Implications of transient ischaemic dilatation and impaired left ventricular ejection fraction reserve in patients with normal stress myocardial perfusion imaging and elevated coronary artery calcium
Authors: Wong JJJ , Yew MS 
Published: July 2021

Abstract

Funding Acknowledgements
Type of funding sources: None.

Introduction
Stress only (SO) instead of stress/rest single photon emission computed tomography myocardial perfusion imaging (MPI) is encouraged if perfusion and left ventricular ejection fraction (LVEF) are normal on SO images. Concurrent coronary artery calcium (CAC) scoring has also been recommended to assess atherosclerotic burden in ‘normal’ MPIs. However, the safety of SO MPI in high CAC cases is unclear as additional rest imaging may show transient ischaemic dilation (TID) and/or impaired LVEF reserve (iLVEFr) which are markers of severe coronary artery disease (CAD) and indicate ‘balanced ischaemia’.

Purpose
We aim to assess the incidence and outcomes of TID and iLVEFr in stress/rest MPIs with normal SO images and elevated CAC.

Methods
Retrospective analysis of all normal stress/rest MPIs performed between 1 March 2016 to 31 January 2017 with concurrently measured CAC &gt;300. A SO protocol was not in place then. Prone post stress images were routinely done. Known CAD cases were excluded. A reader reviewed only the post stress supine/prone images and excluded cases ineligible for SO MPI (non-homogenous perfusion, LVEF ≤50%, abnormal wall motion). The remaining cases were assessed for TID (software derived TID ratio &gt;1.20) and iLVEFr (stress LVEF – rest LVEF ≤-5%). Coronary angiography (CAG) and major adverse cardiac events (MACE, defined as cardiac death, non fatal myocardial infarction, revascularisation) within 24 months post MPI were traced using electronic medical records.

Results
There were 230 cases included (mean age 71, 56.5% male) of which 43 (18.7%) had TID and/or iLVEFr (9 TID, 22 iLVEFr, 12 both). There were no significant differences in baseline characteristics, CAC and aspirin/statin use between cases with or without TID and/or iLVEFr (Table 1). More patients in the TID and/or iLVEFr group underwent elective CAG [10 (23.3%) vs 10 (5.3%), p = 0.001] although CAG diagnosis of severe CAD (left main, 3-vessel or 2-vessel disease with proximal left anterior descending involvement) was not different [4/6 (40.0%) vs 5/10 (50.0%), p = 1.000). MACE was significantly higher in the TID and/or iLVEFr group [10 (23.3%) vs 16 (8.6%), p = 0.013], driven by higher elective revascularisation [8 (18.6%) vs 8 (4.3%), p = 0.003] with no significant differences in cardiac death or non fatal myocardial infarction (Table 2).

Conclusion
TID and/or iLVEFr is seen in &lt;20% of cases eligible for SO MPI with high CAC, suggesting that routine rest scan in these cases exposes the majority to unnecessary radiation. Identification of TID and/or iLVEFr is associated with higher 24 month MACE, driven by higher elective revascularisation from more CAG referral. Approximately half of cases in each group had revascularisation for non severe CAD not typically associated with TID and/or impaired LVEFr. Overall cardiac death and non fatal myocardial infarction rates were low and not significantly different between groups with or without TID and/or iLVEFr.