Library
Our library contains articles on the latest in heart care information. These postings feature providers from Reno Heart Physicians so you can learn about these important issues from your doctors.
Implantable Cardiac Defibrillators Save Lives
Sudden cardiac death (SCD) strikes close to half a million Americans annually. And 80 percent of those who experience a sudden death episode die before they can be resuscitated. Of those who survive, many cannot be helped by conventional drug therapies.
"Most people are familiar with the term ‘cardiac arrest,’ which is another name for SCD," says cardiologist Dr. David Smith of Reno Heart Physicians. "We often hear of someone dying from cardiac arrest even though medical rescuers were just a few minutes away. SCD is not a heart attack," notes Dr. Smith, "although it’s often mislabeled as such."
To understand SCD, it is helpful to know how the heart works.
The heart is a four-chambered pump with its own unique system of electrical conduction circuitry. The sino-atrial (SA) node, the heart’s natural pacemaker, tells the heart muscle to beat 60 to 100 times per minute. "When blocked arteries or progressive cardiovascular disease cause the heart to malfunction, a chain reaction of abnormal electrical impulses can occur within the heart," says Dr. Smith.
"Actually, during SCD there may be an ample supply of blood to the heart, but the heart can’t pump effectively due to disturbances in the electrical system. These disturbances, known as ventricular arrhythmias, include ventricular tachycardia (abnormally rapid heart rate) and ventricular fibrillation (abnormal heart muscle rhythm)," notes Dr. Smith.
If ventricular tachycardia or fibrillation occurs, abnormal pulses take over the normal heartbeat function of the SA node. The heart beats so fast that it doesn’t have time to pump enough blood to the brain or other parts of the body. "Unconsciousness usually follows in a matter of seconds, and death can result quickly unless immediate action is taken," says Dr. Smith. "However, an electrical shock or pacing therapy from an Implantable cardiac Defibrillator (ICD), can restore normal electrical activity and normal contractions to the heart."
"In fact, in clinical studies ICDs have been shown to be 99 percent effective in preventing Sudden cardiac Death. Recent studies have shown that they prolong life compared with conventional medical therapy in patients who are at high risk of dangerous ventricular arrhythmias. One recent study found that people who received an ICD had a 39 percent reduction in deaths in the first year compared with people who received heart rhythm medications alone," notes Dr. Smith.
Implantable Caregiver Defibrillators (ICD) are small automatic devices that can detect and treat patients with ventricular arrhythmias. While traditional antiarrhythmic drug therapies may prevent the occurrence of arrhythmias in some patients, they have been shown to be inferior to ICDs in saving lives.
Current ICDs are about the size of a pager and are implanted in the upper chest in a relatively simple surgical procedure that lasts for about an hour. Today’s ICD can respond to fast or irregular heart rates with a range of programmed therapies that can be tailored to the patient’s condition by a cardiologist. "It is important to realize that ICDs, like drugs, do not cure the underlying disease that causes the arrhythmia. Instead, the ICD terminates the arrhythmia and can store records of the episode for the cardiologist to evaluate at a later time," notes Dr. Smith.
The first ICD was successfully implanted on February 4, 1980, by Dr. Michael Mirowski at Johns Hopkins University. Unlike today’s ICD, where cardiologists have a wide range of programmable therapy options, the first ICDs were simple, nonprogrammable, high energy, shock-only devices, designed to interrupt abnormally fast heartbeats. At that time, the ICD battery longevity was approximately one year. Today’s advanced technology allows an ICD a life of approximately five to seven years before the battery needs to be changed.
"In 1998 alone, over 30,000 ICD devices have been implanted and the number of implants are expected to triple within five years because of continuing advances in the technology and availability of smaller sized ICD units, making them more comfortable to persons of smaller stature," notes Dr. Smith.
Dr. Smith, who has performed over 200 ICD implants, is a board certified cardiologist with an additional board certification in cardiac Electrophysiology—the study of the heart’s electrical mechanisms. He specializes in the diagnosis and treatment of heart rhythm disorders at Reno Heart Physicians. Additionally, Dr. Smith performs electrophysiologic (EP) testing, which is a procedure for diagnosing potentially serious arrhythmias. The EP test uses catheters (long, thin, flexible tubes) that are passed to the heart through veins and arteries. The catheters test the heart’s electrical system and its susceptibility to arrhythmias.
"EP testing is not usually the first step in diagnosing and treating rhythm disorders of the heart," says Dr. Smith. "Normally an electrocardiogram (ECG) is run by the patient’s family physician. The ECG is a non-invasive test that can be very revealing about the disease state of the heart. If a further work-up is needed, the family physician will generally refer the patient to a cardiologist."
According to Dr. Smith, once a patient has an ICD implant, "most of the things you handle or work around on a daily basis are not going to effect the implant. However, the ICD system is sensitive to strong electrical or magnetic fields. You should be careful around potential sources of strong electrical or magnetic fields such as, large stereo speakers, ‘boom boxes,’ magnetic wands that are used by airport security, industrial equipment such as power generators and cellular phones."
Symptoms of a heart rhythm problem can include dizziness, weakness, fainting spells, shortness of breath, palpitation (a fluttering, strong, or fast heartbeat), or chest pain and discomfort. "If you begin to experience any of these symptoms you should seek the advice of a qualified medical professional."