cardio is recommending a ct angiogram, through the promise trial at my center, and not a calcium score test.

The cardio had also given me an rx for 25 mg metroprolol 2x daily and nitrostat.   (this on top of my 30mg benazepril).  But my resting pulse rate is typically 47-55, so how low would the metro send it?  The cardio said try it as an "experiment."  He seems to be continuing to interpret my throat tightening as angina.  The throat tightening is a sensation of not being able to physically get enough air across my throat.  I am able to take deep breaths and catch my breath but there is a sensation of resistance.  This resolves after a few mins after I stop peak exercise.

I made an appt with my primary to ask her opinion of both the angio and the rx. I asked her if she would get the CT angiogram.  But instead of weighing in, she said, "let me get you an authorization for a second cardio opinion."

But a second cardio opinion will go in my electronic file.  Sorry for being so long winded.

[CCFHeart MD25]

A coronary ct at this point is used to help risk stratify patients. You have undergone 2 exercise stress tests that have been interpreted as normal. A coronary calcium ct will not add any incremental information, and will only add radiation exposure. It will not be able to determine anything about microvascular disease.  It is reassuring that you have had two normally interpreted exercise stress tests utilizing two different imaging modalities.