1. Atrial Flutter: An Electrophysiologic Overview
Welcome to ATRIAL FLUTTER – AN ELECTROPHYSIOLOGIC OVERVIEW. This module contains a discussion of the various characteristics of atrial flutter. ECG recognition and treatment of atrial flutter will also be explored. Focus is given to the use of radiofrequency (RF) ablation as a treatment for atrial flutter.
MAJID HAGHJOO, M.D
DEPARTMENT OF PACEMAKER AND ELECTROPHYSIOLOGY
RAJAIE CARDIOVASCULAR MEDICAL AND RESEARCH CENTER (RCMRC)

2. Objectives – Atrial Flutter
Identify mechanisms and characteristics of atrial flutter
Recognize ECG and intracardiac electrograms depicting different types of atrial flutter
Discuss treatment options for atrial flutter

3. Outline – Atrial Flutter
I. Description
II. Characteristics
Definition
Types and features
Mechanism
Circuit recognition
ECG and intracardiac recognition
This module will start by discussing the characteristics and ECG findings of atrial flutter.

4. Outline – Atrial Flutter
Pacing techniques
Entrainment
Treatment options
RF ablation
Future directions
The module will then discuss treatment options of atrial flutter, with an emphasis on RF ablation.

5. Atrial Flutter Rapid and regular form of atrial tachycardia
Usually paroxysmal
More common in men than women (M/F: 4.7:1).
Sustained by a macro-reentrant circuit.
In most cases, circuit is confined to the right atrium and left atrium is passive bystander.
In some types of atrial flutter, arrhythmia circuit located in left atrium.
Episodes can last from seconds to years.
Chronic atrial flutter usually progresses to atrial fibrillation.
Atrial flutter is a rapid and regular form of reentrant atrial tachycardia.
It is usually paroxysmal, and it is sustained by a macro-reentry circuit located in the right atrial myocardium.
Flutter episodes can last from seconds to years.
Patients presenting with paroxysms of atrial flutter often have normal hearts, whereas patients with chronic atrial flutter usually have underlying heart disease. Chronic atrial flutter eventually converts to chronic atrial fibrillation.

6. Atrial Flutter
A unique population in which atrial flutter occurs commonly is in patients in the first week after open heart surgery (a third of postoperative SVTs)
It is also seen in association with:
chronic obstructive pulmonary disease
mitral or tricuspid valve disease
thyrotoxicosis
repair of congenital cardiac lesions in which the atria, most often the right atrium, is considerably incised, such as with the Mustard, Senning, or Fontan procedure or those with enlargement of the atria, especially right atrium.

7. Reentry Circuit of Common Atrial Flutter
Anatomic barriers within the right atrium sustain the macro-reentry circuit.
The AV node plays no part in the flutter circuit, so drugs aimed at altering the conduction of the AV node have no effect on the atrial rate.
Morady F. N Engl J of Med. 1999;340:

8. Types and Features
Flutter Type Mechanism Atrial rate Cure
Typical * Counterclockwise RFA
Macro-reentry
Reverse typical * Clockwise RFA
Atypical Macro-reentry RFA
* 90% of atrial flutters fall into the typical or reverse typical category.

9. Mechanisms of A-Flutter
Typical (counterclockwise and clockwise)
A rapid and regular form of atrial tachycardia that is sustained by a macro-reentrant circuit which utilizes a cavotricuspid isthmus
Atypical
Atrial reentry is independent from cavotricuspid isthmus
Mostly, reentry occur around scar tissue after surgery
In some cases, reentry occur around left atrium
Depending on the type of atrial flutter, the mechanism will vary. A discussion of each type of flutter follows, along with ECG and intracardiac recording examples. A macro-reentrant circuit can be defined as any arrhythmia pathway in which the electrical impulse travels through a relatively large region of tissue. Arrhythmias caused by macro-reentrant circuits often can be cured by ablation of a critical portion of the circuit.
Atypical atrial flutter does not use the critical isthmus as used in Type I flutter.
Macro-reentrant atrial tachycardia occurs frequently after surgery for congenital heart disease.

10. Typical Flutter Mechanism: Induction: Termination:
Counterclockwise macro-reentrant circuit that utilizes a cavotricuspid isthmus to sustain circuit
Induction:
Fast atrial pacing and/or the introduction of multiple premature beats near the low septum
Termination:
Rapid atrial pacing faster than the flutter rate
Cardioversion
Spontaneous
Pharmacologic therapy
With counterclockwise flutter, a macro-reentrant circuit exists. This circuit is sustained by a critical isthmus.
Induction of counterclockwise flutter can be accomplished with rapid atrial pacing and/or the introduction of multiple premature beats near the low septum.
Termination of counterclockwise flutter may be accomplished with rapid atrial pacing, cardioversion, or with the use of medications, such as Ia, Ic, or class 3 antiarrythmic drugs.
The arrhythmia may also convert spontaneously.

11. Isthmus Conduction Typical Flutter
The mechanism of counterclockwise flutter is further illustrated on this slide. A counterclockwise flutter circuit can travel between (A) the IVC (inferior vena cava) and CS (coronary sinus) os and/or (B) between the tricuspid annulus and the CS os. The key is that the isthmus is the critical portion of the circuit and the target for ablation.
Typical Flutter
Conover: Electrocardiography. 4th ed. Mosby 1998; 75.

12. ECG Recognition Typical atrial flutter
Undulating atrial activity without a baseline
Atrial rate: bpm
Rhythm: Regular
Ventricular rate: Variable
Dependent upon:
AV node conduction properties
Usually a 2:1, 4:1 fixed conduction ratio
Recognition: “Sawtooth” appearance on the surface ECG (negative deflections in inferior leads and positive deflection in V1)
Atrial flutter is distinguished from atrial tachycardia by the faster rate.
1:1 AV conduction ratio in atrial flutter may be seen in: Wolf-Parkinson-White syndrome (most common); Lown-Ganong-Levine syndrome; Exercise; Catecholamine therapy; Phenytoin therapy; Class I antiarrhythmic drug therapy

13. ECG Recognition
Notice the “sawtooth” pattern of the flutter waves in this rhythm strip. This is typical of counterclockwise atrial flutter. The atrial rate can be bpm. The ventricular response is fast, but it is regular.

14. Other Methods of A-Flutter Recognition
If diagnosis of atrial flutter is not clear from a standard ECG, any of a number of maneuvers can be useful:
Vagal maneuvers (CSM, Valsalva maneuver)
EGM recording by esophageal, transvenous, or epicardial electrodes
Pharmacologic agent: adenosine, esmolol, verapamil, diltiazem, or edrophonium. In the presence of wide QRS tachycardia, drug intervention to establish the diagnosis of atrial flutter is dangerous and contraindicated; DC cardioversion is indicated.
Atrial flutter is distinguished from atrial tachycardia by the faster rate.

15. Intracardiac Recording Typical Flutter
This slide contains an intracardiac recording of counterclockwise flutter. In counterclockwise flutter, the crista catheter is draped around the lateral RA with the proximal catheter superior and the distal catheter inferior. As you can see from the activation sequence, the high crista is activated first then the low crista, then the CS proximal, and then the His.
Texas Cardiac Arrhythmia, P.A.

16. Intracardiac Recording Counterclockwise Flutter
Zipes, catheter Ablation of Arrhythmias, Futura publishing.

17. Reverse Typical Flutter
Mechanism:
Clockwise macro-reentrant circuit that utilizes a cavotricuspid isthmus to sustain circuit
Induction:
Fast atrial pacing and/or the introduction of multiple premature beats
Termination:
Rapid atrial pacing faster than the flutter rate
Cardioversion
Spontaneous
Pharmacologic therapy
As the name implies, with this flutter the macro-reentrant circuit is clockwise.
Pacing techniques for induction and termination of this arrhythmia, are similar to those used in counterclockwise flutter.
Treatment is similar to that discussed with counterclockwise flutter.

18. ECG Recognition Clockwise atrial flutter
Undulating atrial activity without a baseline
Atrial rate: bpm
Atrial rhythm: Regular
Ventricular rate: Variable
Dependent upon:
AV node conduction properties
Usually a 2:1, 4:1 fixed conduction ratio
Recognition: “notched” upright pattern on the inferior surface ECG (positive deflections in inferior leads and negative deflection in v1)
ECG characteristics of clockwise flutter are similar to those discussed in identifying counterclockwise flutter. A distinguishing difference is the pattern of the flutter waves. A “notched” upright pattern is often seen on the surface ECG inferior leads.

19. ECG Recognition Texas Cardiac Arrhythmia, P.A.
This slide shows a 12 lead ECG depicting clockwise flutter.
Texas Cardiac Arrhythmia, P.A.

20. ECG Comparison Counterclockwise Clockwise
Note that the inferior leads (II, III and aVF) of counterclockwise flutter have a characteristic initial, broad “sawtooth” negative deflection followed by a less pronounced positive wave.
In contrast, clockwise flutter has predominately upgoing flutter waves in the inferior leads that are typically notched and end with a slightly negative component.
Counterclockwise
Clockwise
Zipes, catheter Ablation of Arrhythmias, Futura publishing

21. Intracardiac Recording Reverse Typical Flutter
This slide is an intracardiac recording of clockwise flutter. The crista catheter is positioned the same as noted in the counterclockwise recording of atrial flutter. Notice that the activation sequence is reversed from before. The low crista is activated before the high crista, then His A, and then the CS.
Texas Cardiac Arrhythmia, P.A.

22. Intracardiac Recording Reverse Typical Flutter
Zipes, catheter Ablation of Arrhythmias, Futura publishing

23. Atypical Flutter Mechanism: Induction: Termination:
Macroreentry that does not utilize cavotricuspid isthmus
Macroreentry occur mostly around surgical incision
Rare cases depends on functional barrier
Induction:
Atrial pacing at faster rates than the flutter rate
Termination:
Difficult with programmed pacing
Cardioversion
Pharmacologic therapy
In atypical flutter the reentry circuit may be confined to anatomic barriers including atrial tissue around the fossa ovalis, Bachman’s bundle, and the coronary sinus ostium. The true circuit for this type of flutter is unknown.
Rapid, atypical atrial flutter may be a transitional rhythm between typical flutter and atrial fibrillation.
Programmed pacing can convert the rhythm to atrial fibrillation. Ablation of true atypical flutter is not generally achievable at this time due to the unknown nature of the circuit.
Pharmacologic therapy may consist of any drug that influences conduction velocity and the refractory period. The specific drugs are the same as with AFL.

24. ECG Recognition Atypical atrial flutter
Undulating atrial activity without a baseline
Atrial rate: 340 to 433 bpm
Atrial rhythm: Variable (flutter-fib)
Ventricular rate: Variable
Dependent upon:
AV node conduction properties
Recognition:
Very fast rate and variable cycle length on surface ECG, may progress to atrial fibrillation
A difference in atypical flutter, when compared to counterclockwise and clockwise flutter, is the atrial rate and rhythm. In addition, this rhythm may progress to atrial fibrillation. Of note, some sources do not class this as “flutter”. Instead, it may be referred to as atrial tachycardia from a atriotomy scar, etc.

25. Incisional Atrial Flutter
Atrial rate: Sometimes varies
Mechanism: Incisional macroreentry
Complication of surgery
Congenital heart disease
Treatment: Ablated with good success using focused activation mapping to transect the isthmus of conductive tissue
The location of critical isthmus of conduction can vary depending on the location of the scarring. A thorough knowledge of the patient’s history of heart surgery is needed. This arrhythmia may be seen with big atriotomy scars like ASD repairs or with CABG surgery (where the RA is incised to go on bypass).

26. Evaluation of Atrial Flutter

27. Confirmation of Flutter Circuit
Confirm direction of rotation
During the EP study the direction of the flutter circuit should be confirmed
Flutter should be present before the patient enters the lab, if not, attempts should be made to induce the tachycardia
Direction can be confirmed by using a multi-pole catheter positioned around the tricuspid annulus, and pacing near the isthmus
The direction of flutter is not as important as establishing isthmus dependence. Frankly, counterclockwise and clockwise are ablated the same. For some unknown reason, in clockwise flutter isthmus block is harder to obtain.

28. Atypical Flutter mimicking typical flutter

29. Activation Sequence of Typical Atrial Flutter (LAO View)

30. Fluoroscopic PA and LAO views of a multipolar reference catheter

31. Concealed Entrainment
Used to verify that isthmus is utilized by the tachycardia
Pace the isthmus at a cycle length 20 to 40 msec shorter than the tachycardia cycle length
No change on surface ECG
No change on intracardiac recordings
Tachycardia resumes its original cycle length upon termination of pacing
By pacing near the critical isthmus, entrainment pacing techniques can be used to verify that the isthmus is utilized, and therefore can be ablated. Concealed entrainment is observed when pacing at the critical isthmus. No changes should be observed in the flutter pattern on the surface ECG or the intracardiac recordings. The tachycardia will return to its original cycle length after termination of pacing.

32. Entrainment Pacing
Concealed entrainment: Post-pacing interval=flutter cycle length
220
220
220
220
220 S S S S S
250
250
250
250

33. Treatment of Atrial Flutter

34. Treatment Options: Acute A-Flutter
Pharmacologic therapy
Rapid Atrial Pacing
Direct Current Cardioversion
Two separate goals are used to treat atrial flutter. The first goal is to terminate the flutter and prevent a recurrence. The second goal is to control the ventricular response during the arrhythmia.

35. Treatment Options: Acute A-Flutter
Pharmacologic therapy for rhythm control
IV ibutilide
Oral flecainide, single dose of 300 mg
Oral propafenone, single dose of 600 mg
Pharmacologic therapy for rate control
IV calcium channel blockers (verapamil, diltiazem)
IV beta-blockers (esmolol)
Two separate goals are used to treat atrial flutter. The first goal is to terminate the flutter and prevent a recurrence. The second goal is to control the ventricular response during the arrhythmia.

36. Treatment Options: Acute A-Flutter
Rapid Atrial Pacing
Method of choice in postcardiac surgery atrial flutter
Pacing should be performed from high right atrium because the appearance of positive atrial complexes in ECG lead II is the hallmark of interruption of atrial flutter
Ramp pacing at a rate about 10 bpm faster than flutter rate and then gradually increased until the atrial complexes in lead II become positive
Burst pacing at a rate 120% to 130% of the flutter rate and continued for 15 to 30 seconds until the atrial complexes in lead II become positive; if flutter continued, pacing rate should be increased by 5 to 10 bpm.
Recommended minimum duration of pacing is 10 seconds and stimulus strength of at least 10 mA is needed.
When esophageal pacing is used : a duration of at least 9 to 10 ms and up to 30 mA in strength is needed. Pacing should be initiated at a relatively slow rate to demonstrate that no ventricular capture is inadvertently produced.

37. Treatment Options: Acute A-Flutter
Direct Current Cardioversion
Contraindicated in patients after having recently eaten or those with COPD
Using a standard shock, at least 50 J is generally recommended. Because 100 J is virtually always successful and virtually never harmful, it should be considered as the initial shock.

38. Treatment Options: Chronic A-Flutter
Pharmacologic therapy
Currently class IA, IC and III antiarrhythmic agents have demonstrated efficacy in suppression of atrial flutter.
In the absence of structural heart disease, class IC are the drugs of choice; class III likewise may be effective.
Catheter ablation therapy
Two separate goals are used to treat atrial flutter. The first goal is to terminate the flutter and prevent a recurrence. The second goal is to control the ventricular response during the arrhythmia.

39. RF Ablation of Typical Flutter
Cavotricuspid isthmus is the target for typical and reverse typical flutter ablation
The endpoint of ablation is bidirectional isthmus block persisting for minutes
The precise point of the isthmus that the ablation line should cross is variable, however it is usually midway between the septal and the anterior RA (6 o’clock of the TR in a 45° LAO view)

40. Oblique View of Right Atrium
Superior Vena Cava
Crista Terminalis
Fossa Ovalis
Pectinate
Muscle
A review of landmarks is helpful, before discussing ablation techniques.
Eustachian
Ridge
Orifice of Coronary Sinus
Inferior Vena Cava
Netter F. Atlas of Human Anatomy. 1989;Plate 208.

41. RF Ablation of Typical Flutter
A linear lesion needs to be created to sever the macroreentrant circuit
The lesion starts from the tricuspid annulus and runs back to the IVC
The lesion must be constant and contain no skips, otherwise the circuit can remain
Termination will occur during RF delivery
Bi-directional block is confirmed for acute success. Ablation of isthmus dependent flutter (clockwise and counterclockwise) depends on complete, bi-directional block at the isthmus.

42. Catheter Location for Atrial Flutter Ablation
Crista
Free wall

43. Atrial Flutter Ablation
AFL termination
This slide depicts termination of atrial flutter during RF current delivery.

44. Conduction Block
Before the ablation, pacing near the CS os would allow the impulse to travel in both directions, eventually colliding on the lateral wall.
After ablation, pacing near the CS os only allows the impulse to travel in one direction, eventually terminating at the line of block.
Singer: Interventional Electrophysiology. Williams & Wilkins 1997; 367.

45. Isthmus Block: Activation sequence during pacing
Proximal CS pacing
Low RA pacing

46. Assessing isthmus block during CS pacing
No block
No CTI block
CTI block

47. Other Markers of Conduction Block
Increase in trans-isthmus conduction time
differential pacing
Double potentials
ms interval between potentials along entire ablation line
Reversal of electrogram polarity on the opposite side of the ablation line from the pacing site
Change in p-wave morphology pacing lateral to the ablation line
This slide summarizes potential markers of conduction block in the common flutter isthmus. First, an increase in trans-isthmus conduction time with differential pacing so that after block is achieved, pacing on one side results in a long conduction time to the opposite side.
If you move the pacing site a little bit further from the line of block, you will see that the conduction time to the opposite side decreases when you have block. This increases when there still slow conduction through the flutter isthmus. Secondly, double-potentials, as we discussed, with a relatively long interval of more than 100 to 110 milliseconds between the two potentials. We like to see this present along the entire ablation line.
If we move our pacing site a little bit further from the line of block, then the conduction time from the pacing site to the potential generated by the wave front activates the distal side of the line becomes shorter and that to the proximal side becomes a little bit longer and the opposite occurs if there is still conduction through the isthmus. Thirdly, reversal of the electrogram polarity on the opposite side of the line of block, when block is achieve, and finally one can also look for changes in P-wave morphology when pacing in the low lateral right atrium on the free wall side of the line of block and these are all reviewed nicely in the references listed at the bottom of this slide.
On a daily basis, we find that interpreting the double-potentials and simply doing differential pacing is quite useful. There are times where the double-potentials are not easily detectible in the common isthmus, particularly if you have had to do a lot of RF and you have low amplitude signals everywhere through the isthmus. Then it is useful to have some of these other markers to help confirm when you have conduction block.

48. Isthmus Block: Differential pacing

49. Isthmus Block: Double potentials

50. Isthmus Block: Change in electrogram configuration beyond the line of ablation

51. Complicating factors in atrial flutter ablation

52. Fragmentation of isthmus electrograms after radiofrequency application

53. Fragmented continuous electrogram at the gap of the ablation line

54. Terminal crest permeability: mimicking isthmus conduction

55. Success Rates of Catheter Ablation of Atrial Flutter
Acute Follow-up Long-Term Study # Success (%) (mo) Success (%)
Feld
Cosio
Lesh
Calkins
Kirkorian
Fischer
Steinberg
Poty
Saxon
Cauchemez
Nakagawa
Poty *
Fischer

56. Complications of Flutter Ablation
Pain: especially if close to the septal RA
- pain is usually controlled by IV sedation
AV block: especially if RFA applicated close to low portion of Koch' triangle around the CS ostium
- Av block may be related to vagal effect
- AV block was completely reversible spontaneously or preventable by atropine
There are no report of tricuspid valve dysfunction or coronary artery obstruction

57. Clinical course and recurrences
Since adoption of isthmus block as an endpoint, recurrence rates less than 10% are commonly reported.
Appearance of other types of flutter during follow-up is unusual.
The main problem during follow-up is atrial fibrillation, usually paroxysmal form, in ≥ 30% of patients.

58. Summary
Atrial flutter ablation is effective way for Atrial Flutter control with low risk of complications.
Improved mapping techniques along with enhanced imaging will improve the success rate of flutter ablations.
This module has discussed the various types of atrial flutter, along with treatment modalities. The use of RF ablation for atrial flutter is a new treatment option for selected patients with atrial flutter.