Impact of the Charlson Comorbidity Index score on risk prediction by single-photon emission computed tomography myocardial perfusion imaging following myocardial infarction

Comorbidity is common among patients with myocardial infarction (MI). We examined whether comorbidity level modified the single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI)-based prediction of 5-year risk of MI and all-cause death in patients with MI. This cohort study included patients with prior MI having a SPECT MPI at Aarhus University Hospital, Denmark, 1999-2011. Using nationwide registries, we obtained information on comorbidity levels (low, moderate, and severe) and outcomes. We computed risk and hazard ratios (HRs) with 95% confidence intervals (CIs) for MI and all-cause death, comparing normal (no defects) versus abnormal scan (reversible and/or fixed defects) using Cox regression adjusting for sex, age, and comorbidity level. We identified 1,192 patients with MI before SPECT MPI. The 5-year risk for patients with normal versus abnormal scans were 11.7% versus 18.3% for MI, and 8.0% versus 13.2% for all-cause death, respectively. The overall 5-year adjusted HR (aHR) of MI was 1.56 (95% CI: 1.09-2.21), 1.33 (95% CI: 0.82-2.15) with low comorbidity, 1.39 (95% CI: 0.68-2.83) with moderate comorbidity, and 2.53 (95% CI: 1.14-5.62) with severe comorbidity. Similarly, the 5-year aHR for all-cause death was 1.39 (95% CI: 0.90-2.14) overall; 2.33 (95% CI: 0.79-6.84) with low comorbidity, 2.05 (95% CI: 0.69-6.06) with moderate comorbidity, and 1.07 (95% CI: 0.64-1.80) with severe comorbidity. We conclude that comorbidity level may modify the 5-year risk prediction associated with an abnormal SPECT MPI scan in patients with previous MI.