SPECT blood flow improves per-vessel sensitivity of myocardial perfusion imaging to detect ischemia

Objectives: SPECT myocardial blood flow (MBF) imaging can be performed using modern solid state SPECT cameras. It is an additive technique to traditional relative myocardial perfusion imaging (MPI). The additional clinical benefit of MPI remains to be proven and its promise is largely based on prior PET MBF data (1,2,3). We sought to determine whether SPECT MBF would improve the sensitivity of ischemia detection by MPI.

Methods: Consecutive patients undergoing clinical SPECT MPI had MBF performed. A comprehensive electronic medical record review was undertaken to determine 12-month cardiovascular follow-up. In patients who underwent anatomical downstream testing, absolute MBF was calculated for the global left ventricle and individual myocardial vessels (LAD, LCx and RCA) at rest and stress. SPECT findings (MBF and MPI) were evaluated on a per-vessel and per-patient analysis.

Results: 195 patients were included with a mean age of 71 years old. Indications for SPECT MPI were chest pain (20%), previous percutaneous coronary intervention (PCI; 15%), and dyslipidemia (10%). 25 patients without prior CABG had downstream anatomical testing with invasive or CT coronary angiography. Global and per-vessel values for MBF were defined in 7 patients who had non-obstructed or normal coronaries. Per-patient and per-vessel analysis demonstrated improved sensitivity of MBF to detect stenosis ≥ 70% in comparison to MPI: per-patient MBF 85% versus 77% for MPI (p<0.01); and per-vessel, LAD analysis MBF 90% versus 60% for MPI (p<0.01). Low per vessel sensitivity of SPECT was attributed to multivessel disease in 40% of cases.

Conclusions: In this small series of consecutive patients SPECT MBF was more sensitive that MPI at detecting myocardial ischemia on a per vessel and per patient analysis. These results are promising but will require further validation in a larger prospective cohort or through multicenter studies.