Incremental prognostic value of SPECT CT based visual calcium score burden for outcomes prediction
Authors: Al-Darzi W , Makki T , Saco R , Van Harn M , Ananthasubramaniam K 
Published: July 2021

Abstract

Funding Acknowledgements
Type of funding sources: Other. Main funding source(s): Astellas Pharma US

Background
Coronary calcium is an important non-perfusion finding on SPECT CT attenuation correction (AC) and has been shown to help decrease equivocal interpretation and identifying atherosclerosis despite normal perfusion. Although correlations with measured calcium score have been good, an easy visual calcium score (VCS) for CT AC calcium and its prognostic value has not been well established.

Purpose
We aimed to evaluate the role of VCS calculated from low-dose CT for AC in predicting outcomes stratified by SPECT (normal versus abnormal).

Methods
A retrospective data review of patients who underwent cardiac SPECT CT at our center from January 2009 -August 2012 with a mean follow up of 4.5 years. Baseline characteristics and outcomes were collected. VCS scoring was established as follows and was completed on all scans by three senior cardiology fellows. When not congruent, consensus with third reader was established. Presence of visual calcium in any of the following arteries was recorded as a score of 1 with VCS range 0-6: left main, left anterior descending, left circumflex, right coronary, ascending aorta, and descending thoracic aorta. Subjects were divided into 3 groups based on the VCS of &lt;2, 2-4, and &gt;4. Normal versus abnormal SPECT was defined as summed stress score/summed difference score of &lt;4/&lt;2 and &gt; =4/&gt; =2 respectively. Major adverse cardiac events (MACE) defined as presence of heart failure, myocardial infarction, and/or cardiac death.

Results
538 consecutive patients with SPECT CT were evaluated. Mean age was 63.3 years with 54% females. There were 463 (86%) normal SPECT and 75 (14%) abnormal SPECT. Using VCS, there was a statistically significant increase in the percentage of MACE over the period of follow-up with step wise increase in VCS severity in normal SPECT group (p-value = 0.001), although not significant in the abnormal MPI group (Figure 1). There was a higher mortality with increasing VCS in both normal and abnormal SPECT (p= &lt;0.001 and p = 0.014 respectively). Using a multivariate logistic regression model in patients with normal SPECT, there were higher odds of death (OR 1.26) with every 1 point of VCS increase controlling for age, sex, baseline heart rate, history of dialysis, diabetes and stroke (95% confidence interval 1.09, 1.45; p-value = 0.002).

Conclusion
This study highlights the importance of factoring CT AC calcium in risk assessment of SPECT. CT AC calcium represents an easily available and important adjunctive risk marker during SPECT interpretation. A simple VCS as derived in this study can help with the additive risk stratification in both normal and abnormal SPECT and is of an incremental prognostic value for MACE. Clinicians interpreting SPECT should include coronary calcification on AC CT routinely in reports to help management and prognostication decisions. Our study shows that VCS can be a simple easily adopted tool for consistent reporting.