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Out-of-hospital defibrillation has been shown to improve survival in out-of-hospital cardiac arrests. The maximum performance of defibrillation-based systems is dependent on the proportion of cardiac arrests due to tachyarrhythmias. We reviewed 4248 reported arrests in the Heartstart Scotland database. We identified 3489 arrests due to cardiac or unknown cause. From this group we selected 258 cases known to be conscious on arrival of the crew. We were able to retrieve electrocardiographic data on the period within 2 min of the arrest in 106 cases. The first recorded rhythm at the arrest was ventricular fibrillation in 64%, ventricular tachycardia 4%, bradycardia in 28% and electromechanical dissociation in 4%. Defibrillatory shocks were delivered to 96% of patients in ventricular fibrillation and 60% of these patients survived. None of the patients with bradycardic arrests survived. Preceding chest pain was noted in 79% of patients subsequently developing ventricular fibrillation as the cause of arrest compared to only 37% of those suffering bradycardic arrests. It would appear that public awareness of the importance of early contact with the emergency services after the onset of chest pain could substantially improve the survival from out-of-hospital arrests.

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The Heartstart Scotland project for out-of-hospital defibrillation covers the whole of Scotland, a population of approximately 5,102,400 (14.9% > 65 years, 48.3% male). All 395 ambulances in Scotland have been equipped with an automated external defibrillator and crews are trained in basic cardiopulmonary resuscitation and defibrillator use (EMT-D). Between 1 May 1990 and 30 April 1991 a total of 1700 cardiac arrests was reported by the ambulance service. Of the 1676 arrests which we could trace, 63% were witnessed. A total of 1383 (83%) of all patients were declared dead on arrival at hospital or in the emergency department, 119 (7%) died in hospital and 174 (10%) were discharged alive. Of the 174 survivors, 87% were conscious and normal at discharge, 9% had moderate residual disability and 2% severe disability. Survival of patients discharged alive from hospital was 85% at 1 year. Defibrillation was undertaken in 71% of the reported cardiac arrests. Survival of bystander witnessed arrests was increased from 7 to 15% with bystander CPR (P < 0.005). If the cardiac arrest was witnessed by the ambulance crew and required defibrillation, survival to discharge was 39%. Of bystander witnessed arrests reached while still in VF (n = 643), 11% were discharged alive. Patients who were defibrillated within 4 min of arrest had a 43% survival rate to hospital discharge.

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During the Heartstart Scotland project all 407 ambulances in Scotland were equipped with automated external defibrillators (AEDs). All cases of chest pain or collapse aged over 10 years were monitored and multiple 3-s rhythm strips recorded in a solid state memory module. A shockable rhythm was defined as an organised rhythm of > or = 180 beats/min or a disorganised rhythm of > or = 100 beats/min and amplitude > 0.1 mV. We analysed all the stored rhythm strips in two patient populations to determine the ability of the AED and ambulance crews to detect a shockable rhythm and to initiate appropriate defibrillation. The first population comprised 493 patients, all of whom had received shocks. A total of 4741 rhythm strips were analysed, of which 1461 were true positives, 33 false positives, 3161 true negatives and 86 false negatives. Overall sensitivity of the AED was 94.4% and specificity 99.0%. The second population comprised a random sample of 200 shocked and 200 non-shocked arrests. The combined group contained 4154 rhythm strips of which 562 were true positives, 12 false positives, 3460 true negatives and 120 false negatives. Overall sensitivity of the system (AED+crew) was 82.4% and specificity 99.7%. However, only 66 of the 120 false negatives were attributable to the AED giving a sensitivity of 90.3% for the AED. The sensitivity of the AED is dependent on the prevalence of shockable rhythms, but will be within the range 90.3-94.4% for most emergency medical services. We conclude that early management of potentially lethal arrhythmias by ambulance technicians using AEDs is practical with acceptable sensitivity and specificity.

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OBJECTIVE: To determine the outcome of out of hospital defibrillation in Scotland during the year after the introduction of automated external defibrillators in October 1988. DESIGN: Retrospective analysis of ambulance service reports and hospital records. SETTING: Scottish Ambulance Service and acute receiving hospitals throughout Scotland. MAIN OUTCOME MEASURES: Delay from cardiac arrest to first defibrillator shock; vital state on arrival at hospital accident and emergency department; survival to hospital discharge. RESULTS: During the study period 268 defibrillators were purchased by public subscription and 96% of the 2000 ambulance crew underwent an eight hour training programme in cardiopulmonary resuscitation and defibrillation. A total of 1111 cardiac arrests were recorded, and defibrillation was indicated and undertaken in 602 (54%) patients, mean age 63 (range 14-92) years. A spontaneous pulse was present on arrival at hospital in 180 (30%) of the defibrillated patients, and 75 (12.5%) were subsequently discharged alive. As expected, the likelihood of survival was inversely related to the delay from the onset of cardiac arrest to the time of the first shock and was greater in the case of witnessed arrest. If ventricular fibrillation occurred after the arrival of the ambulance, survival to discharge was 33%. CONCLUSIONS: An effective scheme for out of hospital defibrillation can be introduced rapidly, and with limited training implications and costs, by the use of automated external defibrillators in ambulances.

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