DISCUSSION

Atrial fibrillation is one of the most common arrhythmias seen in accident and emergency departments. It is most commonly attributable to medical disorders and usually occurs in the elderly population.^1–3 It is associated with detectable organic heart diseases in about 70% of patients and may also arise secondary to severe chest trauma.⁴ There are various reports in the literature regarding uncommon aetiologies of atrial fibrillation such as electrical injury, high protein diet, high alcohol intake, excessive exercise, electroconvulsive therapy, hypoglycemia, sigmoidoscopy, and dental extraction.^5–8 A patient with newly diagnosed atrial fibrillation warrants a full investigation of the aetiopathogenesis of this common arrhythmia because it may be associated with unusual pathology.⁹ It has been reported in the literature that cardiac rhythm disorders can occur after head injury as well as after cerebral stimulation.^10,11

There are various pathophysiological mechanisms that may cause atrial fibrillation. It may be attributable to morphological changes in the heart such as acute or chronic stretch or possible changes in the cellular electrophysiology.¹² It may also arise resulting from disorders of autonomic tone with several studies emphasising the importance of autonomic nervous system in the initiation and perpetuation of atrial fibrillation.¹

We considered the possibility of three causes for the atrial fibrillation in our patient such as paroxysmal atrial fibrillation attributable to an autonomic disorder, blunt chest trauma, and head injury with basal skull fracture.

Vagally mediated atrial fibrillation occurs more frequently in young healthy men. The age of onset is usually between 30–50 years and it occurs in subjects with normal heart where vagal influence predominates.¹³ Atrial fibrillation usually occurs at night, and reverts to normal sinus rhythm in the morning. It is not triggered by physical exertion and emotional stress. However, the relaxation that follows physical efforts or emotional stress is frequently associated with the onset of atrial fibrillation. This seems to be consistent with the occurrence of atrial fibrillation in our patient, but we ruled out this aetiology as the atrial fibrillation lasted for two days.

We considered the possibility that our patient might have fallen on his radio and sustained chest trauma, which would have caused the atrial fibrillation. However, there was no evidence of injury to the chest. Furthermore, the most common arrhythmias after myocardial contusion are sinus tachycardia, supraventricular tachycardia, atrial or ventricular premature contractions, conduction disorders, and non-specific ST segment and T wave changes.¹⁴ Atrial fibrillation after chest trauma is very rare and reported only in elderly patients. Large studies of patients with chest trauma or sternal fractures found no cases of isolated atrial fibrillation particularly in young patients.^15,16 It is theoretically possible that a heavy blow to the anterior chest, timed appropriately in the cardiac cycle, could propagate an ectopic impulse, precipitating an atrial or ventricular dysarrhythmia. However, its applicability to humans is unclear, as ectopic rhythms are distinctly less common in clinical practice.¹⁷ Therefore, it is not likely that atrial fibrillation in our patient was attributable to the chest trauma.

Recent research on the pathology of head injury has focused on the changes occurring at cellular level in the first few hours after head injury. Trauma is hypothesised to produce widespread depolarisation of neurons and excessive release of excitatory neurotransmitters, which cause excitotoxic effects on postsynaptic neurons.¹⁸ In experimental animal studies, Mauck et al noted that stimulation of the distal cut end of the right vagosympathetic trunk evoked bradycardia with hypotension, and in one instance, a brief run of atrial fibrillation. There were no other arrhythmias.¹¹ It has also been reported that sub-arachnoid haemorrhage causes a stress response with increased concentrations of plasma catecholamines and serious cardiac arrhythmias.¹⁹

Atrial fibrillation in young, healthy patients without pre-existing heart disease may account for up to one third of all cases.¹ It may be attributable to physiological stress of trauma such as hypovolaemia, acidosis, electrolyte imbalances, and excessive catecholamine release.¹⁷ Alcohol ingestion may promote atrial fibrillation by increasing catecholamine release or by increasing the vagal outflow because of the associated nausea and vomiting.²⁰ It may also be attributable to thyrotoxicosis and pneumonia.²¹ Idiopathic or lone atrial fibrillation may also be considered in younger patients with atrial fibrillation.²²

This case illustrates that atrial fibrillation may be detected in otherwise fit young patients with an isolated head injury and no other obvious precipitating factors. It is very important that full investigations are carried out to exclude other causes before atrial fibrillation is attributed to a head injury. However, it is not always possible to determine the exact cause of atrial fibrillation.

Contributors

PM initiated the idea, did the literature search, and wrote the paper. GO helped in the literature search and writing the paper. MS and DAE involved in the management of the patient and helped in writing the paper. PM acts as the guarantor of the paper.