Evaluating cardiac dynamic CZT-SPECT for the measurement of the coronary flow reserve and the determination of the normal values in patients with suspected cardiac micro vascular disease

Reduced coronary flow reserve (CFR) is a strong indicator of major adverse cardiovascular events. It is observed in INOCA and MINOCA. Measuring the CFR is now more recommended in clinical practice, particularly in patients with multiple cardiovascular risk factors.

Different modalities for CFR measurement exist, each with their pros and cons. PET is the most validated modality for measuring CFR, followed by cardiac MR. Both modalities are expensive and not widely available. Cardiac dynamic CZT-SPECT (CD-SPECT) will become more available and less expensive in the future.

The current challenges are how to perform reproducible measurements of the CFR and determining the limit values for normal and decreased CFR. There is a heterogeneity of methods to acquire, to process and to calculate the CFR and not so many studies are done. A well founded and standardized study protocol is needed. An in-house study has been designed including, at the time of writing, 82 patients with multiple cardiac risk factors, all genders and ages. Among those patients 27 had no significant coronary stenosis. The goal is to determine the correct way of performing the CFR measurement and to determine the normal values of CFR.

The CFR cut-off value for CD-SPECT seems to be around 1.5 lower than PET where normal is > 2.0. All patients underwent a one day CD-SPECT rest study followed by a stress study for CFR measurement. Done with Technetium 99m Tc-tetrofosmin through a pump injection (LT Opticvantage®, 30ml/sec, 15 sec). The stress phase was induced with Regadenoson (400mcg) protocol using MyoSpect® GE-Healthcare and calculated with the AlgotMCS6=530C Ottawa Heart Inst. program.

26 patients had no significant coronary stenosis on coronary CT-scan by a Siemens Somaton® force 2x192 following the Cury RC Card Comp Tomography 2016 protocol). A patient had a normal invasive coronarography. In the subgroup with normal coronary arteries, all had a normal myocardial perfusion scintigraphy. 41% had a CFR > 1.5 and 59% a CFR > 1.5. In the group of diabetic patients 19% had a CFR > 1.5. Among those with lowered CFR, 54% were female, age did not demonstrate a significant impact. The preliminary results from this pilot study encourage us to extend our observation to a broader sample.