Preparation for EP procedures is similar to that for cardiac catheterization (see Chapter 20). Patients are kept fasting and usually sedated during EP studies. The degree of sedation depends on the type of study being performed and the preferences of the center performing the procedures. A peripheral intravenous line is required for administration of medicine. Systemic anticoagulation may be used during EP studies to decrease the incidence of thromboembolic complications.¹ Appropriate emergency and resuscitation equipment is required for all EP procedures.

During invasive EP testing, spontaneous and pacing-induced intracardiac and surface electrical signals are recorded. The normal timing and sequence of electrical activation can be observed and measured during a normal or baseline rhythm. Abnormal timing and electrical activation sequences are recorded and studied during tachyarrhythmias. Programmed electrical stimulation may also be used to induce and analyze paroxysmal arrhythmias that are the same as or similar to a patient’s clinical arrhythmia.²

Flexible catheters with at least 2 and up to 10 electrodes are introduced percutaneously. The catheters are advanced using fluoroscopy into the heart. The right and left femoral, subclavian, internal jugular, and median cephalic veins are the most commonly used venous access sites. One to several catheters may be placed depending on the type of study to be performed (Fig. 18-1). The usual intracardiac recording sites include the high right atrium, right atrial appendage, right ventricular apex, right ventricular outflow tract, coronary sinus, the His bundle region, and occasionally the left atrium. In addition, a roving catheter can be used to map intracardiac electrograms arising from different regions of the heart during tachycardia. Occasionally, the left ventricle is used during a diagnostic study for programmed electrical stimulation if VT cannot be induced from the right ventricle.

After the catheters are in place and connected to the physiologic recording equipment, intervals are measured from both the 12-lead electrocardiogram (ECG) and the intracardiac electrograms in the baseline state (Fig. 18-2). The AH interval is a measurement of conduction time from the low right atrium through the atrioventricular (AV) node to the His bundle and is an approximation of AV node conduction time. The AH interval can vary a great deal depending on the patient’s autonomic state and measures approximately 55 to 120 milliseconds.² The HV interval represents conduction time from the onset of His bundle depolarization to the onset of ventricular activity. The normal HV interval measurement is 35 to 55 milliseconds.³ After baseline recordings, various pacing techniques may be performed to assess the patient’s electrical conduction system. Refractory periods for the atrium, AV node, and ventricle are recorded. The presence of retrograde or ventricular-atrial conduction is noted, as is the activation sequence. Attempts to induce and document the arrhythmia using the introduction of extrastimuli in either the atrium or the ventricle are then made. Intravenous isoproterenol or epinephrine may be used to help induce arrhythmias or reveal accessory pathway (AP) or slow pathway conduction.

The patient must be adequately prepared before the study and should understand that arrhythmia induction is often one of the primary goals of the study. The electrophysiologist attempts to gather as much information as possible depending on the type of arrhythmia induced and how well it is hemodynamically tolerated. Special physiologic recording equipment is able to document simultaneously every beat in 12-lead ECG and intracardiac electrogram format. Induced arrhythmias can then be reviewed and analyzed after they are terminated. It is important to note the method of arrhythmia termination. Tachycardias may be self-terminating or require antitachycardia pacing to stop them. Occasionally, it is necessary to cardiovert or defibrillate the patient to stop the arrhythmia. It is usually necessary to wait until the patient loses consciousness before defibrillation to prevent painful shock in an awake state.

If the patient is hemodynamically stable during a ventricular arrhythmia, attempts to map its origin can be performed, particularly if ablation is planned (see the section titled “Interventional EP and Catheter Ablation”). Atrial arrhythmias are usually well tolerated and allow for extensive mapping. Recordings are made at various locations in the heart and compared with a reference signal, either a surface ECG lead or a stable intracardiac electrogram. The site of earliest activation is closest to the site where the arrhythmia originates. Occasionally, the clinical arrhythmia cannot be induced or is not sustained long enough for adequate mapping.

Horowitz reviewed the experience of his EP laboratory and the laboratories of five others. During a 4-year period, 8,545 EP studies were performed on 4,015 patients. Five deaths (0.12%) occurred, all caused by intractable VF. The complications that occurred most frequently after EP studies were cardiac perforation (0.5%) and major venous thrombosis (0.5%). Cardiac perforation and pericardial effusion resolved without treatment in most patients; five patients required pericardial drainage or open repair. The femoral catheter site was the location of thrombosis for 95% of the 20 patients with venous thrombosis. Pulmonary emboli followed venous thrombosis in nine patients (0.2%).¹ A slightly higher incidence of venous thrombosis (1.1%) and pulmonary emboli (1.6%) was found in a study by DiMarco et al. including 359 patients during 1,062 EP studies.⁴ They reported a 10% incidence of the use of countershock to terminate unstable VT; all patients returned to their original rhythms without complications. Systemic or catheter site infections were reported in 1.7% of patients in the study by DiMarco et al. but were not reported in Horowitz’s study. Major hemorrhage and arterial injury are uncommon complications of EP studies and are substantially less than those with standard cardiac catheterization. In general, the actual risk of death from electrophysiological study procedures approaches zero because reentrant VT or fibrillation induced under controlled conditions can be quickly terminated.⁵

A list of indications for EP testing is provided in Display 18-1. Specific clinical indications are discussed in the subsequent sections. Indications for testing supraventricular tachyarrhythmias are discussed in the section titled “Interventional EP and Catheter Ablation.”