In the context of suspected AF, a thorough cardiovascular examination is necessary. Past medical history of cardiac disease as well as non-cardiac conditions (e.g.Presence of pre-existing cardiac disease.Other important areas to cover in the history include: For this reason, it is essential that patients presenting with symptoms or signs of a TIA or stroke are also asked about the features of AF. It is also important to remember that a transient ischaemic attack or stroke can be the presenting feature of AF. Syncope: due to bradycardia, particular in paroxysmal AF when sinus rhythm is restored because the SAN can take a few seconds to wake up.Increasingly, AF is identified via patient-initiated monitoring (e.g. In some patients, AF can be asymptomatic, even when causing tachycardia and therefore may be an incidental finding during a clinical examination or when performing a 12-lead electrocardiogram (ECG). chronic kidney disease and obstructive sleep apnoea)Ĭaffeine intake is not typically a risk factor although it is often blamed for palpitations. hypokalaemia or hyponatraemia)Īs well as the causes of AF discussed above, the following risk factors are associated with an increased likelihood of developing AF: 2,4 Non-cardiac causes of atrial fibrillation Other causes of AF can be split into cardiac and non-cardiac causes. It is important to address these conditions/risk factors to improve prognosis and maintenance of sinus rhythm if a rhythm control strategy is intended. Typically, the mechanism is that they cause the atria to stretch. Numerous conditions/risk factors can increase the substrate and or triggers for AF. The consequence of this is blood stasis within the atria which increases the chance of thrombosis (Virchow’s triad) and subsequently embolic complications including transient ischaemic attacks (TIA), stroke and systemic embolisation. The presence of chaotic electrical activity within the atria also results in ineffective atrial contraction. Young patients with slick AV nodes are often very symptomatic and tachycardic. In AF, the ventricular rate is very variable and depends on the speed of AVN conduction. The resulting chaotic electrical activity is intermittently conducted through the AVN which gives rise to the characteristic irregularly irregular ventricular rate seen in AF. AF begets AF as AF causes the atria to dilate and increases AF substrate. The combination of trigger and substrate leads to an increased likelihood that an atrial ectopic triggers AF and the atria sustain it. 2 Atrial ectopics from the pulmonary veins trigger micro re-entry circuits in the atria causing chaotic electrical activity and sustained AF.Ĭonditions including hypertension or mitral regurgitation cause the atria to stretch which changes their electrical properties increasing the substrate for AF. The arrhythmia often originates from left atrial myocytes which extend as sleeves around the pulmonary veins. Pathophysiology of atrial fibrillationĪF is a type of supraventricular cardiac arrhythmia meaning the origin of the arrhythmia arises from above the ventricles. 3įor more information, see the Geeky Medics guide to the cardiac conduction system. The electrical conduction system of the heart. The AVN briefly delays the impulse which then travels through the Bundle of His, down the left and right bundle branches and finally to the Purkinje fibres resulting in ventricular contraction. The electrical impulses travel through the atria causing atrial contraction and to the atrioventricular node (AVN) which lies between the atria and ventricles. The sympathetic branch of the nervous system increases the rate of impulse generation from the SAN whereas the parasympathetic branch decreases the rate of impulse generation. The rate at which these impulses are generated is under the influence of the autonomic nervous system. You might also be interested in our medical flashcard collection which contains over 1000 flashcards that cover key medical topics.īefore understanding the pathophysiology of AF, it is important to understand the normal cardiac conduction system.Ĭardiac electrical impulses are first generated in the sinoatrial node (SAN) which is found in the right atrium.

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