Catheter Ablation – A Report

Catheter ablation is an excellent non-pharmacologic option for some types of Ventricular fibrillation. The goal of catheter ablation is to destroy the substrate of the tachycardia with as small a lesion as possible. The first step in catheter ablation is to position an electrode catheter so that its ablating electrode is adjacent to the arrhythmogenic substrate, through a process called mapping. The ablating electrode is almost always at the distal end of the catheter and is usually larger than the other electrodes on the catheter. Once it is determined that the ablating electrode is in a suitable location, adjacent either to the focus of a tachycardia or to vulnerable point of a re-entrant circuit, up to 100 W of radiofrequency electrical energy 150Hz to 1 MHz is then delivered through the electrode to a reference electrode patch on the patient’s chest wall. The purpose is to heat the myocardium adjacent to the ablating electrode and to destroy the arrhythmogenic substrate. Ablation creates injury by heating the myocardium at the electrode-tissue interface to a temperature of up to 70 degree centigrade. The residuum of radiofrequency ablation is a well demarcated spherical or oval zone of coagulation necrosis. Other catheter based approaches are undergoing evaluation, including microwave energy ultrasound and cryotherapy. Different mapping techniques are used for different types of ventricular fibrillation that arise from a small focus, such as the idiopathic VT that arise from the RV ping. In activation mapping, the ablating electrode is positioned at the site in the ventricle that is activated earliest during each beat of tachycardia. This is the site from which the VT arises. Local activation of this site is usually 20-40 milliseconds earlier than the onset of QRS in the 12 lead surfaces. ECG during VT originates should duplicate the QRS morphology of the clinical VT. The chance for a successful ablation at such a site will be high. Success rates of at least 90% have been reported for ablation of these VT’s. In the case of idiopathic VT’s arising from the inferoseptal wall of the left ventricle, the ablating catheter is also positioned at the site of earliest activation during VT.