Balanced ischemia is a thing in SPECT imaging. Does it also exist in cardiac PETs?
The short answer is yes, though quantification of myocardial blood flow means it's less likely we'll miss these patients. The attached study from Finland looked at 286 patients who had CCTAs with questionable lesions and subsequent PETs. Of the patients with reduced myocardial blood flow in all three coronary territories, 72% had relative defect(s) while 28% had balanced reductions. The authors say this group makes up almost 2% of the total population who undergo diagnostic testing, which imo is not a small number.
I also like that we have CCTAs to review for these patients. The authors share that of this group who had reduced myocardial blood flow in all three coronary territories on their PET, the CCTAs between patients with a relative defect and patients with balanced defects were not significantly different in terms of prevalence of 3v disease on CT. Put another way, 5 of 46 patients had significant 3v disease on CCTA but balanced/"normal" perfusion on PET, potentially leading to a false negative if not for myocardial blood flow quantification. I like this picture that gives some sense of prevalence:
Figure 1. Patients undergoing coronary CTA for suspected CAD
Being male and having a smoking history were the risk factors associated with reduced myocardial blood flow in all three coronary territories. I will also link this paper which showed that peak LV tracer uptake during stress minus rest as well as peak RV/LV uptake during stress minus rest both have predictive value with respect to CAD extent, too. Interestingly, peak LV uptake during stress alone was not a helpful parameter.
Cardiac PET was just becoming a common thing as I was finishing my fellowship, so, it's been interesting to learn about it primarily on my own. Thanks for joining me!
Abraham A, Kass M, Ruddy TD, et al. Right and left ventricular uptake with Rb-82 PET myocardial perfusion imaging: Markers of left main or 3 vessel disease. Journal of Nuclear Cardiology. 2009;17(1):52-60. doi:https://doi.org/10.1007/s12350-009-9153-2
Maaniitty T, Stenström I, Saraste A, Knuuti J. Extensive and balanced reduction of myocardial blood flow in patients with suspected obstructive coronary artery disease: 15O-water PET study. International Journal of Cardiology. 2021;338:1-7. doi:https://doi.org/10.1016/j.ijcard.2021.06.012
