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 Q    WHAT DOES SOMEONE WITH AN ARRHYTHMIA EXPERIENCE?

 A   Surprisingly, the symptoms of a heart rate that's too fast or too slow are very similar, because in both situations the end result is an insufficient amount of blood reaching the vital organs, such as the brain. In the slow (brady) arrhythmias, symptoms are dizziness, lightheadedness, feeling faint or actually fainting. People with very slow heart rates have trouble exercising and may feel fatigued or short of breath. If the heart actually stops or if the rate is too slow to sustain the vital organs, sudden death can result.

Fast (tachy) arrhythmias cause many of the same symptoms, because a very fast ventricular rate means the ventricles don't have time to fill with blood between beats and therefore can't pump enough blood through the body. People feel dizzy or lightheaded and can faint. They also generally feel the heart beating fast -- palpitations -- and may experience chest pain, a sign that the heart is beating so fast that it's demanding more blood than its arteries can supply. Like those with slow heart rates, people with very fast heart rates may also have difficulty with exercise. They may feel short of breath or fatigued.

 Q    CAN ARRHYTHMIAS BE TREATED?

 A   Yes. Medications, electronic devices and electrosurgery are the main treatments. Cardiac arrhythmias, particularly bradyarrhythmias due to conduction blocks, are among the most treatable of medical disorders.

 Q    HOW ARE TREATMENTS CHOSEN?

 A   In neuromuscular disorders, the first step is often to assess the cause of the abnormal heart rate or rhythm and determine whether or not the conduction system itself is the primary problem. A referral to a cardiologist is often part of the assessment process.

The doctor will listen to the heart with a stethoscope and probably order an EKG to see how the electrical system is behaving. The doctor may also request a special 24-hour EKG recording called Holter monitoring to see how the heart responds to different activities. More extensive studies can be done if needed.

The internist, pediatrician, cardiologist or neurologist needs to look at the "whole picture" in the person with an arrhythmia, particularly when neuromuscular disease is involved.

Respiratory status is a factor. If the person with the arrhythmia isn't breathing well because his respiratory muscles are weakening, this should be addressed, possibly with noninvasive assisted ventilation. (For more on assisted ventilation, see previous Quest stories Breathe Easy: Options Offered for Respiratory Care and A Breath of Fresh Air: Respiratory Care Can Improve Quality of Life, and the MDA pamphlet "Breathe Easy.")

General cardiac condition can affect conduction. If the patient is known to have a degenerating myocardium (cardiomyopathy), treatment for this condition may be the first step in controlling the arrhythmia.

Dietary factors, smoking and medications can play a role. Caffeine and tobacco can cause cardiac arrhythmias, particularly in people susceptible to them for other reasons, such as existing cardiac damage. Many medications, such as over-the-counter cold medicines containing pseudoephedrine and certain anti-depressants known as tricyclics, can also lead to arrhythmias. Ironically, many medications used to treat heart disease can themselves cause arrhythmias, so an early step in diagnosis and treatment may be to take a careful look at which medications the patient has been taking and either change medications or adjust dosages.

 Q    WHAT ARE THE COMMON TREATMENTS FOR ARRHYTHMIAS?

 A   Anti-arrhythmic medications are mostly for tachyarrhythmias. There are dozens of drugs today to specifically treat cardiac arrhythmias, mostly to treat the fast type. Unfortunately, when a patient also has cardiomyopathy, as people with neuromuscular disorders often do, most of these drugs can be dangerous and have to be used with extreme care, if at all.

Amiodarone (Cordarone), an anti-arrhythmic medication, has a good track record in people with neuromuscular disease who also have cardiomyopathy.

The medications chart below lists some of the anti-arrhythmics you may encounter. Most work by blocking ion channels and thereby changing the way sodium, calcium and potassium ions flow across cell membranes in the heart. These ion flow patterns determine the heart's rate and rhythm, but they themselves respond to many influences, notably chemicals secreted by the nervous system. Some anti-arrhythmics block these "upstream" chemical signals, while others act on the "downstream" ion channels, while still others act at both sites.

Anti-arrhythmics are divided into classes based on how they work. Digoxin (Lanoxin) isn't classed with the other anti-arrhythmic drugs. It's usually used to treat cardiomyopathy and heart failure, but it can also be used -- with caution -- as an anti-arrhythmic.

In addition to the anti-arrhythmic drugs, people with atrial standstill or atrial fibrillation or flutter (which occur in EDMD) need anti-coagulant (anti-clotting) medications to reduce the risk of clot formation and stroke. Doctors may use aspirin or, if that's not effective, warfarin (Coumadin, Panwarfin, Sofarin) for this purpose.

Electronic devices can be used for tachy- and bradyarrhythmias. Cardiac pacemakers were originally developed to treat bradyarrhythmias caused by failure of the SA node to pace the heart or failure of conduction through the heart.

Today, there are many kinds of pacemakers, including some that can correct tachyarrhythmias as well as brady- arrhythmias.

There are also devices known as implantable cardioverter-defibrillators (ICDs) which deliver a safe type of electric shock to stop a potentially lethal fast heart rhythm by "resetting" the heart's conduction system.

Modern technology allows all these therapies to be delivered via a single electronic device. In some situations, there's an advantage to implanting two separate devices.

Today's implantable electronic devices are about the size of a small pager and usually require only minor surgery at the time of insertion or battery changing (about every five years).

The "brain" of the pacemaker -- the pulse generator -- is usually placed in the chest area just under the skin (see "If You're Facing Pacing"). Attached to the pulse generator are one or more insulated wires that can sense the heart's electrical activity and modify it by delivering impulses. These impulses either supplement or override the patient's own heart rate and rhythm.

Minor surgery can remove small areas where cells are abnormal. Doctors can insert a catheter (very thin tube) into the heart via a blood vessel to destroy small areas of abnormal conduction tissue by burning, freezing or radio waves. This technique can sometimes be used when the precise area that's causing the arrhythmia has been identified. A pacemaker may be required afterward.

In rare instances, open-heart surgery can be used to accomplish the tissue destruction.

IF YOU'RE FACING PACING

Today's electronic cardiac pacing devices are extremely sophisticated and very dependable. Your doctor and the manufacturer will provide specific information about your device as well as any necessary precautions. You should always carry with you your medical information and the manufacturer's information about the device.

Most people find they feel much better with a pacemaker or pacemaker/ICD and are sometimes able to resume activities they had abandoned because of excessive fatigue or other symptoms.

Pacemakers and implantable cardioverter-defibrillators (ICDs) are usually placed in the chest, as shown in this X-ray photo of the Profile™ MD, an ICD made by St. Jude Medical Cardiac Rhythm Management Division, Sylmar, Calif. Photo courtesy of St. Jude Medical.

After you get your pacemaker, you'll need regular checkups, during which the doctor will "interrogate" the device using a special computer. He can reprogram it to match any changes in your condition.

Most people can work, exercise and have a normal sex life with a pacemaker or ICD. Microwave ovens, computers, portable telephones and most devices found in the average home and office pose no danger to the person with a modern device. Electric wheelchairs also pose no hazard. The metal in the implanted device may set off the sensor in security systems, so you'll have to show your ID card to get around this kind of problem. Cellular phones that can be used over long distances require some precautions, such as not holding the phone too close to the pacemaker.

Ironically, the most serious threats to safety for the pacemaker wearer come from medical equipment -- MRI scanners, transcutaneous electrical nerve stimulators used for pain control, therapeutic ultrasound equipment and the type of radiation used to treat tumors. Always tell your doctor, dentist or any other medical practitioner that you have a pacemaker or ICD. Ordinary X-rays are safe. In fact, the manufacturer of the implantable device usually designs it so that it can be clearly identified on an X-ray if other information isn't available.

Pacemakers and ICDs are "Y2K-safe"; they won't quit on Jan. 1, 2000.

To find out more about pacemakers and ICDs, check the Web sites of manufacturers. These include Medtronic (www.medtronic.com), St. Jude Medical (www.sjm.com) and Guidant (www.guidant.com).  

Consultants for this article were William Groh, a specialist in electrophysiology of the heart at Indiana University, Indianapolis; Stanley Goldberg, a pediatric cardiologist specializing in echocardiography at University of Arizona Medical Center, Tucson; and William Lewis, a specialist in heart failure at the University of California at Davis. Massimo Pandolfo, a neurologist at the University of Montreal, was a consultant on heart problems in Friedreich's ataxia. Louis Ptacek, a neurologist and geneticist at the University of Utah in Salt Lake City, was consulted about heart problems in ion channel disorders.

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