Atrial fibrillation (AF) is a leading cause of arrhythmia-related hospitalizations. To terminate AF, the conduction pathways that sustain the rhythm must be permanently altered. Conventional treatments of AF include open heart surgery, drug therapy or electrical cardioversion. Antiarrhythmic drug therapy is often ineffective and creates intolerable side effects in many patients. Surgical treatment typically involves the Maze procedure in which the atrium is compartmentalized by incisions that block electrical conduction. The procedure is effective, but is associated with significant surgical mortality and lengthy recovery periods.
Radio frequency (RF) catheter ablation has become the treatment of choice for many symptomatic arrhythmias, such as atrioventricular (AV) nodal reentrant tachycardia, AV reciprocating tachycardia, idiopathic ventricular tachycardia, and primary atrial tachycardias. It is a powerful alternative to implantable devices and antiarrhythmic drugs, and a truly curative procedure. Most recently, ablation procedures mimicking the surgical Maze procedure have been attempted. In such AF ablation therapy, anatomical incisions are generated via electrical ablations and linear transmural lesions are created to block arrhythmic reentrant circuits. In these ablation procedures, single- electrode catheters can be used in a drag-and-burn fashion. However, the procedure time can be very long ($> 10$ hrs). To avoid such undesirable procedure durations, RF ablation systems that create linear lesions by simultaneously applying ablation currents to multiple electrodes have recently been developed. With a multi-electrode system, RF energy can be delivered to each electrode with a different voltage and phase angle, resulting in many current pathways, and more effective therapeutic lesion generation. Thus, the lesion dimension and uniformity can be shaped by controlling the current distribution among different pathways.
This talk comprises two parts. In Part I, the influence of ablation electrode size, position and RF phase angle on the current pathways of a three-band electrode system is analyzed. The analysis is based on a homogeneous integral equation model. When the RF energy is delivered asynchronously, both bipolar and unipolar currents contribute to ablation heating and lesion creation. The phase angle between adjacent electrode pairs has paramount impact on the current distribution among bipolar and unipolar pathways and thus renders an efficient control over lesion depth and uniformity.
In Part II, a multi-electrode finite element model is used to analyze temperature profiles and lesion depths during phased linear AF ablation. Temperature profiles, lesion depth and lesion uniformity are found to be significantly influenced by various ablation parameters such as power delivery phase angle, blood flow rate, tissue and blood conductivity. The effects of these parameters on lesion size can be analyzed and compared in simulated power-controlled or temperature-controlled ablation procedures.
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