It is important to identify the factors related to survival of patients undergoing primary percutaneous coronary intervention for ST-segment elevation acute myocardial infarction. Our objective was to determine the interactive effect of the door-to-balloon (DTB) time and onset-to-door (OTD) time on longer term mortality for patients with ST-segment elevation acute myocardial infarction. The present study was a retrospective cohort analysis of the effect of the DTB time and OTD time on longer term (median follow-up 413 days) mortality for patients undergoing primary percutaneous coronary intervention in New York from January 1, 2004 to December 31, 2006, adjusting for the effect of other important risk factors. The patients with ST-segment elevation acute myocardial infarction with a DTB time of <90 minutes and OTD time of <4 hours had the lowest longer term mortality (3.51%). Patients with a DTB time <90 minutes and OTD time of ≥4 hours had significantly greater mortality than patients with an OTD time of <4 hours and DTB time of <90 minutes (adjusted hazard ratio 1.54, 95% confidence interval 1.04 to 2.30), as did patients with a DTB time of ≥90 minutes and OTD time of ≥4 hours (adjusted hazard ratio 1.48, 95% confidence interval 1.05 to 2.09). For an OTD time of <4 hours and DTB time of ≥90 minutes, mortality showed a trend toward being greater compared to shorter OTD and DTB times (adjusted hazard ratio 1.29, 95% confidence interval 0.95 to 1.77). In conclusion, the combination of short (<90 minutes) DTB time and short (<4 hours) OTD time was associated with the lowest longer term mortality rate.
The purpose of the present study was to use data from the New York State Percutaneous Coronary Intervention Reporting System to study the independent effect of the onset-to-door (OTD) time and door-to-balloon (DTB) time on longer term mortality for patients with ST-segment elevation myocardial infarction (STEMI) transported directly to a STEMI hospital and to determine whether these outcomes differed depending on whether the patients were at high risk.
Methods
The main database used in the present study was the New York State Percutaneous Coronary Intervention Reporting System registry, which was developed in 1991 for the purpose of collecting information on all patients undergoing percutaneous coronary intervention (PCI) in New York’s nonfederal hospitals. Deaths occurring among New York State patients after discharge from the hospital were obtained by matching the Percutaneous Coronary Intervention Reporting System to New York’s Vital Statistics death file using patient-specific identifiers.
The primary focus of the study was New York State patients without previous revascularization who had undergone primary PCI for STEMI from January 1, 2004 to December 31, 2006, with an OTD of <12 hours. All patients directly transported to New York hospitals were followed up through December 31, 2006 to detect the end points, except for patients who had received thrombolytic therapy (n = 524) or had invalid or missing DTB or OTD times (n = 957). No significant differences were found in the patient demographics or risk factor prevalence between the patients included in or excluded from the study. The median follow-up time was 413 days. The study was limited to New York patients so that death after discharge could be confirmed using New York vital statistics data. The remaining group consisted of 5,092 patients who had undergone PCI, and the primary end point in the study was risk-adjusted mortality during the entire 3-year study period.
The frequencies for a wide variety of risk factors (i.e., demographic, ventricular function, number of diseased vessels, previous myocardial infarction, and a large number of co-morbidities) were computed, and differences in prevalence for each of these risk factors were examined for patients stratified by their OTD time (<4 vs >4 hours) and DTB time (<90 vs >90 minutes). Significant differences were identified using chi-square tests. The cutoff points of 4 hours for OTD time and 90 minutes for DTB time were chosen after preliminary analyses of the relation between OTD and mortality and DTB and mortality.
The multivariate relations between DTB and mortality and OTD time and mortality were examined by developing Cox proportional hazards models with robust variance estimation to account for the clustering effects of hospitals on the survival times. Individual time ranges were created from the preliminary analysis findings, and various ranges were compared to the range with the shortest time (<4 hours for OTD time and <90 minutes for DTB time) after adjusting for significant independent control variables. Candidate independent variables for the models included a variety of demographic factors and measures of ventricular function, extent of coronary artery disease, and co-morbidities. A test for trend in mortality rates across the ranges was also conducted.
The relative effect of 4 combinations of DTB intervals (on either side of 90 minutes) and OTD intervals (on either side of 4 hours) on longer term mortality were also tested using a Cox proportional hazards model with robust variance estimation.
The combination of OTD <4 hours and DTB < 90 minutes was used as a reference, and the other 3 combinations were treated as independent variables, in addition to the risk factors mentioned.
The data were then limited to “high-risk” patients, and the analyses with the combinations of OTD and DTB times were repeated. “High-risk” was defined as the patient characteristics associated with an adjusted hazard ratio of ≥2 in the model predicting mortality. This included patients with one or more of the following characteristics: age ≥75 years, multivessel disease, ejection fraction <30%, hemodynamic instability or shock, and creatinine >2.5 mg/dl or requiring dialysis.
All tests were conducted at the p = 0.05 level, all confidence limits were two-sided, and all analyses were conducted using Statistical Analysis Systems, version 9.1 (SAS Institute, Cary, North Carolina).
Results
Table 1 lists the patient risk factors stratified by the DTB time (<90 minutes) and OTD time (<4 hours). The median follow-up period was 413 days. As indicated in Table 1 , 2,368 patients (46.5%) had a DTB time of <90 minutes and 4,092 patients (88.9%) had an OTD time of <4 hours; 1,878 patients (36.9%) had both an OTD time of <4 hours and a DTB time of <90 minutes.
| Variable | DTB Time <90 min | DTB Time ≥90 min | p Value | ||||
|---|---|---|---|---|---|---|---|
| OTD Time <4 h | OTD Time ≥4 h | OTD Time <4 h | OTD time ≥4 h | DTB Time | OTD Time | All | |
| Patients | 1,878 | 490 | 2,214 | 510 | |||
| Age (years) | 0.0002 | 0.38 | 0.007 | ||||
| <55 | 40.4% | 39.8% | 35.6% | 35.7% | |||
| 55–64 | 28.7% | 27.1% | 29.1% | 25.7% | |||
| 64–74 | 16.7% | 18.8% | 17.0% | 18.2% | |||
| 75–84 | 11.6% | 12.5% | 14.4% | 15.9% | |||
| ≥84 | 2.6% | 2.9% | 3.9% | 4.5% | |||
| Women | 24.6% | 28.6% | 30.1% | 32.0% | <0.0001 | 0.08 | <0.001 |
| Black | 5.7% | 8.0% | 7.6% | 8.8% | 0.02 | 0.06 | 0.03 |
| Ejection fraction (%) | <0.0001 | 0.007 | <0.001 | ||||
| <20 | 0.8% | 0.4% | 1.5% | 0.6% | |||
| 2–29 | 3.7% | 5.1% | 6.0% | 8.0% | |||
| 30–39 | 13.3% | 16.3% | 16.3% | 16.3% | |||
| 40–49 | 28.0% | 29.0% | 26.7% | 30.2% | |||
| ≥50 | 54.3% | 49.2% | 49.6% | 44.9% | |||
| Carotid/cerebrovascular disease | 2.7% | 2.9% | 4.3% | 5.5% | 0.0008 | 0.34 | 0.005 |
| Peripheral vascular disease | 2.7% | 3.1% | 4.2% | 3.1% | 0.02 | 0.56 | 0.06 |
| Hemodynamically unstable or shock | 3.8% | 3.9% | 5.0% | 4.5% | 0.06 | 0.761 | 0.29 |
| Heart failure | 0.007 | 0.88 | 0.05 | ||||
| This admission | 3.1% | 3.9% | 4.9% | 4.9% | |||
| Before this admission | 0.4% | 0.6% | 0.3% | 0.0% | |||
| None | 96.5% | 95.5% | 94.8% | 95.1% | |||
| Malignant ventricular arrhythmia | 1.1% | 1.2% | 1.9% | 1.4% | 0.05 | 0.58 | 0.21 |
| Chronic obstructive pulmonary disease | 3.3% | 3.7% | 3.8% | 3.5% | 0.48 | 0.96 | 0.87 |
| Diabetes mellitus | 11.1% | 18.6% | 17.2% | 19.4% | <0.0001 | 0.0003 | <0.001 |
| Creatinine >2.5 mg/dl or dialysis | 0.7% | 1.8% | 1.2% | 1.0% | 0.39 | 0.24 | 0.12 |
| Anatomic group | 0.007 | 0.08 | 0.002 | ||||
| One vessel without left anterior descending artery disease | 35.0% | 32.5% | 30.1% | 28.4% | |||
| One vessel nonproximal left anterior descending artery disease | 10.8% | 13.7% | 12.5% | 11.4% | |||
| One vessel proximal left anterior descending artery disease | 16.0% | 13.5% | 15.1% | 13.5% | |||
| Two vessel without left anterior descending artery disease | 6.3% | 8.4% | 7.5% | 9.6% | |||
| Two vessel nonproximal left anterior descending artery disease | 11.6% | 10.8% | 11.3% | 13.7% | |||
| Two vessel proximal left anterior descending artery disease | 10.0% | 8.6% | 11.6% | 8.2% | |||
| Three vessel nonproximal left anterior descending artery disease | 5.6% | 7.8% | 5.9% | 7.8% | |||
| Three vessel proximal left anterior descending artery disease | 4.7% | 4.9% | 6.0% | 7.3% | |||
| Admission time | <0.0001 | 0.008 | <0.001 | ||||
| Weekday 8:00 a.m. –3:59 p.m. | 45.1% | 44.9% | 26.4% | 33.5% | |||
| Weekday 4:00 p.m. –7:59 a.m. | 34.2% | 35.1% | 40.3% | 36.7% | |||
| Weekend 8:00 a.m. –3:59 p.m. | 9.4% | 8.8% | 13.8% | 13.7% | |||
| Weekend 4:00 p.m. –7:59 a.m. | 11.2% | 11.2% | 19.5% | 16.1% | |||
Significant differences were found among the DTB time and OTD time groups for many patient risk factors. Older patients, black patients, women, those with lower ejection fractions, carotid/cerebrovascular disease, peripheral vascular disease, heart failure, diabetes mellitus, multivessel disease, and those admitted on weekends had longer DTB times. Patients who had lower ejection fractions, diabetes mellitus, and were admitted on weekdays had longer OTD times.
The adjusted hazard ratios for mortality for the different ranges of OTD time (<2 hours, 2 to 3.9 hours, and ≥4 hours) are listed in Table 2 . OTD times of <2 hours were associated with the lowest mortality rates, but the mortality for OTD times of 2 to 3.9 hours was not significantly greater. The adjusted hazard ratio was greatest for patients with OTD times of ≥4 hours, and no significant linear trend was seen toward lower mortality rates with shorter OTD times.
| OTD Time (h) | Patients (n) | Observed Mortality Rate (%) | Adjusted Hazard Ratio ⁎ | 95% Confidence Interval | p-value |
|---|---|---|---|---|---|
| Trend | 1.14 | 0.95–1.36 | 0.16 | ||
| <2 | 2,708 | 4.9% | 1.00 | ||
| 2–3.9 | 1,384 | 5.3% | 1.01 | 0.77–1.31 | 0.96 |
| ≥4 | 1,000 | 6.8% | 1.29 | 1.03–1.60 | 0.02 |
⁎ Adjusted for all patient risk factors listed in Table 1 .
Table 3 lists information on the relation between the DTB time and mortality for 3 ranges of DTB times (<90 minutes, 90 to 179 minutes, and ≥180 minutes). As indicated, relative to patients with a DTB time of <90 minutes, patients with a DTB time of 90 to 179 minutes and those with a DTB time of ≥180 minutes had greater, although not significantly greater, mortality rates. No significant linear trend was seen toward lower mortality rates with shorter DTB times.
| DTB Time (min) | Patients (n) | Observed Mortality Rate (%) | Adjusted Hazard Ratio ⁎ | 95% Confidence Interval | p Value |
|---|---|---|---|---|---|
| Trend | 1.13 | 0.93–1.37 | 0.22 | ||
| <90 | 2,368 | 4.1% | 1.00 | ||
| 90–179 | 2,207 | 6.3% | 1.16 | 0.89–1.51 | 0.28 |
| >180 | 517 | 7.4% | 1.26 | 0.82–1.93 | 0.29 |
⁎ Adjusted for all patient risk factors listed in Table 1 .
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