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Types of Palpitations
Extra heart beats are normal and most people are unaware that they have occurred. Every muscle cell in the heart has the potential to generate an electrical signal that can spread outside the normal electrical pathways and bundles to try to generate a heart beat. Many extra beats are normal variants and can be nothing more than an occasional irritant, but others can be dangerous - either acutely or chronically. Extra beats that originate in the atrium tend not to be as serious as those that come from the ventricle.
Abnormal heartbeats are classified by the location where they originate, if they happen occasionally or if they are clustered in runs, and if they resolve by themselves (self-limiting).
PACs and PVCs
Premature atrial contractions (PAC) are just as the name describes. The pacemaker or SA node in the atrium decides to send a signal out before the heart is quite ready, and while it conducts normally and the heart beats, it is felt as a slight flop or thump in the chest.
A similar situation can occur with the ventricle if it becomes a little irritable and generates an extra beat, known as premature ventricular contractions (PVC). This beat fires the ventricle when there is little blood in the heart to pump, and again a flop or thump can be felt by the person.
PACs and PVCs in isolation are a normal variant. They can be asymptomatic, and an individual may not be aware of them.
Supraventricular Tachycardia (SVT)
If the electrical system in the atrium becomes irritable, it can cause the upper chamber to beat very fast, sometimes 150 beats or more per minute. The AV node senses each beat and sends it to the ventricle which itself responds with a beat. Because the electricity is generated above the ventricle and then passed down, the whole group of disorders is classified as supraventricular tachycardias (supra= above, tachy=fast).
Some supraventricular tachycardias are a normal response to specific situations. In times of stress, when the body wants to send more blood and oxygen to the body, like with exercise, trauma or illness, the heart rate rises in response to adrenalin that is secreted by the body to meet its physiologic demand. Caffeine, pseudoephedrine, and other stimulants can also cause this type of rapid heart beat. Because all the electrical impulses begin in the SA node, this is called sinus tachycardia.
Some supraventricular tachycardias occur because of short circuits in the electrical conducting pathways in the atrium causing the heart to beat fast without apparent cause. Paroxysmal supraventricular tachycardias (PSVT) occur without warning and may last for seconds to hours. Specific types of paroxysmal supraventricular tachycardias have been identified because of recognized inborn wiring errors. One such type is Wolfe-Parkinson-White syndrome (WPW syndrome). Precipitating factors may include caffeine or alcohol consumption, over-the-counter cold medications, electrolyte abnormalities, and excess thyroid hormone.
Atrial Fibrillation and Flutter
Atrial fibrillation and atrial flutter occur when all the muscle cells of the atrium start acting like pacemakers and start firing on their own. This barrage of electricity does not allow the atrium to have an organized contraction. Instead, it jiggles like a bowl of Jello. Many of these electrical signals are passed on erratically by the AV node to the ventricle, and it tries to respond as best as possible, leading to a rapid, irregular heart rate.
There are a couple of complications with this rhythm. Since the atrium does not get a unified electrical signal, it does not pump. This allows blood to settle in the crevices of the atrium, and blood clots can form. They, in turn, can break away and travel in the bloodstream to block the circulation at other sites, causing strokes and other vascular problems. Moreover, without the atrium beating, blood flows by gravity into the ventricles and approximately 15% of the heart's ability to pump blood to the rest of the body is lost, making the heart less efficient in meeting the needs of the body.
Ventricular Tachycardia and Fibrillation
Ventricular tachycardia (V Tach) is a potential life-threatening situation in which the ventricle starts firing quickly on its own. When people have coronary artery disease, the heart muscle can lack enough blood supply and become irritable. The electrical system doesn't tolerate this well and causes this abnormal heart rhythm. This rhythm may or may not allow the ventricle to beat in an organized way.
Ventricular fibrillation (V Fib) is not compatible with life since the ventricle has lost its ability to beat in an organized fashion, and the ventricle fibrillates or jiggles instead of beating, and the heart cannot pump blood to the body. This rhythm is what often causes sudden death after a heart attack.
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