What is electrophysiologic examination and catheter radiofrequency ablation? An electrophysiologic test is a method that accurately evaluates the function of the heart’s electrical activity. This test allows the doctor to detect abnormalities in the heart that cause arrhythmias (abnormal heart rhythms). During the test, the doctor inserts a special electrode catheter (a long, flexible, bendable wire) into a vein and introduces it into the heart. The inserted catheter can both detect electrical impulses in different parts of the heart and deliver electrical stimulation to different parts of the heart. Catheter-based radiofrequency ablation is a nonsurgical technique that disrupts the abnormal electrical conduction pathways in the heart that cause tachyarrhythmias. Most tachyarrhythmias can be eradicated with radiofrequency ablation. In cardiac catheter ablation, a special electrode catheter is introduced into the heart, the tip of the electrode is placed next to the abnormal electrical conduction pathway, and radiofrequency energy (heat) is delivered to the electrode, which heats up and destroys the myocardial tissue containing the abnormal conduction pathway (ablates it), thereby eliminating the arrhythmia. Catheter-based radiofrequency ablation can be performed for most tachyarrhythmias, including paroxysmal supraventricular tachycardia, preexcitation syndrome, atrial tachycardia, atrial flutter, atrial fibrillation, ventricular tachycardia, and ventricular tachycardia. The success rate of ablation for simple arrhythmias such as supraventricular tachycardia and preexcitation syndrome can reach more than 95-98%, while the success rate for complex arrhythmias such as atrial tachycardia, atrial flutter, ventricular premature, idiopathic ventricular tachycardia, and so on can reach more than 85-90%, and the current success rate for atrial fibrillation is 80-90% for paroxysmal atrial fibrillation, and 60-80% for persistent and chronic atrial fibrillation. The success rate of reablation will be further improved. Cardiac electrophysiology and catheter radiofrequency ablation are two very similar procedures. In fact, your physician may decide to perform both procedures in the catheterization laboratory. Of course, your physician will carefully discuss this possibility with you before the test. Why is electrophysiology important? An electrophysiologic study provides more precise and detailed information about the electrical activity of the heart than other diagnostic methods. It can help your doctor make an accurate diagnosis and choose the most effective treatment. Electrophysiologic testing is a mandatory step prior to radiofrequency ablation. Electrophysiology is the most effective diagnostic method for serious, life-threatening arrhythmias and for persistent arrhythmias that cannot be diagnosed by other methods. How does the heart work? Before we go into the details of electrophysiology, let’s first understand how the human heart works. The heart is like a “pump” The human heart is a hollow, muscular organ that pumps blood continuously throughout the body. The heart can be divided into four parts, or chambers, two on the “left” side and two on the “right” side. The upper chambers on each side are called the atria, which are responsible for receiving blood from all parts of the body back to the heart; the lower chambers on each side are called the ventricles, which are responsible for pumping blood out of the heart. The lower chambers on each side are called ventricles and are responsible for pumping blood out of the heart. The four chambers work together to contract and pump blood, powering the circulation and allowing blood to flow throughout the body carrying oxygen and nutrients. The heart’s electrical conduction system The heart’s rhythmic diastolic activity depends entirely on its electrical conduction system, which conducts electrical impulses to every part of the heart. The sinus node is a specialized group of cells located in the right atrium, which is the origin of the normal electrical impulses throughout the heart. The sinus node is the heart’s “natural pacemaker” and determines the rhythm of the heart. The impulses from the sinus node travel along fixed pathways throughout the atria, triggering atrial contractions and pushing blood into the ventricles. The impulse travels out of the atria and subsequently arrives at the AV node, which is located between the atria and the ventricles. Under normal conditions, the AV node is the only electrical pathway connecting the atria and ventricles. The AV node acts as a “relay station” where each electrical impulse slows down and stops briefly before reaching the ventricles, allowing the ventricles enough time to fill with blood. After the “stop” at the AV node, the impulse continues its journey down to the ventricles through a bundle of specially differentiated muscle fibers. In the ventricles, these muscle bundles are dispersed into countless small fibers, which form a “grid” that carries the impulse throughout the ventricles, causing the ventricular muscles to contract and pumping blood out of the heart. Normal heart rate The human heart rate changes with the amount of activity, in the resting state, the heartbeat between 60 and 80 times per minute. When activity increases, the sinus node sends out impulses more frequently and the heart rate increases to meet the body’s increased demand for oxygen. Abnormal Heart Rhythm An abnormal heart rhythm, or arrhythmia, is an abnormal change in the rate or form of the heartbeat. When an arrhythmia occurs, the heartbeat becomes too slow, too fast, or irregular. You may experience palpitations during an arrhythmia episode. In addition, arrhythmias may cause symptoms such as dizziness, fainting, chest pain or shortness of breath. Sometimes, arrhythmias go unnoticed without causing significant discomfort. Severe arrhythmias can cause the heart to beat too slowly or too fast, making the heart unable to work efficiently (pump blood) and even threatening the patient’s life. How do doctors diagnose arrhythmia? When your doctor suspects that you have an arrhythmia, he or she will use one or more diagnostic tests to determine the presence of the arrhythmia and whether your symptoms are caused by the abnormal rhythm. An electrocardiogram (ECG or EKG) is a simple way to record the electrical activity of the heart. An ECG records a series of waveforms that represent electrical activity in different parts of the heart. By carefully analyzing the sequence of the heart’s electrical activity in the ECG, the doctor can make a diagnosis of the arrhythmia. Ambulatory ECG monitoring (Holter) allows the ECG to be recorded continuously over a period of time, usually 24 hours, during which the patient’s daily activities are unaffected. This test can capture abnormal heart rhythms that cannot be detected by a resting ECG. Event recorders can record cardiac activity over days or weeks, and can therefore detect abnormal heart rhythms that occur very infrequently. When symptoms appear, the patient turns on the recorder, and the recorded ECG can be transmitted by telephone to the doctor’s office or hospital. When these basic tests fail to reveal the necessary information, electrophysiologic tests can be used to identify the problem and select the appropriate treatment. Types of Arrhythmias Arrhythmias can be divided into 2 main categories: l Tachyarrhythmias l Bradyarrhythmias Below is a brief description of the most common arrhythmias that may require electrophysiologic testing, but not every arrhythmia mentioned will require electrophysiologic testing. Tachyarrhythmias Tachyarrhythmias (tachycardias) can originate in the atria, AV node, or ventricles. Because the ventricles are the main bearers of the heart’s pumping function, rapid abnormal rhythms that occur in the ventricles tend to have more serious consequences. Supraventricular tachycardia (SVT) SVT is a group of rapid arrhythmias that originate in the upper chambers of the heart, often due to the presence of abnormal conduction pathways between the atria, AV node, or ventricles. Atrioventricular nodal refractory tachycardia (AVNRT) is the most common type of supraventricular tachycardia and is primarily caused by the presence of an additional conduction pathway in or near the AV node. Once an impulse enters this abnormal pathway, it has the potential to cause a circular conduction pattern in which the heart contracts with each loop of impulse conduction, resulting in rapid and regular heart beats. Pre-excitation syndrome (WPW) This abnormal rhythm occurs because of an abnormal “bridge” between the atria and the ventricles called an additional bypass, which allows electrical impulses to bypass the AV node and travel from the atria to the ventricles. The presence of the bypass allows electrical impulses to bypass the AV node and go from the atria to the ventricles. In patients with preexcitation syndrome, the impulse passes through the AV node to the ventricles and can then be retrograded through the bypass to the atria, triggering another contraction, which can lead to tachyarrhythmia if the impulse continues to travel along this loop. Atrial Fibrillation Atrial fibrillation occurs when multiple parts of the atria send impulses in an uncoordinated manner, triggering very rapid and ineffective contractions of the atria. The AV node acts as a “relay” between the atria and the ventricles, allowing only some of these impulses to travel down to the ventricles, resulting in an irregular, unstable, and abnormally fast heart rhythm. Atrial fibrillation can be occasional (paroxysmal atrial fibrillation) or constant (persistent or chronic atrial fibrillation). Ventricular tachycardia (VT) This arrhythmia occurs due to the presence of an abnormal current pathway in the ventricles, usually located at the site of a myocardial infarction or other heart disease damage. If an impulse enters the abnormal pathway, it may induce cyclic excitation, resulting in tachycardia. Ventricular tachycardia usually doesn’t stop on its own, and worse, it sometimes progresses to life-threatening ventricular fibrillation and cardiac arrest. Ventricular Fibrillation Ventricular fibrillation occurs when multiple parts of the ventricle give off impulses in a rapid and uncoordinated manner. At this point, the ventricles begin to pump ineffectively, which can lead to a cessation of blood flow. If urgent treatment is not given to restore the heart rhythm, the patient often dies within minutes. Slow arrhythmias (bradycardia) Bradycardia consists of 2 basic types: Sick sinus node syndrome (SSS) In this condition, the sinus node loses its normal pacing function. It may send insufficient electrical signals, miss some electrical signals, or suddenly send too many electrical signals. As a result, the heart may beat too slowly (sinus bradycardia), pause for long periods of time (sinus arrest), or beat fast and slow (bradycardia-tachycardia syndrome). Heart block An interruption in the path of impulses traveling to the ventricles, which can be partial or complete. In a complete block, all impulses generated by the sinus node are not transmitted down to the ventricles, which are then controlled by “potential pacing points” that are less frequent and reliable than the sinus node. As a result, conduction block often results in a slow and erratic heartbeat.