>The normal heart beats 60 to 100 times each minute. In well-trained athletes or even in select non-athletic individuals completely at rest, the heart may beat as slowly as 40 to 50 times each minute. Entirely healthy, normal individuals have occasional extra beats or minor changes in rhythm. These can be caused by drugs (caffeine), stress, or for no apparent reason. Dysrhythmias become serious only when they are prolonged or when they do not result in the desired mechanical contraction of the heart.
>Physiologically significant extra heartbeats may originate in the upper chambers of the heart (supraventricular tachycardia or atrial dysrhythmia) or in the lower chambers of the heart (ventricular tachycardia). The cause may be due to a short-circuit or an extra conduction pathway for the impulse or secondary to some other cardiac pathology. People who have episodes or periods of rapid heartbeat are at risk for losing consciousness during these events. There are also conditions where the person has a fairly stable dysrhythmia (e.g., fixed atrial fibrillation), but they usually have additional cardiovascular and other health problems that coincide with their rhythm disturbance. A slow heart rate or heart block may cause symptoms, too.
>Fitness and Diving Issue The more serious dysrhythmias, like ventricular tachycardia and many types of atrial rhythm disturbances, are incompatible with diving. The risk for any person developing a dysrhythmia during a dive is, of course, losing consciousness while underwater. Supraventricular tachycardias are unpredictable in onset and are often triggered by immersing the face in cold water. Someone who has had more than one episode of this type of dysrhythmia should not dive.
>An individual with any cardiac dysrhythmia needs a complete medical evaluation by a cardiologist prior to engaging in scuba diving. In some cases, thorough conduction (electrophysiologic) studies can identify an abnormal conduction pathway and the problem can be corrected. Recently, doctors and researchers have determined that people with some dysrhythmias (e.g., certain types of Wolff-Parkinson-White Syndrome) may safely participate in diving after a thorough evaluation by a cardiologist. Also, in select cases, some people with stable atrial dysrhythmias (e.g., uncomplicated atrial fibrillation) may dive safely if a cardiologist determines that there are no other significant health problems.
>Medication Used in Treatment
>Most dysrhythmias that require medication are medically disqualifying for safe diving. Exceptions may be made on a case-by-case basis in consultation with a cardiologist and diving medical officer.
>For more information on cardiovascular conditions, see the complete article by Dr. James L. Caruso on Cardiovascular Fitness and Diving from the July/August 1999 issue of Alert Diver.