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)
