CZT SPECT regional myocardial flow reserve: can it enhance risk stratification?

Numerous studies indicate that patients with diminished capacity for maximal hyperemia face an unfavorable cardiovascular prognosis. The presence of compromised coronary flow reserve is linked to a higher incidence of adverse cardiovascular outcomes (1). SPECT equipment featuring high-performance CZT detectors has been utilized for the quantitative evaluation of coronary flow at rest and during maximal hyperemia. Incorporating Myocardial Flow Reserve (MFR) into SPECT MPI for CAD screening using CZT SPECT may aid in identifying high-risk patients. In one study utilizing CZT SPECT, all regions with a regional CZT MFR ≤ 1.8 exhibited an invasive CFR < 2 (2). The clinical utility of regional CZT-derived MFR data is still under evaluation but could assist in risk stratification.

To describe the frequency of abnormal MFR in patients referred for CZT SPECT and determine if regional MFR data could contribute to risk stratification in this context.

Methodology: One hundred consecutive patients with suspected CAD or known CAD were referred for CZT SPECT between October 7th, 2021, and December 30th, 2022. Patients underwent pharmacological stress myocardial perfusion scintigraphy and rest imaging using a D-SPECT device (Spectrum Dynamics) with dynamic tomographic image acquisition (dynamic SPECT) following administration of 99mTc-sestamibi via an injection pump (Bracco) at a flow rate of 1 ml/second. The dynamic tomographic images were analyzed using Cedars Sinai's QPS kinetic ® software to calculate MFR. MFR values < 2, either regional or global, were considered abnormal. Statistical analysis employed a significance level of 5% and included the Chi-square and Fisher exact test.

We evaluated 100 patients (15 men) with a mean age of 71.4 years. Of these 100 exams: 13 exhibited MFR < 2.0 (Group A); 51 had MFR between 2.0 and 3.0 (Group B); and 36 had MFR > 3.0 (Group C). In Group B, 14 patients displayed MFR in any of the 3 coronary territories below 2.0 (27%). Group C had no patients with reduced regional MFR. Myocardial ischemia was more prevalent in patients in Group A compared to Group B (54% vs. 19%; p = 0.01) and in Group B compared to Group C (19% vs. 3%; p = 0.02). Patients with regional MFR < 2.0 in Group B exhibited a higher incidence of myocardial ischemia compared to patients in Group B with normal regional MFR (35% vs. 10%; p = 0.02).

A decreased regional MFR as measured by CZT SPECT is observed in one out of four patients with MFR between 2.0 and 3.0; and is associated with an increased prevalence of myocardial ischemia. These findings suggest a potential additional benefit in risk stratification that may be derived from regional quantitative blood flow assessment with CZT SPECT.