ABC of resuscitation. The automated external defibrillator

Toward Miniaturization of Defibrillators: Design of a Defibrillation Charge/Discharge Circuit

Sudden cardiac death (SCD) is caused by a change in heart rhythm. Ventricular fibrillation (VF) is the most common cause of SCD, and electrical defibrillation is the most effective method of terminating VF. Miniaturization of defibrillators has extraordinary significance. In this study, we proposed a miniaturized design for the defibrillator charge/discharge circuit. The core circuit, composed by low-operating-voltage and surface-mount elements, achieved a size of 4.9 cm × 4.9 cm. We specially designed a voltage management system to power the system by a low-voltage battery. The proposed circuit could quickly charge the storage capacitor to 800 V within 8 s and release a biphasic exponential truncated waveform whose pulse width and delivered energy could be adjusted flexibly. With further optimization and suitable batteries and capacitors, this defibrillator charge/discharge circuit can be used for miniaturized wearable cardiac defibrillators (WCDs) and implantable cardioverter defibrillators (ICDs).

Out-of-Hospital Cardiac Arrest in a Teaching Hospital in Hong Kong: Descriptive Study Using the Utstein Style

Objective

To describe, using the Utstein template, the characteristics of patients presenting with out-of-hospital cardiac arrest to a university teaching hospital in the New Territories of Hong Kong, and to evaluate survival.

Design

Prospective study.

Setting

The emergency department of a teaching hospital in the New Territories, Hong Kong.

Participants

Patients older than 12 years with non-traumatic out-of-hospital cardiac arrest who were transported to the hospital between 1 July 2002 and 31 December 2002.

Main outcome measures

Demographic data, characteristics of cardiac arrest and response time intervals of the emergency medical service presented according to the Utstein style, and also survival to hospital discharge rate.

Results

A total of 124 patients were included (49.2% male; mean age 71.9 years). The majority of cardiac arrests occurred in patients' home. The overall bystander cardiopulmonary resuscitation (CPR) rate was 15.3% (19/124). The most common electrocardiographic rhythm at scene was asystole, whilst pulseless ventricular tachycardia (VT)/ventricular fibrillation (VF) was found in 18.0%. The overall survival was 0.8% (1/124), and survival to hospital discharge was significantly higher for patients with VF or pulseless VT than those patients with other rhythms of cardiac arrest (11.1% versus 0%). The median witnessed/recognised collapse to defibrillation time was 14 minutes. The median prehospital time interval from collapse/recognition to arrival at hospital was 33 minutes.

Conclusion

The prognosis of out-of-hospital cardiac arrest in Hong Kong was poor. Major improvements in every component of the chain of survival are necessary.