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Our heart beats a whopping 40 million times a year. And what makes it beat? Electrical impulses. The heart's electrical system controls the pumping action of the heart and gives it a rhythm. The normal rhythm is 60 to 100 beats per minute when we are at rest.
The impulses originate in specialised cells called sinus nodes in the upper right chamber of the heart. It then spreads to both the upper chambers (atria) of the heart which causes them to contract simultaneously. The impulses then travel down to the atrioventricular node to the ventricular muscle of the heart through the ventricular wall which cause the ventricles to contract, both at the same time and oxygen rich blood from the lungsis pushed into the body.
When you have a heart disease or abnormality in your heart, the heart's electrical system malfunctions and rapid electrical signals are produced. This causes your heart to beat faster, that is, more than 100 beats per minute. This is called tachycardia. The increase in heart rate can be in atria or ventricles, or in all four chambers of the heart.
Depending on where the electrical system of the heart malfunctions, tachycardia is clumped into four major groups
I. Atrial fibrillation
This is the most common type of tachycardia where the heart's upper chambers (atria) beat irregularly and chaotically more than 100 beats per minute up to 175 beats or even more.
In atrial fibrillation, the impulses don't begin in sinus node, rather, they begin in the pulmonary veins in the left atrium spreading out the signals throughout the atria in a rapid, disorganized way (not in a regular pattern). The erratic signaling causes the upper chambers to quiver. Hence the term 'fibrillation'. This confuses the ventricles and they too start beating very fast. But the impulses don't reach the ventricles as fast as they arrive. So the ventricles don't beat as fast as the atria. This creates a fast, irregular heart rhythm because the atria and ventricles no longer beat in a coordinated way.
This leads to heart failure in which the heart cannot pump enough blood to meet the body's needs.
It is not a life threatening condition but may require emergency attention in some cases.
Symptoms:
You may not observe any symptoms at all or you may experience the following symptoms
Causes of atrial fibrillation:
Related to the heart
Not related to heart
II. Atrial flutter
Atrial flutter is similar to atrial fibrillation, except here, the impulses are more organized and less chaotic than in atrial fibrillation. In atrial flutter, the heart beats faster but in a regular pattern.
The impulse originates mostly originates in the right atrium but not in the sinus node. Instead it involves the circuit around tricuspid valve situated in the partition of the right atrium and the right ventricle. Less commonly, the impulse can originate in the other areas of right atrium or even left atrium causing the heart to beat fast as much as 150 beats per minutes.
During atrial flutter the atrium beats up to 300 times a minute and every second beat gets through to the ventricle resulting in heart rate of 150.
Although atrial flutter is not a life threatening condition, sustained atrial flutter can cause strain to the heart, so seek medical attention immediately.
Symptoms: You may not see any symptoms but if you do symptoms could be
Causes include
III. Supraventricular tachycardia
Supraventricular tachycardia is also a form of atrial tachycardia that originates in the sinus node as it should but some sort of abnormality in the sinus node causes the erratic signaling. For example, the most common one is called AV-node reentry where the electrical signals go round and round the sinus node.
In another form, the electrical signal splits up into two because of abnormality in the sinus node; one signal goes to the ventricle and another signal goes back to the atrium.
In yet another form, an extra electrical pathway is present which goes from atria to the ventricles but by-passes the sinus node. Example of such tachycardia is Wolff-Parkinson-White Syndrome.
In most cases, the problem is temporary, lasting for about a few seconds, minutes or hours, and is not life threatening.
Causes of supraventricular tachycardia include
IV. Ventricular tachycardia
Ventricular tachycardia is a condition in which the electric impulse originates in the ventricles causing a heart rate of 170 beats per minute or more. This type of tachycardia is characterized by at least three irregular heartbeats in a row. Because of the rapid heart rate the ventricles don't fill up and don't contract efficiently, so they can't pump enough blood into the body.
Ventricular tachycardia is life threatening condition if it lasts more than a few seconds in some cases. Get prompt medical attention.
Symptoms include
Ventricular tachycardia can be caused by
V. Ventricular fibrillation
Ventricular fibrillation is the most serious form of tachycardia. In this type of tachycardia, rapid, chaotic electric impulses that originate in ventricles cause the ventricle muscles to quiver in an uncontrolled twitching way instead of contracting to pump the blood out to the body. So, the heart pumps little or no blood. This could be fatal if the heart rhythm is not restored within minutes.
Symptoms include
Causes of ventricular tachycardia include
Reference:
http://www.nhlbi.nih.gov/health/health-topics/topics/af/
mayclinic.org
http://circ.ahajournals.org/content/112/22/e334.full#sec-3
http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/Tachycardia-Fast-Heart-Rate_UCM_302018_Article.jsp
http://www.nlm.nih.gov/medlineplus/ency/article/007200.htm
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