One of the critical components of an electrophysiology study is the evaluation of conduction. Concepts presented in this chapter are in the order in which they are usually evaluated during a routine electrophysiology study. The first concept, conduction, can be assessed by pacing a proximal structure and assessing the delivery of the electrical impulse to a more distal structure. For example, atrioventricular conduction is assessed by pacing the atrium and examining the particular heart rate in which conduction block occurs, preventing ventricular depolarization. In addition, the site of the conduction block can also be assessed. The second concept relates to the response of cardiac tissue to premature extrastimuli: this is called refractoriness. In order to assess refractoriness of a particular myocardial structure (atrium, AV node, His bundle, or ventricle), programmed electrical stimulation is performed. In this manner, stimulation of a site of myocardium (atrium or ventricle) is performed in which 8–10 paced beats at a fixed heart rate are delivered. A premature stimulus after the constant drive train is then delivered at progressively shorter intervals.
First, it is important to place the intracardiac pacing catheters (standard four-poled catheters called quadripolar catheters) in the correct positions in the heart. A catheter is typically placed via introducer sheaths through the right femoral vein (or alternatively, the left femoral vein) and inserted so that one of the catheter’s poles makes contact in the high right atrium. Other locations such as the right atrial appendage or the lateral right atrium may also be acceptable.