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This page is courtesy of Florida Electrophysiology Associates; The leader in the Southeast United States in complex catheter ablation procedures

Normal Sinus Rhythm

The normal electrical system of the heart consists of the sinus node (or SA node) which resides in the right upper chamber of the heart.  This natural pacemaker provides impulses which travel through the heart normal electrical system to the two lower chambers (the ventricles) resulting in a normal heart beat.  The hearts natural pacemaker will vary the rate it fires depending upon the demands placed upon the body it serves.  However, for any given heart rate, during normal sinus rhythm the heart rhythm and pulse are regular. Want to know if you're in fibrillation?  Assuming you don't have a pacemaker, a quick way to check is to simply take your pulse.  If it's regular, then you're not in atrial fibrillation (you may not necessarily be in a normal rhythm but a regular non-artificially paced rhythm is never atrial fibrillation).  The normal rate of firing of the natural pacemaker and thus the two upper chambers of the heart is between about 50 and 140 beats per minute depending on the patients age, physical status, activity level, etc.  You will note on the above illustration. that there is a signal called a "P"- wave seen on the EKG during normal rhythm and occurring just prior to the much larger "RS" complex.  The P-wave represents contraction of the two upper chambers (the right and left atrias) during normal rhythm. The "RS" complex (also called the "QRS" complex) represents contraction of the two lower chambers of the heart in response to the atrial contraction.  In normal sinus rhythm, the P-wave occurs before and actually causes the QRS complex as is evident in the above illustration.

Atrial Fibrillation

In atrial fibrillation, the rate of firing of the two upper chambers is around 500 beats per minute. The patient would have a cardiac arrest if all of these impulses were transmitted to the two lower pumping chambers (the ventricles) and the heart is not designed to move any blood at these very fast rates.  Fortunately, a natural circuit breaker called the AV-node (denoted by the yellow-orange structure in the illustration) only permits so many fast impulses from the atria to actually reach the ventricles and cause a contraction.  AV nodal conduction of these impulses however occurs in an irregular fashion.  Thus, the lower chambers beat irregularly during atrial fibrillation as at times several impulses are conducted while at other times they are blocked.  The pulse during atrial fibrillation (in the absence of artificial pacemakers) will therefore be irregular.  Note in the above illustration that the QRS complex (which represents contraction of the ventricles) is very irregular.  Also, note the absence of obvious P-waves.  Instead of P-waves, a very irregular fine rhythm is seen between the QRS complexes.  This represents the two atrias firing at around 500 beats/minute in an irregular fashion.  When fibrillation occurs, both the right and left atria are in fibrillation while the lower chambers are very irregular.  The pulse rate during fibrillation will depend on a variety of factors including the patients age and medication usage but can range from very very fast to relatively slow.  Patient symptoms too can vary greatly from one individual to another with some people not even aware of the fibrillation while others are extremely symptomatic with this arrhythmia.


Home What causes A fib. Who Gets A. fib A Fib Palliations A Fib Cures Coumadin Risks of Having A. Fib Famous Fibrillators