Abstract
Aims
The elderly are at risk of pericarditis from conditions such as malignancy, renal disease, and after cardiac surgery. However, the burden of pericarditis and, especially, the long-term outcomes associated with pericarditis have not been described before among the elderly.
Methods and results
We examined hospitalization rates; in-hospital, 30-day, and 1-year all-cause mortality rates; all-cause 30-day readmission rates; length of stay and health care expenditure for Medicare beneficiaries aged 65 years or older with a principal discharge diagnosis of pericarditis from 1999 to 2012. A total of 45 504 hospitalizations were identified. The hospitalization rate for pericarditis remained stable at 26 per 100 000 person-years across the study period and was consistently higher among men and the oldest old. The adjusted all-cause 30-day mortality rates decreased from 7.6% [95% confidence interval (CI) 6.9–8.2] in 1999 to 5.7% (95% CI 4.5–7.1) in 2012 and all-cause 1-year mortality rates decreased from 19.7% (95% CI 18.8–20.8) in 1999 to 17.3% (95% CI 15.3–20) in 2011 respectively. The 30-day all-cause readmission rate remained unchanged at 18% across the study period. The length of stay ranged from a mean of 5.8 days in 1999 to 5.5 days in 2012. The consumer price index adjusted cost per hospitalization increased from $8404 in 1999 to $9982 in 2012.
Conclusion
The hospitalization rate for acute pericarditis has remained unchanged among older adults. Although mortality rates associated with pericarditis have improved, hospitalization for pericarditis continues to signal a high risk of dying within a year.
Keywords: Pericardial disease, Health outcomes research, Hospitalization, Mortality
Introduction
Compared with other major cardiovascular conditions (e.g. myocardial infarction and heart failure),1,2 there are limited data available on the admissions and outcomes of other cardiovascular conditions that cause significant morbidity, such as acute pericarditis in the USA. Acute pericarditis frequently manifests as chest pain with characteristic electrocardiographic changes, occasionally accompanied by a pericardial effusion. Given its clinical characteristics, it is frequently considered in the differential diagnosis of ST-segment elevation myocardial infarction and is associated with significant discomfort and may recur in up to 20% of cases. Recurrent events are costly, difficult to treat, and, infrequently, may lead to serious complications such as cardiac tamponade or constrictive pericarditis.3–5
The elderly are an important growing subgroup that are at a higher risk for pericarditis from aetiologies such as end-stage renal disease, malignancy, acute myocardial infarction, and cardiac surgery.6–8 However, little is known among older adults about the hospitalization rates of acute pericarditis, outcomes and costs, and the patterns across demographic subgroups.
Accordingly, we chose to analyse 100% data of Medicare fee-for-service beneficiaries from 1999 to 2012 to describe the health care burden associated with acute pericarditis nationally in the USA by describing the hospitalization rate for acute pericarditis as well as examining the long-term outcomes and costs associated with these hospitalizations.
Methods
Data sources
Using the Centers for Medicare and Medicaid Services (CMS) inpatient Standard Analytical Files, we analysed all inpatient admissions of fee-for-service beneficiaries aged 65 years or older from 1999 to 2012. Medicare’s inpatient Standard Analytical Files contain patient demographics and procedural and diagnostic information for hospitalizations based on the International Classification of Diseases, Ninth Revision–Clinical Modification (ICD-9-CM) as well as dates of hospital admission and discharge disposition. We included patients who had participated for at least 1 month in fee-for-service and resided or were hospitalized in the USA. Because Medicare fee-for-service beneficiaries were enrolled in the fee-for-service programme throughout the year, some beneficiaries were in fee-for-service for the entire year, while others were in fee-for-service for a few months. We calculated person-years for each beneficiary to account for new enrolment, disenrolment, or death during the study period (e.g. if a beneficiary enrolled in fee-for-service for 3 months, this beneficiary contributed 3/12 person-years into the calculation). We then linked the person-years beneficiary data to the Medicare inpatient claims to identify beneficiaries who had one or more pericarditis hospitalization in the USA from 1 January 1999 to 31 December 2012. A pericarditis hospitalization was defined as discharge from an acute care hospital with a principal ICD-9-CM discharge diagnosis of pericarditis using the following codes: 420.90 (acute pericarditis unspecified), 420.91 (acute idiopathic pericarditis), 420.99 (other acute pericarditis), 420.00 (acute pericarditis in diseases classified elsewhere), 423.9 (pericardial disease not otherwise specified), or 391.0 (acute rheumatic pericarditis). These ICD-9 codes have been used to identify cases of acute pericarditis.9
Patient characteristics and co-morbidities
We examined the demographic and clinical characteristics of patients with acute pericarditis over time. Demographic variables included age (65–74, 75–84, and ≥85 years), gender, and race. We determined race using the Medicare denominator file, which is based on data from the Social Security Administration. We selected co-morbidities in categories of cardiovascular disease (hypertension, diabetes mellitus, atherosclerotic disease, unstable angina, previous myocardial infarction, previous heart failure, peripheral vascular disease, stroke, and cerebrovascular disease except stroke), geriatric conditions (dementia, functional disability, and malnutrition), and miscellaneous (pneumonia, respiratory failure, cancer, depression, and trauma) based on the method used by the CMS for profiling hospitals for acute myocardial infarction and heart failure.10,11 We identified these co-morbidities from primary or secondary diagnosis codes of all patient hospitalizations for any cause 1 year before the initial hospitalization for acute pericarditis. The 1998 inpatient data were used to obtain co-morbidity information in patients who were hospitalized for acute pericarditis in 1999.
Outcome measures
For each year, we determined the hospitalization rate for acute pericarditis. This was calculated by dividing the total number of acute pericarditis hospitalizations in a year by the corresponding number of person-years of fee-for-service enrolment for that year. All rates were reported per 100 000 person-years.
For patients with multiple hospitalizations, a random hospitalization was selected to determine the in-hospital, 30-day, 1-year all-cause mortality, and 30-day all-cause readmission rate consistent with the methodology adopted by the CMS publicly reported measures.10,11 We used the date of admission as the ‘time zero’ for all mortality measures. The 30-day all-cause readmission rate was calculated as the percentage of patients who were discharged alive, not transferred to another acute care hospital, and readmitted to any hospital within 30 days of discharge from the index hospitalization. Among the patients who were readmitted in 2012 we examined the principal discharge diagnosis for the repeat hospitalization to identify common causes that lead to readmission.
Additionally, we determined the hospital length of stay as the difference between the discharge and admission dates. Medicare expenditures were measured as the mean Medicare payment per hospitalization, adjusting for the annual consumer price index inflation rate and using 1999 as the index year (http://www.bls.gov/data/inflation_calculator.htm).
Statistical analysis
Changes in patient characteristics and outcomes were examined over time. We used the Mantel–Haenszel χ2 test to evaluate whether these changes over time were statistically significant. We stratified trends by age, gender, and race.
We fitted a mixed model with a Poisson link function and state-specific random intercepts to assess the rates of hospitalization for acute pericarditis adjusted for age, gender, and race. We considered the acute pericarditis hospitalization rate during 1999 as the referent and calculated the incidence rate ratio for each subsequent year by including indicator variables for the subsequent years in the mixed model.
To obtain national trends in all-cause mortality and readmission rates adjusted for patient demographics and co-morbidities, we fitted the mixed model with a logit link function and hospital-specific random intercepts. Using data from 1999 as the referent and indicator variables for each subsequent year, we calculated the adjusted odds ratio for all-cause mortality for subsequent years. Using the method described by Zhang and Yu,12 we converted the odds ratio values to risk ratio estimates. We then multiplied the risk ratio for each year by the all-cause mortality and readmission rate in the baseline year (1999) to calculate the adjusted all-cause mortality and readmission rates respectively across years.
We conducted the analyses using SAS version 9.3 64-bit Windows version (SAS Institute Inc., Cary, NC, USA). All statistical testing was two sided, and P < 0.05 was considered statistically significant.
Results
Patient characteristics
The final sample consisted of 407 253 428 unique Medicare beneficiaries aged 65 years or older with at least 1 month of enrolment in Medicare fee-for-service during the study period (391 553 231 person-years) leading to 45 504 hospitalizations for acute pericarditis from 1999 to 2012. The mean age of hospitalized patients with acute pericarditis was approximately 75 years. The overall study cohort was reflective of the Medicare population nationally with 53% female and 88% White patients (Table 1). Some co-morbidities such as history of hypertension (49.8–67.8%), history of diabetes mellitus (21.1–28.5%), history of renal failure (6.0–17.6%), and history of pneumonia (14.2–20.7%) increased over time, whereas history of prior myocardial infarction (4.7–4.5%) and malignancy (16.7–17.3%) remained stable (Table 1).
Table 1.
Baseline demographics and clinical characteristics of Medicare fee-for-service beneficiaries aged 65 years or older hospitalized with acute pericarditis, 1999–2012a
| Characteristics | 1999–20000 | 2001–02 | 2003–04 | 2005–06 | 2007–08 | 2009–10 | 2011–12 |
|---|---|---|---|---|---|---|---|
| Number of hospitalizations | 12 616 | 13 329 | 14 524 | 14 934 | 14 114 | 13 334 | 13 672 |
| Demographics (%) | |||||||
| Age (year), mean (SD) | 75.8 (6.9) | 76.0 (7.1) | 76.0 (7.1) | 76.1 (7.3) | 76.3 (7.5) | 76.0 (7.5) | 76.3 (7.7) |
| Female | 54.4 | 53.3 | 54.3 | 55.5 | 54.5 | 53.5 | 53.0 |
| White | 88.1 | 87.9 | 87.6 | 87.0 | 86.6 | 86.0 | 85.9 |
| Black | 8.2 | 8.3 | 8.4 | 9.0 | 8.9 | 9.6 | 9.1 |
| Other raceb | 3.7 | 3.8 | 4.0 | 4.0 | 4.5 | 4.4 | 5.1 |
| Cardiovascular conditions (%) | |||||||
| Hypertension | 49.8 | 55.5 | 58.4 | 59.2 | 64.4 | 65.5 | 67.8 |
| Diabetes mellitus | 21.1 | 23.0 | 24.4 | 26.0 | 27.4 | 27.4 | 28.5 |
| Atherosclerotic disease | 34.2 | 34.8 | 34.3 | 34.5 | 35.0 | 34.2 | 34.7 |
| Unstable angina | 6.5 | 5.8 | 4.9 | 4.3 | 3.4 | 3.1 | 3.1 |
| Prior myocardial infarction | 4.7 | 4.3 | 4.3 | 4.0 | 4.2 | 4.1 | 4.5 |
| Prior congestive heart failure | 16.3 | 17.6 | 17.9 | 17.8 | 17.4 | 17.5 | 18.4 |
| Peripheral vascular disease | 7.1 | 7.2 | 8.0 | 7.9 | 7.9 | 8.3 | 8.1 |
| Stroke | 1.8 | 1.5 | 1.4 | 1.5 | 1.5 | 1.6 | 1.4 |
| Cerebrovascular disease (other than stroke) | 3.8 | 4.2 | 3.7 | 3.3 | 3.6 | 3.5 | 3.7 |
| Geriatric conditions (%) | |||||||
| Malnutrition | 3.2 | 3.3 | 3.8 | 4.0 | 5.5 | 6.4 | 7.4 |
| Functional disability | 1.9 | 1.8 | 1.9 | 1.9 | 1.9 | 2.6 | 2.3 |
| Dementia | 3.5 | 4.4 | 4.3 | 4.9 | 5.6 | 5.3 | 4.6 |
| Other conditions (%) | |||||||
| Renal failure | 6.0 | 6.6 | 7.8 | 10.2 | 13.1 | 16.0 | 17.6 |
| Pneumonia | 14.2 | 15.3 | 16.2 | 18.3 | 19.0 | 20.7 | 20.7 |
| Respiratory failure | 3.5 | 3.7 | 4.1 | 4.6 | 6.3 | 7.4 | 8.1 |
| COPDc | 23.9 | 25.3 | 27.5 | 27.3 | 25.7 | 22.8 | 23.0 |
| Cancer | 16.7 | 17.1 | 18.0 | 16.6 | 17.5 | 16.6 | 17.3 |
| Depression | 4.9 | 6.1 | 6.4 | 6.9 | 7.4 | 7.2 | 7.5 |
| Trauma | 4.2 | 4.7 | 5.7 | 5.9 | 5.5 | 5.1 | 5.3 |
Data have been combined in 2 year intervals for brevity.
Other race includes Asian, Hispanic, North American Native, or other not specified.
COPD, chronic obstructive pulmonary disease.
Hospitalization rate for acute pericarditis
The overall acute pericarditis hospitalization rate remained stable at 26 per 100 000 person-years throughout the study period (Table 2). Acute pericarditis hospitalization rates remained consistently higher in older persons (particularly those aged 75–84 years) and men compared with other demographic subgroups throughout the study period, without a shift in trends across each single subgroup (Table 2). Hospitalization rate for acute pericarditis was similar across different racial subgroups over the initial study period from 1999 to 2005. From 2006, the hospitalization rate for Blacks was consistently higher compared with Whites (Table 2).
Table 2.
Hospitalization rates per 100 000 person-years for acute pericarditis in Medicare fee-for-service, 1999–2012a
| 1999 | 2000 | 2002 | 2004 | 2006 | 2008 | 2010 | 2012 | |
|---|---|---|---|---|---|---|---|---|
| Person-years | 26 479 079 | 26 768 087 | 28 345 999 | 29 109 293 | 28 452 501 | 27 675 586 | 27 696 576 | 28 292 163 |
| Number of hospitalizations | 6928 | 6900 | 7430 | 8193 | 7957 | 7489 | 7199 | 7285 |
| Overall rate (per 100 000 person-years) | 26 | 26 | 26 | 28 | 28 | 27 | 26 | 26 |
| Age (years; per 100 000 person-years) | ||||||||
| 65–74 | 26 | 26 | 25 | 26 | 26 | 24 | 24 | 23 |
| 75–84 | 28 | 27 | 28 | 31 | 32 | 31 | 29 | 31 |
| ≥85 | 22 | 21 | 23 | 26 | 27 | 27 | 24 | 27 |
| Gender (per 100 000 person-years) | ||||||||
| Male | 29 | 29 | 29 | 31 | 29 | 28 | 28 | 27 |
| Female | 24 | 24 | 24 | 26 | 27 | 26 | 25 | 25 |
| Race (per 100 000 person-years) | ||||||||
| White | 26 | 26 | 27 | 29 | 28 | 27 | 26 | 26 |
| Black | 28 | 26 | 27 | 29 | 31 | 31 | 31 | 29 |
All rates reported per 100 000 person-years.
Data have been presented individually for the years 1999 and 2012, i.e. initial and final years of the study and in 2-year intervals for the intervening period for brevity.
Mortality rates
The all-cause in-hospital mortality rate for patients hospitalized with acute pericarditis decreased from 4.9% [95% confidence interval (CI) 4.4–5.5] to 2.8% (95% CI 2.4–3.2) (P < 0.001). The adjusted 30-day and 1-year all-cause mortality rates decreased from 7.6% (95% CI 6.9–8.2) to 5.7% (95% CI 4.5–7.1) (P = 0.001) and from 19.7% (95% CI 18.8–20.8) to 17.3% (95% CI 15.3–20.0) (P < 0.001) during the study period, respectively (Table 3). With regard to subgroups, a consistent improvement in risk-adjusted all-cause mortality (30-day and 1-year) was noted for the age groups 65–74 years and 75–84 years with all-cause mortality rates relatively unchanged among Medicare beneficiaries ≥85 years (Figure 1A). Men and women had similar risk-adjusted 30-day and 1-year all-cause mortality rates, which declined over time (Figure 1B). Blacks, on average, had a higher all-cause mortality rate compared with Whites, and there was a consistent improvement in short-term and long-term all-cause mortality rates across both groups (Figure 1C). Additionally, the difference in all-cause mortality between these groups declined across the study period (Figure 1C).
Table 3.
Trends in outcomes associated with acute pericarditis hospitalizations among Medicare fee-for-service beneficiaries aged 65 years or older, 1999–2012
| Outcomesa | 1999 | 2000 | 2002 | 2004 | 2006 | 2008 | 2010 | 2012 |
|---|---|---|---|---|---|---|---|---|
| Mortality (95% confidence interval) (%) | ||||||||
| In-hospital | 4.9 (4.4–5.5) | 4.3 (3.8–4.9) | 4.4 (3.9–4.9) | 4.4 (4.0–5.0) | 3.6 (3.2–4.0) | 3.3 (2.9–3.8) | 3.3 (2.9–3.7) | 2.8 (2.4–3.2) |
| Adjusted all-cause 30-day | 7.6 (6.9–8.2) | 7.6 (6.9–8.2) | 7.4 (5.9–8.6) | 7.5 (6.0–9.0) | 6.8 (5.5–8.4) | 7.0 (5.5–8.4) | 6.6 (5.3–8.0) | 5.7 (4.5–7.1) |
| Adjusted all-cause 1 year | 19.7 (18.8–20.8) | 20.0 (17.7–22.4) | 19.4 (17.1–21.9) | 19.2 (17.1–21.8) | 17.8 (15.8–20.1) | 18.1 (16.0–20.5) | 17.6 (15.5–20.0) | 17.3 (15.3–20.0) |
| Adjusted all-cause 30-day readmission | 18.5 (17.5–19.6) | 19.1 (16.8–21.7) | 19.5 (17.2–22.2) | 19.7 (17.4–22.3) | 19.8 (17.5–22.5) | 20.8 (18.4–23.5) | 19.8 (17.5–22.6) | 18.3 (16.2–21.0) |
| Length of stay (days), mean (SD) | 5.8 (5.9) | 5.8 (6.0) | 5.9 (6.0) | 5.9 (6.0) | 5.9 (5.7) | 5.7 (5.2) | 5.7 (5.1) | 5.5 (6.1) |
| Costb ($), mean (SD) | 8404 | 8513 | 9400 | 9643 | 9814 | 9646 | 10 041 | 9982 |
Data have been presented individually for the years 1999 and 2012, i.e. initial and final years of the study and in 2-year intervals for the intervening period for brevity.
Costs for subsequent years were adjusted using the consumer prince index calculator to adjust for inflation (reference year 1999).
Figure 1.
(A) Trends of risk-adjusted 30-day and 1-year all-cause mortality rates across different age subgroups of patients hospitalized with acute pericarditis, 1999–2012. (B) Trends of risk-adjusted 30-day and 1-year all-cause mortality rates across different gender subgroups of patients hospitalized with acute pericarditis, 1999–2012. (C) Trends of risk-adjusted 30-day and 1-year all-cause mortality rates across different racial subgroups of patients hospitalized with acute pericarditis, 1999–2012.
Readmission rates
The adjusted 30-day all-cause readmission rate remained unchanged through the study period ranging from 18.5% (95% CI 17.5–19.6%) in 1999 to 18.3% (95% CI 16.2–21%) in 2012 (Table 3). Over time, all-cause rehospitalization rates among patients with acute pericarditis were higher in older individuals (particularly those aged ≥85 years), women and Blacks (Figure 2A–C). The most common principal discharge diagnosis codes for readmission identified were 511.9 (pleural effusion not otherwise specified) in 8%, 427.31 (atrial fibrillation) in 5.1%, and 486 (pneumonia) in 4.7% of the patients, respectively.
Figure 2.
(A) Trends of risk-adjusted 30-day all-cause readmission rates across different age subgroups of patients hospitalized with acute pericarditis, 1999–2012. (B) Trends of risk-adjusted 30-day all-cause readmission rates across different gender subgroups of patients hospitalized with acute pericarditis, 1999–2012. (C) Trends of risk-adjusted 30-day all-cause readmission rates across different racial subgroups of patients hospitalized with acute pericarditis, 1999–2012.
Length of hospital stay and costs
The length of stay associated with acute pericarditis hospitalization was stable ranging from 5.8 days per hospitalization in 1999 and 5.5 days per hospitalization in 2012 (Table 3). The costs associated with pericarditis hospitalization after adjustment for inflation using the consumer price index calculator increased from $8404 per hospitalization in 1999 to $9982 per hospitalization in 2012 (P = 0.001, Table 3).
Discussion
In a large, national population of older adults, we demonstrate that hospitalization rates of acute pericarditis have remained unchanged over the last decade. Hospitalization rates were consistently higher among men and the oldest old in the study period. Hospitalization costs and readmission rates remain considerable and deserve further attention. Despite significant improvement in the 30-day and 1-year all-cause mortality rates, the absolute rates are conspicuously elevated, with approximately one in six patients with acute pericarditis dying over the subsequent 1 year.
The stable hospitalization rate of 26 per 100 000 person-years in our study contrasts with previous reports from the Nationwide Inpatient Sample and Finland.13,14 Kumar et al.13 noted a hospitalization rate of 13 per 100 000 person-years in 2003 that decreased to approximately 9 per 100 000 person-years in 2012 among patients older than 65 years of age in the Nationwide Inpatient Sample, while Kyto et al.14 observed an incidence rate of approximately 5 per 100 000 person-years among the elderly in the Finnish population. A potential explanation for this discordance in study findings could be from differences in inclusion criteria with exclusion of patients with prior history of myocardial infarction and/or pericardiotomy from the previous studies, with especially the latter being an important aetiology of acute pericarditis among the elderly.7 Additionally, while treatment of acute myocardial infarction has advanced significantly in the last decade with faster revascularization times possibly leading to a decrease incidence of pericarditis, there has been an increase in the prevalence of risk factors such as malignancies (especially lung and breast cancer) and advanced kidney disease in the Medicare population as well over the last decade15,16 contributing to an overall stability in hospitalization rates.
The higher acute pericarditis hospitalization rate for men compared with women observed in our study appears to be consistent with prior studies.13,14 In contrast, racial differences in acute pericarditis hospitalizations have not been described. In our study, we observed a marginally higher acute pericarditis hospitalization rate among Blacks. The reason for this increased hospitalization rate is unclear and could possibly be from an increased burden of risk factors such as chronic kidney disease among Blacks.17,18
To our knowledge, this is the largest study to present data on outcomes associated with acute pericarditis beyond the initial hospitalization. One-year all-cause mortality rate associated with acute pericarditis is significant, with one in six not surviving to 1 year. Given the largely non-fatal nature of acute pericarditis, this high mortality rate is likely reflective of serious underlying disease processes, rather than being directly from pericardial inflammation/effusion. Mitiku and Heidenreich19 demonstrated that the presence of even small pericardial effusions was associated with significantly higher 1-year mortality after adjusting for clinical characteristics with an effusion simply reflecting a sicker substrate. A small fraction of increased all-cause mortality could be also attributed to the treatment of chronic sequelae of acute pericarditis such as constrictive pericarditis with procedures like pericardiectomy that are known to be fairly morbid.20 Despite this significant mortality, we noted relative declines of almost 25% and 12% in 30-day and 1-year all-cause mortality rates. This is possibly secondary to the improvement in care provided for underlying conditions leading to pericarditis, as well as development of advanced imaging modalities allowing for clarification of diagnosis and treatment of pericarditis in uncertain cases.21,22
The 30-day all-cause readmission rate for acute pericarditis in our study was ∼20% and did not change during the study period. The recurrence rate of acute pericarditis has been demonstrated to be 20–50% with most recurrences occurring on average 3–5 months after the index episode.5,23 Hence, a 30-day window might be early to note any effect, if any, of drugs like colchicine on reducing readmissions caused by pericarditis recurrence.22 Additionally, in line with prior studies that noted one-fifth of all Medicare beneficiaries are readmitted within a month of discharge for reasons distinct from their original hospitalization,24,25 the most common causes of readmission in our study were distinct from the initial pericarditis admission.
Health care expenditure associated with an acute pericarditis hospitalization was surprisingly high, especially given its benign clinical nature and comparable to other common cardiovascular conditions. The annual inflation-adjusted Medicare payments for an acute pericarditis hospitalization was $9900 in 2012 compared with $14 000 for myocardial infarction and $8500 for heart failure in 2011, respectively.1 Similarities in length of stay were also noted between acute pericarditis hospitalization (average 5.5 days in 2012) compared with myocardial infarction (average 5.3 in 2011) and heart failure (average 5.2 in 2011), respectively.1 This increased health care utilization could be explained by the frequent use of invasive testing for exclusion of conditions such as acute coronary syndrome26 and pulmonary embolism and from management of underlying disease processes such as malignancies, renal failure, or myocardial infarction leading to pericarditis.
Our study has several limitations. First, our analysis was limited to Medicare fee-for-service beneficiaries, and we cannot comment on trends in patients enrolled in Medicare Advantage programmes and in patients <65 years of age or patients. This is important since the aetiology of pericarditis varies by age and tends to be relatively benign, e.g. viral infections among the young compared with diseases with relatively poorer prognosis such as malignancy, renal disease causing pericarditis among the elderly. Second, the observational nature of our study precludes us from commenting on causal mechanisms linking pericarditis with worse outcomes among the elderly. Third, although we adjusted for available potential confounders, we are unable to account for unmeasured confounders that could be affecting our study estimates with acute pericarditis simply being a marker of a sicker patient. Fourth, our study might underestimate the true burden of recurrent pericarditis episodes since some episodes are milder in nature that do not require hospitalization such as those managed as an outpatient or discharged directly from the emergency department. Our study focuses exclusively on hospital utilization for acute pericarditis. Fifth, we lack data regarding the precise cause of mortality to better understand the relationship between acute pericarditis and mortality in the elderly. Sixth, we do not have information about the use of important medications such as colchicine that have shown to reduce recurrence rates of acute pericarditis. Finally, pericarditis is a clinical diagnosis and the use of administrative codes might have introduced some bias. However, these codes have been validated in a prior study for identification of cases of pericarditis.9
In conclusion, in a nationally representative cohort, we demonstrate that the hospitalization rate for acute pericarditis among the elderly has remained unchanged over the last decade. Although all-cause mortality rates associated with pericarditis have improved, hospitalization for pericarditis continues to signal a high risk of dying and all-cause readmission within a year. Hospitalization for acute pericarditis is associated with substantial costs that have increased with time.
Conflict of interest: H.M.K. is a recipient of research agreements from Medtronic and from Johnson & Johnson (Janssen), through Yale, to develop methods of clinical trial data sharing; is the recipient of a grant from the Food and Drug Administration and Medtronic, through Yale, to develop methods for post-market surveillance of medical devices; works under contract with the Centers for Medicare & Medicaid Services to develop and maintain performance measures; chairs a cardiac scientific advisory board for UnitedHealth; is a participant/participant representative of the IBM Watson Health Life Sciences Board; is a member of the Advisory Board for Element Science and the Physician Advisory Board for Aetna; and is the founder of Hugo, a personal health information platform. B.B. is supported by the National Heart, Lung, and Blood Institute, National Institutes of Health, through grant number T32 HL007854. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. All other authors have nothing to disclose.
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