Editing Atrial flutter (section)

====Type I====
[[Image:AtrialFlutter12.JPG|thumb|300px|right|Type I atrial flutter, counterclockwise rotation with 3:1 and 4:1 [[AV node|AV nodal]] block.]]
[[File:Aflut.jpg|thumb|300px|Atrial flutter with a two to one block. Note the P waves hiding in the T waves in leads V1 and V2]]
Type I atrial flutter, also known as common atrial flutter or typical atrial flutter, has an atrial rate of 240 to 340 beats/minute.  However, this rate may be slowed by [[antiarrhythmic agents]].{{citation needed|date=February 2021}}

The reentrant loop circles the right atrium, passing through the [[cavo-tricuspid isthmus]] – a body of fibrous tissue in the lower atrium between the [[inferior vena cava]], and the [[tricuspid valve]].<ref name="Sawhney2009"/>  Type I flutter is further divided into two subtypes, known as counterclockwise atrial flutter and clockwise atrial flutter depending on the direction of current passing through the loop.<ref name="Sawhney2009"/>
* Counterclockwise atrial flutter (known as cephalad-directed atrial flutter) is more commonly seen.  The flutter waves in this rhythm are inverted in ECG leads II, III, and aVF.<ref name="Sawhney2009"/>
* The re-entry loop cycles in the opposite direction in clockwise atrial flutter, thus the flutter waves are upright in II, III, and aVF.<ref name="Sawhney2009"/>