Invasive EP study: how is an electrophysiology study of the heart done?

An EP study examines the electrical signals that control how the heart works. “Invasive” means that an instrument is inserted inside the body. An electrode is a thin wire that senses the signal, and a catheter is a thin, flexible instrument that is passed through a blood vessel to the heart.

According to MedlinePlus, an EP study may be needed to:

• look into the signs of an arrhythmia (heart rhythm disorder);
• find out where in the heart a known arrhythmia starts;
• choose the most suitable treatment;
• assess future risk, especially the risk of sudden cardiac death;
• see whether a medicine is keeping the rhythm under control;
• find out whether a pacemaker or an ICD (cardioverter-defibrillator) is needed.

According to the ACC summary of the 2022 ESC guideline, an EP study is used to assess risk in some patients. For example, when coronary artery disease, an ejection fraction (the share of blood the left ventricle pumps out with one beat) of 40% or lower, and short ventricular tachycardia that stops on its own occur together. The same applies to some cardiomyopathies (diseases of the heart muscle) and to sarcoidosis (a disease in which inflammatory nodules appear in organs).

MedlinePlus says the following:

• do not eat or drink anything for 6–8 hours before the test;
• do not change your medicines without talking to your cardiologist;
• a sedative is usually given;
• arrange in advance for someone to take you home.

Because the test may turn into ablation, the advice on the MedlinePlus ablation page is also useful: tell your doctor about all your medicines, including blood thinners; let them know if you have a cold or a fever.

MedlinePlus describes the steps as follows:

1. In the hospital lab, the groin or neck area, sometimes both, is cleaned and numbed.
2. Thin guiding tubes (sheaths) are placed there.
3. Electrodes are passed through them to the heart, and the doctor follows their path on a moving X-ray image.
4. The heart's electrical signals are recorded.
5. To find the source of an unusual rhythm, that rhythm may be triggered on purpose with a signal or a medicine.

The person stays awake. You may feel pressure where the catheter goes in, and it may sometimes feel as if your heart is skipping beats or beating fast.

According to MedlinePlus, an EP study lasts from 1 hour to several hours. If ablation is added, it may take longer, and sources differ here: the MedlinePlus ablation page says 4 hours or more, and a leaflet from Southampton hospital in Britain says 2–4 hours for atrial fibrillation ablation.

MedlinePlus calls this test very safe in most cases, but the risk is not zero. It lists the following:

• arrhythmias;
• bleeding;
• blood clots and the blocking of a blood vessel by them (embolism);
• cardiac tamponade, that is, blood collecting around the heart and squeezing it;
• heart attack;
• infection;
• damage to a vein;
• a drop in blood pressure;
• stroke.

This list means these things may happen, not that they will certainly happen to you. Your doctor will tell you your personal risk based on the condition of your heart.

According to MedlinePlus, an abnormal result may point to:

• atrial fibrillation or flutter;
• heart block: the signal does not pass from the atria to the ventricles;
• sick sinus syndrome: the heart's natural pacemaker does not work well;
• supraventricular tachycardia;
• ventricular fibrillation and ventricular tachycardia;
• WPW syndrome: the heart has an extra electrical pathway.

Catheter ablation or pacemaker implantation may be done during the test itself. Ablation (radiofrequency ablation, RFA, is one type of it) creates a scar in the small area of heart tissue that caused the rhythm problem. So ask in advance: if the cause is found, will ablation be done in the same session?

If ablation was done, according to the MedlinePlus ablation page, pressure is applied to the catheter site, you lie still for at least 1 hour, sometimes up to 5–6 hours, and you go home the same day or the next day. Over the next 2–3 days, there may be tiredness, an aching feeling in the chest, skipped beats or a fast, irregular heartbeat.

According to textbook descriptions, in a transesophageal EP study an electrode is inserted into the esophagus and stimulates and records the atria without entering the heart; it is less invasive, but it does not replace a test done from inside the heart.