Ventricular fibrillation is perhaps the most deadly arrhythmia of all. In V-fib, as it is commonly called, chaotic impulses cause the ventricles of the heart to quiver instead of actively pumping blood. In a study published by the American Heart Association and titled “Evidence for multiple mechanisms in Human Ventricular Fibrillation”, researchers concluded that the mechanisms that sustain ventricular fibrillation remain controversial. Some experimental studies support the idea of a single source, yet others support the idea of multiple interacting sources. Their findings from the human heart indicate that both mechanisms exist and are not mutually exclusive during human Ventricular Fibrillation (American Heart Association, 2006).
Without an effective heartbeat, however, blood pressure decreases rapidly, instantly cutting off blood supply to the vital organs including the brain. Most people in ventricular fibrillation lose consciousness within seconds and require immediate medical attention including cardiopulmonary resuscitation or CPR. The chances of survival are increased with CPR but with ventricular fibrillation, the heart must be shocked in order to try and stimulate the electrical activity of the heart so it can beat again on its own. If the heart cannot be stimulated by the shocks delivered, death will result within minutes. Most cases of V-fib are linked to some form of heart disease and are frequently triggered by a Myocardial Infarction (heart attack). In the event one survives an episode of V-fib, it would be recommended that an implantable device called an implantable cardioverter-defibrillator or ICD be placed within the heart. An ICD is a battery powered unit that is implantable near the left collarbone. One or more electrodes run from the device into the veins of the heart and continuously monitor the heart rhythm. If the device detects a rhythm that is too slow, it paces the heart like a pacemaker would. If the device detects ventricular tachycardia or ventricular fibrillation, it sends out shocks to reset the heart to a normal rhythm.
The last tachyarrhythmia is called Long QT syndrome. This is a heart rhythm disorder that carries an increased risk of fast, chaotic heartbeats. The rapid heartbeats of Long QT syndrome are caused by changes in the part of the heart that causes it to beat, and may lead to fainting. In some cases, the heart rate can become so chaotic that it can cause sudden death. People can be born with a genetic mutation that puts them at risk for Long QT syndrome. In addition to the genetic mutation, some common medications can even cause this arrhythmia.
Although a heart rate less than sixty beats per minute while at rest is considered bradycardia, a low resting heart rate does not always signal a problem. If physically fit, one may have an efficient heart capable of pumping an adequate amount of blood with fewer than sixty beats per minute at rest. However, if a slow heart rate exists and the heart is not pumping a sufficient amount of blood, several bradycardias can arise.
Sick Sinus syndrome is one example of a bradycardia. In this arrhythmia, if the sinus node, which is responsible for setting the pace of the heart, is not sending impulses correctly, the heart rate may be too slow, or it may speed up and slow down irregularly. Sick sinus can also be caused by scarring near the sinus node that is disrupting the travel of impulses. Another slow heart rate arrhythmia is called Conduction Block syndrome. A block of the heart’s electrical pathways can occur and depending upon the location of the blockage, the impulses between the upper and lower halves of the heart may be slowed or blocked. If the signal is completely blocked, certain cells can maintain a steady heartbeat, although usually much slower than normal. Some blocks may cause no signs or symptoms, while others may cause skipped beats or bradycardia.
