Author + information
- Received October 11, 2017
- Revision received December 18, 2017
- Accepted January 9, 2018
- Published online April 2, 2018.
- Chun Shing Kwok, MBBS, MSc, BSca,b,∗ (, )
- Sunil V. Rao, MDc,
- Jessica E. Potts, MSca,
- Evangelos Kontopantelis, PhDd,
- Muhammad Rashid, MBBSa,
- Tim Kinnaird, MDe,
- Nick Curzen, BM, PhDf,
- James Nolan, MDa,b,
- Rodrigo Bagur, MD, PhDg and
- Mamas A. Mamas, BMBCh, DPhila,b
- aCentre for Prognosis Research, Institute for Primary Care and Health Sciences, Keele Cardiovascular Research Group, Keele University, Stoke-on-Trent, United Kingdom
- bRoyal Stoke University Hospital, Stoke-on-Trent, United Kingdom
- cDepartment of Cardiology, Duke Clinical Research Institute, Durham, North Carolina
- dUniversity of Manchester, Manchester, United Kingdom
- eDepartment of Cardiology, University Hospital of Wales, Cardiff, United Kingdom
- fUniversity Hospital Southampton NHS Foundation Trust & Faculty of Medicine, University of Southampton, Southampton, United Kingdom
- gDivision of Cardiology, Department of Medicine, London Health Sciences Centre, and Epidemiology and Biostatistics, Western University, London, Canada
- ↵∗Address for correspondence:
Dr. Chun Shing Kwok, Keele Cardiovascular Research Group, Centre for Prognosis Research, Institute for Primary Care and Health Sciences, Stoke-on-Trent ST4 7QB, United Kingdom.
Objectives This study aimed to examine the 30-day unplanned readmissions rate, predictors of readmission, causes of readmissions, and clinical impact of readmissions after percutaneous coronary intervention (PCI).
Background Unplanned rehospitalizations following PCI carry significant burden to both patients and the local health care economy and are increasingly considered as an indicator of quality of care.
Methods Patients undergoing PCI between 2013 and 2014 in the U.S. Nationwide Readmission Database were included. Incidence, predictors, causes, and cost of 30-day unplanned readmissions were determined.
Results A total of 833,344 patients with PCI were included, of whom 77,982 (9.3%) had an unplanned readmission within 30 days. Length of stay for the index PCI was greater (4.7 vs. 3.9 days) and mean total hospital cost ($23,211 vs. $37,524) was higher for patients who were readmitted compared with those not readmitted. The factors strongly independently associated with readmissions were index hospitalization discharge against medical advice (odds ratio [OR]: 1.91; 95% confidence interval [CI]: 1.65 to 2.22), transfer to short-term hospital for inpatient care (OR: 1.62; 95% CI: 1.38 to 1.90), discharge to care home (OR: 1.57; 95% CI: 1.51 to 1.64), and chronic kidney disease (OR: 1.50; 95% CI: 1.44 to 1.55). Charlson Comorbidity Index score (OR: 1.28; 95% CI: 1.27 to 1.29) and number of comorbidities (OR: 1.18; 95% CI: 1.17 to 1.18) were independently associated with unplanned readmission. The majority of readmissions were due to noncardiac causes (56.1%).
Conclusions Thirty-day readmissions after PCI are relatively common and relate to baseline comorbidities and place of discharge. More than one-half of the readmissions were due to noncardiac causes.
Percutaneous coronary intervention (PCI) is the most common revascularization modality for the treatment of coronary disease, accounting for 3.6% of all invasive procedures in the United States in 2011 (1). As the mean in-hospital mortality after PCI is <1% (2), readmissions after PCI are increasingly recognized as an important post-discharge outcome. In addition, rate of readmission increasingly used as a quality-of-care indicator at the institutional level, in addition to being an important burden to patients and the local health care economy (3).
The nature and impact of readmissions is complex. Despite efforts to reduce early readmissions, readmissions rates after PCI have been reported to be between 4.7% and 15.6% (3). Hospital readmissions may act as a surrogate of the quality of care received from the initial hospitalization (4), as they may result from actions taken or omitted during the initial hospital stay (5), or they may be a consequence of incomplete treatment or failure of services to coordinate post-discharge care (6,7). Unplanned readmissions can also be considered an adverse outcome for patients. From the health service perspective, the financial impact of readmissions is significant, with a readmission within 30 days associated with financial penalties (8). Furthermore, in the United States, the Affordable Care Act includes financial penalties for hospitals that have risk-adjusted readmissions rates for specific conditions exceeding specific benchmarks (9), whereas in the United Kingdom, hospitals do not receive any additional payments for treatment if patients are readmitted within 30 days (10).
In this study, we aimed to examine: 1) the 30-day unplanned readmissions rate; 2) predictors of readmission including comorbidity burden; and 3) causes of readmissions after PCI using the Nationwide Readmissions Database (NRD), the largest all-payer database of hospital readmissions in the United States.
Participants and study design
The NRD provides a nationally representative sample of all-age, all-payer discharges from U.S. nonfederal hospitals produced by the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality (11). This database is constructed from the discharge-level data of hospitalizations from 21 geographically dispersed participating states which represents 49.3% of the total U.S. population and 49.1% of all U.S. hospitalizations (12). Readmissions are determined through the deidentified unique patient linkage number assigned to each patient, which allows tracking of patients across hospitals within a state during a calendar year.
Individual patients in the NRD dataset are assigned up to 15 procedure codes for each admission to hospital. We defined patients with PCI with procedure code 0066 (PTCA OR: CORONARY ATHER), 3606 (INSERT CORON ART STENT), and 3607 (INSERT DRUGELUTING CRNRY AR). Only patients who were discharged alive after PCI were considered in the analysis. Planned readmissions were excluded, which were defined by readmissions within 30 days, which were classified as elective.
Outcomes and measurements
The primary outcome was the rate of unplanned readmission within 30 days of hospitalization with PCI. We included patients who underwent PCI with discharge dates in 2013 and 2014 with 30-day follow up. We excluded patients admitted in December of both calendar years because they would have not 30-day follow-up and patients who had planned readmissions. Total cost of index admission and readmissions (where relevant) for each patient was determined by multiplying the hospital charges with the Agency for Healthcare Research and Quality’s all-payer cost-to-charge ratios for each hospital.
We used International Classification of Diseases-9th Revision (ICD-9) codes to define clinical variables including smoking status, dyslipidemia, coronary artery disease, previous myocardial infarction, previous PCI, previous coronary artery bypass grafting (CABG), previous stroke or transient ischemic attack (TIA), atrial fibrillation, dementia, and receipt of circulatory support. The other comorbidity variables in the analysis were available via the Elixhauser comorbidities (13), which included alcohol misuse, chronic lung disease, heart failure, diabetes, valvular heart disease, peptic ulcer disease, hypertension, renal failure, obesity, cancer, fluid and electrolyte disorders, depression, peripheral vascular disease, hypothyroidism, liver disease, anemia, and coagulopathy. The paralysis variable from the Elixhauser comorbidities was used as a surrogate for hemiplegia, connective tissue disease, and leukemia where defined by Clinical Classifications Software codes 210, 211, and 39, respectively. Combining these variables enabled us to compute the Charlson Comorbidity Index. The number of comorbidities was the sum of the comorbidities included in the analysis. Procedural ICD-9 codes were used to define multivessel disease, bifurcation disease, circulatory support, vasopressor use, intra-aortic balloon pump use, fractional flow reserve use, intravascular ultrasound, and drug-eluting stent use. Diagnostic ICD-9 codes were used to define in-hospital outcomes including complete heart block, TIA or stroke, cardiogenic shock, cardiac arrest, acute kidney injury, major bleeding, blood transfusion, vascular complication, and emergency CABG. Additional data were collected on length of stay in hospital, hospital bed size, hospital location and hospital teaching status, and discharge destination. The causes of readmission were determined by the first diagnosis based on Clinical Classification Software codes, which are presented in detail in Online Table 1.
Statistical analysis was performed on Stata version 14.0 (StataCorp, College Station, Texas). The survey estimation commands were used to estimate the sample size as recommended by the Agency of Healthcare Research and Quality. Descriptive statistics are presented according to readmission status for all included variables. The statistical differences between readmitted and nonreadmitted patients for continuous and categorical variables were compared using the t test and chi-square test, respectively. Multiple logistic regressions were used to identify independent predictors of 30-day readmissions after PCI. Further regressions were used to determine predictors of noncardiac and cardiac readmissions. The logistic regression models were adjusted for age, sex, year, elective admission, weekend admission, diagnosis of acute myocardial infarction, primary expected payer, median household income, smoking, alcohol misuse, dyslipidemia, hypertension, diabetes mellitus, obesity, heart failure, coronary artery disease, previous myocardial infarction, previous PCI, previous CABG, previous valve disease, atrial fibrillation, previous TIA or stroke, peripheral vascular disease, pulmonary circulatory disorder, peptic ulcer disease, chronic lung disease, chronic kidney disease, liver disease, hypothyroidism, fluid and electrolyte disorders, anemia, cancer, depression, dementia, hospital bed size, hospital location, hospital teaching status, multivessel disease, bifurcation lesion, circulatory support, vasopressor use, intra-aortic balloon pump use, fractional flow reserve, intravascular ultrasound use, drug-eluting stent, in-hospital complete heart block, TIA or stroke, cardiogenic shock, cardiac arrest, acute kidney injury, major bleeding, blood transfusion, vascular complications, emergency CABG, length of stay, and discharge destination. Two separate regression univariable regressions were performed to evaluate the predictive value of Charlson Comorbidity Index and number of comorbidities on readmission status. The mean cost of index admission for PCI and the costs associated with readmissions were computed and are shown graphically. The causes of readmission within 30 days are presented in figure format as noncardiac and cardiac. A flow diagram was used to describe patient outcomes (in-hospital death) for both admissions and readmissions.
A total of 862,649 patients underwent PCI between 2013 to 2014. After exclusion of 21,116 patients who died during the index admission (2.4%) and another 8,105 patients who had planned PCI readmission within 30 days, 833,344 patients with PCI procedures were included in the analysis. At 30 days, 77,982 (9.3%) participants had an unplanned readmission.
The baseline characteristics of the participants during their initial hospital episode are shown in Table 1. Participants who were readmitted were more likely to be older (67.3 years of age vs. 64.5 years of age), women (39.4% vs. 31.3%), and admitted on the weekend (22.8% vs. 22.3%). Significant differences were also observed depending on the primary expected payer and median household income where private health care (30.2% vs. 18.2%) and higher median household income (highest quartile: 21.3% vs. 19.6%) was associated with reduced rates of readmissions.
Multimorbidity was also more prevalent among patients who were readmitted within 30 days. Specifically, the mean number of comorbidities was 5.7 in the readmitted group compared with 4.9 in the no-readmission group, with a higher Charlson Comorbidity Index score in the readmitted group (1.9 vs. 1.3; p < 0.001). Significant differences were observed in treating hospital characteristics, with differences observed based on bed size of the hospital and teaching status but not based on location. Significant differences were recorded for in-hospital complete heart block (1.4% vs. 1.1%), TIA or stroke (3.7% vs. 3.1%), acute kidney injury (1.0% vs. 0.6%), major bleeding (1.1% vs. 0.7%), blood transfusion (0.11% vs. 0.05%), and vascular complications (1.0% vs. 0.7%), which were all more frequent in the readmission group.
For the first admission for PCI, length of stay was greater in patients who were readmitted (4.7 days vs. 3.9 days), and they were more likely to be transferred to another institution (8.9% vs. 4.7%) or go to a care home on discharge (14.1% vs. 7.2%). The mean cost for the index PCI and total cost for index and first readmission were $23,211 ± $19,605 and $37,524 ± $25,679, respectively (Figure 1).
The independent predictors of 30-day readmission are shown in Table 2. Factors around discharge and discharge destination were most associated with unplanned readmission. Patients self-discharging against medical advice (odds ratio [OR]: 1.91; 95% confidence interval [CI]: 1.65 to 2.22; p < 0.001), short-term hospital (OR: 1.62; 95% CI: 1.38 to 1.90; p < 0.001), care home (OR: 1.57; 95% CI: 1.51 to 1.64; p < 0.001), and transfer to other institution (OR: 1.41; 95% CI: 1.32 to 1.50; p < 0.001) were independently associated with unplanned readmission within 30 days. Comorbidities were also associated with readmission, with the largest ORs observed in chronic kidney disease (OR: 1.50; 95% CI: 1.44 to 1.55; p < 0.001), liver disease (OR: 1.42; 95% CI: 1.30 to 1.55), atrial fibrillation (OR: 1.41; 95% CI: 1.36 to 1.46; p < 0.001), and chronic lung disease (OR: 1.36; 95% CI: 1.31 to 1.40; p < 0.001). Participants who had private insurance (OR: 0.67; 95% CI: 0.64 to 0.70; p < 0.001), no insurance (OR: 0.69, 0.64 to 0.74; p < 0.001), elective index admission (OR: 0.70; 95% CI: 0.66 to 0.74; p < 0.001), and drug-eluting stent (OR: 0.82; 95% CI: 0.80 to 0.85; p < 0.001) were independently associated with a decreased risk of unplanned 30-day readmission. Comorbidity burden as defined by Charlson Comorbidity Index (OR: 1.28; 95% CI: 1.27 to 1.29; p < 0.001) or number of comorbidities (OR: 1.18; 95% CI: 1.17 to 1.18; p < 0.001) was independently associated with readmission.
The causes of readmission are shown in Figure 2. The readmissions due to noncardiac causes were slightly more common (56.1%). Among the noncardiac causes for readmission the most common causes were nonspecific chest pain (14.8%), infection (12.3%), gastrointestinal disease (10.4%), respiratory disease (8.6%), and major bleeding complications (5.9%). Among cardiac causes for readmission the most common causes were coronary artery disease including angina (31.6%), heart failure (25.1%), acute myocardial infarction (21.6%), arrhythmias (15.8%), and pericarditis (1.5%).
Table 3 shows the predictors of noncardiac and cardiac readmissions after PCI. Factors with significant associations only for noncardiac readmissions were hypertension, dementia, and vascular complications. Factors with significant associations only for cardiac readmission were smoking, urban location, and an index hospitalization occurrence of complete heart block and stroke or TIA.
Figure 3 shows a flow diagram in-hospital mortality for index procedure, cardiac, and noncardiac causes of unplanned readmission. The in-hospital mortality rate for patients undergoing index PCI was 2.4%, whereas the in-hospital death among those who had an unplanned readmission was 3.1% for noncardiac readmissions and 2.8% for cardiac readmissions.
Our analysis of 833,344 PCI procedures demonstrates that unplanned readmissions within 30 days of the index PCI are common (9.3%). The majority of readmissions within 30 days are noncardiac (56%), with female sex, chronic kidney disease, liver failure, atrial fibrillation, increasing comorbidity burden, and discharge location among the strongest predictors of unplanned 30-day readmission. Patients who experienced an unplanned readmission for noncardiac reasons tended to be younger, with more comorbidities, including alcohol misuse, cancer, and dementia, whereas patients who are readmitted for cardiac reasons are more likely to have in-hospital complications at their index PCI event. Finally, unplanned readmissions were associated with increased mortality rates and health care costs.
Our study overcomes several limitations in the existing literature on unplanned readmissions following PCI. The largest study of readmissions after PCI currently published described a cohort of Medicare patients between 2000 to 2012 and reported a 30-day readmission rate of 15.8% (14). One of the most important limitations of this study was that it did not distinguish between unplanned and planned readmissions, which may explain why their reported readmission rate was higher compared with the current study in which planned readmissions were excluded. Furthermore, a planned admission for a staged procedure or investigation has neither the health care cost implications, nor the impact on hospital services that an unplanned readmission will have. Second, the study was undertaken in a Medicare cohort, which limits generalizability to all admissions, in contrast to our study, which included Medicaid, private and uninsured patients, as well as Medicare patients. We observed in the current study that the Medicare cohort had the highest proportion of patients with readmission 65.0% versus 51.8%. This suggests that a study including only Medicare patients would be a higher risk cohort for unplanned readmission that may not be representative of the wider PCI practice within the United States. Third, the study focused on PCI outcomes from procedures undertaken over 15 years ago and therefore may not represent contemporary practice and its associated outcomes. Other studies have also evaluated readmissions after PCI but are limited because they are small studies derived from either single, or a small number of centers (15–18), or are derived from procedures undertaken more than 10 years ago, which may not be relevant to modern PCI practices (19,20).
Although our previous work has shown that comorbidity burden has important prognostic impact in PCI (21,22), we find for the first time the comorbidity as defined by the Charlson Comorbidity Index score and number of comorbidities are an important predictive tool for unplanned readmissions. It is not clear whether measures such as greater emphasis on management of comorbid conditions during the index procedure may reduce readmissions or whether comorbidity burden is a surrogate for a higher risk cohort. An area for future research may be determining if better management of comorbid illness and closer follow-up once discharged may reduce unplanned readmissions.
We found that noncardiac causes are more common, which may reflect the worsening comorbid burden in patients who undergo PCI overtime. Furthermore, PCI practices have evolved, with improved drug-eluting stent designs with thinner struts, which reduce stent thrombosis (23,24) and powerful antiplatelet agents, which reduce major adverse cardiovascular events (25,26) and stent thrombosis (26,27). Newer tools, such as fractional flow reserve, help to characterize lesions that require treatment and use of intravascular imaging modalities, such as intravascular ultrasound and optical coherence tomography, optimize stent deployment, which has also been shown to improve patient outcomes (28,29). These changes in PCI practices may serve to reduce cardiac causes of readmission.
Another potential reason for the dominance of noncardiac readmissions may relate to the decline in length of stay, which may influence the management or optimization of non–cardiac-related comorbidities because improvements in PCI practices facilitate early discharge to reduce associated hospital expenditure. Although our analysis suggests that the majority of 30-day unplanned readmissions are noncardiac in origin, it is important to note that they may still relate or occur as a consequence of the index PCI procedure. For example, patients post-PCI are advised to seek medical attention if they experience chest pain, which may explain the increased rates of noncardiac chest pain reported in our analyses. Other causes of readmission such as bleeding complications may directly relate to the PCI procedure as potent antiplatelet agents prescribed increased the propensity toward such bleeding complications, even if such bleeding events are classified as noncardiac causes of readmission.
Our results support our previous systematic review that identified that female sex, pre- or periprocedural myocardial infarction, peripheral vascular disease, diabetes, renal failure, and nonelective PCI were associated with more readmissions, although data were mostly derived from single centers with small sample sizes and often in less contemporary cohorts (3). Other studies have also identified other predictors that were not evaluated in the current study. For example, Hannan et al. (20) reported reduced ejection fraction, ≥3 diseased vessels, and malignant ventricular arrhythmias as a predictor of readmission. Harjai et al. (18) also found PCI to left anterior descending artery, lesion length >28 mm, aspirin dose, and proton pump inhibitor use were predictive of readmission. Factors that predispose to readmission after PCI will most probably depend on the risk profile of the cohort and the case mix, such as proportion of cases that were elective or emergency. Although additional studies (16,17,30) have looked at predictors, this is the largest study to date and the first to study characteristics, predictors, and outcomes in a national cohort.
Although readmissions are important from a financial perspective, it may not be the ideal quality of care indicator. The Quality of Care and Outcomes Research in Cardiovascular Disease and Stroke Working Group described principles of selection of performance measures (31), but readmissions meet some but not all criteria with concerns raised by a previous editorial on readmissions after transcatheter aortic valve replacement (32). First, unplanned readmissions are meaningful, as they are a health care expenditure and burden to patients. Second, measurements of unplanned readmissions are easily documented, reliable in hospital databases, and can be used to compare different health care providers. However, it is unclear that adjustment for patient variability will enable performance of the health care system to have direct impact on unplanned readmission rates. Furthermore, it is uncertain if unplanned readmissions can be modified by improvements in processes of care. There are many studies that have tested interventions aimed to reduce readmissions (33), but there are currently no measures with good evidence base that have been shown to reduced readmission after PCI.
The prevention of 30-day hospital readmissions has been previously reviewed by Leppin et al. (33). Although none of the studies in the review were in PCI settings, their reviewed classified different discharge interventions such as a comprehensive discharge planning and home follow-up protocol for elderly, which has been shown to reduce readmissions and health expenditures (34). Other interventions have been tested such as telephone follow-up (35), telemonitoring (36), and self-management–focused education programs (37). The only study of PCI patients tested an intervention, which involved initial patient readmission risk assessment and used a discharge checklist to ensure access to appropriate medications and close follow-up of high-risk patients, which resulted in a reduction of 30-day readmissions after PCI from 9.6% to 5.3% (38). Targeting specific causes of readmission may be an important area for future research. For example, specific care paths for recognized causes of readmission after PCI in the emergency room could preclude admission or direct patients for observation rather than inpatient status. Education for appropriate assessment and management of cardiac or procedure-related complication may also have a role in reducing readmissions.
Our study has several strengths. First, this is a large contemporary nationwide cohort that provides results that are generalizable to current PCI practices. The data are nearly complete with no missing data and previous studies using the NRD only having published data derived from 1 year (39). In addition, we could explore difference in predictors of all unplanned readmissions as well as noncardiac and cardiac readmissions and further explore mortality and length-of-stay outcomes for patients for both the index and readmission according to causes.
Our study is also subject to the common limitations of retrospective analyses of administrative data. Our data were collected from administrative claims sampled from 21 states, which account for 49% of the U.S. population and hospitalizations, but the results of the current study may not be generalizable to all regions, as geographic heterogeneity in outcomes could not be explored (40). Second, although we were able to review data over a 2-year period, the overall data comprise 2 unique datasets corresponding to each in the period 2013 and 2014, and no linkage is possible between years. Third, even though we were able to adjust for a variety of variables and comorbidities, there is still the risk of residual confounding, as the study is observational in nature, and the NRD dataset does not capture measures of frailty that are known to affect PCI outcomes (41). Finally, causes of readmission were identified using the primary discharge diagnosis codes, which may be subject to reporting biases, although previous studies have used a similar approach for TAVR readmissions (42,43).
Our results suggest that 30-day readmissions in the United States is common and comorbid illnesses and places of discharge are important factors that influence readmissions. Clinicians should focus on the optimization of the management of any comorbid condition during a patient's index admission for PCI and consider developing outreach programs to patients discharged to short-term hospitals, other institutions, and care homes. There are important financial consequences of such readmissions, and further strategies to reduce the prevalence should be explored.
WHAT IS KNOWN? Unplanned rehospitalizations following PCI carry significant burden to both patients and the local health care economy and are increasingly considered as an indicator of quality of care.
WHAT IS NEW? Our analysis of 833,344 PCI procedures demonstrates that unplanned readmissions within 30 days of the index PCI are common. Most readmissions were due to noncardiac causes (56.1%), and comorbidities and discharge location are strong predictors of unplanned 30-day readmission.
WHAT IS NEXT? Future work should explore if optimization of the management of any comorbid condition during a patient's index admission for PCI and outreach programs to patients discharged to short-term hospitals, other institutions, and care homes may reduce early readmissions.
Financial support was provided by the North Staffs Heart Committee. This work was conducted as a part of Dr. Kwok’s PhD research, which was supported by Biosensors International. Dr. Curzen has received unrestricted research grant support from Boston Scientific, Haemonetics, Heartflow, and Philips Volcano; has received speaker fees from Boston Scientific and Heartflow; has received travel sponsorship from Edwards and Lilly/D-S; and has served as a consultant for Haemonetics. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbrevations and Acronyms
- coronary artery bypass grafting
- confidence interval
- International Classification of Diseases-9th Revision
- Nationwide Readmissions Database
- odds ratio
- percutaneous coronary intervention
- transient ischemic attack
- Received October 11, 2017.
- Revision received December 18, 2017.
- Accepted January 9, 2018.
- 2018 American College of Cardiology Foundation
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