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Abstract
Background The characteristics of patients who survive out-of-hospital cardiac arrest (OHCA) are incompletely known. The characteristics of survivors of OHCA during a period of 16 years in Sweden are described.
Methods All the patients included in the Swedish Cardiac Arrest Registry between 1992 and 2007 in whom cardiopulmonary resuscitation was attempted and who were alive after 1 month were included in the survey.
Results In all, 2432 survivors were registered. Information on initial rhythm at their first ECG recording was missing in 11%. Of the remaining 2165 survivors, 80% had a shockable rhythm and 20% had a non-shockable rhythm. Only a minority with a shockable rhythm among the bystander-witnessed cases were defibrillated within 5 min after cardiac arrest. This proportion did not change during the entry period. Among survivors found in a non-shockable rhythm, the majority were bystander-witnessed cases and a few had a delay from cardiac arrest to ambulance arrival of <5 min. Of all survivors, more women (27%) than men (18%) were found in a non-shockable rhythm (p<0.0001). During the 16 years in which the register was used for this study, the proportion of survivors found in a shockable rhythm did not change significantly. The cerebral performance categories score indicated better cerebral function among patients found in a shockable rhythm than in those found in a non-shockable rhythm.
Conclusion Among survivors of OHCA, a substantial proportion was found in a non-shockable rhythm and this occurred more frequently in women than in men. The proportion of survivors found in a shockable rhythm has not changed markedly over time. Survivors found in a shockable rhythm had a better cerebral performance than survivors found in a non-shockable rhythm. The proportion of survivors who were bystander-witnessed and found in a shockable rhythm and defibrillated early is still remarkably low.
- Resusitation
- ventricular fibrillation
- coronary artery disease (CAD)
- delivery of care
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Introduction
Sudden cardiac death is one of the most common causes of death, a major health problem in the western world and commonly due to myocardial ischaemia accompanied by ventricular fibrillation (VF).1 Despite many years of effort and development of different strategies, the survival rate is still low after out-of-hospital cardiac arrest (OHCA).2–5
Early defibrillation of VF has become the therapeutic paradigm to obtain pulse-giving rhythm and therefore automated external defibrillators (AED) have been introduced in the community.6 7
Since ECG recording of the initial rhythm in patients with OHCA became available, the proportion of patients found in a shockable rhythm has decreased.8 9 This would imply that the number of OCHA victims who are found in a non-shockable rhythm should have increased. The reason is not known, but various mechanisms have been suggested, including an increase in ambulance response time and an increasing proportion of patients with end-stage heart disease.
More men than women receive implantable cardioverter defibrillators (ICD) and it has been debated whether there is a true undertreatment of women or if VF might be less common in the initial phase of OHCA.10 11
Against this background, this study was undertaken in Swedish survivors of OHCA from a 16-year period addressing the following questions: (1) Is the proportion of OHCA survivors with a non-shockable rhythm at the initial ECG recording increasing? (2) Is there any gender-related difference with regard to shockable versus non-shockable rhythm? (3) What is the proportion of survivors who are bystander-witnessed and defibrillated early? (4) Is there a relation between cerebral performance among the survivors and the initial rhythm?
Method
Inclusion criteria and organisation
The Swedish Cardiac Arrest Registry was started in 1990 and covers about 70% of OHCA patients in Sweden, which has 9.1 million inhabitants and covers an area of 450 300 square kilometres, large parts of which are sparsely inhabited and most people live in cities or towns. The registry is a collaboration between the Federation of Leaders in Swedish Ambulance and Emergency Services and the Swedish Resuscitation Council, and a more detailed description is given elsewhere.12 All patients entered into the registry between 1992 and 2007 in whom cardiopulmonary resuscitation (CPR) was attempted and who survived for at least 1 month were included in the study. The study was approved by the ethics committee of Gothenburg, Sweden.
Definitions
The Utstein style of reporting has been used throughout the manuscript.13 Shockable rhythm refers to VF or pulseless ventricular tachycardia (VT) while non-shockable rhythm refers to asystole or pulseless electrical activity.
Aetiology
The ambulance crew ascribed the possible cause of OHCA to nine different groups: heart disease, lung disease, accident, sudden infant death syndrome, suicide, intoxication, suffocation, drowning and other. In this study, all groups were presented together.
Analysed variables
The patients were divided into three groups as crew-witnessed, bystander-witnessed or unwitnessed. The delay from collapse or call (if unwitnessed) to defibrillation or ambulance arrival was divided into ≤5 min or >5 min. For a comparison of changes over time, the population was divided into four 4-year periods. Patients were also analysed according to gender.
Estimation of cerebral function
Cerebral function at hospital discharge was evaluated retrospectively in a subset of OHCA survivors. This subset consisted of OHCA survivors from the Gothenburg city area with approximately 500 000 inhabitants. The reason was that a cardiac registry was started earlier in this part of Sweden and included the Cerebral Performance Categories (CPC) score. All cases registered between 1982 and 2006 were included in this subset analysis. The CPC score was estimated as follows.
CPC 1 Good cerebral function. Conscious and alert. Can work and live a normal life. There might be minor psychological or neurological defects such as mild dysphasia.
CPC 2 Moderate cerebral dysfunction. Conscious. Cerebral function is good enough to allow part-time work in a sheltered environment, using public transport and managing activities of daily living. However, there might be more severe cerebral sequealae involving hemiplegia and dysarthria.
CPC 3 Severe cerebral dysfunction. Conscious. Dependent on others for activities of daily living due to severe cerebral dysfunction (at an institution or at home with exceptional support from family members or others).
CPC 4 Coma. No verbal or psychological communication with others.
CPC 5 Brain dead.
Statistics
The Fisher exact test was used for the evaluation of proportions which were calculated with all survivors as the denominator minus patients with missing information with regard to the variable under study. The Wilcoxon two-sample test was used for the evaluation of changes over time. Owing to the large number of analyses, a p value of <0.01 was regarded as significant.
Results
During the entire period 43 982 patients were entered in the study (figure 1). Information about vital status after 1 month was available for 99% of patients. Of these, 2432 (6%) survived to 1 month and constitute the study cohort.
Flow scheme on all patients in whom cardiopulmonary resuscitation was started. CA, cardiac arrest.
There was no information on initial rhythm in 11% of the survivors, while 80% of the remaining 2165 cases were found in a shockable rhythm at ambulance arrival and the rest in a non-shockable rhythm.
Witnessed or non-witnessed collapse and time to defibrillation
Most survivors belonged to the bystander-witnessed subgroup among both those found in a shockable and those found in a non-shockable rhythm. However, more than one-third of survivors were crew-witnessed cases. Only a minority of the OHCA survivors had a delay of ≤5 min until arrival of the rescue team (table 1). Most survivors who had a bystander-witnessed OCHA were found in a shockable rhythm but were defibrillated >5 min after cardiac arrest.
Distribution of survivors of OHCA in relation to initial rhythm, witnessed status, delay to start of treatment, aetiology and event location and divided according to gender
Approximately 80% of survivors had a cardiac aetiology. The most common non-cardiac aetiologies (in order of frequency) were pulmonary disease, drug overdose and drowning. Slightly more than one-third had a cardiac arrest at home and nearly half of the survivors received bystander CPR. Thirteen per cent of all survivors were found in a non-shockable rhythm and were never defibrillated (ie, never had a shockable rhythm).
Gender perspective
Among all the survivors, 28% were women, 27% of whom were found in a non-shockable rhythm compared with 18% of men (p<0.0001, table 1).
There was a significant difference with regard to the 13% of survivors who were found in a non-shockable rhythm and never defibrillated. This group constituted 19% of all survivors among women versus 11% among men (p<0.0001). The proportion of survivors with a cardiac aetiology was higher among men, whereas the proportion of survivors with a cardiac arrest at home was higher among women. The proportion of survivors who had received bystander CPR was higher among men.
Differences in older and newer time spans
The proportion of survivors found in various rhythms did not change markedly, but the proportion that was bystander-witnessed found in VF and defibrillated within 5 min was lower during the latter part of the entry period. There was a relative decrease in cardiac aetiology over time (table 2).
Changes over time in the proportion of survivors of OHCA according to initial rhythm, witnessed status, delay of start of treatment, aetiology and place. Figures are given in percent(%)
Cerebral function
According to the CPC score, cerebral function was better among survivors found in a shockable rhythm than in those found in a non-shockable rhythm (p=0.0006, figure 2).
Distribution of patients according to cerebral performance category (CPC) score at hospital discharge among patients found in shockable (n=454) and non-shockable rhythm (n=88).
Discussion
The focus in this study was on the survivors of OHCA, in contrast to previous studies within this field of research. The main finding was that approximately 20% of almost 2200 survivors over a 16-year period had a non-shockable rhythm as recorded on the first ECG.
As a consequence, a substantial number of OHCA patients benefit from CPR despite being found in a non-shockable rhythm. Similar factors are important for the chance of survival in patients with a non-shockable rhythm as for found in a shockable rhythm.14 Thus, if a patient with asystole is treated with CPR at an early stage, the chances of survival are much higher.15 Patients found in asystole in the hospital environment, where treatment is started earlier, have a greater chance of survival.16
During the last two decades the proportion of OHCA patients found in a shockable rhythm has decreased and this could lead to the assumption that the number of survivors found in a shockable rhythm has also declined. This assumption was not confirmed. Thus, the proportion of survivors recruited from the shockable rhythm pool remained unchanged. The most plausible explanation for this finding is that survival has increased among patients found in a shockable rhythm but not among patients found in a non-shockable rhythm.
Witnessed or unwitnessed collapse and time to defibrillation
The majority of survivors (>90%) had a witnessed collapse. Patients with a witnessed cardiac arrest appear to be the group to focus on in the future. Although we know that there is a strong relationship between survival and time to treatment in both shockable and non-shockable rhythm, few survivors were defibrillated or reached by an ambulance within 5 min after collapse or calling for an ambulance, respectively. It is quite possible that more lives could be saved with good or better preservation of brain function if this delay could be shortened because, during these first few minutes, the chance of survival is greatest.17
Gender perspective
Twenty-eight percent of the survivors were women, which is similar to the proportion of women in the registry (30%). The mean age of survivors was similar in women (64.4 years) and men (64.3 years). Female survivors were more frequently found with a non-shockable rhythm than male survivors, but we have no information about whether this was associated with a different comorbidity.
Previous reports have indicated that women experience less VT/VF than men.10 18 19 The reason for this is not clear and needs further investigation. One reason might be that ischaemic heart disease is a more common aetiology in men than in women with OHCA. There might also be a difference in arrhythmia mechanisms between the sexes related, for example, to a difference in heart size (as for atrial fibrillation which is more prone to develop in larger atria20) and in the influence of hormones in response to stressors.21 There have been discussions about why women receive ICD to a lesser extent than men.9 This should be related to the fact that women less frequently suffer OHCA and furthermore, when they do, they are less frequently found in VF.
Cerebral function among survivors in relation to observed arrhythmia
We found that survivors who were found in a shockable rhythm had signs of better cerebral function than those found in a non-shockable rhythm. The underlying cause can only be speculated upon. A prolonged anoxia from cardiac arrest until the return of spontaneous circulation is a possible contributory factor.
Differences in older and newer time spans
We have previously shown that the proportion of survivors of OHCA has increased, although the proportion of victims found in a shockable rhythm has decreased.9 22 23 Our hypothesis of an increasing proportion of survivors with a non-shockable rhythm could, however, not be confirmed. Survival has been reported to increase only among patients found in a shockable rhythm but not among those found in a non-shockable rhythm.24 Furthermore, the proportion of patients with an OHCA that was crew-witnessed is increasing.22 The interpretation has been that patients with warning symptoms of OHCA call earlier for an ambulance. In line with this assumption, it seems that an increasing proportion of patients with an OHCA had crew-witnessed events among those found in a non-shockable rhythm.
During the last 4-year period, 46% of survivors received bystander CPR and 35% had a cardiac arrest that was crew-witnessed. This means that a minority of survivors (19%) were recruited from the group of patients who had a delayed CPR start (neither crew-witnessed nor bystander CPR). The corresponding figure for the first 4 years of the survey was higher (27%).
On the other hand, the proportion of patients who were defibrillated early did not increase in spite of efforts to distribute automated external defibrillators in the Swedish community. In fact, the opposite was found. One contributory factor might be the increase in ambulance response time that has taken place in Sweden during the last decade,24 despite the efforts that have been made to reduce the delay to defibrillation.
Among survivors found in a non-shockable rhythm, the majority never converted to VF and therefore did not require defibrillation. This is in agreement with a previous report.25 The proportion of survivors who fulfilled these criteria tended to increase over time.
Limitations
Information on initial rhythm was missing in 11% of patients (n=267). The range in the possible proportion of survivors found in a non-shockable rhythm therefore theoretically varies between 18% and 29%. At these two extremes, either none of the cases with missing information was calculated as having a non-shockable rhythm (18%) or all the cases with missing information were calculated as having a non-shockable rhythm (29%). The conclusion would have been similar in both scenarios.
Another important limitation is the lack of knowledge about the initial rhythm at the time of collapse. It takes at least a few minutes from collapse to ECG recording and the rhythm may have changed during that time, which might affect the allocation of survivors to the two main groups.
No comparison with the non-survivors was performed so any conclusions about predictors of survival cannot be drawn.
Further implications
The observation that about 20% of survivors of OHCA are found in a non-shockable rhythm highlights the need to know more about post-resuscitation care in this group, especially since they appear to have relatively poor cerebral function. At present there are no specific guidelines relating to the treatment of this subgroup when they survive.
Conclusion
Among survivors after OHCA, a substantial proportion was found in a non-shockable rhythm and more frequently among women. Estimated cerebral function is poorer among survivors found in a non-shockable rhythm. The proportion of survivors found in a shockable rhythm did not change markedly over time, although recent work reported that the proportion of OCHA victims found in VT/VF has decreased. More survivors came from the subgroup that was defibrillated >5 min after OCHA, possibly because this group has grown. The proportion of survivors who were bystander-witnessed and found in a shockable rhythm and defibrillated early was still low.
References
Footnotes
Linked articles 207076.
Funding This study was supported by grants from the Laerdal Foundation for Acute Medicine.
Competing interests None.
Ethics approval This study was conducted with the approval of the ethics committee of Sahlgrenska University Hospital.
Provenance and peer review Not commissioned; externally peer reviewed.