Heart, Lung and Circulation (2015) 24, 234–240 1443-9506/04/$36.00 http://dx.doi.org/10.1016/j.hlc.2014.09.015
ORIGINAL ARTICLE
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI Diagnosis and Direct Transfer for Primary PCI Ahmad Farshid, BMBS a,b*, Chris Allada, MBBS a, Jaya Chandrasekhar, MBBS a, Paul Marley, Dip App Sci a, Darryl McGill, MBBS, PhD a, Simon O’Connor, MBBS a, Moyazur Rahman, MBBS a, Ren Tan, MBBS a, Bruce Shadbolt, PhD b,c a
Cardiology Unit, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia College of Medicine, Biology and Environment, Australian National University, Canberra, ACT 2601, Australia c Centre for Advances in Epidemiology and Information Technology, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia b
Received 18 July 2014; received in revised form 15 September 2014; accepted 20 September 2014; online published-ahead-of-print 30 September 2014
Background
We sought to determine if our regional program for pre-hospital STEMI diagnosis and direct transfer for primary PCI (PPCI) was associated with shorter ischaemic times and improved survival compared with ED diagnosis.
Methods
STEMI diagnosis was made at the scene by pre-hospital ECG or in local EDs depending on patient presentation. Ambulance ECGs were transmitted to our ED for cath lab activation. Patient variables and outcomes at 12 months were recorded.
Results
We treated 782 consecutive patients with PPCI during January 2008-June 2013. Cath lab activation was initiated prior to hospital arrival (pre-hospital) in 24% of cases and by ED in 76% of cases. Median total ischaemic time was 154 min for pre-hospital and 211 minutes for ED patients (p < 0.0001). Mortality at 12 months was 7.9% in the ED group compared with 3.7% in the pre-hospital group (p = 0.036). On multivariate Cox regression analysis including baseline and procedural variables, pre-hospital activation remained an independent predictor of mortality (HR 0.45, 95% CI 0.20-1.0, p = 0.03).
Conclusions
Pre-hospital diagnosis of STEMI and direct transfer to the cath lab reduced total ischaemic time by 57 minutes and mortality by >50% following PPCI. Further efforts are needed to increase the proportion of STEMI patients treated using this strategy.
Keywords
Myocardial infarction STEMI Myocardial reperfusion Ambulances Primary percutaneous coronary intervention Pre-hospital triage
*Corresponding author. Cardiology Unit, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia. Tel.: +61 2 6244 2178., Email: [email protected] © 2014 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ). Published by Elsevier Inc. All rights reserved.
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Introduction Primary PCI for STEMI is the standard of care where timely PCI is available in experienced centres [1]. Door-to-balloon time (DTB) has been shown to correlate well with patient outcomes and has become a key performance indicator [2,3]. However total ischaemic time is emerging as a more appropriate focus of attention as it includes the pre-hospital phase of STEMI where delays can be substantial [4]. Apart from patient presentation delays, there can be important delays related to transfer of STEMI patients from non-PCI hospitals, assessment in ED or arrival of cath lab personnel after activation by ED. In Australia only 12% of hospitals offer routine PPCI and the PCI hospital may not be the closest hospital to the patient [5]. For this reason we and other health service networks in Australia developed a system of field triage by ECG capable ambulance personnel and direct transfer to the cath lab [6–8]. Recent literature indicates that direct transfer for primary PCI is associated with a lower incidence of adverse events [9–11]. Our aim was to determine if a strategy of pre-hospital cath lab activation and direct transfer for PPCI in our network resulted in shorter ischaemic and treatment times and improved outcomes.
Methods Setting We performed an analysis of the prospective PPCI registry at The Canberra Hospital, a tertiary referral hospital in the Australian Capital Territory offering a 24-hour, seven days a week, primary PCI service with on-site cardiothoracic surgery. The Territory with its surrounding region has a population of approximately 600,000 people. The catchment area of the hospital in addition to the local emergency department, includes two other emergency departments 15 km away with a travel time of 20-30 minutes. In 2009 ambulances in our region were gradually equipped with Lifepak (Physio-Control, USA) 12 lead ECG systems with Lifenet software for ECG transmission. Paramedics were trained and assessed in 12 lead ECG interpretation as part of their initial training for the award of Advanced Diploma of Paramedical Science. As part of the pre-hospital ECG project, this training was refreshed and expanded during regular clinical training updates occurring each year. Ambulance paramedics performed 12 lead ECGs on suspected MI patients and transmitted ECGs showing STEMI to our ED for confirmation and cath lab activation. A system of cath lab activation was already in place for patients who presented to ED and were diagnosed with STEMI.
Procedure STEMI was diagnosed if a patient had clinically suggestive symptoms associated with ST-segment elevation of >0.1 mV in at least two contiguous precordial or adjacent limb leads (>0.2 mV in leads V2-V3), left bundle branch block, or extensive ST-segment depression in the precordial leads representing
235
posterior myocardial infarction. All STEMI patients received aspirin 300 mg, clopidogrel 600 mg or prasugrel 60 mg (if < 75 years, >60 kg in weight and no history of TIA/CVA) and unfractionated heparin 5000U intravenously prior to arrival in the cath lab. Pretreatment with prasugrel became available in 2011. These medications were given at the scene by paramedics for pre-hospital activation patients and in ED for ED activation patients. PCI procedures were performed by six operators through femoral or radial artery access. Treatment with glycoprotein IIb/IIIa inhibitors and the use of aspiration devices were at the discretion of the operator.
PCI Registry Consecutive STEMI patients treated with primary PCI were prospectively entered into the Canberra Hospital PCI registry. There were no exclusion criteria. Patients who died after the start of the procedure were entered in the registry and included in the analysis, but patients who died before the start of the procedure were not included. Patient demographics, symptom onset and treatment times, procedural variables and in-hospital outcomes were prospectively recorded and entered into the Registry. The PCI Registry was approved by ACT Health Research Ethics Committee and consent for data collection and follow up was obtained from all patients. Follow-up data is routinely collected in hospital and at 12 months by letter, phone-call, clinic review or review of files.
Definitions and Endpoints Pain onset time was the time recalled by the patient as the onset of symptoms. First medical contact (FMC) was defined as time of arrival of ambulance at the scene or patient arrival time at the first emergency department. Door time was defined as the time of patient arrival at the first hospital. Balloon time was defined as time of first device used for reperfusion. Door-to-balloon time was the interval between arrival at the first hospital to the time of first device used for reperfusion. MACE was defined as the composite of death, stent thrombosis, target vessel revascularisation, recurrent MI and stroke. Stent thrombosis was defined as definite stent thrombosis by angiography. MI was defined according to the third universal definition of MI [12]. Stroke was defined as a new focal neurological deficit following catheterisation or intervention lasting more than 24 hours and confirmed by imaging. Cardiogenic shock was defined as a systolic BP 90 mmHg or requirement for inotropic therapy. The primary efficacy endpoint was the incidence of death after 12 months follow up. Secondary endpoints were the incidence of MACE and the individual components of MACE, as well as pain to balloon time and FMC to balloon time.
Statistical Analysis The primary objective of the study was to compare the incidence of mortality during 12-month follow-up in STEMI patients with pre-hospital diagnosis and direct ambulance transfer, with those referred by ED for primary PCI.
236
A. Farshid et al.
Categorical data were analysed with chi-square tests and continuous variables were analysed by Student’s t-test or Wilcoxon rank-sum test. Multivariate Cox proportional hazards analysis was used to assess the relationship of direct transfer with mortality during follow up. Factors entered into the model included age, sex, cardiac risk factors, presentation with out-of-hospital cardiac arrest, cardiogenic shock, use of prasugrel and glycoprotein IIb/IIIa inhibitors and initial TIMI 0 flow. A forward likelihood ratio method was used to enter factors into the regression model. All analyses were 2-tailed and a p value of 0.05 was considered significant. Analyses were performed using SPSS version 22 software (IBM, New York).
Results We treated 782 consecutive patients with PPCI during January 2008 to June 2013. Cath lab activation followed STEMI diagnosis in ED in 592 cases (76%) (PCI centre ED in 342 cases (44%), other EDs in 250 cases (32%)) and by pre-hospital diagnosis in 190 cases (24%). Baseline characteristics for the ED and pre-hospital activation patients are shown in Table 1. The patients were well matched with regards to age, sex, vascular risk factors and prior revascularisation. In the ED group eight patients (1.4%) experienced outof-hospital cardiac arrest compared with four patients (2.1%) in the pre-hospital group (p = 0.48). The incidence of cardiogenic shock was 29 (4.9%) in the ED group and five (2.6%) in the pre-hospital group (p = 0.18). Procedural and lesion variables are shown in Table 2. Prasugrel was used in 18% of ED patients and 38% of prehospital patients (p < 0.0001), reflecting a change in our practice in 2011 when prasugrel became available. The use of radial access was low overall, but more frequent in prehospital patients (7.5% v 3.2% p = 0.016). Severity of coronary
disease and lesion complexity were similar in the two groups. Initial TIMI 0 flow was present in 60% of ED and 58% of pre-hospital patients (p = 0.93). The diameter, length and type of stent used (bare metal or drug eluting) as well as deployment pressures were not significantly different in the two groups. Median time intervals for presentation and treatment are shown in Fig. 1. Pain to FMC and FMC to balloon times were significantly shorter for pre-hospital patients. Median total ischaemic time was 154 min for pre-hospital and 211 minutes for ED patients (p < 0.0001). Median DTB times in minutes (inter-quartile range) were 40 (30-57) for pre-hospital activation patients, 77 (57-116) for PCI Centre ED and 115 (90-162) for transferred patients (p < 0.0001). The proportion of patients with FMC to balloon time of < 120 min was 84% for pre-hospital and 65% for ED patients (p < 0.0001) (Fig. 2). Follow-up was for a mean of 324 days in both groups (p = 0.99) and long-term follow-up was complete in 97% of patients in both groups (p = 0.84). The incidence of adverse events during follow up is shown in Table 3. Total mortality was 7.9% in the ED group compared with 3.7% in the pre-hospital group (p = 0.036). Kaplan Meyer survival curves for pre-hospital and ED activation patients also showed a significant advantage of pre-hospital activation (Fig. 3). The incidence of reinfarction, stent thrombosis, target vessel PCI and CABG was not significantly different in the two groups. The incidence of MACE was significantly lower in the pre-hospital group (7.5% versus 16.1%, p = 0.002), driven mainly by a lower mortality rate (Table 3). Multivariate Cox Regression analysis was performed to determine independent predictors of mortality during follow up and the results are shown in Table 4. Age, sex, diabetes and other baseline risk factors, presentation with outof-hospital cardiac arrest, cardiogenic shock, use of prasugrel
Table 1 Baseline characteristics for the ED and Pre-Hospital activation patients. ED (n = 592)
Pre-Hospital (n = 190)
P
62.0 13.2
62.2 13.4
0.84
Females
132 (22.2%)
46 (24.6%)
0.49
Diabetes
112 (18.8%)
27 (14.4%)
0.17
Hypertension
253 (42.5%)
69 (36.9%)
0.18
Smoker
165 (27.7%)
49 (26.2%)
0.69
Reformed Smoker
107 (18.0%)
30 (16.0%)
0.55
Hyperlipidaemia Family History IHD
176 (29.5%) 161 (27.0%)
60 (32.1%) 41 (21.9%)
0.51 0.17
BMI
27.9 5.0
27.4 4.7
0.38
Prior PCI
99 (17.1%)
26 (14.3%)
0.37
Prior CABG
30 (5.2%)
6 (3.7%)
0.27
4 (2.1%)
0.48
5 (2.6%)
0.18
Age
Out-of-hospital cardiac arrest Cardiogenic Shock
8 (1.35%) 29 (4.9%)
IHD, ischaemic heart disease, BMI, body mass index, PCI, percutaneous coronary intervention, CABG, coronary artery bypass graft.
237
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Table 2 Procedural and lesion variables for ED and Pre-Hospital activation patients. ED (n = 592)
Pre-Hospital (n = 190)
P
Radial Access 1 vessel disease
19 (3.2%) 286 (49.2%)
14 (7.5%) 102 (54.6%)
0.016 0.21
2 vessel disease
174 (30.0%)
51 (27.3%)
0.48
3 vessel disease
121 (20.8%)
34 (18.1%)
0.36
Clopidogrel
484 (82.6%)
112 (62.6%)
60 years, smoking, family history of IHD, cardiogenic shock, initial TIMI 0 flow and pre-hospital activation were found to be significant predictors of mortality over the one year follow-up period.
Discussion When we embarked on a system of field triage of STEMI patients and direct cath lab transfer in the Australian Capital Territory in 2009, there was scant data on clinical outcomes
Figure 1 Median presentation and treatment intervals in minutes for ED and Pre-Hospital activation patients. Pain indicates onset of ischaemic symptoms; FMC, first medical contact; Balloon, first device used for reperfusion.
238
A. Farshid et al.
Figure 2 Proportion of ED or Pre-Hospital activation STEMI patients who received Primary PCI within 90 minutes or 120 minutes of first medical contact. FMC; first medical contact, Balloon; first device used for reperfusion.
with this approach. Since that time there has been increasing evidence that this strategy reduces time to treatment significantly and is associated with improved clinical outcomes [9–11]. Previous studies of pre-hospital ECG for STEMI in the Australian setting have consistently shown reductions in treatment delay, but have not shown a significant reduction in mortality [6–8], possibly due to the small size of the studies. In this analysis of STEMI treatment in our region, pre-hospital diagnosis and direct transfer was found to be an independent predictor of one-year mortality. Using protocoldriven contemporary pharmacotherapy and modern interventional techniques, we found a relatively low incidence of adverse events in the overall cohort at 12 months which compares favourably with other STEMI outcome data. Pre-hospital diagnosis and direct transfer was associated with a reduction in total ischaemic time of approximately 57 minutes in our study compared with ED activation. Prehospital diagnosis of STEMI at the scene enables the
ambulance paramedics to activate the cath lab before arrival and bypass non-PCI hospitals and the ED at the PCI centre upon arrival. Other studies have also documented similar time savings which have been shown to be associated with improved survival [9,10]. A recent study of 12581 STEMI patients with pre-hospital ECG in the US showed that ED bypass occurred in only 10.5% of patients and was associated numerically with a lower mortality, but not after multivariate adjustment [13]. Earlier reperfusion and myocardial salvage is likely the main mechanism for reduced incidence of adverse events in direct transfer patients. This theory is supported by the observation that shorter ischaemic times are associated with a lower incidence of slow flow and better LV function [10,14]. Door-to-balloon has been found to be associated with lower mortality in some large studies and registries [2,3]. As a result, DTB has been the main focus of efforts to improve STEMI care and is incorporated into national guidelines as
Table 3 Incidence of major adverse cardiac events during follow up in ED and Pre-Hospital activation patients.
Mean follow up
ED
Pre-Hospital
(n = 592)
(n = 190)
324 222
324 170
P
0.99
days Stent Thrombosis
10 (1.7%)
3 (1.6%)
0.95
Reinfarction
26 (4.4%)
7 (3.7%)
0.71
Target Vessel PCI CABG
25 (4.0%) 12 (2.0%)
6 (3.2%) 1 (0.5%)
0.60 0.12
Death
47 (7.9%)
7 (3.7%)
0.036
MACE
96 (16.1%)
14 (7.5%)
0.002
PCI, percutaneous coronary intervention; CABG, coronary artery bypass graft surgery; MACE, major adverse cardiac events.
Figure 3 Kaplan Meyer survival curve for primary PCI patients with Cath Lab activation Pre-Hospital or in the Emergency Department.
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Table 4 Predictors of mortality on Cox regression analysis. Hazard
95% CI
P
Ratio Univariate Analysis Age >60
4.16
2.15-8.07
ORIGINAL ARTICLE
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI Diagnosis and Direct Transfer for Primary PCI Ahmad Farshid, BMBS a,b*, Chris Allada, MBBS a, Jaya Chandrasekhar, MBBS a, Paul Marley, Dip App Sci a, Darryl McGill, MBBS, PhD a, Simon O’Connor, MBBS a, Moyazur Rahman, MBBS a, Ren Tan, MBBS a, Bruce Shadbolt, PhD b,c a
Cardiology Unit, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia College of Medicine, Biology and Environment, Australian National University, Canberra, ACT 2601, Australia c Centre for Advances in Epidemiology and Information Technology, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia b
Received 18 July 2014; received in revised form 15 September 2014; accepted 20 September 2014; online published-ahead-of-print 30 September 2014
Background
We sought to determine if our regional program for pre-hospital STEMI diagnosis and direct transfer for primary PCI (PPCI) was associated with shorter ischaemic times and improved survival compared with ED diagnosis.
Methods
STEMI diagnosis was made at the scene by pre-hospital ECG or in local EDs depending on patient presentation. Ambulance ECGs were transmitted to our ED for cath lab activation. Patient variables and outcomes at 12 months were recorded.
Results
We treated 782 consecutive patients with PPCI during January 2008-June 2013. Cath lab activation was initiated prior to hospital arrival (pre-hospital) in 24% of cases and by ED in 76% of cases. Median total ischaemic time was 154 min for pre-hospital and 211 minutes for ED patients (p < 0.0001). Mortality at 12 months was 7.9% in the ED group compared with 3.7% in the pre-hospital group (p = 0.036). On multivariate Cox regression analysis including baseline and procedural variables, pre-hospital activation remained an independent predictor of mortality (HR 0.45, 95% CI 0.20-1.0, p = 0.03).
Conclusions
Pre-hospital diagnosis of STEMI and direct transfer to the cath lab reduced total ischaemic time by 57 minutes and mortality by >50% following PPCI. Further efforts are needed to increase the proportion of STEMI patients treated using this strategy.
Keywords
Myocardial infarction STEMI Myocardial reperfusion Ambulances Primary percutaneous coronary intervention Pre-hospital triage
*Corresponding author. Cardiology Unit, The Canberra Hospital, Yamba Drive, Garran, Australian Capital Territory, Australia. Tel.: +61 2 6244 2178., Email: [email protected] © 2014 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ). Published by Elsevier Inc. All rights reserved.
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Introduction Primary PCI for STEMI is the standard of care where timely PCI is available in experienced centres [1]. Door-to-balloon time (DTB) has been shown to correlate well with patient outcomes and has become a key performance indicator [2,3]. However total ischaemic time is emerging as a more appropriate focus of attention as it includes the pre-hospital phase of STEMI where delays can be substantial [4]. Apart from patient presentation delays, there can be important delays related to transfer of STEMI patients from non-PCI hospitals, assessment in ED or arrival of cath lab personnel after activation by ED. In Australia only 12% of hospitals offer routine PPCI and the PCI hospital may not be the closest hospital to the patient [5]. For this reason we and other health service networks in Australia developed a system of field triage by ECG capable ambulance personnel and direct transfer to the cath lab [6–8]. Recent literature indicates that direct transfer for primary PCI is associated with a lower incidence of adverse events [9–11]. Our aim was to determine if a strategy of pre-hospital cath lab activation and direct transfer for PPCI in our network resulted in shorter ischaemic and treatment times and improved outcomes.
Methods Setting We performed an analysis of the prospective PPCI registry at The Canberra Hospital, a tertiary referral hospital in the Australian Capital Territory offering a 24-hour, seven days a week, primary PCI service with on-site cardiothoracic surgery. The Territory with its surrounding region has a population of approximately 600,000 people. The catchment area of the hospital in addition to the local emergency department, includes two other emergency departments 15 km away with a travel time of 20-30 minutes. In 2009 ambulances in our region were gradually equipped with Lifepak (Physio-Control, USA) 12 lead ECG systems with Lifenet software for ECG transmission. Paramedics were trained and assessed in 12 lead ECG interpretation as part of their initial training for the award of Advanced Diploma of Paramedical Science. As part of the pre-hospital ECG project, this training was refreshed and expanded during regular clinical training updates occurring each year. Ambulance paramedics performed 12 lead ECGs on suspected MI patients and transmitted ECGs showing STEMI to our ED for confirmation and cath lab activation. A system of cath lab activation was already in place for patients who presented to ED and were diagnosed with STEMI.
Procedure STEMI was diagnosed if a patient had clinically suggestive symptoms associated with ST-segment elevation of >0.1 mV in at least two contiguous precordial or adjacent limb leads (>0.2 mV in leads V2-V3), left bundle branch block, or extensive ST-segment depression in the precordial leads representing
235
posterior myocardial infarction. All STEMI patients received aspirin 300 mg, clopidogrel 600 mg or prasugrel 60 mg (if < 75 years, >60 kg in weight and no history of TIA/CVA) and unfractionated heparin 5000U intravenously prior to arrival in the cath lab. Pretreatment with prasugrel became available in 2011. These medications were given at the scene by paramedics for pre-hospital activation patients and in ED for ED activation patients. PCI procedures were performed by six operators through femoral or radial artery access. Treatment with glycoprotein IIb/IIIa inhibitors and the use of aspiration devices were at the discretion of the operator.
PCI Registry Consecutive STEMI patients treated with primary PCI were prospectively entered into the Canberra Hospital PCI registry. There were no exclusion criteria. Patients who died after the start of the procedure were entered in the registry and included in the analysis, but patients who died before the start of the procedure were not included. Patient demographics, symptom onset and treatment times, procedural variables and in-hospital outcomes were prospectively recorded and entered into the Registry. The PCI Registry was approved by ACT Health Research Ethics Committee and consent for data collection and follow up was obtained from all patients. Follow-up data is routinely collected in hospital and at 12 months by letter, phone-call, clinic review or review of files.
Definitions and Endpoints Pain onset time was the time recalled by the patient as the onset of symptoms. First medical contact (FMC) was defined as time of arrival of ambulance at the scene or patient arrival time at the first emergency department. Door time was defined as the time of patient arrival at the first hospital. Balloon time was defined as time of first device used for reperfusion. Door-to-balloon time was the interval between arrival at the first hospital to the time of first device used for reperfusion. MACE was defined as the composite of death, stent thrombosis, target vessel revascularisation, recurrent MI and stroke. Stent thrombosis was defined as definite stent thrombosis by angiography. MI was defined according to the third universal definition of MI [12]. Stroke was defined as a new focal neurological deficit following catheterisation or intervention lasting more than 24 hours and confirmed by imaging. Cardiogenic shock was defined as a systolic BP 90 mmHg or requirement for inotropic therapy. The primary efficacy endpoint was the incidence of death after 12 months follow up. Secondary endpoints were the incidence of MACE and the individual components of MACE, as well as pain to balloon time and FMC to balloon time.
Statistical Analysis The primary objective of the study was to compare the incidence of mortality during 12-month follow-up in STEMI patients with pre-hospital diagnosis and direct ambulance transfer, with those referred by ED for primary PCI.
236
A. Farshid et al.
Categorical data were analysed with chi-square tests and continuous variables were analysed by Student’s t-test or Wilcoxon rank-sum test. Multivariate Cox proportional hazards analysis was used to assess the relationship of direct transfer with mortality during follow up. Factors entered into the model included age, sex, cardiac risk factors, presentation with out-of-hospital cardiac arrest, cardiogenic shock, use of prasugrel and glycoprotein IIb/IIIa inhibitors and initial TIMI 0 flow. A forward likelihood ratio method was used to enter factors into the regression model. All analyses were 2-tailed and a p value of 0.05 was considered significant. Analyses were performed using SPSS version 22 software (IBM, New York).
Results We treated 782 consecutive patients with PPCI during January 2008 to June 2013. Cath lab activation followed STEMI diagnosis in ED in 592 cases (76%) (PCI centre ED in 342 cases (44%), other EDs in 250 cases (32%)) and by pre-hospital diagnosis in 190 cases (24%). Baseline characteristics for the ED and pre-hospital activation patients are shown in Table 1. The patients were well matched with regards to age, sex, vascular risk factors and prior revascularisation. In the ED group eight patients (1.4%) experienced outof-hospital cardiac arrest compared with four patients (2.1%) in the pre-hospital group (p = 0.48). The incidence of cardiogenic shock was 29 (4.9%) in the ED group and five (2.6%) in the pre-hospital group (p = 0.18). Procedural and lesion variables are shown in Table 2. Prasugrel was used in 18% of ED patients and 38% of prehospital patients (p < 0.0001), reflecting a change in our practice in 2011 when prasugrel became available. The use of radial access was low overall, but more frequent in prehospital patients (7.5% v 3.2% p = 0.016). Severity of coronary
disease and lesion complexity were similar in the two groups. Initial TIMI 0 flow was present in 60% of ED and 58% of pre-hospital patients (p = 0.93). The diameter, length and type of stent used (bare metal or drug eluting) as well as deployment pressures were not significantly different in the two groups. Median time intervals for presentation and treatment are shown in Fig. 1. Pain to FMC and FMC to balloon times were significantly shorter for pre-hospital patients. Median total ischaemic time was 154 min for pre-hospital and 211 minutes for ED patients (p < 0.0001). Median DTB times in minutes (inter-quartile range) were 40 (30-57) for pre-hospital activation patients, 77 (57-116) for PCI Centre ED and 115 (90-162) for transferred patients (p < 0.0001). The proportion of patients with FMC to balloon time of < 120 min was 84% for pre-hospital and 65% for ED patients (p < 0.0001) (Fig. 2). Follow-up was for a mean of 324 days in both groups (p = 0.99) and long-term follow-up was complete in 97% of patients in both groups (p = 0.84). The incidence of adverse events during follow up is shown in Table 3. Total mortality was 7.9% in the ED group compared with 3.7% in the pre-hospital group (p = 0.036). Kaplan Meyer survival curves for pre-hospital and ED activation patients also showed a significant advantage of pre-hospital activation (Fig. 3). The incidence of reinfarction, stent thrombosis, target vessel PCI and CABG was not significantly different in the two groups. The incidence of MACE was significantly lower in the pre-hospital group (7.5% versus 16.1%, p = 0.002), driven mainly by a lower mortality rate (Table 3). Multivariate Cox Regression analysis was performed to determine independent predictors of mortality during follow up and the results are shown in Table 4. Age, sex, diabetes and other baseline risk factors, presentation with outof-hospital cardiac arrest, cardiogenic shock, use of prasugrel
Table 1 Baseline characteristics for the ED and Pre-Hospital activation patients. ED (n = 592)
Pre-Hospital (n = 190)
P
62.0 13.2
62.2 13.4
0.84
Females
132 (22.2%)
46 (24.6%)
0.49
Diabetes
112 (18.8%)
27 (14.4%)
0.17
Hypertension
253 (42.5%)
69 (36.9%)
0.18
Smoker
165 (27.7%)
49 (26.2%)
0.69
Reformed Smoker
107 (18.0%)
30 (16.0%)
0.55
Hyperlipidaemia Family History IHD
176 (29.5%) 161 (27.0%)
60 (32.1%) 41 (21.9%)
0.51 0.17
BMI
27.9 5.0
27.4 4.7
0.38
Prior PCI
99 (17.1%)
26 (14.3%)
0.37
Prior CABG
30 (5.2%)
6 (3.7%)
0.27
4 (2.1%)
0.48
5 (2.6%)
0.18
Age
Out-of-hospital cardiac arrest Cardiogenic Shock
8 (1.35%) 29 (4.9%)
IHD, ischaemic heart disease, BMI, body mass index, PCI, percutaneous coronary intervention, CABG, coronary artery bypass graft.
237
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Table 2 Procedural and lesion variables for ED and Pre-Hospital activation patients. ED (n = 592)
Pre-Hospital (n = 190)
P
Radial Access 1 vessel disease
19 (3.2%) 286 (49.2%)
14 (7.5%) 102 (54.6%)
0.016 0.21
2 vessel disease
174 (30.0%)
51 (27.3%)
0.48
3 vessel disease
121 (20.8%)
34 (18.1%)
0.36
Clopidogrel
484 (82.6%)
112 (62.6%)
60 years, smoking, family history of IHD, cardiogenic shock, initial TIMI 0 flow and pre-hospital activation were found to be significant predictors of mortality over the one year follow-up period.
Discussion When we embarked on a system of field triage of STEMI patients and direct cath lab transfer in the Australian Capital Territory in 2009, there was scant data on clinical outcomes
Figure 1 Median presentation and treatment intervals in minutes for ED and Pre-Hospital activation patients. Pain indicates onset of ischaemic symptoms; FMC, first medical contact; Balloon, first device used for reperfusion.
238
A. Farshid et al.
Figure 2 Proportion of ED or Pre-Hospital activation STEMI patients who received Primary PCI within 90 minutes or 120 minutes of first medical contact. FMC; first medical contact, Balloon; first device used for reperfusion.
with this approach. Since that time there has been increasing evidence that this strategy reduces time to treatment significantly and is associated with improved clinical outcomes [9–11]. Previous studies of pre-hospital ECG for STEMI in the Australian setting have consistently shown reductions in treatment delay, but have not shown a significant reduction in mortality [6–8], possibly due to the small size of the studies. In this analysis of STEMI treatment in our region, pre-hospital diagnosis and direct transfer was found to be an independent predictor of one-year mortality. Using protocoldriven contemporary pharmacotherapy and modern interventional techniques, we found a relatively low incidence of adverse events in the overall cohort at 12 months which compares favourably with other STEMI outcome data. Pre-hospital diagnosis and direct transfer was associated with a reduction in total ischaemic time of approximately 57 minutes in our study compared with ED activation. Prehospital diagnosis of STEMI at the scene enables the
ambulance paramedics to activate the cath lab before arrival and bypass non-PCI hospitals and the ED at the PCI centre upon arrival. Other studies have also documented similar time savings which have been shown to be associated with improved survival [9,10]. A recent study of 12581 STEMI patients with pre-hospital ECG in the US showed that ED bypass occurred in only 10.5% of patients and was associated numerically with a lower mortality, but not after multivariate adjustment [13]. Earlier reperfusion and myocardial salvage is likely the main mechanism for reduced incidence of adverse events in direct transfer patients. This theory is supported by the observation that shorter ischaemic times are associated with a lower incidence of slow flow and better LV function [10,14]. Door-to-balloon has been found to be associated with lower mortality in some large studies and registries [2,3]. As a result, DTB has been the main focus of efforts to improve STEMI care and is incorporated into national guidelines as
Table 3 Incidence of major adverse cardiac events during follow up in ED and Pre-Hospital activation patients.
Mean follow up
ED
Pre-Hospital
(n = 592)
(n = 190)
324 222
324 170
P
0.99
days Stent Thrombosis
10 (1.7%)
3 (1.6%)
0.95
Reinfarction
26 (4.4%)
7 (3.7%)
0.71
Target Vessel PCI CABG
25 (4.0%) 12 (2.0%)
6 (3.2%) 1 (0.5%)
0.60 0.12
Death
47 (7.9%)
7 (3.7%)
0.036
MACE
96 (16.1%)
14 (7.5%)
0.002
PCI, percutaneous coronary intervention; CABG, coronary artery bypass graft surgery; MACE, major adverse cardiac events.
Figure 3 Kaplan Meyer survival curve for primary PCI patients with Cath Lab activation Pre-Hospital or in the Emergency Department.
Shorter Ischaemic Time and Improved Survival with Pre-hospital STEMI
Table 4 Predictors of mortality on Cox regression analysis. Hazard
95% CI
P
Ratio Univariate Analysis Age >60
4.16
2.15-8.07
