Abstract
To determine whether door-to-balloon (DTB) times of patients presenting with ST-elevation myocardial infarction (STEMI) were reduced in patients transported by emergency medical services (EMS) compared to those who were self-transported. DTB time is an important measure of hospital care processes in STEMI. Use of EMS may expedite in-hospital processing and reduce DTB times. A total of 309 consecutive STEMI patients who underwent primary percutaneous coronary intervention in our institution were analyzed. Excluded were patients who received fibrinolytics, presented in cardiac arrest, were intubated, or were transferred from another hospital. EMS-transported patients ( n = 83) were compared to self-transported patients ( n = 226). The primary outcome measure was DTB time and its component time intervals. Secondary end points included symptom-to-door and symptom-to-balloon times, and correlates for DTB > 90 minutes. A higher percentage of EMS-transported patients reached the time goal of DTB < 90 minutes compared to self-transported patients (83.1 versus 54.3%; p < 0.001). EMS-transported patients had shorter DTB times [median (IQR) minutes, 65 (50–86) versus 85 (61–126); p < 0.001] due to a reduction of emergency department processing (door-to-call) time, whereas catheterization laboratory processing (call-to-balloon) times were similar in both groups. EMS-transported patients had shorter symptom-to-door [median (IQR) hours, 1.2 (0.8–3.5) versus 2.3 (1.2–7.5); p < 0.001] and symptom-to-balloon [median (IQR) hours, 2.5 (1.9–4.7) versus 4.3 (2.6–9.1); p < 0.001]. Independent correlates of DTB times > 90 minutes were self-transport (odds ratio 5.32, 95% CI 2.65–10.70; p < 0.001) and off-hours presentation (odds ratio 2.89, 95% CI 1.60–5.22; p < 0.001). Use of EMS transport in STEMI patients significantly shortens time to reperfusion, primarily by expediting emergency department processes. Community education efforts should focus not only on the importance of recognizing symptoms of myocardial infarction, but also taking early action by calling the EMS.
1
Introduction
Rapid reperfusion with percutaneous coronary intervention (PCI) is the gold standard therapy for patients presenting with ST-segment elevation myocardial infarction (STEMI) when promptly available . Delays in door-to-balloon (DTB) times correlate with increased morbidity and mortality . Achieving a DTB time of < 90 minutes has become a quality measure of the hospital system performance dealing with STEMI care . With the identification of key strategies to enhance hospital system performances , several programs have been successfully implemented to help meet the DTB < 90-minute time goals with timely access to primary PCI .
To address the continuum of care for STEMI patients from the onset of symptoms to arrival at the emergency department (ED), the use of emergency medical services (EMS) may potentially facilitate rapid transport, early assessment and treatment, and expedited communication of information with the accepting ED. However, EMS has been shown to be underutilized , and a significant proportion of STEMI patients still arrive at the ED via their own transportation.
MedStar Washington Hospital Center (Washington, DC) is a primary PCI facility with around-the-clock cardiac catheterization capabilities catering to Washington, DC, a highly urbanized area with EMS coverage provided fully by the DC Fire and EMS. In addition, it serves as a referring PCI center for other facilities in DC, as well as parts of Maryland and Virginia. MedStar Washington Hospital Center is located in the heart of Washington, DC, and with DC Fire and EMS as the single EMS provider for Washington, DC, this offers us a unique opportunity to analyze modes of transport for STEMI patients within DC, and its impact on pre- and in-hospital care processes leading to reperfusion. Specifically, we aimed to determine if the use of EMS transport may actually reduce overall DTB times by reducing certain components of in-hospital processing times.
2
Methods
2.1
Patient population
This retrospective analysis included all patients from January 2007 to December 2012 who presented to the MedStar Washington Hospital Center ED with a STEMI and subsequently underwent primary PCI. Patients who were transferred from a referring institution, patients who suffered cardiac arrest, patients who were intubated, and patients who were given fibrinolytic therapy before the PCI were excluded. The patients were categorized into whether they were self-transported (“self”) or transported by EMS.
2.2
DC Fire and EMS
DC Fire and EMS provides EMS coverage to Washington, DC, an urban city of 68.3 square miles, through 58 medical units (or ambulances) and is managed by a centralized 911 dispatch call system. The ambulances have 12-lead electrocardiogram (ECG) capabilities that are transmissible to the receiving ED at MedStar Washington Hospital Center. All patients are transported to the ED where a formal ECG is performed. Based on the qualifying criteria for STEMI, the ED physician contacts the on-call interventionalist. When activation of the catheterization laboratory is considered appropriate, the on-call interventionalist contacts a central number to mobilize the catheterization laboratory team, and the patient is transferred to the catheterization laboratory. Because the system does not allow for pre-activation of the catheterization laboratory team from the ambulance, none of the patients bypassed the ED en-route to the catheterization laboratory.
2.3
Self-transport
The term ‘self-transport’ refers to patients who arrive at the ED using transportation that did not involve EMS. These modes of transportation include public transportation, taxi, self-driven or driven by others, or walked to the hospital. These patients may have also visited another healthcare facility after symptom onset, before arriving at the ED by non-EMS transport. They also go through the usual triaging process in the ED. Following a diagnosis of STEMI on ECG, the interventionalist and the catheterization laboratory team are mobilized in the usual manner.
2.4
Study definitions and end points
The following time points were defined and collected contemporaneously for each STEMI patient ( Fig. 1 ): symptom onset time (from patient recall); door time (time of first registered hospital contact); ECG time (time of inciting STEMI ECG leading to decision to activate the catheterization laboratory); call time (time of call to interventionalist); lab time (time of patient arrival to the cardiac catheterization laboratory); case start time (time of first sheath insertion); and balloon time [time of introduction of first device (balloon catheter, aspiration thrombectomy catheter or stent) restoring antegrade flow]. Time intervals were then calculated from these time points. Door-to-call is to be taken as ED processing time interval, and call-to-balloon is to be taken as laboratory processing time interval.
Off-hours presentation was defined as any weekend presentation or weekday presentation from 5 pm to 8 am. ECG criteria defining a STEMI included the presence of at least 1 mm ST-segment elevation in at least 2 contiguous leads, or the occurrence of a new left bundle branch block. Angiographic success was defined as a residual stenosis of < 30% with thrombolysis in myocardial infarction grade III flow.
The primary end point was DTB time. Secondary end points were the DTB component times, symptom-door and symptom-balloon times. In-hospital outcomes evaluated were death, cardiac death, Q-wave MI, urgent coronary artery bypass graft surgery, and urgent repeat PCI of target lesion.
2.5
Interventional treatment
PCI was performed according to guidelines current at the time of the procedure. All patients received an aspirin loading dose of 325 mg, as well as either clopidogrel (600 mg), prasugrel (60 mg) or ticagrelor (180 mg) loading. Anticoagulation regimens were chosen at the operator’s discretion and included unfractionated heparin adjusted to targeted activated clotting time, or bivalirudin 0.75 mg/kg followed by an infusion of 1.75 mg/kg/hr for the duration of the procedure. The interventional strategy, utilization of adjunct pharmacotherapy, such as glycoprotein IIb/IIIa inhibitors, and device choice were at the operator’s discretion. Dual antiplatelet therapy was recommended for ≥ 12 months for all patients post procedure.
2.6
Data collection
Clinical, procedural, and follow-up data were prospectively collected and stored in a central database. A dedicated data coordinating center performed all data management and analyses. Pre-specified clinical and procedural data and in-hospital complications were obtained from hospital charts reviewed by independent research personnel blinded to the study objectives. Primary source documents were obtained for all events and were used to adjudicate STEMI cases by physicians not involved in the procedures, and who were unaware of the study objectives. The time points and time intervals pertaining to STEMI management and system performance were adjudicated and verified by physicians not involved in the study. The institutional review boards at MedStar Washington Hospital Center (Washington, DC) and the MedStar Health Research Institute (Washington, DC) approved this study.
2.7
Statistical analysis
Statistical analysis was performed using SAS version 9.1 (SAS Institute Inc., Cary, NC). Continuous variables are presented as mean ± standard deviation (SD) if normally distributed, or median ± interquartile range (IQR) if non-normally distributed. Student’s t test and Wilcoxon rank-sum test were used for comparisons of normally and non-normally distributed continuous data, respectively. Categorical variables are expressed as frequencies and percentage, and compared using chi-square test or Fisher’s exact test as appropriate. A multivariate logistic regression model was used to determine the independent correlates of DTB > 90 minutes, expressed as odds ratio, with 95% confidence interval. Variables were selected on the basis of overall clinical relevance, with particular attention given to clinical and procedural factors that may delay time to reperfusion. Variables included self-transport (versus EMS), off-hours presentation (versus on hours), age, female gender, body mass index, diabetes, peripheral vascular disease, prior PCI, prior coronary artery bypass grafting, placement of intra-aortic balloon pump, and American College of Cardiology/American Heart Association type C lesion. A p value < 0.05 is considered statistically significant.
2
Methods
2.1
Patient population
This retrospective analysis included all patients from January 2007 to December 2012 who presented to the MedStar Washington Hospital Center ED with a STEMI and subsequently underwent primary PCI. Patients who were transferred from a referring institution, patients who suffered cardiac arrest, patients who were intubated, and patients who were given fibrinolytic therapy before the PCI were excluded. The patients were categorized into whether they were self-transported (“self”) or transported by EMS.
2.2
DC Fire and EMS
DC Fire and EMS provides EMS coverage to Washington, DC, an urban city of 68.3 square miles, through 58 medical units (or ambulances) and is managed by a centralized 911 dispatch call system. The ambulances have 12-lead electrocardiogram (ECG) capabilities that are transmissible to the receiving ED at MedStar Washington Hospital Center. All patients are transported to the ED where a formal ECG is performed. Based on the qualifying criteria for STEMI, the ED physician contacts the on-call interventionalist. When activation of the catheterization laboratory is considered appropriate, the on-call interventionalist contacts a central number to mobilize the catheterization laboratory team, and the patient is transferred to the catheterization laboratory. Because the system does not allow for pre-activation of the catheterization laboratory team from the ambulance, none of the patients bypassed the ED en-route to the catheterization laboratory.
2.3
Self-transport
The term ‘self-transport’ refers to patients who arrive at the ED using transportation that did not involve EMS. These modes of transportation include public transportation, taxi, self-driven or driven by others, or walked to the hospital. These patients may have also visited another healthcare facility after symptom onset, before arriving at the ED by non-EMS transport. They also go through the usual triaging process in the ED. Following a diagnosis of STEMI on ECG, the interventionalist and the catheterization laboratory team are mobilized in the usual manner.
2.4
Study definitions and end points
The following time points were defined and collected contemporaneously for each STEMI patient ( Fig. 1 ): symptom onset time (from patient recall); door time (time of first registered hospital contact); ECG time (time of inciting STEMI ECG leading to decision to activate the catheterization laboratory); call time (time of call to interventionalist); lab time (time of patient arrival to the cardiac catheterization laboratory); case start time (time of first sheath insertion); and balloon time [time of introduction of first device (balloon catheter, aspiration thrombectomy catheter or stent) restoring antegrade flow]. Time intervals were then calculated from these time points. Door-to-call is to be taken as ED processing time interval, and call-to-balloon is to be taken as laboratory processing time interval.
Off-hours presentation was defined as any weekend presentation or weekday presentation from 5 pm to 8 am. ECG criteria defining a STEMI included the presence of at least 1 mm ST-segment elevation in at least 2 contiguous leads, or the occurrence of a new left bundle branch block. Angiographic success was defined as a residual stenosis of < 30% with thrombolysis in myocardial infarction grade III flow.
The primary end point was DTB time. Secondary end points were the DTB component times, symptom-door and symptom-balloon times. In-hospital outcomes evaluated were death, cardiac death, Q-wave MI, urgent coronary artery bypass graft surgery, and urgent repeat PCI of target lesion.
2.5
Interventional treatment
PCI was performed according to guidelines current at the time of the procedure. All patients received an aspirin loading dose of 325 mg, as well as either clopidogrel (600 mg), prasugrel (60 mg) or ticagrelor (180 mg) loading. Anticoagulation regimens were chosen at the operator’s discretion and included unfractionated heparin adjusted to targeted activated clotting time, or bivalirudin 0.75 mg/kg followed by an infusion of 1.75 mg/kg/hr for the duration of the procedure. The interventional strategy, utilization of adjunct pharmacotherapy, such as glycoprotein IIb/IIIa inhibitors, and device choice were at the operator’s discretion. Dual antiplatelet therapy was recommended for ≥ 12 months for all patients post procedure.
2.6
Data collection
Clinical, procedural, and follow-up data were prospectively collected and stored in a central database. A dedicated data coordinating center performed all data management and analyses. Pre-specified clinical and procedural data and in-hospital complications were obtained from hospital charts reviewed by independent research personnel blinded to the study objectives. Primary source documents were obtained for all events and were used to adjudicate STEMI cases by physicians not involved in the procedures, and who were unaware of the study objectives. The time points and time intervals pertaining to STEMI management and system performance were adjudicated and verified by physicians not involved in the study. The institutional review boards at MedStar Washington Hospital Center (Washington, DC) and the MedStar Health Research Institute (Washington, DC) approved this study.
2.7
Statistical analysis
Statistical analysis was performed using SAS version 9.1 (SAS Institute Inc., Cary, NC). Continuous variables are presented as mean ± standard deviation (SD) if normally distributed, or median ± interquartile range (IQR) if non-normally distributed. Student’s t test and Wilcoxon rank-sum test were used for comparisons of normally and non-normally distributed continuous data, respectively. Categorical variables are expressed as frequencies and percentage, and compared using chi-square test or Fisher’s exact test as appropriate. A multivariate logistic regression model was used to determine the independent correlates of DTB > 90 minutes, expressed as odds ratio, with 95% confidence interval. Variables were selected on the basis of overall clinical relevance, with particular attention given to clinical and procedural factors that may delay time to reperfusion. Variables included self-transport (versus EMS), off-hours presentation (versus on hours), age, female gender, body mass index, diabetes, peripheral vascular disease, prior PCI, prior coronary artery bypass grafting, placement of intra-aortic balloon pump, and American College of Cardiology/American Heart Association type C lesion. A p value < 0.05 is considered statistically significant.
3
Results
A total of 309 consecutive STEMI patients who underwent primary PCI were analyzed, of which 226 arrived by self-transport, and 83 were transported by EMS. The baseline and procedural characteristics in both groups were similar. ( Tables 1 and 2 ). The majority of patients from both groups presented to the ED during off hours. A significantly higher percentage of EMS-transported patients achieved the time goals of DTB < 90 minutes and DTB < 120 minutes compared to self-transported patients. ( Fig. 2 ) Median DTB times were 20 minutes shorter if patients arrived by EMS compared to self-transport (65 versus 85 minutes; p < 0.001) ( Fig. 3 ).
| Self ( n = 226) | EMS ( n = 83) | p Value | |
|---|---|---|---|
| Age (years ± SD) | 60.9 ± 12.1 | 58.7 ± 14.1 | 0.18 |
| Men | 153 (67.7%) | 54 (65.1%) | 0.66 |
| Ethnicity | |||
| European American | 47 (20.8%) | 12 (14.5%) | 0.21 |
| African American | 154 (68.1%) | 61 (73.5%) | 0.37 |
| Hispanic | 12 (5.3%) | 4 (4.8%) | 1.00 |
| Asian | 4 (1.8%) | 5 (6.0%) | 0.06 |
| Body mass index (kg/m 2 ) | 28.5 ± 5.9 | 29.0 ± 6.3 | 0.56 |
| Systemic hypertension ⁎ | 184 (81.8%) | 65 (78.3%) | 0.49 |
| Diabetes mellitus | 77 (34.2%) | 23 (27.7%) | 0.28 |
| Hyperlipidemia | 166 (73.5%) | 52 (62.5%) | 0.07 |
| Current smoker | 97 (42.9%) | 46 (55.4%) | 0.05 |
| Family history of coronary artery disease | 92 (41.8%) | 21 (25.3%) | 0.008 |
| Previous myocardial infarction | 36 (16.0%) | 15 (18.1%) | 0.66 |
| Previous percutaneous coronary intervention | 37 (17.1%) | 9 (10.8%) | 0.18 |
| Previous bypass graft surgery | 15 (6.7%) | 2 (2.4%) | 0.17 |
| Previous congestive heart failure | 20 (8.9%) | 12 (14.6%) | 0.15 |
| Chronic renal insufficiency ⁎⁎ | 26 (11.6%) | 11 (13.3%) | 0.69 |
| Peripheral vascular disease | 18 (8.0%) | 3 (3.6%) | 0.18 |
| Cardiogenic shock | 27 (12.0%) | 6 (7.2%) | 0.23 |
| Congestive heart failure (Killip III/IV) | 10 (4.5%) | 4 (4.9%) | 1.00 |
| Left ventricular ejection fraction (%) | 40 ± 15 | 40 ± 18 | 0.94 |
| Off-hours presentation | 145 (64.2%) | 60 (72.3%) | 0.18 |
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