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Cardiac Arrhythmias - Atrial Flutter

Image courtesy of St. Jude Medical

Atrial Flutter - So basic, yet so complex….

          When I first started working in EP, it seemed to me that atrial flutter was one of the easiest rhythms to deal with. Check for the saw tooth pattern, put in a duo-deca, verify activation sequence, entrain if there was any doubt and then burn the isthmus. Verify bidirectional block by pacing, hunt down the gap if there was one and call it a day. These were fun, easy cases, at least that is what I thought back then.

          Then I got involved with cardiac mapping and things started to change. Some cases got easier. Finding a gap with the EnSite Array can be done in a matter of seconds. Those pesky gaps that weren’t located just below the valve or down at the eustachion ridge above the IVC had now become easy targets. Other cases became more difficult. With the advanced mapping capabilities of the array, physicians were using it more and more to map complex flutters, some of which I had never encountered before.

There were upper and lower loop flutters, crista flutters, bi-atrial flutters, scar mediated flutters and the ever popular left atrial flutters. It quickly became apparent that there was more to atrial flutter than I had previously realized.

          This is a defining moment in anyone’s EP career; the moment you realize that atrial flutter is actually one of the most complex rhythms you can encounter. The simple right atrial isthmus dependant flutters are just the tip of the iceberg and they represent only one variant of this macro reentrant rhythm. Now that it had become apparent that I did not know as much as I thought I knew, Idid what we all do to learn more about flutter, I went to the books to see what the experts had to say.

The Different Types of Flutter

          The definitions of atrial flutter that I found only emphasized the fact that atrial flutter is a complex beast. I have a number of sources I routinely use for research and they did not all agree on what the definition of flutter was. As I am not qualified to define atrial flutter, I have included here, some of the different definitions of atrial flutter and the source where they were obtained. Information from several of these sources has been included below. I would encourage anyone who reads this section to consult these texts for further reading. It will definitely expand your knowledge of what flutter really is.

Flutter as described by Fogoros

The first tome I investigated was the original EP handbook, Electrophysiology Testing 3rd edition by Richard N. Fogoros, M.D. This was the first book in my library and I still refer back to it from time to time. The following information was found in this book (pages 103, 235-237).

Atrial Flutter General Description
• The atrial rate is regular and in excess of 220 beats/min
• The surface ECG usually displays a typical saw tooth pattern.
• Atrial flutter can usually be terminated by pacing.
• Atrial flutter usually displays some degree of AV block, usually at a 2:1 ratio.
Typical Atrial Flutter
• The crista terminalis acts as the electrical barrier that defines the reentrant circuit.
• The flutter wave must pass through the right atrial isthmus between the IVC and the Tricuspid Valve annulus.
Atypical Flutter
• Atypical flutter, while reentrant in nature, follow pathways other than that of the typical flutter.
• These are most often scene in patients who have had cardiac surgery and who have a surgical scar in the atrium.

Flutter as described in Cardiac Electrophysiology – From Cell to Bedside 3rd Edition. This text was authored by Dr. Douglas P. Zipes and Dr. Jose Jalife.

Atrial Flutter – General Description
• AFL is rapid, regular atrial rhythm originating from atrial reentry
• Is the most regular of arrhythmias
• Conduction through AV node usually shows some degree of block with 2:1 or 4:1 being common.
• Block through the AV node may be variable

Type I Flutter
• Rate 240-350bpm
• Primarily denoted by the fact that it can be entrained and interrupted by rapid atrial pacing
• Scar flutters are type I as the can be entrained by rapid atrial pacing
• Two types of Non-scar Type I
     o Common
           Negative flutter waves in II, III and aVF
           Up septum, down free wall
     o Uncommon
           Positive flutter waves in II, III and aVF
           Down septum, up free wall
• Both common and uncommon AFL utilize the RA for the complete circuit – LA activation is entirely passive
• The critical isthmus is bounded by the tv annulus and the IVC orifice, the Eustachian ridge and the ostium of the coronary sinus
• Common and Uncommon use the same circuit but conduct in opposite directions

Type II Flutter
• Rate 340bpm or greater
• Pacing often deteriorates into AF
• Entrainment difficult

Flutter as described in The Handbook of Cardiac Electrophysiology, A Practical Guide to Invasive EP Studies and Catheter Ablation. Authors; Francis D. Murgatroyd, M.D., Andrew D. Krahn, M.D., George L. Klein, M.D., Raymond K. Yee, M.D. and Allan C. Skanes, M.D.; Sections 3.3 on page 60 and section 3.5 on page 66.

Typical Flutter
• Typical flutter, which is also known as common flutter, is a macro-reentrant circuit confined to the right atrium. Left atrial activation is passive.
• Wave front emerges from a zone of slow conduction between the tricuspid valve annulus and the ostium of the coronary sinus.
• It ascends the septum, then across the posterior right atrium and travels downward and then lateral between the tricuspid valve and the crista terminalis.
• The wavefront is funneled into the right atrial isthmus between the tricuspid valve annulus and the inferior vena cava.
• A line of functional block exists along the crista terminalis where the ascending and descending wavefronts collide.
• Typical atrial flutter is the most frequent of the rapid (>200 beats/min) atrial tachycardias.

Atypical Flutter
• The most frequent form of atypical flutter is similar to typical flutter but it rotates in a clockwise fashion, completely opposite to that of typical flutter.
• Atypical flutter is characterized by upright P waves in the inferior leads and inverted P-waves in lead V1.
• The cycle length of atypical flutter is similar to that of typical flutter.
• Atypical flutter, like typical flutter is isthmus dependant and requires passage through the right atrial isthmus between the IVC and the Tricuspid Valve annulus.

Note that in the text of this book, it does not seem to be the authors believe that the rhythm described as clockwise flutter is a true atypical flutter. This is described as the next variant, or “Truly Atypical Flutter”.
• Truly atypical flutter tends to have a shorter cycle length than typical flutter and it’s clockwise variant.
• It also tends to be more unstable and may deteriorate into atrial fib.
• Studies suggest numerous possible circuits including one that circles around the pulmonary veins.

Finally, the Scar-Related Flutters are defined.
• This form of atrial flutter utilizes a scar from an atriotomy or an atrial patch or baffle.
• Scar related flutter occur most commonly in patients who have had surgery to correct a congenital defect.
• Scar related flutters are not generally isthmus dependant.

As you can see, there is a fair amount of variability in the descriptions of atrial flutter. From my own experience in the field, I have heard the following method used to describe flutters;
Typical Atrial Flutter
• Typical atrial flutter is right atrial isthmus dependant.
• Typical flutter is usually counterclockwise in rotation when viewed in the LAO projection.
• There is clockwise typical flutter that utilizes the same circuit as the counterclockwise version, only in a reverse direction. For this reason, both the clockwise and the more common counterclockwise atrial flutters are grouped as Typical Atrial Flutter.
Atypical Atrial Flutter
• Atypical Flutter is often used to describe any circuit that is not dependant upon the right atrial isthmus.
• Included in this group are scar mediated flutters, upper loop flutters, crista flutters and left atrial flutters.

Based upon the variations in terminology, it is apparent that a standardized terminology that accurately describes the different types of macro-reentrant arrhythmias needs to be established. Until that time, I would recommend becoming familiar with all the various definitions. In this web site, the descriptions of atrial flutter utilized will conform to the last set listed on the page listed in bold, italic font.

Wells Classification of Atrial Flutter - Excellent article on Atrial Flutter

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