Nicole Harper
UNVR 195A
December 8, 1999
Ventricular Arrhythmia and Ventricular Fibrillation
Every year thousands of Americans suffer from various heart problems. Some of these problems include something referred to as ventricular fibrillation. Ventricular fibrillation can be described as an irregularity in the hearts rhythm of beating. There are different reasons for this irregularity and some of them will be discussed in the following paragraphs. The book The Self Made Tapestry gives the simple description that "the heart forgets how to beat" (p. 69).
When a persons heart "forgets how to beat" it first goes through what is called cardiac arrhythmia or simply a new rhythmic pattern where the heart beats about five times faster than normal (Ball p. 69). If the arrhythmia is not corrected within a certain period of time the heart will begin to fibrillate and the person will have a heart attack and possibly die. Fibrillation happens in the lower chambers of the heart (Britannica1). According to a book about arrhythmia, ventricular fibrillation "is the terminal cardiac event in 40 to 50 percent of all patients" making it the "most dangerous of the cardiac arrhythmias (Bellet p. 207). Ventricular fibrillation and arrhythmia can obviously be severely dangerous and fatal if not corrected. Each of them causes the heart to have abnormal wave patterns (spiral waves instead of target waves) that are unhealthy. Spiral waves are commonly caused by damaged tissue in the heart that is caused by blood clots (Ball p. 69). These obstacles cause a break in the target wave pattern causing irregular wave patterns that subsequently cause the heart waves to act abnormally. They are called spiral waves because they actually look like spirals. When viewed in color simulation you can see a beautiful pattern (http://www.math.utah.edu/~keener/research.html). Surprisingly enough, a person does not necessarily have to have a "bad" heart to have either one of these conditions; this could happen to someone with a perfectly healthy heart (Britannica2). The question is why does it happen if there is not always a serious heart problem?
In some instances the hearts natural pacemaker, the sinus node, fails to maintain a regular heartbeat (Britannica2). The electrical waves that signal the heart to beat somehow get disrupted or the pathway to the heart is disrupted causing the heart to have abnormal beating patterns (Britannica2). Often times, people do not even know that their heart’s beating pattern has been disrupted. Sometimes the disruption is so minuscule that it is unnoticed and the heart resumes normal beating without any external assistance. Luckily, patients that have serious troubles with this problem can be treated in two common ways. In one, an "electric shock is applied to override abnormal impulses" and in the other the treatment is to take drugs which "directly affect the sensitivity of the heart muscle and conduction rate of electric impulses" (Britannica2). Another reason why the heart goes through cardiac arrhythmia can be because of external instances. Some of these instances include but are not limited to, getting shocked, wrong chemical balances (from drug intake) or stress.
So what are the conditions of a healthy heart without any fibrillation? With each beat of the heart there is an electrical wave that passes completely through the heart. This wave of electricity causes the heart to contract and pump blood (Ball p. 69). The wave pattern that a heart has during normal beating can be determined and seen from an electrocardiographic diagnosis (Ball p. 69). Through continuous electrocardiographic monitoring the exact occurrence of ventricular fibrillation can be determined and studied (Bellet p. 207). The pattern of a regular heartbeat would look something like this.
The site http://www.math.utah.edu/~keener/research.html has a better graphical image of a heart chamber and wave pattern. If for some reason the heart went through an arrhythmia and then went into ventricular fibrillation, it might look something like this.
Unfortunately some people have chronic problems with having heart attacks because of their sinus node. The sinus node is what causes the heart to pump blood and produce a target pattern. Fortunately, in this day and age there are common treatments for such problems. Pacemakers are designed to replace the sinus node if it doesnt operate properly. A pacemaker replaces the sinus node by taking over the functions it performs. A pacemaker produces artificial electric waves so that the heart will beat with a normal rhythm and produce regular wave patterns. With a pacemaker implanted a person often lives a normal and healthy life.
The heart is considered to be an excitable medium. An excitable medium means that each wave of electricity to the heart waits until the heart goes back to its natural position before it is released and distributed (Ball p. 69). This prevents the waves from overlapping each other and causing disturbances in the rhythm of the heart. A more simplistic way of understanding excitable media is considering a forest fire. A forest fire can virtually destroy a forest. With some time, a forest can re-grow itself to its original state. Then it may catch fire again and thus have to re-grow again. This process of burning and re-growing is a cycle and if the cycle keeps happening a pattern of burning and re-growing is formed. This pattern is considered to be a periodic oscillation. The forest fire illustration is comparable to a heartbeat because it always goes back to its "resting" position much like a heart does when it beats.
Periodic oscillations then have sub-categories of patterns. For example, when the pattern of the heart beating continues in a rhythmic pattern, the periodic oscillations can form target patterns. A target pattern is similar to a bull's eye. This can be described by the formation that occurs when you drop water or another liquid onto the surface of another liquid (i.e. a bowl of water with a drop of water in the center). When you do this, rings appear. These rings periodically move outward from the center. A spiral pattern is a type of defect and looks much like a pinwheel. It wraps itself around a center point forming a spiral shape. Target waves and spiral waves are often called traveling waves because their patterns "move." The circles of a target wave move in an outward motion and the spiral wave keeps curling around itself thus each are "moving" waves. As stated earlier, spiral waves are caused when there is an obstacle causing the target wave to have a defect. When the heart forms a defect like this, the result is the heart goes through cardiac arrhythmia and can begin to fibrillate.
As we have seen, there are various reasons why a heart might beat abnormally and cause abnormal wave patterns or oscillations. It could be because of spiral waves, sinus node failure, stress, chemical imbalances, or getting shocked. No matter the cause, the heart is an excitable media and the patterns of this media change based on various reasons. The point is that the heart does not always beat regularly. Sometimes there are instances when the heart has a different rhythm and wave pattern. No matter the case, if the abnormality lasts too long it will be fatal.