The Basic EP Study

The Basic Electrophysiologic Study

An electrophysiologic, or EP, study provides information that is key to diagnosing and treating arrhythmias.

EP studies most often are recommended for patients with symptoms indicative of heart rhythm disorders or for people who may be at risk for Sudden Cardiac Death.

What EP Studies can do.

Intracardiac electrophysiologic studies (EPS) are utilized to diagnosis and treat arrhythmias:

  1) Sinus Node Dysfunction

  2) Intraventricular and AV conduction disturbances,

  3) Supraventricular Tachycardia's (SVT)

  4) Ventricular tachycardia's (VT's),

  5) Preexcitation syndromes (WPW)

  6) Ventricular fibrillation (VF).

The diagnostic electrode catheters

Diagnostic electrode catheters consist of insulated wires attached to electrodes. At the proximal (near) end of the catheter, each wire is attached to a plug that can be connected to an external recording or pacing device.

A common electrode catheter is quadripolar. It has two electrode pairs that can be used to record EGM information at two intracardiac sites or record and pace simultaneously. Typically, the proximal pair records electrical activity and the distal pair delivers pacing stimuli.

Electrode size varies from 2 mm to 8 mm and electrode spacing from 2 mm to 10 mm. Close spacing (2 mm) provides detail in a small area of tissue. Greater spacing (5 to 10 mm) reflects a larger tissue area. All electrodes are numbered. The distal electrode is always number 1.

Electrode catheters are available in a variety of sizes and shapes (e.g., halo, basket). Catheters may have multiple electrode pairs that can record multiple IEGMs simultaneously, such as the Decapolar catheter.

Placement of Catheters

HRA Catheter

The high right atrial (HRA) catheter is placed in the lateral wall of the high right atrium, near the junction of the SVC and as close to the SA node as possible.

The HRA catheter is positioned away from the ventricles, so it senses atrial activity only. The HRA EGM is somewhat aligned with the surface P-wave since both represent atrial depolarization.

HIS Catheter

The His bundle (HIS) catheter is placed across the posterior aspect of the tricuspid valve, as close to the His bundle as possible. It straddles the major structures of the AV conduction system.

The HIS catheter electrodes sense electrical signals in the low right atrium, AV node, His bundle, and a portion of the right ventricle. Proper catheter placement is essential for recording conduction time. The catheter is generally maneuvered until the best electrode recording pair is established.

The HIS EGM has three major deflections:

            − The A spike (first deflection) represents depolarization of the low right atrium as the electrical impulse enters he AV node. It is loosely aligned with the HRA signal and the surface P-wave.

           

            − The H spike (second deflection) represents His bundle depolarization as the impulse exits the AV node. It is loosely aligned with the surface PR interval.

           

            − The V spike (third deflection) represents depolarization of the right ventricle near the HIS catheter. It is loosely aligned with the surface QRS complex.

Note: No deflection is produced as the electrical impulse travels through the AV node because AV conduction is slow.

CS Catheter

The coronary sinus (CS) catheter is placed posterior and slightly inferior to the tricuspid valve. It is close to the posterior aspect of the mitral valve.

The CS catheter follows the coronary sinus which lies in the AV groove. The proximal electrodes are more atrial and the distal electrodes lie directly between the atria and the ventricles.

Because the CS catheter lies in the AV groove, the CS EGM records both atrial and ventricular signals. From left to right, the atrial component of the CS EGM is loosely aligned with the atrial component of the HIS and HRA signals and the surface P-wave.

RV Catheter

The right ventricular (RV) catheter is placed in the right ventricular apex (RVA). It should not sense atrial or His bundle signals as they are out of range.

The RVA EGM records electrical activity in the right ventricle and right bundle branch. From right to left, the RV signal can be loosely aligned with the ventricular component of the CS and HIS signals and the surface QRS complex.

Now that the Catheters in Placed

Its time for the EP Study.

                        The EP Study can be broken down into 3 parts:

                                    1) Basic Intervals

                                    2) Atrial Study

                                    3) Ventricular Study

(See Part II   Basic Intervals)