Atrial fibrillation: Beyond "irregularly irregular"

Nursing, 2003 by Josephson, Linda, McMullen, Maureen

Learn to recognize and manage atrial fibrillation in its various forms.

ATRIAL FIBRILLATION (AF) is the most frequently encountered sustained arrhythmia found in clinical practice. Affecting about 2.2 million Americans, sustained AF becomes more prevalent as people age: Only 0.5% of those under age 60 develop AF, but 10% of those over age 80 do. Men are more likely to develop AF, but women are more likely to die of it.

Although it can have a profound effect on a patient's quality of life, AF is seldom life-threatening and can usually be controlled with medication. In this article, we'll look closely at what causes AF and how to treat it.

What causes AF?

Atrial fibrillation most often is associated with underlying cardiac disease. Cardiac damage may precede or cause AF; new-onset AF also complicates 10% to 15% of all acute myocardial infarctions.

According to the American College of Cardiology/ American Heart Association/European Society of Cardiology (ACC/AHA/ESC) practice guidelines, AF may be classified as follows:

* AF triggered by acute, temporary conditions, such as pericarditis, pulmonary embolism, or hyperthyroidism. When the condition is successfully treated, AF may resolve.

* "Zone AF" or AF without associated heart disease. Most people with this type of AF are under age 60, with no clinical or echocardiographic evidence of cardiopulmonary disease.

* AF associated with heart disease, such as coronary artery disease (CAD), valvular heart disease, hypertension, or left ventricular hypertrophy

* neurogenic AF, in which heightened vagal tone (vagal AF) or adrenergic tone (adrenergic AF) triggers AF in susceptible patients.

What happens during AF?

Classically described as an irregularly irregular cardiac rhythm with no detectable organized atrial activity, AF is characterized by uncoordinated atrial contractions (caused by multiple foci firing in the atria) with subsequent deterioration of atrial mechanical function.

Because no single impulse depolarizes the atria, fibrillatory waves replace the P wave on electrocardiogram. The R-R interval is irregular because only random impulses reach the AV node and result in ventricular depolarization. However, the QRS complex has a normal shape unless the patient has a preexisting bundle-branch block, aberrant ventricular conduction, or anomalous AV conduction.

The ACC/AHA/ESC practice guidelines recognize these patterns:

* Newly discovered AF describes a first-detected episode of AF, which may or may not be self-limited or symptomatic; the duration of episodes and the existence of previous undetected episodes may be unknown.

* Recurrent paroxysmal AF describes two or more episodes of AF that terminate spontaneously.

* Persistent AF describes AF that is sustained; this may be either the first presentation or the culmination of recurrent episodes of paroxysmal AF This type of AF includes cases of long-standing AF (AF longer than 1 year), in which cardioversion hasn't been attempted or indicated, usually leading to permanent AF

* Permanent AF occurs when sinus rhythm can't be sustained after cardioversion or when the patient and cardiologist have decided to allow AF to continue without further efforts to restore sinus rhythm.

Effects on the corthoc chambers

Atrial fibrillation produces electrophysiologic and physical changes in the atria, with recurrent episodes of AF eventually leading to sustained AE Dilation and blood stagnation in the left atrium encourage thrombus formation, which increases the risk of stroke.

Patients who are successfully

cardioverted electrically may experience decreased atrial mechanical function (atrial stunning) for several moments to several weeks. Atrial stunning seems to be the result of the arrhythmia, not the energy level used during cardioversion.

The effect of AF on the ventricles includes the loss of atrioventricular (AV) synchrony, an inappropriately rapid heart rate, and an irregular ventricular rhythm. Loss of AV synchrony means the atria can't contribute to the ventricular end-diastolic volume, decreasing stroke volume and cardiac output (CO).

Also, CO is decreased because of the irregularity of AF, which creates an entirely random R-R interval and continually changing diastolic filling time. Because the heart can pump out only the blood it receives, the changing diastolic period results in wide fluctuations (up to 15%) in stroke volume.

Patients also are at risk for developing tachycardia-associated myopathy

Watching for signs

The classic symptom of AF is palpitation, but for patients with persistent AF, breathlessness and poor exercise tolerance are more common. Patients with persistent AF are also apt to experience fatigue, lassitude, a feeling of general ill health, a decrease in mental acuity, poor concentration, irritability, and sleep disturbances.

Patients with paroxysmal AF, unlike those with a persistent pattern of AF, may feel well physically between episodes, unless their medications are causing adverse reactions. But the sudden, unpredictable nature of their arrhythmic episodes can have a serious psychological effect, causing feelings of helplessness and vulnerability.