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Cardiac arrhythmia is defined in Taber's Cyclopedic Medical Dictionary as "Irregular heart action caused by physiological or pathological disturbances in the discharge of cardiac impulses from the sinoatrial node or their transmission through conductive tissue of the heart."25 Cardiac arrhythmias (Table 6–2) can be a result of many different etiologies from severe electrolyte imbalances to hypertrophic cardiomyopathy and various other disease processes.17
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Cardiac arrhythmias are not considered highly prevalent in the general population because only about 0.4 percent of people, mostly white men, experience atrial fibrillation.7 This percentage increases slightly in older populations. Often the medications do not repair or correct the problem or disease process that is occurring in the abnormal heart, but instead control arrhythmias and assist the heart in maintaining a natural rhythm. In recent years, physicians have also controlled cardiac arrhythmias with device-based techniques such as implantable pacemakers or defibrillators.8 For the athletic trainer, it would be wise to understand the implications of both treatment options because athletes with arrhythmias may present to the athletic trainer with either of these treatment plans.
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Interestingly, arrhythmias may be present and then disappear for unknown reasons.26 This phenomenon can certainly cause problems for the active athlete and the healthcare provider. Arrhythmias can result in syncope, which can be fatal in certain sports such as diving, downhill skiing, and gymnastics. For athletes participating in sports in which a sudden loss of consciousness can result in death, closely monitored drug therapy becomes more significant. Additionally, certain illegal drugs such as cocaine can also cause arrhythmias and result in death, as in the case of in Maryland basketball player and Boston Celtic draftee Len Bias.
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Zipes recommends that all athletes with a diagnosed arrhythmia who are deemed fit to participate in athletics should be reevaluated after they have participated in a conditioning program for their sport to determine if any conditioning effects are noted in the athlete's arrhythmia.26 Athletic trainers should also be vigilant in encouraging the athlete to maintain compliance in taking their prescribed medication. Too often athletes think that they are feeling better or want to reduce an adverse effect of a drug by discontinuing its use, leading to potentially lethal consequences.
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To understand which drugs are used in differing situations, a basic understanding of the different types of cardiac arrhythmias is necessary. Some of these are benign changes in cardiac rhythm requiring no treatment. Others are life threatening.
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Irregular heart rhythms are common in the developing hearts of children and adolescents. Sinus arrhythmia, the most common type, produces changes in heart rate with normal respiration. It requires no treatment.
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Irregular beats can occur in the atria or atrioventricular junction (premature atrial contraction [PACs]) or supraventricular premature beats) or from the ventricle (PVCs). The diagnosis of these rhythms cannot be made by simple auscultation; it requires an electrocardiogram.
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Premature atrial contractions are usually of little hemodynamic significance and often resolve spontaneously or require no treatment. Occasionally they become more common with caffeine or sympathomimetic medications (e.g, cold-care preparations). Rarely are they associated with structural heart abnormalities. At times, irregular atrial rhythms such as atrial flutter or atrial fibrillation occur in older individuals and may require treatment.
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Abnormal rhythms in the ventricles are also common. Some medication treatments may actually worsen ventricular ectopy. Premature ventricular contractions increase with age and may be benign in several instances: (1) isolated contractions, (2) when they are uniform and associated with a normal corrected QT interval, (3) when the cardiac physical examination is normal, (4) when the family history is negative for sudden cardiac death, and (5) when they disappear with exercise.11 A person may feel the heart pound or beat when these extra beats occur. This sensation does not worsen the prognosis, and reassurance can be given.
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Implications for Activity
Athletes with arrhythmias who have been cleared for athletic participation could still have complications. The use of medications to control the arrhythmia must be taken in the proper dosages, at the correct time(s), and will produce some adverse effects. Additionally, the athlete may be taking other over-the-counter (OTC) drugs or supplements that could affect the overall efficacy of the anti-arrhythmic drug. This could lead to complications or even death if not monitored by the treating physician. Athletic trainers should also be vigilant in encouraging athletes to maintain compliance in taking their prescribed medication.
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If the rhythm is determined to be significant by cardiac evaluation and appropriate studies, the cardiologist may recommend antiarrhythmic medication.
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The drugs discussed in this chapter as being indicated for cardiac arrhythmias often do not repair cardiac tissue that has fallen into a diseased state, but instead alter the dysfunctional rhythm and allow the heart an improved functional capacity. The medications prescribed for arrhythmia are divided into four basic classifications.
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The sodium channel-blocking drugs are typically divided into three subclassifications. However, for the athletic trainer, it is more important to understand the mechanism of action of this entire classification rather than the technical aspects of how each subclass alters the heart rhythm. The sodium channel blockers inhibit sodium channel activity, which, in turn, retards cell membrane excitability. For a more detailed explanation of the Class I arrhythmic medications, one can read Ciccone or Smith and Reynard.4,22
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Beta-adrenergic blocking agents make up this class of drugs that work to control arrhythmias by antagonizing the stimulation of the heart via the sympathetic system. The beta blockers were the first antiarrhythmic drugs produced to assist people with tachycardia. Originally, when cardiac responses were determined, they were divided into the "alpha effects," which were excitatory in nature, and the "beta effects," which were inhibitory in nature. The beta blockers come by their name because of their inhibitory role in the control of arrhythmias.
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The mechanism of action of these drugs is not clear, but it may involve potassium and sodium exchange. In any event, they stabilize cell membrane excitability to control heart rhythm.
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Beta blockers have been used as performance-enhancing aids to control heart rhythm, breathing, and muscular movement in biathlons, riflery, archery, shooting, and synchronized swimming. These agents are banned as performance aids, and the athlete must be aware of the regulations of the relevant sports organizations' governing bodies.
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When athletes use beta blockers, they must understand that they may have difficulty in achieving their maximal heart rate. This can affect performance and endurance. Athletes who take beta blockers need to understand the ramifications of reducing their maximum heart rate, which is what happens when they take these drugs as prescribed. Beta blockers do not allow the athlete's heart rate to reach maximum, so the athlete must use a perceived exertion protocol (such as that utilized in the graded treadmill test in exercise physiology laboratories.)
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The drugs in this classification direct their effect by delaying repolarization. They do this by blocking the potassium channels of the cardiac muscle. These drugs may also have an effect on the sympathetic control of the heart rhythm.
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The drugs in this classification control heart rhythm by slowing the calcium activity of the sinus and atrioventricular (AV) nodes. These drugs slow conduction velocity, mainly at the AV node, and thus slow the heart rate.
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The recognized and expected adverse effects of this class of drugs are lethargy, fatigue, bradycardia, hypotension (orthostatic), and sometimes a feeling of cold in the extremities. Some people experience additional adverse effects such as rashes, pruritus, headache, nausea, diarrhea, swelling, behavioral disturbances, disorientation, and other problems. If the athlete is experiencing any of these additional adverse effects, he or she should consult his or her physician immediately. Despite their purpose—reducing arrhythmia— one of the most common adverse effects of the anti arrhythmic drugs is an increase in rhythm disturbances. Because they work to control a single type of arrhythmic activity, these drugs can result in other types of cardiac arrhythmias.8
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Antiarrhythmic Drug Interactions
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It appears that there are numerous drug interactions involving antiarrhythmic drugs, and the physician should discuss with the athlete and athletic trainer any drug interactions that can occur. We have organized a short table of drug interactions (Table 6–3) so that the athletic trainer can get an idea of the interaction possibilities with this class of drugs.
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Pacemakers were first implanted in 1958 and since that time have undergone dramatic improvements in design and function. Implantable cardioverter defibrillators (ICDs) were first used in 1980 to control life-threatening ventricular arrhythmias. These, too, have progressed in design and function since inception. In recent years a number of clinical trials were completed demonstrating the effectiveness of both types of devices for control of cardiac arrhythmias.2,10,21 The athletic trainer should be aware of the types of device therapy available to control cardiac arrhythmias and any precautions to follow to make sure that the athlete is safe as he or she participates in a sport.
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The purposes of these devices are to detect the heart rhythm and treat abnormalities. They can be set to treat bradycardia, tachycardia, or ventricular fibrillation by either pacing or synchronized cardioversion.9 Implantation can be performed transvenously and no longer requires hospitalization or open-heart surgery. The use of ICDs to prevent sudden cardiac death is currently being evaluated.16
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The ICD is not a common treatment in competitive athletics. In the rare case when an athlete requires an ICD, clearance for participation should be given by the prescribing cardiac electrophysiologist. The athletic trainer will want to discuss with the athlete's physician any special precautions or arrangements that should be made to ensure the safety of the athlete.