Atrial flutter pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]


Atrial flutter is a form of cardiac arrhythmia characterized by an atrial rate ranging from 240 to 400 beats per minute. It is the most common atrial tachycardia after atrial fibrillation, with a uniform and regular continuous wave-form.[1] It is caused by a reentrant rhythm in either the right or left atrium. Some degree of atrio-ventricular block is usually associated with atrial flutter. Similar to atrial fibrillation the rate of ventricular beating depends on the degree of conduction through the atrioventricular node. The usual scenario is 2:1 or 4:1 conduction but occasionally there can exist a 1:1 conduction.


Normal Conduction in the Heart

  • The natural pacemaker of the heart, the sinoatrial (SA) node is located in the right atrium. Impulses originate from this sinus node and travel accross the atrium to reach the AV node.
  • The atrioventricular node is an area of specialized conducting tissue between the atria and the ventricles of the heart, which conducts the normal electrical impulse from the atria to the ventricles.
  • The atrioventricular node delays impulses for ~0.1 second before allowing impulses through to the His-Purkinje conduction system, which spreads impulses to the ventricular walls. The reason it is important to delay the cardiac impulse is to ensure that the atria have ejected their blood into the ventricles before the ventricles contract.[2]

Conduction in Atrial Flutter

Typically initiated by a premature electrical impulse arising in the atria, atrial flutter is propagated due to differences in refractory periods of atrial tissue. This creates a self-perpetuating loop of electrical activity moving around the atrium.

In Type 1 atrial flutter most commonly the conduction is in counterclockwise direction around the tricuspid valve causing a caudocranial activation of the atrial septum. Clockwise activation around the tricuspid annulus is less common compared to the counterclockwise direction and is called isthmus dependent flutter or reverse typical atrial flutter. The slowly conducting reentrant circuit is believed to be located in the low right atrial isthmus.

Type 2 atrial flutter also known as atypical flutter usually results from an intra-atrial reentrant circuit that is short. It is believed to be originating from abnormal anatomy in the right atrium or the left atrium (surgical scars, irregular pulmonary veins, disturbed mitral annulus).

The impact and symptoms of atrial flutter depend on the heart rate of the patient. Heart rate is a measure of the ventricular rather than atrial activity. Impulses from the atria are conducted to the ventricles through the atrio-ventricular node. Due primarily to its longer refractory period, the AV node exerts a protective effect on heart rate by blocking atrial impulses in excess of about 180 beats/minute (This block is dependent on the age of the patient, and can be calculated roughly by subtracting patient age from 220). If the flutter rate is 300/minute only half of these impulses will be conducted, giving a ventricular rate of 150/minute, i.e., 2:1 block. The addition of rate-controlling drugs or conduction system disease can increase this block substantially (see image below).

Line of Block.JPG


  1. Dhar S, Lidhoo P, Koul D, Dhar S, Bakhshi M, Deger FT (2009). "Current concepts and management strategies in atrial flutter". South. Med. J. 102 (9): 917–22. doi:10.1097/SMJ.0b013e3181b0f4b8. PMID 19668035. Unknown parameter |month= ignored (help)
  2. Campbell, N., & Reece, J. (2002). Biology. 6th ed. San Francisco: Benjamin Cummings.

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