Irregular heart beats can be generated when the heart’s own nervous system malfunctions.
This is similar to the computer control system of a car: you never know that it is there until it fails and the car does not run. With the heart muscle it can be more devastating because a life depends on the proper functioning of all of the components. Fortunately there are two back-up systems for this electrical control system of the heart which helps to prevent death as we will see below.
The electrical signal for a heart beat is generated in the sinus node and it travels from there through the right atrium into the atrioventricular node (AV node), a cluster of nerve cells on top of the dividing wall between both heart chambers.
From there two bundles of nerve fibers (the right and left bundle branches) travel through the heart septum ( the dividing wall between the right and the left heart chambers). These bundles branch out into smaller and smaller fibers which connect with the muscle fibers of the heart muscle of both chambers. Here is a link to a site that explains these nerve connections between the sinus node and the heart muscle cells in more detail.
Don’t get confused about the medical terminology
Should you find yourself slightly confused about this medical jargon above, don’t worry, you are in good company. I just included this for those of you who like to know more details than you normally hear in the news. Once these anatomical facts are grasped, it follows then that any interruption of this system will lead to a slowing down of the electrical transmission.
Irregular heart beats
For instance, if the sinus node malfunctions, this has the name “sick sinus syndrome”.
If the atrium blocks the transmission of electrical impulses, it might want to compensate by firing extra electrical impulses. A person with this condition suffers from “atrial fibrillation”. When there is a blockage of a bundle branch, physicians call this a “right or left bundle branch block”. When the block occurs at the AV node level, they call this a “complete or incomplete heart block”.
Pacemaker needed for complete heart block
When this occurs the heart rate is about half the normal rate. This usually requires a pacemaker. This would be the scenario of the second backup computer having given up. It only makes sense that a physician installs an outside computer (the pacemaker). Finally, when there is blockage of nerve fibers within the muscle wall the most serious of the arrhythmias, namely “ventricular fibrillation” results. An implantable cardioverter-defibrillator (ICD) can prolong life in these circumstances.
1. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapters 197, 202, 205 and 207.
2. Braunwald: Heart Disease: A Textbook of Cardiovascular Medicine, 6th ed., 2001, W. B. Saunders Co.
3. D C Bauer: Audio-Digest Family Practice Vol. 49, Iss. 09, March 2, 2001.
4. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.
5. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier