A total of 3010 patients were diagnosed with incident MI from 1987–2010 and survived the index MI hospitalization. In-hospital survival improved over time, from 89.0% from 1987–92 to 95.8% from 2005–2010 (p<0.001). The mean age at MI diagnosis was 67 years, 40.5% of patients were female, and 31.2% had ST-elevation MI (). The frequency of hypertension, hyperlipidemia, diabetes, obesity, COPD, and anemia increased over time. The proportion of patients with STEMI decreased from 39.1% in 1987–1992 to 24.1% from 2005–2010 (p for trend <0.001). Median length of stay was 5 (25th–75th percentile 3–8) days during the index MI admission and was shorter for those undergoing revascularization (median 5 vs. 6 days, p=<0.001). Length of stay varied by treatment strategy with median length of stay of 4, 7, and 11 days for those treated with PCI, fibrinolysis, and CABG, respectively.
Baseline Patient Characteristics
The proportion receiving a coronary angiogram and/or reperfusion/revascularization in-hospital after MI increased over time (p for trend<0.001). The majority (n=1541, 79.9%) of patients receiving reperfusion and/or revascularization had PCI, while 282 (14.6%) had CABG and 261(13.5%) fibrinolysis. There were 1144 (56.0%) patients with NSTEMI and 636 (68.8%) with STEMI who had PCI or CABG. A total of 158 (10.3%) patients undergoing PCI suffered a complication; 91 (5.9%) had a vascular or bleeding complication, 4 (0.3%) had stroke, and 72 (4.7%) had acute renal failure, though none had to start dialysis. Among patients with vascular or bleeding complications, 57 (62.6%) had access site complications; most were groin hematomas (n=38). A total of 34/91 patients (37.4%) had gastrointestinal bleeding requiring transfusion, while the remainder had bleeding at other sites. Only 5 (1.9%) patients receiving fibrinolysis and 5 (1.8%) undergoing CABG suffered a periprocedural stroke. There were 439 patients who underwent angiogram without reperfusion or revascularization. Among them, 13 (3.0%) had a vascular or bleeding complication, and 22 (5.0%) had acute renal failure, 3 of whom had to start dialysis.
30-day Readmissions After MI
A total of 643 readmissions occurred among 561 (18.6%) patients within 30 days of MI hospital discharge. Of the patients readmitted, 484 were readmitted once, 72 twice, and 5 were readmitted 3 times. Eighty-seven (2.9%) patients died within 30 days, of whom 19 were readmitted at the time of death. The number of readmissions by day within the 30 days following hospital discharge is shown in the . The readmission rates by time period were 137/591 (23.2%) for 1987–1992, 152/694 (21.9%) for 1993–1998, 193/874 (22.1%) for 1999–2004, and 161/851 (18.9%) for 2005–2010. Length of stay for the first readmission ranged from 0 to 64 days (median 3 days, 25th–75th percentile 1–7 days), and was similar for related and unrelated readmissions.
Distribution of 643 Readmissions within 30 Days of Incident Myocardial Infarction.
Causes of readmissions
The reasons for readmission by 1st
ICD-9 code are shown in Appendix Table 1
. The most common reasons were ischemic heart disease, respiratory/chest symptoms, and heart failure. Upon manual review of readmissions, there were 9 readmissions (1.4%) where the abstracted reason was markedly different than the ICD9 code. Cardiac biomarkers were measured in 74.8% of readmissions. Angiography was performed in 23.8% of readmissions (153/643). PCI was performed in 9.5% (61/643) of readmissions, and 6 of these were planned. A total of 24.6% (15/61) of PCIs were repeat PCI of the same culprit vessel treated at index MI because of occlusion. A total of 44 underwent CABG, and 28 of these were planned admissions for surgery. Among those undergoing revascularization during readmission, 46/103 (44.7%) were treated medically during index hospitalization (Appendix Table 2
Overall, 42.6% of readmissions after MI were related to the incident MI or its treatment, while 30.2% were unrelated, and 27.2% were unclear (). The proportion of unrelated readmissions was higher in women and patients with NSTEMI. The proportion of related readmissions decreased over time. The most common reason for “unclear” readmissions was atypical chest pain (frequently coded as ICD9 786). Narrative examples of readmissions are shown in the Appendix
Association Between Index MI Characteristics and Reason for 30-Day Readmissions
Risk Factors for Readmission After MI
Diabetes mellitus, COPD, anemia, higher Killip class at presentation, longer length of stay during incident MI admission, and a complication of either angiography or reperfusion/revascularization during the index admission were independently associated with increased risk of readmission after MI (). After adjustment for potential confounders, the risk of readmission did not change over the study period. To investigate the impact that death had on readmission, we performed two sensitivity analyses (Appendix Table 4
). First, we assumed that patients who died within 30 days survived and were never hospitalized. This resulted in no appreciable differences in results. Second, we assumed that those who died within 30 days were hospitalized on the day of death. Overall results were similar, though there was an increased risk of readmission for patients who had not undergone reperfusion/revascularization or angiogram (adjusted HR 1.42, 95% CI 1.14–1.78). The cumulative incidence of readmission within 30 days stratified by patient and MI characteristics is shown in .
Cumulative Incidence of Readmission at 30 Days After Incident MI Discharge According to Baseline/Incident MI Characteristics
Among those treated with PCI initially (n=1541), complications were associated with increased readmission risk. A stroke, vascular complication, or bleeding event after PCI (adjusted HR 1.66, 95% CI 1.09–2.52, p=0.018) and acute kidney injury (HR 1.92, 95% CI 1.25–2.95, p<0.001) were strongly associated with increased readmission compared with those who had PCI without complications.