Description, Atrial Fibrillation
Atrial fibrillation is characterized by a total disorganization of atrial activity without effective atrial contractions. The atrial rate is generally very fast (300-600 beats per minute), but not all impulses are conducted to the ventricles (they are blocked by the AV node). It is often described as an irregular, irregular (yes, two irregulars) rhythm in that generally, no two consecutive beats are at the same rate. The baseline or space between heart beats often has an irregular appearance to it which is actually the rapid, irregular contractions of the atria.
Atrial fibrillation is relatively common, occurring in up to .5% of the population or 1 out of every 200 people.
Controlled Atrial Fibrillation
The above example shows a well controlled atrial fibrillation with the rate varying from 50-95 beats per minute with an effective average (usually referred to as MVR or minute ventricular rate) of 75 beats per minute. This example and the one below it also show modest ST depression of approximately 2 mm.
Slow Atrial Fibrillation
The example immediately above is the same patient, but now the rate is varying from 26-45 beats per minute with an effective average (also referred to as minute ventricular rate or MVR) of 38 beats per minute.
Rapid Atrial Fibrillation
The above example shows a different patient with a rate varying from 112-250 beats per minute with an effective average rate of 160 beats per minute and some ST depression.
Atrial fibrillation may be either paroxysmal (of sudden onset) and last from a few minutes to many hours, or chronic, when the patient is persistently in atrial fibrillation. Chronic atrial fibrillation is almost always associated with underlying heart disease.
Patients will describe this rhythm variously as palpitations, flutters, rapid rate or irregular rate. A number of treatment options exist. If the patient is in an intermittent atrial fibrillation and if it is rapid and causing symptoms, medications may be used to try to convert the rhythm to normal sinus rhythm or a cardioversion (electric shock to the heart, applied under sedation) may be used. If the rate is slower, the doctor may wait to see if it converts back to a normal sinus rhythm on its own.
For patients with chronic atrial fibrillation, the goal is to control the rate so the effective average is between 50 and 100 beats per minute. This is accomplished through the use of various medications. The first example shows a properly controlled atrial fibrillation. The second example shows a rate which is too slow which was corrected by revising the patient’s medication. Patients with chronic atrial fibrillation are also generally required to take a blood thinner to reduce the risk of clots occurring in the atrium which could cause a stroke.
Newer procedures called ablations are also available to correct atrial fibrillation. In some cases, pacemakers may also be indicated if the physician decides to block the impulses from the atrium from reaching the ventricles if the effective rate is too fast and other options have proven ineffective.
Description, Atrial Flutter
Atrial flutter is a rhythm closely related to atrial fibrillation. Patients may often have both rhythms at different times or may have a rhythm called fibrillation/flutter when the rhythm has characteristics of both or switches back and forth between them. The distinguishing characteristic of atrial flutter is that the P waves are replaced by what are called F waves (flutter waves, which will often appear as a saw tooth waveform as shown in the example below).
The atrial rate in atrial flutter is regular, but fast, ranging from 150-400 beats per minute. As in atrial fibrillation, only some of the impulses reach the ventricles as the rest are blocked by the AV node. In the above example, variously either 1 out of every 3 or 1 out of every 4 Flutter waves reach and cause the ventricles to contract. In the above example, the atrial rate is approximately 215 beats per minute and the ventricular rate varies from 56-72 beats per minute. Treatment options for atrial flutter are essentially the same as for atrial fibrillation.