In order to function optimally, the heart must beat in a rhythmic pattern. Electrical activity is what causes the heart to beat. However, certain conditions and diseases can cause arrhythmia - a misfiring of electrical impulses in the heart that cause it to beat irregularly or at an abnormal rate. Electrophysiology is a specialized field that studies the relationship of the heart to its electrical system, identifying the origin of electrical impulses, the pathways they travel and their effect on the heart muscle. A problem at any point in the electrical pathway can interfere with normal beating, resulting in heart rhythm disorders (arrhythmias), including:
Bradycardia: heartbeats that are too slow - under 60 beats per minute;
Tachycardia: heartbeats that are too fast - over 100 beats per minute;
Supraventricular tachycardia (SVT) - any fast heart rhythm originating in the upper chambers of the heart
Atrial fibrillation/flutter - a fast heart rhythm originating in the upper chambers of the heart in which an abnormal source of electrical stimulation causes the atrium to beat more rapidly than normal.
Ventricular fibrillation: a life-threatening rhythm originating in a ventricle (lower chamber) of the heart.
Ventricular tachycardia: a life-threatening accelerated rhythm originating in a ventricle (lower chamber) of the heart.
Heart blocks: a category of arrhythmias in which the electrical signals from the atria to the ventricles are delayed or not conducted.
DIAGNOSTIC ELECTROPHYSIOLOGY PROCEDURES
Electrophysiology Study (EPS)
This is a procedure used to study abnormal heart rhythms. Using a procedure similar to cardiac catheterization, electrical signals are sent to the heart in order to stimulate an arrhythmia so that doctors can determine where in the heart it started, how it is transmitted through the heart muscle and plan the correct course of treatment.
In order to perform an electrophysiology study, the patient is given a local anesthetic and sedative. Under sterile technique, electrode catheters are fed through a small incision or puncture in the patient's groin or neck and guided through the veins to the chambers on the right side of the patient's heart. Arrhythmias are then triggered and mapped under the controlled environment of the electrophysiology lab.
INTERVENTIONAL ELECTROPHYSIOLOGY PROCEDURES
Cardiac Ablation - also known as cardiac catheter ablation or catheter ablation - is performed with or following an EP study and restores a normal heart beat by scarring areas of the heart where arrhythmias are conducted. When these pathways are eliminated, the arrhythmia can no longer exist. In cryoablation, the pathways are treated with freezing temperatures. In radiofrequency catheter ablation, they are treated with radiofrequency energy, which burns the tissue.
Most often, cardiac ablation is used to treat rapid heartbeats that begin in the upper chambers (atria) of the heart - superventricular tachycardias (SVTs). These include atrial fibrillation, atrial flutter and atrial tachycardia. It can also be used to treat rhythm disorders that begin in the heart's lower chambers (ventricles), the most common of which is ventricular tachycardia.
For many types of arrhythmias, catheter ablation is successful in 90 to 98 percent of cases - eliminating the need for open-heart surgery or long-term drug therapy.
Atrial Fibrillation Ablation
Atrial fibrillation is frequently caused by an abnormal source of electrical stimulation occurring in the area of the atria around the opening of the pulmonary veins. During this procedure, radiofrequency energy is delivered through catheters to this area thereby cauterizing the targeted tissue. This creates a circular scar that blocks any impulses firing from within the pulmonary vein, thereby "disconnecting" the pathway of the abnormal rhythm and preventing atrial fibrillation.
This procedure has an 80 to 85 percent success rate with the first ablation and a 95 percent success rate for subsequent ablation procedures.
A pacemaker is a small, battery-operated, electronic device that is inserted under the skin. Connected to the heart by insulated wires or "leads" the pacemaker helps the heart beat regularly and at an appropriate rate. It can take over for the heart's natural pacemaker, the sinoatrial node, when it is functioning improperly and reset the heart rate to an appropriate pace.
The most common reason for needing a pacemaker is a heartbeat that is too slow to support normal cardiac function. This may be due to heart muscle damage. Sometimes, the drugs prescribed to treat heart failure slow the heart rate. In these cases, a pacemaker may be needed to support the use of medications.
A pacemaker generally has two parts: the generator and the leads. The generator is where the battery and information to regulate the heartbeat are stored. The leads go from the generator to the right upper and lower chambers of the heart, where they are anchored.
Through the leads, pacemakers receive signals from the heart, interpret them, determine the heart's activity and respond when needed by sending signals back to the heart along the leads. The signals cause the heart muscle to begin the contractions that cause a heartbeat.
The pacemaker continuously monitors the heart's natural rhythm and stimulates (paces) one or both upper and lower chambers if the heart rate drops below a certain number of beats per minute. The patient does not feel the electrical signal that is sent from the pacemaker.
Pacemakers have become ever smaller over the years, and today's generators generally weigh less than an ounce. The battery lasts seven to eight years on average and is routinely monitored by electronic circuits and computer memory that combine to generate electronic signals or pacing pulses.
Types of Pacemakers
Three basic types of pacemakers exist to serve different purposes:
Single-Chamber Pacemaker - In a single-chamber pacemaker, only one wire (pacing lead) is placed into a chamber of the heart. Sometimes it is the upper chamber (atrium). Other times it is the lower chamber (ventricle).
Dual-Chamber Pacemaker - Wires are placed in both the right atrium and right ventricle. This allows the upper and lower chambers to beat in a synchronized fashion with the ventricle contracting a split second after the atrium.
Biventricular Pacemaker-- In a healthy heart, both upper chambers (atria) beat together as do both lower chambers (ventricles). Electrical impulses are delivered to the left ventricle in a highly organized pattern of contractions that efficiently pump blood out of the ventricle. In about one-third of patients with congestive heart failure (CHF), the electrical coordination is lost and the right and left ventricles do not beat together. This uncoordinated heart muscle function leads to inefficient ejection of blood from the ventricles and poses the risk of abnormal heart rhythms (arrhythmias). The biventricular pacemaker has leads implanted in the Right atria, the right ventricle and the coronary sinus to sense and pace the left ventricle. This three-lead system allows the pacemaker to sense both ventricles and stimulate in a way that causes them to contract together. This resynchronization can help alleviate symptoms of CHF such as fatigue, shortness of breath and exercise intolerance thereby improving the patient's overall quality of life.
Implantable Cardioverter Defibrillator (ICD)
ICDs are pacemaker-like devices that continually monitor the heart's rhythm and deliver potentially life-saving electrical impulses if a dangerous rhythm - too fast, too slow, or irregular - is detected. The impulse shocks the heart and the source of the abnormal rhythm allowing the normal electrical system to take over. The latest generation of ICDs can also function as pacemakers that continuously regulate heart rhythm, and can be modified to provide resynchronization therapy.
These devices are 99 percent effective in stopping life-threatening arrhythmias (a misfiring of electrical impulses within the heart). They are the most successful therapy for treating ventricular fibrillation (VF) - a primary cause of sudden cardiac death (SCD) and a condition that patients with heart failure are at high risk of suffering.