Repeat Hospitalizations and Their Costs in the 6 Months After Acute Myocarditis
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Background
Readmission metrics after acute myocarditis usually record only whether the first readmission occurs within 30 days. The amount of inpatient care received after the first return and the period over which it was received are unknown.
Methods
We identified adults with a principal diagnosis of acute myocarditis (ICD-10-CM I40.x) in the Nationwide Readmission Database (NRD) from 2016 to 2022. The first qualifying admission in each patient year served as the index, and patients had to be discharged alive and not transferred. We linked every subsequent same-state, same-year admission for any cause within 30, 90, and 180 days. Using survey-weighted methods, we split the return length of stay (LOS) and estimated hospital cost (charges × cost-to-charge ratio, 2022 US dollars) into first-return and beyond-first-return components per index patient; patients without readmission were counted as having zero. The National Inpatient Sample (NIS) provided data on index mortality and costs.
Results
Of the 3,276 sampled index patients eligible for the 180-day follow-up (5,897 for 30 days), 6.5% were readmitted within 30 days and 14.0% within 180 days. Over 180 days, readmissions added 1.51 (95% CI, 1.23–1.79) bed-days and $5,884 (95% CI, 4,352–7,417) per index patient. Readmissions after the first contributed 0.62 (0.42–0.82) days and $2,430 (1,599–3,262), which is 41% of return bed-days and 41% of return costs (95% CI, 34–49 and 33–49, respectively). Counting only the first readmission, therefore, understated the 180-day return burden by 1.7-fold. The beyond-first share rose from 10% at 30 days to 32% at 90 days and 41% at 180 days, and 63% of the 180-day return bed-days accrued after day 30. Most readmissions had a non-cardiovascular (55% of bed-days) or other cardiovascular (33%) principal diagnosis, and myocarditis accounted for 3.5%. In the NIS (2,964 admissions; 71 in-hospital deaths), survivors had a mean index LOS of 4.4 days and a mean cost of $23,867.
Conclusions
After acute myocarditis, approximately two-fifths of the 6-month readmission bed-days and costs were from second and later readmissions. Most accrued after the usual 30-day window and were diagnoses other than myocarditis. First-readmission 30-day metrics substantially understate the post-discharge hospital burden in this population cohort.
What Is Known
Hospitalization for acute myocarditis carries a substantial risk of early readmission; national studies have reported 30- or 90-day readmission rates.
Hospital quality and cost metrics typically consider only the first readmission within 30 days of discharge.
What the Study Adds
In a nationally representative US cohort, 41% of 180-day readmission bed-days and costs after acute myocarditis came from second and later readmissions; first-readmission metrics understated the 180- day return burden 1.7-fold.
Nearly two-thirds of the 180-day return bed-days occurred after day 30, and almost 9 in 10 were for diagnoses other than myocarditis, heart failure, or arrhythmia. These findings support follow-up that extends beyond 30 days and address coexisting conditions.
