Incremental Medical Expenditure and Effectiveness of Early Non-invasive Cardiac Testing in Suspected Acute Coronary Syndrome

Introduction: The relationship between medical expenditure and long-term effectiveness of early (within 72 hours) non-invasive cardiac stress testing (NIT) in reducing future acute myocardial infraction (AMI) is not well understood. We estimated the value of early NIT after an emergency department (ED) evaluation for suspected acute coronary syndrome (ACS). Methods: This was a retrospective cohort study of adult (18+) patients with chest pain, presenting at EDs within the Kaiser Permanente Southern California health system from 10/2015-12/2018. We analyzed the direct medical expenditure associated with medical office visits, hospital facility and ED visits, pharmacy utilization, hospice stays, skilled nursing stays, home health, dialysis, laboratory and radiology utilization during the one year following the index chest pain ED visit. We also identified incidence of AMI during the 1-year follow-up. We used 2-stage residual inclusion instrumental variables (IV) techniques to evaluate the marginal effect of early NIT on total all cause expenditure as well as subgroups of utilization. We used control functions IV techniques to evaluate the marginal effect of NIT on AMI and calculated the number needed to treat (NNT) as the inverse of the absolute risk reduction. All models adjusted for socio-demographics, cardiovascular disease (CVD) history and treatment and non-CVD comorbidities. Results: The cohort included 91250 patients (mean age 58 years, female 58%) and 19% received early NIT. The marginal difference in total expenditure between the early NIT vs controls was $2,583 (95% CI $591 to $4,575) and was mainly related to the index ED visit (Table 1). Those who received early NIT had slightly lower risk of AMI during the 1-year follow-up (risk reduction 1.3% (-1.9% to -0.7%) resulting in NNT of 75. Conclusions: Early NIT offers minor risk reduction of AMI but with an increase of $2583 in expenditure. With a NNT of 75, the cost to avoid one AMI is estimated to be $193,725.