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Atrial Fibrillation

Atrial fibrillation is the only common arrhythmia in which the ventricular rate is rapid and the rhythm very irregular. The atrial rate is 400–600 beats/min, but most impulses are blocked at the atrioventricular node. The ventricular response is completely irregular, ranging from 80 to 180 beats/min in the untreated state (see ECG). Because of the varying stroke volumes resulting from varying periods of diastolic filling, not all ventricular beats produce a palpable peripheral pulse. The difference between the apical rate and the pulse rate is the "pulse deficit"; this deficit is greater when the ventricular rate is high.

Atrial fibrillation is a disorder found in about 2.2 million Americans. During atrial fibrillation, the heart's two small upper chambers (the atria) quiver instead of beating effectively. Blood isn't pumped completely out of them, so it may pool and clot. Atrial fibrillation (AF), the most commonly encountered arrhythmia in clinical practice, is defined by the absence of coordinated atrial systole. The symptoms of atrial fibrillation may be treated with medications which slow the heart rate. Atrial Fibrillation is an important risk factor for stroke , the most feared complication of atrial fibrillation.

Atrial fibrillation itself is rarely life-threatening; however, it can have serious consequences if the ventricular rate is sufficiently rapid to precipitate hypotension, myocardial ischemia, or tachycardia-induced myocardial dysfunction. Although many patients—particularly older or inactive individuals—have relatively few symptoms if the rate is controlled, some patients are aware of the irregular rhythm and may experience it as very uncomfortable. Perhaps the most serious consequence of atrial fibrillation is the propensity for thrombus formation due to stasis in the atria (particularly the atrial appendages) and consequent embolization, most devastatingly to the cerebral circulation. Overall, the rate of stroke is approximately five events per 100 patient-years of follow-up.

The likelihood of developing atrial fibrillation increases with age. Three to five percent of people over 65 have atrial fibrillation. The heart and becomes lodged in an artery in the brain, a stroke results. About 15 percent of strokes occur in people with atrial fibrillation. Atrial Fibrillation may increase mortality up to 2-fold, primarily due to embolic stroke. This risk exists as the lack of coordinated atrial contraction leads to unusual fluid flow states through the atrium that are permissive for formation of thrombus that is then at risk to embolize. However, patients with significant obstructive valvular disease, chronic heart failure or left ventricular dysfunction, diabetes, hypertension, or age over 75 years and those with a history of prior embolic events are at substantially higher risk (up to nearly 20 events per 100 patient-years in patients with multiple risk factors). Patients with one or more of these risk factors for stroke should be treated with warfarin. Patients with none of these factors may be treated with aspirin if conditions are present that increase the risk of warfarin. Patients below the age of 60–65 years without any of these stroke risk factors ("lone atrial fibrillation") may be treated with aspirin or no antithrombotic therapy.

Refractory Atrial Fibrillation ( chronic ablation atrial fibrillation)

Because of trial results indicating that important adverse clinical outcomes (death, stroke, hemorrhage, heart failure) are no more common with rate control than rhythm control, atrial fibrillation should generally be considered refractory if it causes persistent symptoms or limits activity. This is much more likely in younger individuals and those who are very active or engage in strenuous exercise. Even in such individuals, two-drug or three-drug combinations of a -blocker, rate-slowing calcium blocker, and digoxin usually can prevent excessive ventricular rates, though in some cases they are associated with excessive bradycardia during sedentary periods. If rapid ventricular rates persist, amiodarone may be substituted for or added to these agents.

If no drug works, radiofrequency AV node ablation and permanent pacing ensure rate control and may facilitate a more physiologic rate response to activity. There is growing experience with focal ablation of foci in the pulmonary veins that initiate atrial fibrillation, following which sinus rhythm may be restored or maintained. A surgical approach called the Maze procedure can also be used to eliminate the multiple reentry circuits that cause atrial fibrillation, and implantable atrial defibrillators can be used to convert paroxysmal episodes. The role of these latter procedures is limited, however.

Cause of Atrial Fibrillation

Some of the causes not involving the heart include the following:

  • Alcohol use (holiday heart)
  • Pulmonary embolism (a blood clot in the lungs)
  • Pneumonia
  • Enlargement of the left ventricle walls (left ventricular hypertrophy)
  • Coronary heart disease (or coronary artery disease): This results from atherosclerosis, deposits of fatty material inside the arteries that cause blockage or narrowing of the arteries.
  • High blood pressure (hypertension)
  • Cardiomyopathy (disease of the heart muscle) leading to congestive heart failure
  • Hyperthyroidism
  • Hyperstimulation of the vagus nerve , usually by having large meals (" binge eating ")
  • Lung pathology (such as pneumonia , lung cancer , pulmonary embolism , Sarcoidosis )

Symptoms of Atrial Fibrillation

Some common symptoms follows :

  • Palpitations, which are sensations of a racing, uncomfortable, irregular heartbeat or a flopping in your chest
  • Weakness
  • Lightheadedness
  • Shortness of breath
  • Chest pain
  • Unpleasant palpitations or irregularity of the heart beat
  • Mild chest discomfort (sensation of tightness) or pain
  • A sense of the heart racing
  • Lightheadedness
  • Mild shortness of breath and fatigue that limit the ability to exercise

Treatment of Atrial Fibrillation

Treatment methods of Atrial Fibrillation:

  • The main goals of treatment of atrial fibrillation are to prevent temporary circulatory instability and to prevent stroke . Rate and rhythm control are principally used to achieve the former, while anticoagulation may be required to decrease the risk of the latter.
  • The early treatment of Atrial Fibrillation through either rate-control or rhythm-control can prevent this condition and thereby improve mortality and morbidity.
  • An underlying medical condition that caused the atrial fibrillation and that needs treatment itself.
  • When patients are cardioverted from atrial fibrillation to a normal sinus rhythm.
  • Patients who may be safer in a hospital while medications are started.
  • Other treatment options For patients with intermittent or chronic atrial fibrillation, there are two long-term treatment options: rhythm control and rate control. Two large clinical trials have addressed the effectiveness and safety of these two approaches. Before discussing these trials, it is useful to review the meaning of rhythm control and rate control and both the benefits and risks of long-term warfarin therapy.

 


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