Introduction

Atypical atrial flutter is a type of supraventricular tachycardia which originates from a macro-re-entrant circuit in the atria that does not involve the CTI (cavotricuspid isthmus) with ECG patterns differing from the counterclockwise and clockwise typical flutter

 Classification and ECG findings

1. Atypical right atrial flutters - lesion macroreentrant tachycardia (an atriotomy scar or suture line can act as an obstacle to conduction and create reentry – most common) or non-atriotomy related right atrial flutter (areas of low voltage in the right atrium)
2. Atypical left atrial flutters –  left atrial macroreentry (anatomic obstacle like the mitral annulus), post-ablation AF (incomplete ablation lines from either a transvenous catheter ablation or a surgical Maze procedure). The most frequent left atrial flutters are perimitral, peripulmonary veins, septal, roof and posterior wall macro reentry.

‍ECG findings

- P waves are absent
- F waves are regular, but there may be an isoelectric appearance between F waves 
- No clear F wave morphology - atrial scar can alter conduction velocity and direction

- Right atrial flutters – negative F wave in V1

- Left atrial flutters – variable morphology
 - positive or isoelectric F waves in V1
 - often positive F waves in the inferior leads II, III, aVF

- Lower loop re-entry (around the inferior vena cava) - negative F waves in the inferior leads 

- Upper loop re-entry (right atrium) - positive F waves in the inferior leads and negative, flat, or barely positive F waves in lead I.

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Causes

- Right atrial atypical flutter is associated with atrial sutures and patches used for complex congenital heart disease surgery or following surgical atriotomy. Rate control is often difficult due to the regularity and usually slow rate of the tachycardia.

- Left atrial atypical flutters have circuits around electrically silent areas of abnormal tissue, following medical interventions or progressive atrial degeneration/fibrosis (AF ablation, surgery for different conditions with incisions or cannulation).

- In some cases, electrophysiological study is the only way to find the mechanism causing atypical flutter and plan an ablation, when needed.

‍ECG 1

Atypical atrial flutter with variable block

• narrow complex atypical flutter
• atrial rate 375 bpm
• ventricular rate 115 bpm
• positive flutter waves in V1 – suggesting left atrium re-entrant circuit

• positive to almost isoelectric flutter waves in the inferior leads II, III, aVF

ECG 2 

Atypical atrial flutter with 2:1 block

• narrow complex atypical flutter
• positive flutter waves in V1 – suggesting left atrium re-entrant circuit

Management

Decreasing atrioventricular (AV) nodal conduction physiologically with a vagotonic maneuver (such as the Valsalva maneuver or carotid sinus massage) or with a rapidly acting drug (such as adenosine, verapamil, or esmolol) will increase the AV nodal block and reveal the atrial F waves.

Acute therapy

1. Hemodynamically unstable patient – urgent synchronized cardioversion
2. Hemodynamically stable – diagnostic use of adenosine and pharmacological termination or cardioversion 

Adenosine  is useful for diagnostic purposes, - by decreasing atrioventricular (AV) nodal conduction with a vagotonic maneuver or with adenosine the atrial F waves are revealed
! AV node is not involved in the flutter circuit > adenosine does not terminate the rhythm !

Pharmacological termination - i.v. ibutilide or i.v. or oral dofetilide (in-hospital) are recommended for conversion to sinus rhythm

Synchronized cardioversion (low-energy)

High-rate atrial pacing - might be considered for termination of atrial flutter in the presence of an implanted pacemaker or defibrillator

Rate control therapy (not often successful) - Beta blockers (i.v. esmolol, i. v. metoprolol),  Calcium channel blockers (verapamil/diltiazem i.v.)

Chronic therapy

- Catheter ablation – recommended for all symptomatic or recurrent atrial flutters

- Beta-blockers or non-dihydropyridine calcium channel blockers (verapamil or diltiazem) should be considered if ablation is not desirable or feasible

Anticoagulation

-         patients with atrial fibrillation, atrial flutter or any supraventricular tachycardia  with fast atrial action are at risk of thrombus formation and thromboembolism

-         effective anticoagulation is recommended in acute settings pre-cardioversion as well as chronic oral anticoagulation in persistent arrhythmias

-          to estimate embolic risk use CHA2DS2-VASc scoring system

-          to estimate bleeding risk use HAS-BLED risk score

-          oral anticoagulants – warfarin, NOAC (dabigatran, apixaban,..)

-          parenteral anticoagulants – unfractionated heparin or low molecular weight heparin

Picture 1 Treatment of atrial flutter as per ESC guidelines

References

1. JORDAN M PRUTKIN, MD, MHS, FHRS. Electrocardiographic and electrophysiologic features of atrial flutter. UpToDate [online]. [cit. 2021-02-01]. 
2. CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press
3. HARRIGAN, Richard A., William J. BRADY a Theodore C. CHAN. The ECG in Emergency Medicine. Emergency Medicine Clinics of North America [online]. 2006, 24(1) [cit. 2021-01-29]. ISSN 07338627. Dostupné z: doi:10.1016/j.emc.2005.08.001
4. Strauss, David G., et al. Marriott's Practical Electrocardiography. Wolters Kluwer, 2021
5. Brugada J, Katritsis DG, Arbelo E, Arribas F, Bax JJ, Blomström-Lundqvist C, Calkins H, Corrado D, Deftereos SG, Diller GP, Gomez-Doblas JJ, Gorenek B, Grace A, Ho SY, Kaski JC, Kuck KH, Lambiase PD, Sacher F, Sarquella-Brugada G, Suwalski P, Zaza A; ESC Scientific Document Group. 2019 ESC Guidelines for the management of patients with supraventricular tachycardiaThe Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC). Eur Heart J. 2020 Feb 1;41(5):655-720. doi: 10.1093/eurheartj/ehz467. PMID: 31504425.
6. https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-11/Atrial-flutter-common-and-main-atypical-forms

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