Despite these seemingly stringent diagnostic criteria individual cardiologists seem to vary in their differentiation between RBBB and 'normal variant'. It is even possible to manufacture an 'intermittent diagnosis of RBBB by presenting subsequent ECGs to different cardiologists (3).

The aetiology of RBBB is usually considered as either congenital or acquired. A diagnosis of acquired RBBB can be made when the abnormality does not exist on a previous ECG. In the absence of a previous ECG further investigation may be necessary to identify likely causes of acquired RBBB. The congenital group of RBBB diagnoses include those with congenital cardiac defects as well as a group of idiopathic cases in whom the ECG finding is of no functional significance. The acquired group is predominated by those with atherosclerotic heart disease but includes other cardiac disease processes. A differential list of the main causes of RBBB should include the conditions outlined in Table 3.

To this end patients with RBBB are best divided into two groups. The first group are those without evidence of any associated cardiac disease, whether the RBBB is acquired or congenital. The second group are those patients with ECG changes of RBBB as well as other features of cardiac disease. The relevance of this selection method is that these two groups exhibit differing prognosis for incapacitating cardiac events. The decision as to which group a patient belongs in depends on further cardiac investigation which is outlined later.

The second group outlined, those with evidence of other cardiac defects such as past AMI, Ischaemic Heart Disease, or Myocarditis assume the cardiac incapacitation risk of the underlying disease. Therefore a patient with RBBB associated with features of IHD or AMI should be considered unfit to fly. This situation could be reviewed after satisfactory recovery from either coronary bypass surgery or the AMI. Once this recovery is complete consideration will need to be given to the type of flight planned and whether or not a 'fit to fly as or with a copilot' proviso should be made. Similarly a patient suffering from myocarditis is unfit to fly until the disease resolves. RBBB associated with a past history of myocarditis but no other cardiac abnormalities should in no way disqualify flying status. The other causative conditions mentioned should also be considered on their individual merits. Degenerative or destructive diseases of the cardiac conducting system such as a cardiomyopathy may be permanently disabling or a transient phenomenon. Cor pulmonale is virtually always associated with irreversible pulmonary disease in anyone of sufficient age to pilot an aircraft. Cor pulmonale, therefore, would almost universally disqualify from flying. Acute right ventricular strain is usually due to pulmonary embolism in the adult population and the patient with RBBB due to embollzation should be considered unfit to fly until the episode, and an underlying cause if identified, has completely resolved and he/she no longer takes any anticoagulant medication. The fitness to fly of a patient with RBBB subsequent to surgical ventriculotomy or trauma will depend on details of the trauma or underlying pathology.

While those with RBBB and concomitant cardiac disease assume the risk profile of the underlying disease those RBBB cases with no evidence of cardiac disease seem to exhibit no increased risk of incapacitating events (13). Studies have demonstrated that there is no increased risk of sudden death (14 15) or syncope (16) in those found, in adult life, to have congenital RBBB. Similarly the mortality ratio (17 18) is not thought to be increased in acquired RBBB in the absence of other cardiac defects, nor is the incidence of syncope or high grade atrioventricular block (19).

Once an ECG diagnosis of RBBB is made in an aviator or prospective aviator it becomes the medical examiner's responsibility to exclude, beyond reasonable doubt, underlying cardiac pathology that could lead to incapacitating events. The 'further investigations' performed would vary from practitioner to practitioner but would probably be selected from the following list (In approximate order of invasiveness)

While the USAF (20 21) recommends an intensive work-up including cardiac haemodynamic studies, angiography, and electrophysiological evaluation before clearing aircrew with RBBB for flying duties Rowlands (22) argues that there is little reliable return from these investigations in the absence of clinical evidence of cardiac disease. The investigations that I would order would depend on the patient's clinical details and the type of licence involved. An athletic 18 year old with no cardiac risk factors whatsoever and normal examination applying for a private pilots licence would probably prompt me to order a chest x-ray and a thallium scan/stress ECG. A 48 year old obese 747 captain who is still trying to give up smoking because his father died of a heart attack would cause me to order coronary angiography preceded by a stress ECG and/or thallium scan. A 35 year old 767 captain who was otherwise healthy probably also deserves angiography well as the stress test and/or thallium scan to exclude any underlying cardiac pathology.

In summary. Advances in cardiac investigation now allow medical practitioners to identify, in a reasonably reliable fashion, those patients with RBBB who have an increased risk of sudden incapacitation. If RBBB is identified and there are no clinical or investigative features of underlying cardiac disease there is no increased risk of incapacitation. These people should not be restricted in their aviation pursuits. If there is other cardiac pathology associated with the RBBB flying status will need to be reviewed with respect to the underlying disease.