She has a BMI of 35 and a creatinine of 2.5. Her echo is unremarkable with a normal ejection fraction and no valvular abnormalities. She is asymptomatic but with poor functional ability. She doesn't really leave the house. She has mild dyspnea and exertion and is seen pre-op and referred for a SPECT myocardial perfusion image. Her SPECT images are as displayed. The read on this was a probably normal perfusion but limited by diaphragmatic attenuation. The ejection fraction was 74% at rest but did drop slightly to 71% at stress. There were no significant regional wall motion abnormalities noted at either rest or stress. No other high-risk features such as transient ischemic dilation but severe diffuse coronary artery calcium was noted on the CT attenuation images. Because of the severe diffuse CAC and the slight drop in the EF, there was some concern and what would you do next? Would you recommend a stress echo, a cardiac PET, a cardiac CTA or would you do nothing in this scenario? So talking through these possibilities, given her severe CAC and renal insufficiency, the cardiac CTA was deemed to be not appropriate or in the best interest. And given the body had this, there were some concerns about a stress echo. And the concern really being, did we miss balanced ischemia given the high calcium score and the very slight drop in the EF? So because she was pre-op and slightly symptomatic, a cardiac PET was recommended. Here are her PET imaging scans. And you can see both the relative perfusion as well as the bullseye polar plots. This was interpreted as having mild to moderate infralateral ischemia with transient ischemic dilation as well as a shift in the pixel count which signifies a slightly higher risk scan. Looking at the other parameters on her PET scan, her resting ejection fraction was 78% but dropped significantly at stress to 71%. Calcium score was markedly positive at over 1500 with a large predominance in the green area in the left main coronary artery. Her resting flows were about 1.65 which is a bit high for resting flows. We usually recommend or usually see those around 1. Peak stress flows were above 2 which is reassuring but we like to see those double at 2. And her flow reserve was markedly diminished at 1.3. Now some of this may have been due to the high resting flows but even when we corrected the resting flows for rate pressure product for the resting heart rate and blood pressure, the MFR only corrected up to about 1.6 so much of this was still there. You can see that the MFR reduction is diffusely reduced but worst in the circumflex territory. And then again, second would be the worst in the LAD raising concern again for a left main lesion. This patient did go on to cath and was found to have a critical left main into her cirque stenosis. So what are the advantages of PET over SPECT and in particular in this case? So first of all, we know that PET offers consistent high quality images. Because of the higher energy isotope at 511 KeVs, the quality of the images have higher spatial, contrast, and temporal resolution. In addition, there is built-in and robust attenuation correction with PET. Because of these high quality images, you have less equivocal studies. They're either definitely normal or definitely abnormal which raises your sensitivity and sensitivity for obstructive CAD and also provides much stronger prognostic power. When we look at the advantages of PET over SPECT for more of the technical details, again reviewing 511 KeVs over the typical 140 of SPECT, up until about a month ago we were limited to pretty much to pharmacologic imaging with PET because of the much greater availability of rubidium than ammonia in this country. But fluperidase has just been approved and will now allow for exercise stress testing. There's still a lot to be known about how we use this agent but I think that this really opens up the market for exercise and pharmacologic PET in the future. The duration of the study is markedly shorter than SPECT regardless of which isotope you use. And the radiation dose is also about a third of the SPECT dose regardless of the isotope used. I think the most important advantage is though we went through the perfusion, the high quality images, but the ability to do a true stress ejection fraction is very important. With pharmacologic stress, when we are imaging for the gated PET images at the same time that we're giving the vasodilator, gives a much more accurate assessment of how does the ventricle respond to stress. In addition, the ability to quantify coronary blood flow in absolute measurements and calculated reserve is a significant advantage of PET over SPECT. And I really think that the clinical value of PET is the integration of all four of these parameters. So when you can integrate robust relative perfusion with a true stress ejection fraction, coronary artery calcium scoring, and then the absolute flow and myocardial flow reserve, it's really the integration of all four of these parameters that allows for comprehensive risk assessment in our typical symptomatic intermediate risk patient that we're referring for myocardial perfusion imaging. So an explanation in regards to this case, the high coronary artery calcium score establishes the presence of coronary artery disease. It clearly documents that there is atherosclerosis present. The abnormal MFR, despite a normal or mild perfusion, reclassifies the study from low risk to high risk. The low MFR in combination with the high CAC increases the suspicion for significant obstructive coronary artery disease. And the significant drop in EF raises the concern for more significant ischemia and obstructive disease. And we know that a diminished LVEF reserve correlates with the amount of ischemia, the number of vessels involved, and mortality prognostic risk. So the teaching point in this case is that the addition of flow and flow reserve, a quantitative calcium score, and the true stress ejection fraction added incremental information that allowed improved detection of balanced ischemia. My references. Thank you for your attention. For more information, visit www.fema.gov

cardiac PET

coronary catheterization

ischemia

ejection fraction

myocardial flow reserve