Introduction: Cardiac autonomic neuropathy (CAN) is a common complication of diabetes and metabolic syndrome (MetS) resulting from damage to the autonomic nerves that regulate heart rate and vascular tone. In the literature, CAN has been associated with an increased risk of silent myocardial ischemia and myocardial infarction. MetS is itself an established cardiovascular risk factor. Because all patient in this study had both MetS and confirmed CAN, the study describes myocardial perfusion imaging (MPI) findings within this specific population rather than comparing patients with and without CAN. This study aimed to describe the prevalence of myocardial ischemia and its association with transient ischemic dilation (TID), increased right ventricular (RV) uptake, and increased lung uptake on single-photon emission computed tomography (SPECT) MPI in patients with MetS and CAN.
Methods: This cross-sectional, descriptive-analytical study included patients with MetS and confirmed cardiac autonomic neuropathy (borderline or definite CAN) who underwent MPI at the Nuclear Medicine Center of Shahid Sadoughi Hospital, Yazd, Iran, during 2019. Patients whose records were inaccessible or incomplete were excluded. MPI was performed using a 2-day rest/stress protocol with a low-energy high-resolution (LEHR) collimator (140 keV, 20% window); stress was induced by exercise or dipyridamole according to the patient's clinical condition, and [^99mTc]Tc-MIBI (22-25 mCi) was administered for each study, with images acquired on a 64×64 matrix and ECG-gated SPECT acquisition. MetS was defined as three or more of: blood pressure ≥130/85 mmHg, fasting glucose ≥100 mg/dL, triglycerides ≥150 mg/dL, HDL-cholesterol <50 mg/dL (women) or <40 mg/dL (men), or waist circumference >88 cm (women) or >102 cm (men). CAN was assessed with three tests - resting heart rate, the 30:15 heart-rate ratio on standing, and the orthostatic blood-pressure change - each scored 0 or 1 (total score 0-3), classifying patients as no neuropathy (0), borderline CAN (1), or definite CAN (2-3); only patients with borderline or definite CAN were eligible. Demographic data and MPI findings (ischemia, TID, RV uptake, lung uptake) were extracted from clinical records using a standardized checklist and analyzed in SPSS (v.21) with descriptive statistics and chi-square tests; p<0.05 was considered significant.
Results: A total of 268 patients with MetS and CAN were evaluated (mean age 58.11 ± 11.68 years, range 27-84); 83 (31%) were male and 185 (69%) were female. Myocardial ischemia was present in 97 patients (36.2%), TID in 21 (7.8%), increased RV uptake in 20 (7.5%), and increased lung uptake in 11 (4.1%). TID and increased RV uptake were both significantly more frequent among patients with ischemia than among those without (TID: 15/97, 15.5% vs. 6/171, 3.5%, p=0.001; RV uptake: 15/97, 15.5% vs. 5/171, 2.9%, p=0.001), while increased lung uptake did not differ significantly (7/97, 7.2% vs. 4/171, 2.3%; p=0.053). Ischemia prevalence did not differ by sex (p=0.173).
Conclusion: In this selected cohort of patients already diagnosed with both MetS and CAN, myocardial perfusion abnormalities - most notably ischemia, TID, and increased RV uptake - were frequent and tended to co-occur. Because the study lacked a comparison group without CAN, these findings describe the pattern of MPI abnormalities in this population rather than establish that CAN increases ischemic risk. Prospective, controlled studies with confounder adjustment and outcome data are needed before MPI screening can be recommended for this population.