Defibrillator

Overview

A defibrillator delivers a controlled electrical shock across the chest to terminate a life-threatening arrhythmia, most importantly ventricular fibrillation and pulseless ventricular tachycardia, allowing the heart's natural pacemaker to resume an organized rhythm. Modern external units combine the shock function with ECG monitoring, synchronized cardioversion, and non-invasive pacing, and many operate as automated external defibrillators that analyze the rhythm and advise the rescuer.

Therapy energy is generated on the High-Voltage Therapy Board. A high-voltage charging circuit steps battery voltage up through a transformer and rectifier to charge a film energy-storage capacitor, then a biphasic H-bridge of high-voltage switches discharges that capacitor through the patient in a current pulse that reverses polarity partway through, the truncated-exponential biphasic waveform that defibrillates at lower energy than older monophasic designs.

How it works

The Control Board sequences charge and discharge, runs the rhythm-analysis algorithm, and enforces the safety interlocks that arm and disarm the shock. Patient ECG is captured by the ECG Front-End Board, whose analog front-end amplifies and filters the signal behind a defib-proof isolation barrier; the same electrodes carry the shock. The Electrode Pad Assembly of pre-gelled adhesive pads and a shielded high-voltage cable couples energy to the chest, while a separate ECG Patient Cable provides multi-lead monitoring.

The operator interacts through the Display Assembly and the User Interface, whose guarded shock button, energy-select dial, and status LEDs guide the rescue. A Battery Pack powers the unit, and the Self-Test Board runs a daily readiness check, discharging into an internal test load to confirm the high-voltage path is sound. Events and ECG are logged for later review.