Published online before print July 7, 2008, doi: 10.1161/CIRCULATIONAHA.107.734137
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(Circulation. 2008;118:389-396.)
© 2008 American Heart Association, Inc.
Resuscitation Science |
Improved Survival After Out-of-Hospital Cardiac Arrest Is Associated With an Increase in Proportion of Emergency Crew–Witnessed Cases and Bystander Cardiopulmonary Resuscitation
From the Department of Cardiology (J.H., G.R., K.B., M.R.) and Section of Prehospital Care (L.S.), Karolinska Institute, South Hospital, Stockholm, Sweden; and Department of Cardiology, University of Göteborg (J.H., J.L.), Sahlgrenska Hospital, Göteborg, Sweden.
Correspondence to Jacob Hollenberg, Department of Cardiology, South Hospital, Karolinska Institute, SE-118 83 Stockholm, Sweden. E-mail jacob.hollenberg{at}sodersjukhuset.se
Received August 13, 2007; accepted May 2, 2008.
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Abstract |
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Background— Out-of-hospital cardiac arrest (OHCA) is a major public health problem. We sought to describe changes in 1-month survival after OHCA in patients given cardiopulmonary resuscitation (CPR) during the last 14 years in Sweden.
Methods and Results— All patients experiencing OHCA in whom CPR was attempted between 1992 and 2005 and who were reported to the Swedish Cardiac Arrest Register were included in the study. In all, 38 646 patients were included in this survey. The proportion of patients who were admitted alive to a hospital increased from 15.3% in 1992 to 21.7% in 2005 (P for trend <0.0001). The corresponding values for patients being alive after 1 month were 4.8% and 7.3%, respectively (P for trend <0.0001). The increase in 1-month survival was particularly evident among patients found with a shockable rhythm (increase from 12.7% in 1992 to 22.3% in 2005; P for trend <0.0001). The corresponding figures for patients found with a nonshockable rhythm were 1.2% in 1992 and 2.3% in 2005 (P for trend=0.044). Factors that potentially contributed to the improved survival rate were an increase in emergency medical crew–witnessed cases from 9% in 1992 to 15% in 2005 (P for trend <0.0001) and, to a lesser degree, an increase in bystander CPR from 31% in 1992 to 50% in 2005 (P for trend <0.0001). After adjustment for potential risk factors, the increase in survival remained significant.
Conclusions— We found a significant increase in survival after OHCA in Sweden over the last 14 years. The increase was particularly marked among patients found with a shockable rhythm and was associated with an increase in the proportion of crew-witnessed cases and, to a lesser degree, an increase in the performance of bystander CPR.
Key Words: resuscitation • death, sudden, cardiac • ventricular fibrillation • cardiopulmonary resuscitation • heart arrest
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Introduction |
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Sudden cardiac arrest is responsible for >50% of adult deaths due to coronary heart disease1 and is a leading cause of death in the Western world. In Europe, out-of-hospital cardiac arrest (OHCA) affects approximately 300 000 persons annually.2 Despite considerable efforts to improve the various links in the chain of survival,3 OHCA remains associated with an exceptionally poor prognosis.4
Editorial p 328
Clinical Perspective p 396
Previous reports have demonstrated a rather consistent mortality rate after OHCA in Sweden, with 
5% of patients being discharged alive from hospital.5,6 During the last few years, several new strategies to improve survival after OHCA have been introduced. These include prehospital measures such as public access defibrillation,7 defibrillation initiated by first responders,8,9 an increased use of cardiopulmonary resuscitation (CPR) guidance by telephone from dispatchers to bystanders,10 and postresuscitation interventions such as hypothermia, early revascularization,11 an increased use of β-blockers and angiotensin-converting enzyme inhibitors, and internal cardioverter defibrillators.12
Recent studies from the United States13,14 and Europe15,16 point to unchanged or slightly better survival rates after OHCA during the last 2 decades. The aim of the present study was to explore the temporal trends of survival after OHCA in Sweden with regard to factors mainly related to the prehospital phase and resuscitation.
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Methods |
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Register
The present study is based on patient material collected by the Swedish Cardiac Arrest Register, which is a joint venture between the Federation of Leaders in Swedish Ambulance and Emergency Services and the Swedish Council for Cardiopulmonary Resuscitation. Since 1993, the register has been funded by the Swedish National Board of Health and Welfare. This voluntary register was started in 1990 and now covers some 70% of the population in Sweden, which amounts to 8.9 million people. Larger cities (including all major cities in Sweden) and sparsely populated areas with a geographic distribution covering most of Sweden are represented. The ambulance organizations that do not report to the register are not different in terms of education or guidelines. The Swedish Ambulance Cardiac Arrest Register has been described in detail elsewhere.17
Patients and Definitions
All patients with OHCA for whom an ambulance was called were included in the register, with the exception of patients who had obviously been dead for a long time and whose bodies were therefore not taken to a hospital by the ambulance crew. Only cases in which some type of resuscitation measure (airway assistance, chest compressions, administration of drugs, intubation, or defibrillation) was started were included. Patients were enrolled in the study regardless of cause of arrest or age. In-hospital cardiac arrests were not included. Patients admitted alive were defined as patients admitted alive from an emergency department to a hospital ward and who, accordingly, had not been declared dead in the emergency department. A crew-witnessed cardiac arrest was defined as a cardiac arrest that occurred after the arrival of the ambulance crew.
Study Design
For each case of OHCA, the ambulance crews (usually 2 people, 1 of whom was usually a nurse) completed a form with relevant information such as age, place of arrest, bystander CPR (a bystander was defined as someone who started CPR before the arrival of the first ambulance, regardless of their profession), witnesses, resuscitation procedure, probable cause of arrest, intervention times, defibrillation, intubation, drug treatment, type of initial rhythm, and clinical findings at first contact. To estimate the time of cardiac arrest in witnessed cases, the ambulance crews were instructed to interview bystanders about the delay from arrest to placement of the call to emergency medical personnel. It was stressed in written instructions that a maximum effort had to be made to obtain these times. The ambulance crew also classified the probable cause of the arrest by 9 different diagnostic categories (heart disease, lung disease, trauma, drug overdose, suicide, drowning, suffocation, sudden infant death syndrome, and other) based on clinical assessment and bystander information. Their diagnosis was accepted for the present study, and no further control was used among initial survivors during hospitalization. It was emphasized in written instructions to the ambulance personnel that they should extract as much information as possible from relatives and witnesses about what had happened before the cardiac arrest (eg, chest pain, sudden tachypnea, or sudden headache). In ambulances with manual defibrillators, the first recorded rhythm was defined either as ventricular fibrillation (VF), pulseless electrical activity, or asystole. For automated external defibrillators, the rhythm was defined as shockable or nonshockable. In the present study, VF includes patients with pulseless ventricular tachycardia.
The forms were completed during and immediately after the acute event. Each form was sent to the medical director with a copy to the Swedish Cardiac Arrest Register. Another copy was sent later with additional information about whether the patient was dead or alive after 1 month. Any uncertainty about survival was checked against the National Register of Deaths. All data were computerized at a database in Göteborg. The present study was approved by the local ethics committee.
Study End Point
The primary end point was outcome after OHCA, defined as a significant increase in 1-month survival over time.
Statistical Analysis
Proportions are expressed as percentages and continuous variables as medians. Trend tests for association with the time variable of year of OHCA were performed with a Mann–Whitney U test for dichotomous variables and Spearman rank statistic for continuous variables.
Logistic regression was performed to adjust for the influence of other baseline characteristic factors on the association between year of OHCA and 1-month survival. First, we analyzed a model that included the 8 factors from Table 1
together with the variable "year of OHCA." We thereafter removed each of these 8 factors, 1 at a time, to determine how this affected the estimate of time (ie, year of OHCA). Additionally, we performed the corresponding analyses for the subgroup of non–crew-witnessed cases. All probability values are 2-tailed and were considered significant if <0.05.
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The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
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Results |
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In all, 38 646 patients were included in the present survey. Results over time are described in detail in Tables 1 and 2
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During the study period, the proportion of patients who were admitted alive to a hospital ward from the emergency department increased from 15.3% in 1992 to 21.7% in 2005 (P for trend <0.0001). The corresponding value for the proportion of patients alive after 1 month rose from 4.8% to 7.3%, respectively (P for trend <0.0001). The increase in survival to 1 month was particularly marked among patients who had been found in a shockable rhythm. For details about survival, see below.
Number of Cases, Age, and Gender
Minor variations over time with regard to the number of cases per year were found; however, no apparent or consequential increase was observed (Table 1). A minor yet significant increase in median age was observed during the study period. Median age was 71 years both in 1992 and in 2005 but was somewhat higher during some of the other years of inclusion. A similar pattern was observed with regard to the proportion of women, because a significant tendency toward an increased proportion of women was noted even though a proportion of 30% was observed in both 1992 and 2005.
Witnessed Status, Bystander CPR, Rhythm, Place of Arrest, and Cause of Arrest
A significant increase in the proportion of witnessed OHCAs was observed (P for trend <0.0001) owing to an increase in crew-witnessed cases from 9% in 1992% to 15% in 2005 (Figure 1). Nonwitnessed OHCA accordingly declined from 35% in 1992% to 29% in 2005. The proportion of patients receiving bystander CPR before arrival of the ambulance (crew-witnessed cases excluded) increased significantly from 31% in 1992% to 50% in 2005 (P for trend <0.0001). A decrease in patients presenting with VF as the first recorded rhythm from 33% in 1992% to 26% in 2005 (P for trend <0.0001) was noted.
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Most cardiac arrests occurred at home, and the proportion did not change significantly during the study period. The proportion of patients with a presumed cardiac cause of the arrest declined from 73% in 1992% to 63% in 2005 (P for trend <0.0001).
Time Intervals and Patients Admitted Alive to Hospital
The time interval from placement of the call for help to arrival of the ambulance (median) increased from 6 minutes in 1992 to 8 minutes in 2005 (P for trend <0.0001). A similar increase occurred during both daytime and nighttime. The time interval from cardiac arrest to defibrillation (patients with bystander-witnessed VF, median) was judged to be 12 minutes in 1992 and in 2005 (P=NS). Estimated time intervals from cardiac arrest to placement of the call for help remained constant at 5 minutes (median) throughout the study period. An increase in the number of patients being admitted to the hospital alive after successful resuscitation was observed during the study period (Figure 2), with 396 patients (15.3%) in 1992 compared with 585 patients (21.7%) in 2005 (P for trend <0.0001).
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Survival
Total survival to 1 month after OHCA increased significantly from 4.8% in 1992 to 7.3% in 2005 (P for trend <0.0001). Figure 2 describes this increase graphically. After exclusion of bystander CPR and crew-witnessed cases, the significant increase was no longer observed.
Survival of patients found in VF increased from 12.7% in 1992 to 22.3% in 2005 (P for trend <0.0001). Corresponding figures for patients found in nonshockable rhythms were 1.2% and 2.3%, respectively (P for trend=0.0438; Figure 3). No significant increase in 1-month survival was noted within any of the 3 groups of crew-witnessed, bystander-witnessed, or nonwitnessed cardiac arrests (Figure 4). In-hospital survival did not increase significantly during the study period, ranging from 32.6% in 1992 to 34.8% in 2005 (P=NS). Survival rates are presented in detail in Table 2.
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The year of OHCA (ie, estimate of time) remained significantly associated with 1-month survival after adjustment for potential baseline risk factors (Table 3). The factor that had the largest impact on the estimate of time with regard to the increase in survival was crew-witnessed OHCA. Bystander CPR also affected the estimate of time in the same direction, although to a lesser extent. When crew-witnessed cases were excluded, the factor with the largest corresponding impact was bystander CPR. Thus, of the 8 baseline characteristic factors studied, 2 appeared to contribute to the increase in 1-month survival over time: crew-witnessed cases and, to a lesser degree, bystander CPR.
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Discussion |
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Increased Survival
We found a significant increase in survival after OHCA in Sweden over the last 14 years. This increase occurred despite the fact that the proportion of patients in a shockable rhythm declined and the time from cardiac arrest to arrival of an ambulance increased. The increase in survival was particularly prominent during the last few years and was encountered mainly among patients found in a shockable rhythm. It was furthermore associated with an increase in the proportion of crew-witnessed cases and, to a lesser degree, more frequent bystander CPR.
Studies on the epidemiology of and survival after OHCA are numerous, but very few have focused on temporal trends relative to survival. To the best of our knowledge, this is the first study that demonstrates a significant increase over time in total survival to 1 month after OHCA in an entire country during the last decade. In Sweden, this is the first time a total increase in survival has been observed since collection of data on OHCA began in 1990. Furthermore, the present investigation is one of the largest OHCA studies presented so far, reporting survival data after OHCA for almost 40 000 patients.
Proportion of Crew-Witnessed Cases and Time From Onset of Symptoms
A noteworthy increase in the proportion of crew-witnessed cardiac arrests was observed, rising from 8% in 1992% to 15% in 2005. The explanation for this rather unexpected finding is not entirely clear. One possible reason could be that patients and relatives over time have become willing to place a call to the emergency dispatcher for an ambulance sooner after the onset of symptoms. Previous investigations have shown that the large majority of patients who experience an OHCA do have symptoms before the arrest.18,19 Data from Sweden do not reveal any decline during the last 10 years in time interval between onset of symptoms and arrival at the emergency department for patients who have had an acute myocardial infarction (time interval constant at 120 minutes from 1995 to 2005).20 The same appears to be true for 4 US communities in which prehospital delay remained unchanged from 1987 to 2000 for patients who had an acute myocardial infarction.21 However, we do know that more treatments and investigations have been transferred from the hospital to the prehospital arena (eg, fibrinolysis, tele-ECG)22,23 during the last decade, which indicates that ambulance personnel stay with the patient at the scene longer. This together with the unchanged time intervals between onset of symptoms and arrival at the emergency department indicates that emergency dispatchers are called on earlier today than previously. A possible higher awareness of the need for early response could be an effect of educational programs and mass media campaigns about cardiac disease, cardiac arrest, and CPR. Furthermore, an increased amount of time spent on the scene by ambulance personnel may well have contributed to the noted increase in the proportion of crew-witnessed cases.
Increased proportions of patients surviving crew-witnessed cardiac arrest have also been observed by others. Pell and colleagues,24 who studied survival after discharge after OHCA between 1991 and 2001, found a significant increase in the proportion of those discharged alive whose arrest had been witnessed. In particular, the proportion of arrests witnessed by ambulance crew members increased from 33.4% to 51.3%.24 In our investigation, an increase in crew-witnessed cases was the only factor that was associated with an increase in survival in the entire patient group.
Influence of Bystander CPR in Non–Crew-Witnessed Cases
Early CPR can double or triple the survival rate after OHCA.25–27 The considerable increase in the proportion of patients receiving bystander CPR before the arrival of an ambulance (an increase from 31% in 1992% to 50% in 2005, crew-witnessed arrest excluded) found in the present investigation is very satisfying. If bystander CPR was the sole explanation for the overall increase in survival, one would have expected to find a more marked survival increase among bystander-witnessed cases. Therefore, the present data point to a multifactorial explanation for this increase. Moreover, the correlation between bystander-witnessed cases and bystander CPR is not entirely causal, because patients with nonwitnessed cardiac arrest may also receive the benefit of bystander CPR. When excluding crew-witnessed cases, we found the increase in bystander CPR to be the factor that was associated with the increase in survival. The increase in bystander CPR is probably a result of continuous CPR training among health personnel and lay persons in Sweden. At present, approximately 2 million people have been trained in CPR, which is 25% of the population. Another factor that likely contributed to the increase in bystander CPR was the use of CPR guidance by telephone from dispatchers to bystanders, which began in 1997.
A deviation is present in the time window between the changes in survival and changes in resuscitation (bystander CPR and crew-witnessed cases) over time. We have no clear explanation for this pattern.
Ventricular Fibrillation
The increase in 1-month survival was seen mainly in patients who had been found with a shockable rhythm, in whom survival almost doubled from 12.7% in 1992 to 22.3% in 2005. Data pointing to a tendency toward increased survival rates in VF have also been demonstrated elsewhere. Rea and coworkers in Seattle, Wash,14 and Kette and colleagues in northeast Italy15 have presented similar findings; however, in contrast to the present results, neither of those 2 studies demonstrated any increase in total survival over time. This may be owing to differences in patient selection, because only patients with cardiac causes of heart arrest were included in those studies. In accordance with these data from the United States and Italy, we also found a decline in the proportion of patients with VF as the presenting rhythm. The reason for this decrease is not known. Suggested causes include a normal variation over time, the decreasing incidence of coronary heart disease,28 and the presumption that more patients today (with updated therapeutic regimens that include new medications and earlier revascularization) reach an "end-stage" heart disease.29 One might therefore speculate that a larger proportion of OHCA patients currently present with nonshockable rhythms (pulseless electrical activity or asystole) as part of pump failure.30
Survival was markedly and significantly increased among patients found in VF, even though the interval between call and defibrillation did not decline over time. This is probably due to the fact that this time interval measurement excluded crew-witnessed cases (which accounted for a large proportion of the VF survivals), even if these data are not entirely convincing. Other possible contributory explanations for the improvement in survival in VF OHCA include more patients receiving bystander CPR, which works as a bridge to defibrillation by increasing VF amplitude31; improved CPR quality; and a selection of patients with a better chance of survival owing to the decline in the proportion of patients with VF as the presenting rhythm.
In-Hospital Survival
In-hospital survival did not increase significantly over time. Although some in-hospital (ie, postresuscitation) factors have been found to be associated with increased survival after OHCA,11,32,33 most reports point to an association between survival and prehospital factors.25,34–37 Since 2002 to 2003, therapeutic mild hypothermia has become almost fully implemented in most Swedish intensive care units after the publication of 2 randomized controlled studies that demonstrated improved neurological outcome in comatose survivors after VF.38,39 In the present report, however, we consider the contribution of therapeutic hypothermia in the improvement in survival to be minor, a conclusion that is strengthened by the fact that in-hospital survival did not change over time.
Number of Cases, Cardiac Origin, and Time Intervals
In the present investigation, a certain variation over time with regard to the number of cases per year was observed, but no consistent increase was noted. Similar findings have also been reported by others.14 Thus, although the numbers of OHCAs have been almost constant, data from the Council of Official Statistics in Sweden show a population increase somewhat in excess of 10% over time.40 One possible explanation for the decreasing incidence of OHCA is the considerable decrease in acute myocardial infarction in Sweden that has been observed since the late 1980s.41 Furthermore, concomitant with a small decrease in OHCA incidence, a decline in the proportion of cases with cardiac origin was observed. Similar observations have been made elsewhere.28,42 The underlying explanations for these changes in coronary heart disease are assumed to be a consequence of better prevention and treatment, but they may also reflect a larger proportion of elderly patients with significant comorbidities, such as chronic obstructive pulmonary disease.
The present investigation shows a 2-minute-longer interval between emergency call and arrival of an ambulance in 2005 than in 1992. Increased response times theoretically can lead to decreased survival due to delayed time to treatment or increased survival due to a selection bias. Previous investigations clearly point toward the former.25,36,37 Even if we cannot fully exclude a potential impact of selection bias, we consider this 2.0-minute delay to have an extremely low impact on patient selection. This is supported by the fact that Swedish guidelines for when emergency medical services personnel have the right not to start CPR only include obvious clinical signs of death (ie, rigor mortis, head separated from the body, marbling, and livor mortis), and these guidelines have not been modified since the late 1980s. The reasons for the increase in time to ambulance arrival are not evident. There has been no increase in the number of more remote areas involved in the study. Of several possible explanations of why the time interval has increased, the most probable is a marked decline in ambulance density per capita over time. From 1992 to 2005, the number of ambulances per million inhabitants decreased significantly in Sweden’s 2 largest cities, by 19% in Stockholm and by 27% in Göteborg. An increase in traffic congestion in urban areas over time, however, did not contribute to the increased time from call to ambulance arrival, because this increase was similar during the daytime and nighttime. In brief, we demonstrate an increase in survival after OHCA despite the fact that important factors (prehospital time intervals, VF incidence, and presumed cardiac cause) known to be associated with an increased chance of survival25 have worsened over time.
Implications for the Future
This report is extensive, with 38 646 patients included. A study from 2003 by Herlitz and coworkers6 that included 19 791 patients was also based on data from the Swedish Cardiac Arrest Register; however, only those ambulance organizations integrated from the very establishment of the register were included. In the present investigation, all patients in the register were included, the time period covered was extended by 3 years, and a series of new analyses were performed. The main difference compared with the study from 2003 is our finding of an increase in total survival.
The present report is important because it demonstrates the value of patients calling an emergency dispatch center early after they develop symptoms. Many lives could probably be saved if patients with sudden worsening of chest pain and dyspnea were to receive medical treatment and observation more rapidly. Two principal methods exist to achieve this: (1) earlier calls to emergency dispatch centers and (2) shorter time intervals from cardiac arrest to treatment (ie, CPR and defibrillation). Education of patients and relatives and mass media campaigns may well be ways to accomplish the first goal, whereas an increased use of CPR guidance by telephone from dispatchers to bystanders, public access defibrillation (by laypeople and security personnel), and early first-responder defibrillation (by firefighters, police, etc) are methods to accomplish the latter.
Study Limitations
Data on differences in the population over time (eg, demographic changes, variation in medication over time, and underlying medical conditions) were not available in our database. One can assume some minor demographic changes relative to the use of medications in the population. We cannot exclude that some possible changes in population characteristics could have had an effect on the results presented. Second, no information on the neurological condition of the cardiac arrest victims was available. Third, a substantial number of in-hospital variables that could influence survival were not available in the database. These include body temperature, laboratory test levels, revascularization procedures, and medications used. Finally, a 3-year dip in the middle of the period for the number of patients included in the study was observed. Possible errors in data sampling were sought, but no convincing explanation was found. However, this dip in the number of cases was not reflected by corresponding dips in hospital admissions or survival.
Conclusions
We found a significant increase in survival after OHCA in Sweden over the last 14 years. The increase was particularly marked among patients found with a shockable rhythm and was associated with an increase in the proportion of crew-witnessed cases and, to a lesser degree, an increase in bystander CPR.
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Acknowledgments |
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We thank all the bystanders who undertook basic resuscitation and the paramedics, emergency medical technicians, nurses, and physicians who participated in the study. The authors are also grateful to Thomas Karlsson for invaluable help with the statistical analyses.
Sources of Funding
This study was supported by the Swedish Heart and Lung Foundation and Stockholm County Council.
Disclosures
None.
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[Abstract/Free Full Text]
CLINICAL PERSPECTIVE
Out-of-hospital cardiac arrest (OHCA) is a leading cause of death in the Western world and accounts for >50% of deaths due to adult coronary heart disease. Despite considerable efforts to improve the various links in the chain of survival, OHCA remains associated with a poor prognosis. The aim of this study was to explore the temporal trends of survival after OHCA with regard to factors mainly related to the prehospital phase and resuscitation. We examined all patients experiencing OHCA in whom cardiopulmonary resuscitation (CPR) was attempted between 1992 and 2005 in Sweden (n=38 646). The proportion surviving for 1 month after arrest increased significantly from 4.8% in 1992 to 7.3% in 2005. The increase in survival was particularly marked among patients found with a shockable rhythm and was associated with an increase in the proportion of emergency medical crew–witnessed arrests and, to a lesser degree, an increase in the performance of bystander CPR. These findings suggest that many lives could be saved if patients with cardiac symptoms such as chest pain received more rapid assessment from emergency medical teams. Two principal methods can be used to achieve this result: earlier placement of calls to emergency dispatch centers and shorter time intervals from OHCA to treatment (ie, CPR and defibrillation). Education of patients, their families, and the public may well be ways to reach the first group, whereas increased use of CPR, public access defibrillation, and early first-responder defibrillation are methods to reach the latter.
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