By

Teddie Joe Snodgrass, RN, MBA, MSN
Member of The American Medical Writers Association
Revised: 26 July 2009

http://www.HeartyHealth.com/CV/training/a-fib.html

Atrial Fibrillation

Atrial Fibrillation, most commonly referred to as "A-fib," is defined as chaotic electrical activity in the atrium. It stems from the firing of a number of electrical impulses within the heart at a rate of 400 to 600 times per minute, or in other words caused by multiple irritable ectopic foci in the atria leading to a disorganized and uncoordinated twitching or quivering of the atria instead of atria contracting as in a normal heartbeat. These ectopic impulses are conducted, via the heart’s electrical “Conduction System” to the hearts ventricles at irregular intervals – as previously stated at a rate of 400 to 600 beats per minute.

During normal electrical activity, the Sino-Atrial (SA) node which is located in the right atrium (RA) and which is also known as the major pacemaker of the heart fires at the intrinsic rate of 60-100 beats per minutes in a normal conduction environment.

The Atrio-Ventricular (AV) node is the backup pacemaker and gatekeeper of the electrical conduction system of the heart. Its intrinsic rate is rated at 40-60 beats per minutes.

The Bundle of HIS, right and left bundle branches, Purkinje fibers deliver the impulses to the ventricles. These area within the hearts “Conduction System” also act as a backup pacemaker allowing for a ventricular backup intrinsic rate of 20-40 beats per minute.

A normal conduction pathway begins with electrical impulses that originate in the SA node and spread through the atria (causing the atria to contract), then are delayed slightly at the AV node before rapidly spreading to the Bundle of HIS, down the right & left Bundle Branches to the Purkinje fibers (which are like small fingerlike projections into the myocardium causing the ventricles to contract).

The ventricles respond only to those impulses that make it through the AV node from the SA node.  On an ECG representing A-fib, atrial activity is no longer represented by discernable "P" waves but by erratic baseline waves called fibrillatory waves (small looking bumps on the ECG) which simply means that the atria is fibrillating.

No contraction of the atria as a whole means there are no uniform atrial depolarization, which means that there are no "P" wave in the ECG.

Fibrillatory waves vary in size and shape and are irregular in rhythm. Transmission of these multiple atrial impulses into the AV node is thought to occur at random, resulting in an irregular rhythm. Some impulses are conducted into but not through the AV node (they are blocked within the AV node).

The right atrium (RA) is a thin-walled chamber that maintains very low blood pressures. The chamber receives un-oxygenated blood from systemic blood flow and the coronary sinus. It pumps the blood to the right ventricle (RV) through the tricuspid valves. The tricuspid valve is positioned between the RA and RV and has three leaflets or cusps.

Approximately 70% to 80% of the venous blood return passively flows from the RA to the RV. An additional 20% to 30% of blood flow or filling to the right ventricular occurs during atrial contraction which is known as the "atrial kick" at the end of diastolic filling of the ventricles.

The irregular conduction of impulses through the AV node produces a characteristic irregularly irregular ventricular response. And, normally atrial fibrillation means decrease blood pressure due to loss of the atrial kick.

Note: If you see "R" waves that look irregularly irregular on the monitor, suspect atrial fibrillation.

The right coronary artery (RCA) supplies 90% of the blood supply to the SA node and 45% to the AV node. Two-thirds of the coronary blood flow occurs during diastole. Therefore, during tachycardia there is decreased blood flow to the coronary system due to the shorter diastolic interval. Bradycardia type dysrhythmias are common with inferior myocardial infarctions (MI's).

As with other atrial arrhythmias, atrial fibrillation eliminates atrial kick thus causing the atria to quiver rather than contract. That loss, combines with the decreased filling times associated with rapid rates, can lead to clinically significant problems. Left untreated a rapid atrial fibrillation can lead to cardiovascular collapse and thrombus formation.

Acute Myocardial Infarction

Cardiomyopathy

Congestive Heart Failue (CHF)

Congential Heart Disease

Pericarditis

Ischemic Heart Disease

Mitral and tricuspid valve disorders or diseases such as rheumatic heart disease

Chronic Obstructive Pulmonary Disease (COPD)

Hypokalemia

Hypertension

Coronary Artery Disease (CAD)

Digoxin toxicity

Also seen after Cardiac Arterial By-pass Graft (CABG) or other heart surgeries but is usually transient in nature.

Enhanced automaticity

·         P-Wave: Configuration: “P” waves are not discernible. A baseline of fibrillatory waves are seen. Rate: The atrial rate is usually more than 350-400 beats per minutes. Rhythm: The atrial rhythm is chaotic and disorganized.

·         P-R Interval: No “P” waves are identifiable, so no “P-R” interval can be measured.

·         QRS Complex: Configuration: All QRS complexes should be normal and look alike. Rate: The ventricular rate varies. The rate may be slow or very rapid. Rhythm: The R-R interval is completely irregular, with no pattern to the irregularity. Duration: The QRS complex is usually normal.

Atrial Fibrillation causes a complete loss of synchronous atrial and ventricular contractions. This loss of atrial input or atrial kick reduces cardiac output by 10% to 30% therefore Congestive Heart Failure (CHF) may develop.

Atrial Fibrillation is often a chronic rhythm. Over time, thrombi may form on the walls of the quivering atria. Converting atrial fibrillation to a Normal Sinus Rhythm (NSR) with normal atrial contractions may loosen these thrombi and release them into the systemic or pulmonary circulation. Therefore, anticoagulant therapy may be indicated such as Heparin or Lovenox.

Drug therapy includes: Amiodarone, Digoxin, Cardizem, Metoprolol, Propranolol, Verapamil, Quinidine Sulfate*, Procainamide and Rythmol.

Cardioversion may also be used if drugs fail or the patients condition is acute.

·         Assess the patient for signs or symptoms of Congestive Heart Failure (CHF)

·         Monitor serum digoxin levels

·          Monitor your patient's blood pressure.

·          Assess for syncope.

·          Assess for palpitations.

·          Assess for Shortness Of Breath (SOB).

For a list of more Cardiovascular Systems training click here.