Atrial fibrillation is a supraventricular arrhythmia characterized by rapid and disordered depolarization of the atria, where integrated atrial contraction disappears and is replaced by irregular fibrillary atrial muscle twitching. In atrial fibrillation, there is accompanying irregular rapid ventricular contraction, and although paroxysms may occur, yet, mostly atrial fibrillation (AF) becomes a permanent condition (Scott, 1973). AF is the most prevalent arrhythmia seen in clinical practice. Its frequency increases with age and characteristically there is continuous and irregular activity of the ECG baseline caused by rich electrical currents in the atria. According to population-based studies, its prevalence is 5% among individuals 65 or older. Common causes and associated conditions include hypertension, cardiomyopathy, valvular heart disease (especially mitral stenosis), sick sinus syndrome, Wolff-Parkinson-White syndrome (especially in young patients), alcohol use (holiday heart), and thyrotoxicosis.
Atrial fibrillation has a distinct focal source or trigger. These focal points are in the cardiac muscle in the proximal parts of the pulmonary veins. Atrial fibrillation must be differentiated from atrial flutter (uniform flutter waves) and multifocal atrial tachycardia (isoelectric interval between premature atrial contractions that have three or more different morphologic forms). Patients with AF face risks of stroke and heart failure, and the dwindled quality of life because of either AF symptoms like fatigability and palpitations or the often associated cardiovascular diseases like hypertension, heart failure, or valvular disease (Habermann and Ghosh 2008).
Epidemiology of atrial fibrillation
Atrial fibrillation has been recognized as a distinct rhythm since the beginning of the 20th century. In clinical practice, AF is the most common suffered arrhythmia met, yet it remains one of the greatest challenges in heart rhythm disorders. Based on epidemiologic data; nearly 1% of individuals older than 60 years suffer from AF, increasing to more than 5% of individuals aged 65 to 70 years, with the rate of newly diagnosed AF nearly doubling with each decade (Go As et al 2001). Overall, one in four men and women after age 40 develop AF, falling only slightly to one in six in individuals without prior history of cardiac disease such as myocardial infarction (MI) or congestive heart failure (Llyod-Jones et al, 2004). Data from the Rochester Epidemiology Project are consistent with these findings. Further, data point to a significant increase in the age-adjusted prevalence of AF in patients with ischemic stroke when compared with age- and gender-matched controls and was observed both in males and females (Tsang et al 2003). In the United States this translates nearly to 2.3 million people affected by AF, a figure projected to increase to around 3.3 million by 2010 and 5.6 million by 2050. Added to this, the proportion of patients with AF older than 80 years is expected to exceed 50% by 2050 (Kannel and Benjamin 2008).
From the previous discussion, AF may represent a growing epidemic considering a possible underestimation of the prevalence of AF since nearly one third of episodes are asymptomatic. In the Canadian Registry of AF, 21% of patients with newly diagnosed AF were asymptomatic. Further, among untreated patients, asymptomatic episodes of AF are much more common than symptomatic episodes. Besides, in around one fifth of patients, asymptomatic episodes are documented before the onset of symptoms. Further evidence comes from analysis of data gained from permanent pacemaker interrogation, where in patients with a history of atrial fibrillation, up to one in six have silent episodes lasting 48 hours or more (Friberg et al 2003).
Atrial fibrillation also accounts for more than one third of arrhythmia-related hospitalizations in the United States, with more than 2 million hospital admissions in the U.S. over a 5-year period. Added to this is the frequent need for hospitalization, and emergency room visits, in particular, for direct current cardioversion and initiation of antiarrhythmic drug therapy complications as well as episodes of congestive heart failure exacerbation because of inadequately controlled AF. Based on the need for cardioversion, drug therapy, and anticoagulation, the estimated annual cost of treating patients with AF is around 22% higher than for patients without AF. This continues for several years after initial hospitalization. Thus, management of patients with AF imposes significant and continued socioeconomic burden (Khairallah 2004). In 2006, Heeringa et al conducted a retrospective study of a European population, which confirmed the mentioned figures pointing to the lifetime risks to develop AF was similar in European data to North American epidemiological data.
Etiology of atrial fibrillation
The frequency of AF in the population, its occurrence in those with and without cardiac disease, and its strong association with age suggest that there are many etiologies for this arrhythmia, which may share a common pathology and pathophysiology. Table 1 (see appendix) summarizes the etiological and risk factors that predispose to AF (Fuster et al 2006).
AF is associated with almost any type of underlying heart disease that causes changes of the atrial myocardium, including distention, inflammation, hypertrophy, ischemia, fibrosis, and infiltration. Additionally, there are normal age-related changes of the myocardium, including amyloid deposits and fibrosis, perhaps accounting for the increased incidence of AF in the elderly. Parasympathetic or sympathetic nervous system inputs alter atrial electrophysiological properties and can provoke AF. Systemic infections, pulmonary disease and infections, pulmonary embolism, hyperthyroidism, and certain toxins or metabolic abnormalities may promote AF even in the absence of underlying atrial disease. In up to 15% of cases, there is no structural heart disease and no identifiable cause for the arrhythmia; this has been termed lone AF. Several autopsy studies have reported that the most common cardiac diseases associated with AF are coronary artery disease with or without a prior myocardial infarction, rheumatic heart disease, and hypertensive heart disease. However, clinical observation has emphasized that when AF occurs in those with coronary artery disease, left ventricular dysfunction or heart failure is usually present. Currently the most common underlying abnormalities associated with either intermittent or permanent AF are hypertensive heart disease, which increased the risk of AF almost 5-fold and 9-fold in men and women, respectively. Heart failure of any etiology increases the risk by over 4-fold and 14-fold in men and women, respectively (Kowey and Naccarelli 2005). Thus, for the case at hand a diagnosis priority should focus on the coexistence of hypertension, ischaemic heart disease, or heart failure. Other causes should also be looked because understanding of the interrelationship of etiological factors and the disease presentation and possible progression helps in tailoring an effective management plan (Conen et al 2009).
