In patients with Wolff-Parkinson-White (WPW) syndrome, an “accessory pathway,” which commonly has a short refractory period and is capable of rapid conduction, provides a direct electrophysiologic pathway from the atrium to the ventricles independently from the AV node. Lower ventricular response rates in unmedicated older patients suggest underlying conducting system disease. The typical ventricular heart rate in otherwise healthy patients with atrial fibrillation - in the absence of AV blocking drugs- is 150 ± 20 bpm. Physiological AV nodal refractoriness prevents more than half of the 400 to 600 atrial action potentials/minute generated during atrial fibrillation from conduction to the ventricles. Likewise, the larger the left atrium, the less likely that sinus rhythm can be maintained after cardioversion, especially without antiarrhythmic drugs. The larger the left atrium, the higher the risk for atrial fibrillation. Almost any cardiac condition associated with increased left atrial pressure and left atrial enlargement will increase the risk for atrial fibrillation, including left heart failure, chronic hypertension and mitral or aortic valvular heart disease. The exact mechanisms of this remodeling remain unclear. In patients with atrial fibrillation, atrial tissue remodels, showing pathologic changes of fibrosis and inflammation. Less commonly, the foci of atrial fibrillation can be within the right atrium rarely, they are in the superior vena cava or in the coronary sinus. These foci are commonly in the superior pulmonary veins this is an important factor in the electrophysiologic approach to atrial fibrillation, known as pulmonary vein isolation. Pathophysiology – Atrial FibrillationĪtrial fibrillation occurs when irritable foci cause rapid action potentials that result in an atrial heart rate between 400 and 600 beats per minute (bpm). “Recurrent” atrial fibrillation indicates that the patient has experienced two or more AF episodes. “Nonvalvular” does not imply a complete absence of valve disease, and can be used to describe AF in the context of mild mitral stenosis, mitral regurgitation, aortic stenosis, aortic regurgitation, and tricuspid regurgitation. The term “nonvalvular AF”, as used in the current ACC/AHA Atrial Fibrillation Guidelines, describes AF in the absence of moderate-to-severe mitral stenosis or a mechanical heart valve. Atrial fibrillation may also be classified as valvular or nonvalvular. The term “lone atrial fibrillation” is used when AF occurs in the absence of structural heart disease. The term “chronic atrial fibrillation” and the abbreviation “PAF” should be avoided. Permanent atrial fibrillation is present when atrial fibrillation is continuously present for more than 7 days, and there are no interventions planned to restore sinus rhythm. 2014 Hurst’s The Heart, 14th edition Chapter 83, 11a.) Longstanding persistent AF lasts for more than 12 months.(January CT, et al. The term persistent implies a rhythm control patient management strategy intended to return and maintain sinus rhythm. Persistent atrial fibrillation lasts for more than 7 days. By definition, paroxysmal atrial fibrillation lasts for less than 7 days (usually less than 24 hours) (Hurst’s The Heart, 14th edition Chapter 83, 11a) and does not require interventions such as electrical or chemical cardioversion to restore normal rhythm. Paroxysmal atrial fibrillation is self-limiting restoration of sinus rhythm occurs spontaneously. In addition, AF is associated with an increased risk for systemic thromboembolism and stroke.Ĭlinically, atrial fibrillation is classified as paroxysmal, persistent or permanent - the three Ps. Symptoms of atrial fibrillation reflect loss of atrial mechanical activity (atrial contraction) and rapid ventricular heart rates, both of which may reduce the ability to increase cardiac output and, particularly when AF occurs in the setting of other heart disease, may lead to congestive heart failure.
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