Incidence, duration and survival of ventricular fibrillation in out-of-hospital cardiac arrest patients in Sweden
Introduction
Death from cardiac disease is the most common cause of mortality in western countries. Approximately two-thirds of these deaths occur outside hospital [1]. In addition, large numbers of people suffer sudden death from other causes, like suicide, lung disease and drowning.
A large proportion of these persons could be resuscitated with an optimal emergency service organisation. The chance of survival is up to ten times higher for those patients suffering from ventricular fibrillation (VF) compared with those with asystole or pulseless electrical activity (PEA) patients [2]. To estimate the possible effect of out-of-hospital resuscitation organisations on survival, it is therefore necessary to know the percentage of cardiac arrest patients who are initially in VF.
In the numerous reports on out-of-hospital cardiac arrest, there is wide variation in the reported incidence of VF [3]. In almost all of these reports, the calculation is based on the first rhythm analysis after the arrival of the ambulance, with various delays in the time from the cardiac arrest. This underestimates the true incidence of VF, as, in many cases, the initial VF has deteriorated into asystole.
The aim of this study was to indirectly try to analyse the initial incidence and duration of VF based on observations at first ECG recording and the estimated interval between collapse and this recording. Furthermore, we aimed at evaluating the relation between time to defibrillation and survival in out-of-hospital cardiac arrest patients.
Section snippets
Ambulance registry
This study is based on material collected within the Swedish ambulance cardiac arrest registry. The registry was started in 1990 by a few ambulance systems and has successively been joined by more. To date, the registry is based on reports from ≈60% of the ambulance systems in Sweden and includes 5 million of the total of 8.5 million inhabitants in Sweden.
Most of the ambulance organisations included serve communities with <100 000 inhabitants and only recently have the larger cities, i.e.
Results
The age and sex distribution of the patients are given in Fig. 1. The median age was 70 years and the age range was 2–101 years. In all, 28% of the victims were females. The proportion of females increased with age. One hundred and forty patients were children under 10 years of age.
In 70% of the cases the arrest was witnessed; in 60% by bystanders and in 10% by the ambulance crew. Bystander CPR was initiated in 32%. The average time from collapse to first ECG was 14 min.
Discussion
The data from the Swedish Cardiac Arrest Registry are collected from the majority of the ambulance systems in the country. They are likely to reflect the national standard of care for out-of-hospital cardiac arrest patients fairly well.
Limitations of the study
No validation of adherence to the protocol was performed. Instead, a questionnaire was administered to all the medical directors of the participating ambulance organisations, asking them to estimate the accuracy of the representation of the study population. This was expressed as the percentage of the patients they estimated were omitted from the study in their own district. Percentage values in this survey varied from 0 to 30% (mean 5%). This means that one could estimate that the study
Conclusions
This study suggests a high initial incidence of VF among out-of-hospital cardiac arrest patients and a slow rate of transformation into a ‘non-shockable rhythm’. The survival rate for patients with VF and very short delay times was ≈50%, but fell rapidly as the delay increased.
Acknowledgements
This study was carried out for the Swedish Cardiac Arrest Registry. Participating ambulance district physicians: Å Andren-Sandberg MD, L-Å Augustsson MD, S Berglind MD, J Bennis MD, U Björnstig MD, K Brunnhage MD, J Castenhag MD, B Eriksson MD, A Elvin MD, B Engerström MD, L Engerström MD, M Erlandsson MD, L Fernandez MD, J Fischer MD, B Gustavsson MD, S Hagman MD, M Helfner MD, H Huldt MD, M Johansson MD, R Johansson MD, M Kjeldgaard MD, M Larsson MD, Ö Lennander MD, S Leward MD, T Lindgren
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