Transient prolonged stunning induced by dipyridamole and shown on 1-and 24-hour poststress Tc-99m-MIBI gated SPECT

We investigated whether poststress gated SPECT, which was believed to show resting wall motion, revealed stunning induced by dipyridamole stress. Meth ods: In 62 patients with coronary artery disease (n = 57) or chest pain (n = 5), dipyridamole stress gated Tc-99m-hexakis-2-methoxyisobutyl isonitrile (MIBI) SPECT and rest(201)Tl SPECT were performed on the first day; 24-h d elayed Tl-201 SPECT and rest gated Tc-99m-MIBI SPECT were performed on the second day. Stress and rest gated Tc-99m-MIBI SPECT was performed 1 h after injection. The myocardium was divided into 17 segments, and perfusion was scored on a 4-point scoring system (scores, 0-3 for normal to defect); wall motion during first-day poststress gated and second-day rest gated SPECT w as also scored on another 4-point scale (scores, 0-3 for normal to dyskines ia). Results: Thirty-one of 62 patients showed wall motion abnormality that was worse after stress than during resting. Three hundred eight (29%) of t he total 1054 segments showed wall motion abnormality on poststress gated S PECT. In 198 of these segments, wall motion abnormality was the same on pos tstress and rest gated SPECT, and 106 segments showed wall motion that was worse on I-h poststress than on rest gated SPECT. Perfusion was normal eith er during rest (n = 113) or after a 24-h delay (n = 18) in 131 segments wit h the poststress wall motion abnormality. Of these 131 segments, 69 showed the same wall motion abnormality between poststress and resting periods (pe rsistent stunning). However, in 40 segments, abnormal wall motion on I-h po st-stress gated SPECT normalized on rest gated SPECT (transient prolonged s tunning). The other 20 segments showed improvement of wall motion during re st compared with the poststress period but still showed abnormal wall motio n during the resting period (between transient prolonged stunning and persi stent stunning). Stress perfusion decrease was more severe in transient pro longed stunning than in persistent stunning. Poststress wall motion abnorma lity was more severe in persistent stunning. Conclusion: Using gated Tc-99m -MIBI SPECT, stunned myocardium was found on 1-h poststress SPECT compared with normal resting wall motion found on rest gated SPECT on the next day. We conclude that some myocardial walls did not show true resting wall motio n on 1-h poststress gated SPECT; hence, caution is necessary when using wal l motion on 1-h poststress gated SPECT to assess resting wall motion.