Implantable Defibrillator Electrode Systems: A Brief Review

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Abstract
Since the first report of a defibrillation attempt with an intracardiac catheter electrode nearly 30 years ago, investigators have developed implantable electrode systems consisting of metal disks, endocardial catheters, and epicardial patches. These early efforts demonstrated the feasibility of low-energy reversion of ventricular tachyarrhythmias, and also provided some insight into the mechanisms of fibrillation and defibrillation. This review describes the evolution of implantable defibrillator electrode systems. Early investigators attempted defibrillation with submuscularly implanted metal disks or a disk electrode paired with an endocardial catheter electrode. Electrode design emphasis turned to transvenous catheter systems with electrodes placed in the right ventricle and right atrium. A more successful configuration placed the proximal electrode in the superior vena cava. In an effort to ensure proper placement of the distal electrode in humans, the catheter was replaced with an epicardial patch. More recently, a combination of electrodes and multiple pulses has substantially reduced the energy required to defibrillate. Effective electrode systems that can convert lethal arrhythmias with a minimum of energy will aid in making implantable cardioverters and defibrillators the therapy of choice in patients at high risk of sudden coronary death.