An electrophysiology study (EPS) is an invasive test for diagnosis and treatment of ventricular and supraventricular arrhythmias. It is similar to cardiac catheterization, the difference being that an EPS measures cardiac electrical conduction system activity through solid electrode catheters instead of the open-lumen catheters used to measure circulatory system pressures. Chest electrode catheters are almost always inserted into veins because of the greater risk they pose in the arterial system (spasms, occlusion). Using fluoroscopy as a visual guide, the catheters are advanced into the right atrium and right ventricle. An x-ray monitor tracks the catheter location, and a physiologic monitor shows ECG rhythms as well as intracardiac catheter electrograms.

An EPS is highly useful for diagnosing diseases of the cardiac conduction system and provides indications for optimal treatment. In addition to measuring baseline values, the electrode catheters are used to pace the heart in an attempt to induce the same arrhythmia causing the problem. When the patient is taking antiarrhythmic drugs, the EPS can determine how well the medication is working by how easily the arrhythmia can be induced. This is in contrast to the trial-and-error method, in which there is no way to know that a particular drug is ineffective until that drug has failed to resolve the problem, frequently over a significant period of time.

An EPS is indicated to differentiate disorders of impulse formation (supraventricular vs ventricular rhythms). It also provides diagnostic insight into the etiology and mechanism of conduction disorders. An EPS is often part of the workup for syncope, sick sinus syndrome, or tachyarrhythmias. Finally, an EPS is indicated for testing the effectiveness of antiarrhythmic drugs. Each antiarrhythmic drug has certain effects that must be anticipated during the loading phase (e.g., hypotension with quinidine and procainamide, abdominal cramping with quinidine, venous pain with phenytoin). A state of "happy drunkenness" may also occur. IV saline is normally used to support blood pressure in the event hypotension occurs.

His bundle electrography is part of an EPS. It measures the electrical activity of the bundle of His, which carries electrical impulses through the center of the heart. It is performed to help determine the need for a pacemaker or identify the specific location where electrical signals through the heart are blocked (see Figure 16.3).

1. Darken the room.

2. To decrease anxiety, keep the patient informed of what is being done as the procedure evolves.

3. Position the patient on an x-ray table and attach the ECG leads to specific locations.

4. Maintain sterile, aseptic surgical conditions. Usually, one or two sites are chosen and prepared for catheter insertion (right or left antecubital area, right or left groin). The sites chosen depend on where in the heart the catheters have to be placed and the patency and size of the patient's veins. Inject the insertion site with local anesthetic before catheter insertion.

5. As the catheters are advanced toward the desired location, record baseline information. Sometimes, cardiac pacing may be necessary; for example, measuring sinus node recovery times requires pacing atrium until the sinus is fatigued and then measuring the time the sinus takes to recover.

6. After baseline values have been determined, use pacing to induce arrhythmias. If a sustained arrhythmia is induced, make an attempt to terminate the arrhythmia through pacing. Should the patient lose consciousness, use an external cardioverter-defibrillator to terminate the arrhythmia.

7. Hold a continuous, quiet conversation to assess the patient's level of consciousness.

8. After the procedure, remove the catheters and apply a sterile pressure bandage to the catheter insertion site. Manual pressure on the site may be necessary if bleeding occurs.

1. Abnormal EP results may indicate the following conditions:

   1. Conduction intervals longer or shorter than normal

   2. Refractory periods longer than normal

   3. Prolonged recovery times

   4. Induced dysrhythmia in a normal subject

2. Abnormal His bundle electrography results may indicate the following conditions:

   1. Long atrial His (AH) bundle intervals indicate disease in the AV node if sympathetic and vagal influences on the AV node have been eliminated.

   2. Long ventricular His bundle intervals indicate disease in the His-Purkinje system.

   3. Prolonged sinus node recovery times indicate sinus node dysfunction such as sick sinus syndrome.

   4. Prolonged sinoatrial conduction times can indicate sinus exit block.

   5. A wide or split His bundle deflection indicates a His bundle lesion.

   6. Induction of a sustained ventricular and supraventricular tachycardia confirms the diagnosis of recurrent VT (Chart 16.4).

Pretest Patient Care

1. Explain test purpose, procedure, benefits, and risks. Describing possible physical sensations that may be felt helps to reduce patient anxiety. These sensations may include the following:

   1. The sensation of a bug crawling in the arm and neck as the catheter is advanced

   2. Palpitations or racing heart during pacing

   3. Lightheadedness or dizziness (these must be reported when felt)

2. Obtain a signed consent form before the procedure.

3. Draw blood samples for potassium levels and other drug levels if the effectiveness of a drug is to be determined.

4. Perform a standard 12-lead ECG before testing.

5. Ensure that no food or beverage is consumed for at least 3 hours before testing.

6. Be aware that analgesic agents, sedatives, or tranquilizers are usually withheld before the procedure.

7. Ask the patient to void before the procedure is initiated.

8. Allow the patient to wear dentures.

9. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Normal

• Normal EP/His bundle procedure

• Normal conduction intervals, refractory periods, and recovery times

• Controlled, induced arrhythmias