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)

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

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.

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.

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.

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.

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;340:534-544.

Types and Features Flutter Type Mechanism Atrial rate Cure Typical * Counterclockwise 240-340 RFA Macro-reentry Reverse typical * Clockwise 240-340 RFA Atypical Macro-reentry 340-433 RFA * 90% of atrial flutters fall into the typical or reverse typical category.

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.

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.

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.

ECG Recognition Typical atrial flutter Undulating atrial activity without a baseline Atrial rate: 240 - 340 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

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 240 - 340 bpm. The ventricular response is fast, but it is regular.

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.

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.

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

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.

ECG Recognition Clockwise atrial flutter Undulating atrial activity without a baseline Atrial rate: 240 - 340 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.

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

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

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.

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

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.

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.

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).

Evaluation of Atrial Flutter

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.

Atypical Flutter mimicking typical flutter

Activation Sequence of Typical Atrial Flutter (LAO View)

Fluoroscopic PA and LAO views of a multipolar reference catheter

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.

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

Treatment of Atrial Flutter

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.

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.

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.

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.

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.

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 25-30 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)

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.

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.

Catheter Location for Atrial Flutter Ablation Crista Free wall

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

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.

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

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

Other Markers of Conduction Block Increase in trans-isthmus conduction time differential pacing Double potentials 100 - 110 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.

Isthmus Block: Differential pacing

Isthmus Block: Double potentials

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

Complicating factors in atrial flutter ablation

Fragmentation of isthmus electrograms after radiofrequency application

Fragmented continuous electrogram at the gap of the ablation line

Terminal crest permeability: mimicking isthmus conduction

Success Rates of Catheter Ablation of Atrial Flutter Acute Follow-up Long-Term Study # Success (%) (mo) Success (%) Feld 12 83 4 67 Cosio 9 78 18 78 Lesh 18 94 9.6 67 Calkins 16 81 10 69 Kirkorian 22 86 13 77 Fischer 80 90 20 83 Steinberg 16 100 8 75 Poty 12 100 9 92 Saxon 51 88 14 82 Cauchemez 20 95 8 75 Nakagawa 30 100 10 83 Poty 44 98 12.1 50* Fischer 200 95 24 85

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

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.

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.