Healthcare: Cardiovascular Medicine

Cardiac Electrophysiology


Cardiac electrophysiology is the study, evaluation and treatment of heart rhythm disorders.



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Baylor College of Medicine offers expert electrophysiology services.

In order for the heart to do its work of pumping oxygen-rich blood to the body, it needs a trigger or electrical impulse to generate a heartbeat. This electrical impulse originates from the sinus node – the heart's natural pacemaker. The sinus node (SA node) is located in the upper right chamber of the heart called the right atrium. From the sinus node, the electrical impulse travels through the atria causing them to contract then proceeds to the atrioventricular (AV) node. The AV node takes the signal from the atria and passes it across the His bundle to the ventricles. This causes the ventricles to contract and completes one cardiac cycle. The contraction of the ventricle is what you feel when your heartbeats.

Normally, the sinus node delivers electrical impulses at a rate of 60-100 beats per minute. This is called sinus rhythm. Your heart, brain, and body determine the optimum heart rate depending on your activity. For example, your heart may beat slower when sleeping or faster when exercising. You can check your own pulse by pressing gently on the inner aspect of your wrist (beneath the thumb), counting the number of beats over 6 seconds, and multiplying this by 10 (or you can count for the entire minute).

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Problems Related to the Heart's Electrical System


What is cardiac electrophysiology? What are arrhythmias?

Any problem in any of the heart's electrical components results in a heart rhythm disorder also referred to as an arrhythmia.

For example, heart rates below 60 beats per minute are called bradycardia. When your heart rate exceeds 100 beats per minute, that's known as tachycardia. If the tachycardia comes from the upper chambers of the heart it is called supraventricular tachycardia or SVT. If it comes from the lower chambers it is ventricular tachycardia or VT. Examples of specific arrhythmias are listed on the following table:

Examples of Specific Arrhythmias

Slow Rhythms

Fast Rhythms From the Upper Chamber

Fast Rhythms From the Lower Chamber

Sinus bradycardia

Atrial fibrillation


Ventricular tachycardia

AV block

Atrial flutter


Ventricular fibrillation


Atrial tachycardia




AV nodal reentrant tachycardia




Wolff-Parkinson-White Syndrome





What does one feel if he/she has an arrhythmia?

Arrhythmias may go unnoticed (asymptomatic) or may cause the following symptoms:

  • Dizziness or light-headedness
  • Fatigue
  • Palpitations (pounding in the chest)
  • Shortness of breath
  • Chest pain or pressure
  • A fainting or near fainting spell

Both heart rates that are too slow or too fast may cause these symptoms. If the heart beats too slowly, not enough blood (which carries oxygen) is able to circulate in your body. Similarly, if the heart beats too fast, there isn't enough time for it to relax and fill with enough blood for the next heart beat. The result is the same, with not enough blood able to circulate to meet your body's needs.


Diagnostic Studies or Tests


How will I be evaluated? What kinds of tests will my doctor order and why?

When you visit your doctor's office for an electrophysiologic evaluation, after conducting a thorough interview and physical, your doctor will most likely order additional tests. The purposes of these additional tests are:

  • To see if indeed an arrhythmia is present and if it is, to obtain a recording of the rhythm disturbance so that it can be correctly identified.
  • To assess your risk of future adverse events, such as fainting spells and/or recurrent episodes.
  • To guide the treatment plan.
  • To see whether you have underlying heart disease. In general, patients with arrhythmias that occur with underlying heart disease tend to do worse.

Tests are broadly categorized into two types: non-invasive (meaning, no big needles, catheters or cutting involved) and invasive.

Non-Invasive Tests. Non-invasive tests include an electrocardiogram (ECG or EKG), stress test, echocardiogram, Holter monitor, event monitor, signal averaged ECG, tilt test, T-wave alternans test and a cardiac magnetic resonance imaging (MRI) test.

Invasive Tests. The invasive tests that cardiac electrophysiologists use include cardiac catheterization, placement of an implantable loop recorder (ILR, Reveal or Reveal Plus) and electrophysiological testing (EP study).