Assessment of perfusion abnormalities in patients with pacemaker on stress-rest Tc99m-MIBI myocardial perfusion SPECT: Comparison between right ventricular outflow tract (RVOT) vs. apical (RVA) pacing

Objectives We compared the perfusion defects in patients with RVOT and RVA pacing on stress-rest Tc99m MIBI myocardial perfusion SPECT (MPS) using forced cardiac pacing during stress.

Methods A total of twenty six patients (17:M; 9:F, mean age: 44.42±12.14 yrs) with permanent pacemaker (RVOT:13; & RVA:13) underwent stress-rest Tc99m MIBI. No patients had any evidence of coronary artery disease. All patients failed to achieve 85% of maximum predicted heart rate for age (THR) on treadmill and forced pacing was performed to achieve THR which was continued for a minute post tracer injection.

Results The groups were matched for various confounding factor: age (p=0.604); sex (p=0.41); pacemaker implantation indication (p=0.655) and resting heart rate (p=0.979). Pacemaker parameters such as type of pacemaker, lead capture threshold, impedance, % ventricular pacing, period post implantation were similar in both the groups (p=1.000, p=0.644, p=0.648, p=0.161, p=.068 respectively). On MPS, fixed perfusion defects were noted in 3 (23%) and 10 (77%) patients of RVOT & RVA group respectively (p=0.016). Two defects in RVOT & 9 defects in RVA group were small (<10% of LV myocardium) and two (one in each group) were > 10% of LV myocardium in size. All the defects in both the groups were mild except for two defects in RVA which were moderate in severity. The mean period post implantation in patients with defects was 31 months compared to 28 months in patients with no perfusion defects (p = 0.817).

Conclusions Fixed perfusion abnormalities are observed in patients with pacemaker and are independent of time period post implantation. RVOT pacing is associated with fewer myocardial perfusion abnormalities compared to RVA pacing