Comprehensive information about diving and undersea medicine for the non-medical diver, the non-diving physician and the specialist.
material should be copied and taken to your physician for his review.
This material should not be used as a basis for treatment decisions,
and is not a substitute for professional consultation and/or
peer-reviewed medical literature.
CONDUCTION ABNORMALITIES AND PACEMAKERS
Patients with conduction system abnormalities normally demonstrate evidence of cardiac disease as the cause of these abnormalities. Congenital heart disease, certain valvular heart diseases (aortic stenosis with valvular and A-V ring calcification), cardiomyopathy, and coronary heart disease all may be associated with chronic conduction system abnormalities. Most patients with acquired complete heart block, are limited in their capacity to exercise because of inability to increase cardiac output. Patients with acquired complete heart block should be treated along standard clinical lines, and most commonly a permanent pacemaker is implanted to provide adequate cardiac output and heart rate.
Patients with EKG abnormalities (short P-R intervals, with and without QRS abnormalities) may develop rapid heart rate (tachycardia) at rest or during exercise. However, many patients with short P-R intervals are asymptomatic. The finding of a short P-R on the electrocardiogram is not in itself a contraindication to diving. Patients with a history of paroxysmal tachycardia (PAT) should be evaluated for the presence of the pre-excitation syndrome; if recurrent paroxysmal or exercise induced tachycardia is a significant symptom, then appropriate diagnostic and therapeutic procedures should be followed. Exercise syncope may be induced by rapid heart rate syndromes (tachyarrhythmias), and evaluation of the electrocardiogram during exercise will aid in this diagnosis.
Symptomatic Wolf Parkinson White syndrome (an EKG diagnosis) is a contraindication to diving. People with asymptomatic W-P-W syndrome usually are at low risk for arrhythmias and could be certified to dive if there is no exercise syncope with treadmill testing. Catheter ablation of this condition is curative and the person can usually dive afterwards.
Diver candidates with pacemakers should not be permitted into commercial, military or scientific diving. Sport diving must be individualized. If no other heart disease is present, and the pacemaker is tested against pressure up to 130 FSW and exercise tolerance is good (13 METS), then the candidate should be allowed to dive.
Cardiac pacemakers are used to regulate a person's pulse rate (both too slow and too fast). It is implanted in the person's subcutaneous tissue and will be exposed to the same ambient pressures as the diver. For most recreational diving, an adequate pacemaker must be rated to perform at least a maximum depth of 130 feet/40 meters and must operate satisfactorily during conditions of wide pressure changes - as during ascent and descent.
A permanent pacemaker is implanted to provide adequate cardiac output and heart rate. Patients with conduction system abnormalities normally demonstrate evidence of cardiac disease as the cause of these abnormalities. Congenital heart disease, certain valvular heart diseases (aortic stenosis with valvular and AV-ring calcification), cardiomyopathy and coronary heart disease all may be associated with chronic conduction system abnormalities.
In the final analysis the diver's physician should be the final arbiter -- making his decision on the basis of firsthand and bedside information from the patient.
CARDIAC ARRHYTHMIAS (Irregular heart beats)
Patients with or without heart disease may develop a variety of arrhythmias during diving. The importance of the arrhythmia varies depending on the type and on the patient's history. Most arrhythmias are not serious and will have no effect on the diver. Serious arrhythmias are a contraindication to diving.
Premature atrial beats, supraventricular tachycardia, and atrial fibrillation may be associated with diving. Episodic supraventricular tachycardia and atrial fibrillation in the young adult population is usually associated with a normal heart ; however, in the presence of these arrhythmias, one should carefully evaluate the individual to rule out mitral stenosis, hyperthyroidism, and hypertension. Rarely, pulmonary emboli may produce atrial arrhythmias in this asymptomatic population, and this diagnosis should also be considered.
Generally, premature atrial contractions are of no consequence and are found frequently in normal persons. Often stress, alcohol, and caffeine alone or in combination are the cause of supraventricular arrhythmias. In the absence of organic heart disease, and when removal of these stimuli abolishes the arrhythmia, diving can be permitted. In normal individuals, therapy for the arrhythmia may produce more troublesome symptoms than the arrhythmia itself. Thus, care in selection of both therapy and the patient requiring therapy is necessary. After ruling out significant cardiac disease or systematic illness such as hyperthyroidism or hypertension, and evaluation for ingestion of cardiac excitatory agents such as caffeine (coffee, cola drinks, and various combination over-the-counter analgesics), catecholamine-like drugs such as those found in anti-allergy medications, alcohol, and nicotine, prevention of episodic tachycardia can be accomplished with digitalis.
Ventricular arrhythmias manifested as isolated premature ventricular contractions are found in normal individuals in the absence of heart disease, and for diver candidates these should be assessed for their behavior during exercise. Normally, premature contractions which demonstrate a multi-focal pattern, R on T phenomenon, or frequent coupling of sequential premature beats should be considered as serious, and should disqualify the diving candidate.
Well-conditioned candidates may have augmented vagal tone and a resting bradycardia. Often vagal tone may be so high that resting heart rates in the 30's and 40's are present. These are normally well tolerated because of the appropriately increased stroke volume, and normally, athletes do not show significant symptoms because of the bradycardia. Variants of vagotonic rhythms include first degree heart block, and Wenckebach type second degree heart block. Although these rhythms are often benign in a well trained candidate, a test with exercise to abolish the rhythm should be done prior to approval for diving. Failure of these changes to reverse with exercise should raise suspicion of organic heart disease and diving should not be approved.
Diving bradycardia (very slow heart rate) is a unique vagotonic response (astimulus of the vagus nerve) to water immersion which can result in heart rates of 40 - 50/min. in some divers. Rarely a diving candidate will demonstrate profound bradycardia and fainting (syncope) with all exposures to water immersion. There appear to be hypervagotonic syndromes and can be treated with anticholinergic medication (atropine-like medicines). This rare but profound response is a contraindication to diving.