Transient ischemic dilation (TID) of the left ventricle in myocardial perfusion SPECT (MPS) has been shown to be a clinically useful marker of severe coronary artery disease (CAD). However, TID has not been evaluated for 99mTc-sestamibi rest/stress protocols (Mibi-Mibi). We aimed to develop normal limits and evaluate diagnostic power of TID ratio for Mibi-Mibi scans.

TID ratios were automatically derived from static rest/stress MPS (TID) and gated rest/stress MPS from the end-diastolic phase (TID_ed) in 547 patients who underwent Mibi-Mibi scans [215 patients with correlating coronary angiography and 332 patients with low likelihood (LLk) of CAD]. Scans were classified as severe (≥70% stenosis in proximal left anterior descending (pLAD) artery or left main (LM), or ≥90% in ≥2 vessels), mild to moderate (≥90% stenosis in 1 vessel or ≥70%-90% in ≥1 vessel except pLAD or LM), and normal (<70% stenosis or LLk group). Another classification based on the angiographic Duke prognostic CAD index (DI) was also applied: DI ≥ 50, 30 ≤ DI < 50 and DI < 30 or LLk group.

The upper normal limits were 1.19 for TID and 1.23 for TID_ed as established in 259 LLk patients. Both ratios increased with disease severity (P < .0001). Incidence of abnormal TID increased from 2% in normal patients to >36% in patients with severe CAD. Similarly, when DI was used to classify disease severity, the average ratios showed significant increasing trend with DI increase (P < .003); incidence of abnormal TID also increased with increasing DI. The incidence of abnormal TID in the group with high perfusion scores significantly increased compared to the group with low perfusion scores (stress total perfusion deficit, TPD < 3%) (P < .0001). The sensitivity for detecting severe CAD improved for TID when added to mild to moderate perfusion abnormality (3% ≤ TPD < 10%): 71% vs 64%, P < .05; and trended to improve for TID_ed/TID_es: 69% vs 64%, P = .08, while the accuracy remained consistent if abnormal TID was considered as a marker in addition to stress TPD. Similar results were obtained when DI was used for the definition of severe CAD (sensitivity: 76% vs 66%, P < .05 when TID was combined with stress TPD).

TID ratios obtained from gated or ungated Mibi-Mibi MPS and are useful markers of severe CAD.