Programmed electrical stimulation of the heart was introduced by Durrer and colleagues1 as a technique to study the mechanisms of cardiac arrhythmias in humans. A critical adjunct to this earlier work was the development of a catheter method to record His bundle potentials in humans.2 Through the use of these techniques, it is possible to diagnose with certainty various forms of supraventricular and ventricular tachycardia as well as to identify the site of atrioventricular (AV) block. Clinical electrophysiology has undergone transformation from an esoteric subspecialty of cardiology, concerned primarily with diagnosing various cardiac arrhythmias and investigating electrophysiologic (EP) properties of the heart, to an area vital to the management of patients with arrhythmias, including the ability to cure patients by endocardial catheter ablation. This chapter describes the techniques and applications of EP testing.
CATHETER INSERTION AND RECORDING
EP procedures are specialized cardiac catheterizations that involve the recording of intracardiac electrograms and programmed electrical stimulation of the heart.3 Insertion of catheters is almost always performed using the percutaneous technique. The route chosen for catheter insertion depends primarily on the accessibility of the venous or arterial system and the intracardiac catheter position required for study. Recordings of the His bundle electrogram are obtained most easily with a catheter advanced from the femoral vein, which allows the catheter position to be kept stable throughout the study. Placement of the catheter in the right atrium or right ventricle can generally be accomplished easily from any venous route while access to the left atrium and ventricle requires a transseptal approach or retrograde aortic approach.
Recordings of intracardiac electrograms can be either unipolar or bipolar as demonstrated in Figure 16-1. In this example, a quadripolar catheter was situated with its tip at the right ventricular apex. Proximal and distal bipolar electrograms were recorded as well as unipolar electrograms from each pole of the catheter. An electrical field is present during activation of cardiac muscle. In a unipolar lead, the rapid or intrinsic deflection represents activation of the myocardium directly underneath the electrode.4 Thus, only 1 rapid component will be present. The electrogram configuration in a bipolar lead may contain several relatively rapid deflections. The bipolar electrogram is the algebraic sum of the 2 unipolar leads.4 The closer the bipolar spacing, the sharper the electrogram. Unipolar and bipolar electrograms require different filter settings, which vary depending on the equipment used. Typically, unipolar electrograms are more unfiltered—for example, 0.05-400 Hz. Common bipolar settings range from 30-40 Hz to 400-500 Hz.
Bipolar and unipolar electrograms. Simultaneous recordings from electrocardiogram (ECG) leads I and II and bipolar intracardiac electrograms from the high right atrium (HRA), His bundle area (HBE), and right ventricular proximal (RVP) and distal (RVD) electrode pair. Unipolar RV electrograms are recorded using each of the 4 poles from the most proximal (RV4...