Arrhythmias are classified and treated based upon where in the heart they originate, how they manifest themselves and what cardiac functions they affect. For example, sinus arrhythmia is a type of heart rhythm that originates in the heart’s natural pacemaker (sinus node). It is characterized by changing heart rates often associated with breathing. For instance, heart rate may increase when inhaling and decrease when exhaling. It is almost always harmless.

More dangerous is sudden arrhythmia death syndrome (SADS), which is any disorder of the conduction system (e.g., long QT syndrome) that increases the risk of sudden cardiac death. Other types of arrhythmias include:

• Bradycardia (a heart rate of fewer than 60 beats per minute)
  
  
• • Sick sinus syndrome (also known as sinus node dysfunction, brady-tachy syndrome or tachy-brady syndrome). A group of symptoms that indicate bradycardia originating at the sinus node (sinus bradycardia).
     
  • Heart block (also known as atrioventricular block or AV block). May be classified as first degree, second degree (type 1 and 2) or third degree (complete). Heart block refers to a “blockage” in the passage of electrical signals from the atria to the ventricles, resulting in abnormally slow contractions.  
    
    
  • Bundle block branch. Involves the left and/or right bundle branches, which transmit the heart signal to the ventricles. Left bundle branch block (LBBB) is further classified as complete or partial (anterior fascicular block or posterior fascicular block). Right bundle branch block (RBBB) is also classified as complete or partial. Other types of bundle branch block include bifascicular block and trifascicular block.
    
    
• Tachycardia (a heart rate of over 100 beats per minute)
  
  
• • Supraventricular tachycardia (paroxysmal or sustained).Can be paroxysmal (acute attacks) or sustained. Supraventricular tachycardia may involve the AV node (also known as junctional tachycardia) or the atrium. It may be caused by factors such as premature contraction of the upper chambers of the heart or extra conduction pathways that “short circuit” the electrical signal. One of the most common types of sustained supraventricular tachycardia is atrial fibrillation, which affects two million people each year in the United States. Atrial fibrillation is the result of rapid, disorganized signals in the atria that prompt the ventricles to contract irregularly. Although this condition is not directly life-threatening, when the atria fibrillate (or quiver) instead of beating, blood is not effectively passed through the heart’s chambers and may pool in the atria. A blood clot may form and travel throughout the body, which could lead to a stroke or heart attack.
    
    

    

  • Ventricular tachycardias. Affecting the heart’s ventricles, these are generally more serious than supraventricular tachycardias. Among the most serious is ventricular fibrillation, which causes the heart to quiver (fibrillate) rather than beat efficiently. Ventricular fibrillation often leads to sudden cardiac death if not treated immediately. Often, the first sign of ventricular fibrillation is sudden fainting (syncope).