Atrial fibrillation, or AF, is an abnormal rhythm caused by the rapid firing of multiple cells in the atria, the upper chambers of the heart, which cause the atria to quiver ineffectively. Normally, the SA note in the right atrium initiates the electrical signal that induces the atria to contract, forcing blood through the upper chambers to the ventricles. The electrical signal is propagated through the atria to the AV node. At the AV node and beyond into the ventricles, the electrical impulse signals the ventricles to contract, and blood is pumped out of the ventricles to the body. In atrial fibrillation, the rapid and chaotic firing of multiple cells in the atria bombards the AV node with impulses, only some of which get through to signal the ventricles to contract. Thus the atrial rate is much faster than the ventricular rate. Most patients remain conscious when they go into AF, and many do not even know they are in an abnormal rhythm. Some patients are in AF for a long time before the rhythm is discovered.
When treating a stable AF patient, you should not be lulled into complacency. You may find that the rhythm changes on its own, becomes much faster, or causes the patient to have serious symptoms as a consequence of the rhythm. Many hospitals have protocols for the treatment of stable AF, and not all AF is treated in the same way. In some older patients or patients who have had open-heart surgery, the rhythm is dealt with as a natural consequence. In these cases, long-term treatment usually consists of anticoagulation and rate-lowering medications. With younger patients, cardioversion and ablation may be possibilities to consider.
Assessment and Monitoring
Upon assessment of a stable patient, you will certainly be able to hear an irregular heartbeat. It will sound irregularly irregular. The patient may complain of palpitations, dizziness, lightheadedness, or feeling faint, especially upon exertion. Any of these are a sign that you need to keep a close eye on the patient for signs of instability. Patients with this rhythm should have constant cardiac monitoring, whether hardwired or telemetry. It is important to keep track of the rate and rhythm, observing for increases in rate or a change in rhythm, as well as a change in patient symptoms. Chest pain, shortness of breath and/or signs of poor perfusion should be viewed as signs that the patient is becoming unstable and may require acute intervention.
On the monitor, you will see irregularly irregular QRS complexes. The baseline will appear wavy and chaotic, representing multiple P waves that number far greater than the number of QRS complexes. When the heart rate is greater than 100 beats per minute, this is referred to as an uncontrolled ventricular response. Patients will often experience untoward symptoms at 150 beats per minute and above, but some patients may experience symptoms at a lower rate. In addition to continuous cardiac monitoring, these patients should have intravenous access in case treatment is needed.
The goal of treatment in AF is three-fold: to control the rate, to control the rhythm and to prevent stroke.
Medications that are used in the treatment of new onset stable atrial fibrillation include Cardizem (diltiazem), a calcium channel blocker, or metoprolol, a beta blocker. These medications are given to control rate. Depending on the severity of the patient’s symptoms, these medications can be given intravenously or orally. Digoxin is sometimes used, but it is not as effective as calcium channel blockers or beta blockers for active patients. Another controversial medication is amiodarone, which is not FDA approved for AF but is sometimes used when the other medications are contraindicated.
Another type of medication used in AF is an anticoagulant, usually in the form of a heparin drip for new onset atrial fibrillation. This is due to the potential for clotting in the atria when they do not eject blood adequately. These clots can lead to both heart attacks and strokes, so keeping the blood from clotting is very important. Again, close monitoring is needed to ensure the heparin remains within therapeutic range, and this requires serial blood testing. Although heparin does not last long in the system, it can cause serious bleeding. Only by testing and constantly adjusting the heparin drip can you ensure that heparin is within the therapeutic range. Conversion from heparin to warfarin, or Coumadin, is usually begun almost immediately, but it can take several days before oral anticoagulants can maintain the blood within the target range, which is usually 2 to 3 times the normal clotting time.
Cardioversion and Long Term Treatment
Besides medication, other measures can be taken to convert AF. One of these methods is synchronized cardioversion. By administering a shock, the hope is that the SA node will reassert itself and the patient will convert into a normal sinus rhythm. Patients will require sedation, as cardioversion is quite painful. Patients who have been in atrial fibrillation for longer than 48 hours should be anticoagulated before being cardioverted to prevent clots from the atria from traveling through the bloodstream, where they may cause a heart attack, stroke or pulmonary embolism. Sometimes the effects of cardioversion are short-lived, in which case ablation may be an option.
Ablations are performed the same way as cardiac catheterizations. A catheter is inserted into the femoral artery and the catheter is then threaded into the right atrium. Using angiography, the cardiologist attempts to find the cells in the atrium that are firing erratically. Once these cells are identified, the catheter is used to burn or destroy those cells. When those cells are no longer interfering with the SA node, the patient usually converts to a sinus rhythm. Ablation is often more successful than cardioversion.