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..................................................................... RA MRAT may also occur in the absence of previous intervention. Most of these are sustained around areas of ‘electrical silence’ in the RA free wall, probably due to fibrosis.224,264,266

Atypical atrial flutter could also arise from upper loop re-entry in the right atrium with conduction through the gap in the crista terminalis.269 Rate control is often difficult due to the regularity and usually slow rate of the tachycardia. Antiarrhythmic drugs are often ineffective, or their use is limited because of structural heart disease and comorbidities. Radiofrequency ablation of often several critical isthmuses is the most effective treatment. Circuits around scars of longitudinal atriotomy can be mapped and ablated with good long-term results.267,292 However, owing to the complexity of possible substrates and difficulty of reaching critical isthmuses, ablation procedures for these patients should be restricted to experienced operators and centres.

11.1.4.2.2 Left atrium macro2re-entrant atrial tachycardia. Circuits sustaining LA atypical flutter/MRAT are most usually due to electrically silent areas of abnormal tissue, following medical interventions or progressive atrial degeneration/fibrosis.268 Anatomical obstacles such as the ostia of PVs, and mitral annulus, are often involved. Owing to its widespread use, AF ablation is the procedure that frequently causes the lesions able to sustain re-entry circuits, usually after linear ablation or extensive defragmentation. Pre-existing atrial disease is also predictive of macro-re-entry.293 Localized segmental PV disconnection may cause focal tachycardias,294 and circumferential antral ablation may also create MRAT due to gaps in the lines.295299 AT due to a small re-entrant circuit after ablation of AF may possibly be distinguished from macro-re-entry by a shorter P-wave duration. RA MRATs have a higher incidence of negative polarity in at least one precordial lead compared with LA macro-re-entry.300302

Atrial circuits are also created after surgery for different conditions, including mitral valve disease, and are related to incisions or cannulation.303 Surgery to treat AF may also result in macro-re-entry circuits and focal AT.304 Circuits causing atypical left MRAT may also occur in the LA without prior intervention, commonly, but not invariably, associated with significant left heart disease.305 These are based on areas of electrical silence, probably due to fibrosis, engaging anatomical obstacles such as the ostia of the PVs or the mitral annulus, and may be ablated by interrupting critical isthmuses.265,306 Circuits may also happen in the LA septum due to slow conduction caused by atrial disease or antiarrhythmic drugs.307

©ESC 2019

Atrial flutter/MRAT

Amiodarone

(IIb C)

Catheter ablation

(I A) Catheter ablation

in experienced centres (I B) Beta-blocker

or diltiazem or verapamil

(IIa C) Catheter

ablation (IIa B)

No Yes

Yes No

Yes No If ineffective

If ineffective or not tolerated

Symptomatic and

recurrent

Drug therapy

desirable

CTI dependent

flutter

Figure 12 Chronic therapy of atrial flutter/macro-re-entrant atrial tachycardia. CTI = cavotricuspid isthmus; MRAT = macro-re-entrant atrial tachycardia. Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026