The decision on fitness to dive when individuals have a history of cardiac arrhythmia (or evidence which suggests predisposition to such arrhythmias, e.g. Wolff-Parkinson-White or long QT syndromes) must take account of the nature of the arrhythmia (e.g. rate, site of origin, probability of degeneration into a more serious arrhythmia), the frequency and effects of attacks, the presence of associated or causative cardiovascular or non-cardiac diseases, the treatment used and the success of treatment. It is not possible to define every possible circumstance, but these guidelines are intended to cover the most common situations.
Permission to dive will usually be refused if an applicant has either serious underlying cardiac disease (e.g. ischaemic heart disease or cardiomyopathy), or arrhythmias are associated with symptoms which would prove hazardous if they occurred underwater (e.g. syncope, dizziness, dyspnoea, or angina).
Permission to dive will usually be granted when an individual has no evidence of structural cardiac disease but has a history of arrhythmias which are unlikely to cause incapacity in the water, because they do not cause serious symptoms when on land. However permission to dive will usually be accompanied by restrictions on depths and dive times to no-stop diving, so that the diver is always able to make a direct ascent to the surface without risk of being forced to make prolonged decompression stops while suffering the arrhythmia. Restriction to diving only with experienced companions will be a usual requirement.
There are a number of other considerations:
Whether congenital heart disease or valvular disease will disqualify will depend on the severity and nature of the abnormality (see also medical standard on intracardiac shunts).
A history of implantation of cardiac pacemakers, anticoagulation, prosthetic cardiac valves, myocardial revascularisation and myocardial infarction may influence fitness to dive (see respective medical standards)
Underlying metabolic or endocrine abnormalities (e.g. thyrotoxicosis causing paroxysmal atrial fibrillation) should be corrected prior to diving.
The choice of anti-arrhythmic drug may influence fitness (e.g. if b-blockers cause bronchoconstriction their use will constitute a contraindication to diving).
Investigations should be performed in an individual with the Wolff-Parkinson-White syndrome to ensure that the refractory period of the accessory pathway is sufficiently great to prevent degeneration of atrial fibrillation into ventricular fibrillation.
Supraventricular and ventricular ectopic beats will usually be allowed. The exception is when the ectopic beats occur so frequently that symptoms such as dizziness are produced.