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Electrophysiology study of heart function

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An electrophysiology study (EP test or EP study) is a minimally invasive procedure which tests the electrical conduction system of the heart to assess the electrical activity and conduction pathways of the heart. During EPS, sinus rhythm as well as supraventricular and ventricular arrhythmias of baseline cardiac intervals is recorded[1]. The study is indicated to investigate the cause, location of origin, and best treatment for various abnormal heart rhythms. This type of study is performed by a an electrophysiologist and using a single or multiple catheters situated within the heart through a vein or artery.

The procedure is of interest to psychologists as it is an approach used to assess some physical conditions that may be causing anxiety symptoms.

PreparationEdit

It is important for patients not to eat or drink for up to 12 hours before the procedure. This is to prevent vomiting, which can result in aspiration, and even cause severe bleed from the insertion site of the catheter. Failure to follow this simple preparation may result in dangerous consequences. Generally small amounts of water can be consumed up to 2 hours before the exam. Patients should try to schedule the exam at a time when they will be having symptoms and will not need to drive for 2 to 3 days.

ProcedureEdit

This procedure is performed in a cath lab which is a specially equipped operating room. More modern cath labs contain a video X-ray machine and large magnets (2-3 tesla, 2 ft. diameter) for manipulating the electrodes, in addition to other necessary equipment.

An IV tube is generally inserted to keep the patient hydrated and to allow for the administration of sedatives, anesthesia, or drugs.

In order to reach the heart with a catheter, a site will be prepared that will allow access to the heart via an artery or vein, usually in the wrist or groin. This site is then described as the insertion point.

A metal plate is placed underneath the patient between the shoulder blades, directly under the heart. An automated blood pressure cuff is placed on the arm which periodically measures the patient's blood pressure. A pulse oximeter is placed on one of the patient's fingers which steadily monitors the patient's pulse and oxygen saturation of the blood.

The insertion point is cleanly shaved and sterilized. A local anesthetic is injected into the skin to numb the insertion point. A small puncture is then made with a needle in either the femoral vein in the groin or the radial vein in the wrist, before a guide wire is inserted into the venous puncture. A plastic sheath (with a stiffer plastic introducer inside) is then threaded over the wire and pushed into the vein (the Seldinger technique). The wire is then removed and the side-port of the sheath is aspirated to ensure venous blood flows back. It is then flushed with saline. Catheters are inserted using a long guide wire and moved towards the heart. Once in position the guide wire is then removed.

  • NOTE It is standard procedure to use the venous system, and place the catheter's tip in the right atrium at the beginning of the procedure. The advantage of this is that the SA node is in the right atrium, which is the place where the procedure will start testing the pacing system of the heart.

EP StudyEdit

Once the catheter is in and all preparations are complete elsewhere in the lab, the EP study begins. The two large magnets are brought in on either side of the patient. They are large and looming and will sandwich the patient, but are able to precisely control the position of the electrodes that are on the end of the catheters. The X-ray machine will give the doctor a view of the heart and the position of the electrodes, and the magnets will allow the doctor to guide the electrodes through the heart. The magnets are controlled with either a joystick or game controller. The electrophysiologist begins by moving the electrodes along the conduction pathways and along the inner walls of the heart, measuring the electrical activity along the way.

The next step is pacing the heart, this means he/she will speed up or slow down the heart by placing the electrode at certain points along the conductive pathways of the heart and literally controlling the depolarization rate of the heart. The doctor will pace each chamber of the heart one by one, looking for any abnormalities. Then the electrophysiologist tries to provoke arrhythmias and reproduce any conditions that have resulted in the patient's placement in the study. This is done by injecting electric current into the conductive pathways and into the endocardium at various places. Lastly, the electrophysioligst may administer various drugs (proarrhythmic agents) to induce arrhythmia. If the arrhythmia is reproduced by the drugs, the electrophysiologist will search out the source of the abnormal electrical activity. The entire procedure can take several hours.

AblationEdit

If at any step during the EP study the electrophysiologist finds the source of the abnormal electrical activity, he/she may try to ablate the cells that are misfiring. This is done using high energy radio frequencies (similar to microwaves) to effectively "cook" the abnormal cells. This can be painful with pain felt in the heart itself, the neck and shoulder areas.

RecoveryEdit

When the necessary procedures are complete, the catheter is removed. Firm pressure is applied to the site to prevent bleeding. This may be done by hand or with a mechanical device. Other closure techniques include an internal suture and plug. If the femoral artery was used, the patient will probably be asked to lie flat for several hours (3 to 6) to prevent bleeding or the development of a hematoma. Trying to sit up or even lift the head is strongly discouraged until an adequate clot has formed. The patient will be moved to a recovery area where he/she will be monitored.

For patients who had a catheterization at the femoral artery or vein (and even some of those with a radial insertion site), generally recovery is fairly quick as the only damage is at the insertion site. The patient will probably feel fine within 8 to 12 hours after the procedure, but may feel a small pinch at the insertion site. After a short period of general rest, the patient may resume some minor activity such as gentle, short, slow walks after the first 24 hours. If stairs must be climbed, they should be taken one step at a time and very slowly. All vigorous activity must be postponed until approved by an physician.

It is also important to note that unless directed by a doctor, some patients should avoid taking blood thinners and foods that contain salicylates, such as cranberry containing products until the clot has healed. (1–2 weeks)

ComplicationsEdit

As with any surgical procedure, cardiac catheterizations come with a generic list of possible complications. One of the complications that is sometimes reported involves some temporary nerve involvement. Some times a small amount of swelling occurs that can put pressure on nerves in the area of the incision. Venous thrombosis is the most common complication with an incidence ranging between 0.5 and 2.5 %[2]. There have been reports of patients feeling like they have hot fluid like blood or urine running down their leg for up to a month or two after the incision has healed. This usually passes with time, but patients should tell their doctor if they have these symptoms and if they last.

More severe but relatively rare complications include: damage or trauma to a blood vessel, which could require repair; infection from the skin puncture or from the catheter itself; cardiac perforation, causing blood to leak into the sac around the heart and compromising the heart's pumping action, requiring removal using a needle under the breast bone (pericardiocentesis); hematoma at the site(s) of the puncture(s); induction of a dangerous cardiac rhythm requiring an external shock(s); a clot may be dislodged, which may travel to a distant organ and impede blood flow or cause a stroke; myocardial infarction; unanticipated reactions to the medications used during the procedure; damage to the conduction system, requiring a permanent pacemaker; death.

See alsoEdit

ReferencesEdit

  1. Karen.E.Thomas and Peter J. Zimetbaum (2011). Management of Cardiac Arrhythmias, 123–140, Hanumana Press.
  2. (2010) Comprehensive Electrocardiology, 2nd, 1146, Springer.

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