Almost everyone, at one time or another, has experienced a heart “flutter,” or had their heart pound out a rapid beat in times of fear or extreme stress. For thousands of Americans, however, an abnormal heart beat signals a potentially serious, life-threatening condition.
Imagine for a moment what would happen if the drum major and all the wind instruments in a marching band played one piece of music and the drum corps beat out another. The drummers would be marching confidently to their own beat, while the rest of the band scrambled to find some kind of matching rhythm. The result would be organized chaos; a cacophony of ineffective and conflicting noise.
The heart has its own “drum major,” called the sinus node (SA), that sends out impulses to the heart’s upper chambers, called the atria, indicating it is time to beat. This signal travels into the lower chambers (ventricles), telling them to respond in tempo. The atria beat first, followed a split second later by the ventricles. When the heart beats in normal “sinus rhythm,” the blood is pumped efficiently throughout the body, and the “band” all marches to the same drummer.
In some cases, the heart beats too slowly (Bradycardia) and in others, it beats too fast (Tachycardia). These arrhythmias are essentially “electrical” problems. Somewhere along the line, the signals — that are supposed to tell the atria to contract to move blood along to the lower chamber, then prompt the ventricles to pump the blood on to the lungs and body — are “short-circuited.” If the signal is interrupted, or takes a detour, the heart may not beat fast enough. When there are too many signals, the heart beat races. And, if the signal is sent rapidly and irregularly, the heart muscle can quiver or not beat at all (fibrillation).
A Different Drummer...
Since it is the ventricles that do most of the critical pumping of blood, ventricular tachycardia or fibrillation tend to be more serious than rhythm abnormalities in the heart’s upper chambers. In fact, some 350,000 sudden cardiac deaths occur in the United States every year and most are believed to be caused by ventricular tachycardia or ventricular fibrillation. These rhythm disturbances can be brought on by an inadequate oxygen supply to the heart muscle; by disease of the heart muscle itself (cardiomyopathy); even by low levels of potassium in the blood; or it can also be induced by drugs such as digitalis or cocaine.
When the ventricles beat very fast and out of sync, the heart muscle loses pumping efficiency. If it gets to the point that the heart can’t pump at all (cardiac arrest1), the person can die if emergency treatment isn’t initiated at once to return the heart’s rhythm to normal.
People experiencing a problem with the speed and/or pattern of their heartbeat may not have any symptoms at all, or they might feel light-headed or dizzy, be short of breath, or may have chest pain or palpitations.
The symptoms might last for a few minutes, hours, or even days, and then disappear for a long period of time before returning. They may be brought on by exercise or stress, or occur for no apparent reason at all. At the first sign of a problem, it is very important to obtain an accurate diagnosis to determine the nature and cause of the arrhythmia, especially since a rapid heartbeat of ventricular origin can be considered a potentially dangerous medical emergency.
Making The Diagnosis
In addition to providing a complete medical history and undergoing a thorough physical examination, patients may have an electrocardiogram (ECG), which records the heart’s electrical activity; an echocardiogram, which uses sound waves to produce a video picture of your heart at work; or they may be asked to wear a portable ECG monitor to record the heart’s rhythm for 24 hours or more. If these tests do not provide enough information for a conclusive diagnosis, an electrophysiology study (EPS) might be recommended.While cardiologists generally work with the heart’s “plumbing” function, an electrophysiologist is especially trained to work on that organ’s “electrical” system. An EPS — conducted in a specially equipped laboratory — is designed to diagnose and locate the source of an arrhythmia problem and can also determine the effectiveness of specific medications in treating the condition.
The patient is generally under sedation for the electrophysiologic study. A thin, flexible wire (called an electrode catheter) is guided through a small puncture in the groin, neck, chest or arm, through the vein to the heart where it will record electrical activity. The tiny probe discovers where and when signals originate, and how often they are sent. The whole process is monitored on a video screen and can take from one to four hours to complete.
During the study, electrical signals to stimulate the heart can be sent through the catheter to try to provoke an arrhythmia. If an arrhythmia is induced, medications may be administered through the IV line to see how well they stop the abnormality or determine if they can prevent it from reoccurring. In some cases, when an abnormal electrical pathway is present or a wayward group of electrical cells are found to be “misfiring,” radio frequency waves may be sent through a special ablating electrode catheter (catheter ablation) to destroy the abnormal pathway or cells, forcing the heart’s electrical signal to follow the correct course.
In some cases, arrhythmia may be stopped during the study by using the electrode catheter to regulate the heartbeat. An electric shock, or defibrillation, can also be administered externally in cases of emergency to stop an arrhythmia — a technique familiar to almost everyone, thanks to televised medical dramas like “ER.” Because of sedation, there is no discomfort during any of this procedure and, due to the controlled environment, they are very safe.
Implantable Technology
Depending upon the outcome of the EPS, treatment options include managing the arrhythmia through medication, catheter ablation, or by an implanted device to help control the heart’s rhythm. If the problem is a slow rhythm, a pacemaker may be implanted to keep track of the heartbeat and, if necessary, to generate electrical signals that simulate the heart’s natural “instructions.”
If ventricular tachycardia or ventricular fibrillation is diagnosed, an implantable cardioverter defibrillator (ICD) may provide the most effective, long-term treatment option. The ICD is a small electronic device permanently placed in the body to monitor heart rhythms. If it detects excessively rapid heartbeats, it can pace the heart to slow it down. It can also administer one or more electric shocks to return the heart to normal sinus rhythm.
Recently, the National Institutes of Health (NIH) sponsored a comprehensive 1,016 patient study to compare the effectiveness of the implanted defibrillators with anti-arrhythmic medications in the treatment of rhythm abnormalities. While stressing that the ICD therapy may not be right for everyone, results from the first year of the study showed that people at moderate risk from a ventricular arrhythmia were 38 percent less likely to die if they had an implanted cardiac defibrillator than if they were treated with medication.
An earlier study, conducted at the University of Rochester, estimated that with ICDs there would be 50 percent fewer deaths in people who had survived a previous heart attack but who had not yet experienced an episode of cardiac arrest.
This news is especially welcome to people with ventricular tachycardia or ventricular fibrillation. Research indicates that if they have survived one episode of sudden cardiac arrest by being resuscitated, they face a significant risk that they’ll have another one.
The small ICD can be implanted permanently in the chest or abdomen by an electrophysiologist - cardiologist team during a minimally invasive procedure.
A lead from the ICD is inserted through the vein near the collar bone into the bottom chamber on the right side of the heart. There may also be a second lead inserted through the same vein to deliver the pacing or shock therapy. The exact placement and type of equipment, as well as how the device is programmed, is determined by the doctor on a case by case basis.
Following implantation, the patient’s activities may be limited for a brief recovery period as the heart adjusts to its new “conductor.” There are some behaviors or activities that may be curtailed, and will be thoroughly explained by the doctor during follow-up.
Depending on the type of equipment, the device needs to be checked every two to six months. During each follow-up visit, the ICD battery will be checked along with the device’s sensing and pacing performance. The doctor will also review information stored by the ICD about any episodes of arrhythmia the patient may have had between visits.