A notable increase in invasive electrophysiological (EP) testing and catheter ablation procedures performed all over the world has been observed over the past twenty-five years. This activity will focus on the indications, technique, and complications of the electrophysiological study (EPS). The EPS is an invasive procedure that needs catheter placement into the right heart via the femoral vein, using the Seldinger technique. The aim is to stimulate the heart using two pacing techniques: extra-stimulus pacing and incremental pacing. The use of extra stimulus pacing reveals the refractory periods, conduction and activation changes, diagnostic for certain diseases. The incremental pacing helps for observing and measuring the impulse conduction during stress conditions and evaluates the recovery time of normal function at the cessation of stimulation.
The anatomy of the heart and the landmarks necessary for the EP study require clarification to understand the EP concept and intracardiac signals.
Electrophysiologic testing is indicated in patients with different arrhythmias. Even the genesis of arrhythmia is more complicated; it can be summarized in three significant mechanisms: automaticity, triggering, and reentry. Most arrhythmias are reentrant, necessitating a critical isthmus to maintain.
Indications of the EPS
An EPS requires a specialized team composed of one or two electrophysiologists, a technician, and one or two nurses. The electrophysiologist usually manipulates the catheters; the technician is operating the external stimulator, the data acquisition system, and the ablation generator, and the nurse takes direct care of the patient in terms of preparation, hemodynamic status, and pulse-oximetry monitoring, administration of drugs and oxygen.
The EPS is an invasive diagnostic procedure. Discontinue antiarrhythmic therapy for at least five half-lives before the procedure. The patient needs to be after a minimal period of 6 hours of fasting. Anticoagulation therapy should also be discontinued, and hypoglycemic drugs adjusted for the fasting period. One or two peripheral venous access are necessary before the patient arrives in the EP laboratory. Once in the laboratory, surface electrocardiogram (ECG) electrodes are attached to obtain a standard 12 leads ECG integrated into the EP acquisition system. Non-invasive arterial pressure monitoring by a standard blood pressure cuff-monitor is needed. Permanent pulse-oximetry monitoring is via a standard pulse-oximeter. As the classical 12 lead surf ECG provides a significant amount of information about the heart's electrical activity recorded from twelve different perspectives corresponding to each of the twelve leads, each of the intracardiac diagnostic catheters collects information from inside the heart in terms of position, timing, and voltage.
For a standard EPS, a standard number of four catheters is necessary. Depending on the center, the operator can also use three diagnostic catheters during EPS. Every diagnostic catheter has two or multiple electrodes, and for each pair of consecutive electrodes, a distinct intracardiac electrogram gets recorded. Standard intracardiac electrograms are collected and recorded from the high right atrium, His bundle, the apex of the right ventricle, and coronary sinus.  The coronary sinus, a cardiac vein with a posterior trajectory over the left atrioventricular junction, with a diameter that permits the insertion of a diagnostic catheter, is an essential structure. Multiple electrodes (usually decapolar) deflectable catheter inserted in the coronary sinus collects simultaneous electrograms of good quality and amplitude from the left atria and left ventricle.
Fig.1. Electrograms displayed during standard four-catheter EPS in sinus rhythm. Three surface ECG leads display results (I, III, V1). ODH - a bipolar catheter records high right atrium electrogram; HIS- atrial electrogram, His electrogram and ventricular electrogram displayed simultaneously and recorded from the AV junction by a quadripolar or hexapolar catheter, VD- electrogram recorded from the right ventricular apex by a bipolar diagnostic catheter, SCP- proximal coronary sinus, SCM- medium coronary sinus, SCD-distal coronary sinus; all the coronary sinus bipoles record a sharp atrial electrogram and a smaller ventricular electrogram- usually recorded by a hexapolar or decapolar catheter.
Measurements and stimulation protocols
The specific intervals measured during sinus rhythm are:
Sinus node recovery time (SNRT)- is time taken for the sinus rhythm to resume after 30 seconds of overdrive atrial pacing at several cycle lengths (800, 700, 600, 500, 450, 400 and 350 ms). The normal values of the SNRT must be less than 1500ms. The corrected SNRT is the difference between the SNRT and the sinus cycle length; the normal value is below 550 ms.
Atrial extra-stimulus testing consists of a drive train of 8 paced beats at a constant cycle length (600 and 400ms) followed by an extra-stimulus delivered on the same catheter, on the same site. The drive train and the extra stimulus with a progressive decrescent value are repeating until there is a loss of atrial capture. The atrial extra stimulus testing serves for evaluation of the anterograde conduction over the AVN, atrial refractoriness, and induction of specific arrhythmias.
Ventricular extra-stimulus testing is similar to the atrial ventricular pacing. The stimulation is made at the right ventricular apex conventionally. Ventricular extra-stimulus testing is used for the evaluation of the retrograde conduction over the atrioventricular node (concentric atrial activation), presence of the accessory pathways (eccentric activation), ventricular refractoriness, and induction of specific arrhythmias. Multiple extra-stimuli are available for arrhythmia induction.
Incremental atrial pacing supposes stimulation on the high atrial catheter at a cycle length that progressively decreases. Between each decreasing step of the stimulated cycle length, the rhythm is observed several seconds. One of the most valuable observations during this pacing protocol is the Wenkebach cycle length, the stimulated cycle at which the 1:1 atrioventricular conduction over the atrioventricular node stops.
Incremental ventricular pacing is similar to the ventricular pacing. The pacing is delivered from the right ventricular apex. The minimum cycle length of ventricular pacing is 300ms. The observations during incremental ventricular pacing are the assessment of the retrograde Wenkebach cycle length and the pattern of retrograde atrial activation.
Pacing at other sites than the usual ones (high right atrium and ventricular apex) may reveal the accessory pathways. The use of isoproterenol and atropine is widely used for tachycardia induction during the EPS.
As many of the challenging arrhythmic events leading to sudden cardiac death occur in athletes; a good collaboration between interprofessional team members from sports medicine and cardiologist is necessary. However, the complex adaptations induced by exercise present a continuous challenge to the cardiologist asked to evaluate athletes. A unique discipline of sports and exercise cardiology tailoring cardiovascular care in athletes and exercising individuals would be a fabulous resort in the future, allowing safe participation in sports or enhanced physical activity. A patient safety program to design and implement a system that takes into account the concerns of the frontline personnel requires development. An arrhythmia team with medical co-leads with specific responsibilities and roles formed by electrophysiologists and cardiovascular surgeons constitutes the future of the therapeutic strategy regarding complex patients. Besides, the arrhythmia team should include a general cardiologist, a cardiac anesthetist, an intensivist, a nurse coordinator, and not least a patient representative.
A cardiology specialty nurse can assist with setting up the procedure and answering the patient questions, as well as helping with whatever interventions may be necessary based on the outcome of the EPS, which places nursing as a vital component of the interprofessional team, leading to better patient outcomes. [Level 5]
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