Clinical Images

Cavotricuspid-Isthmus Dependent Flutter or Left-Sided Atrial Tachycardia?

Kevin Ming Wei Leong, MBBS, MRCP1;  Fernando Guerrero, BSc2;  Phang Boon Lim, MA, MRCP, PhD1

Kevin Ming Wei Leong, MBBS, MRCP1;  Fernando Guerrero, BSc2;  Phang Boon Lim, MA, MRCP, PhD1

J INVASIVE CARDIOL 2017;29(8):E92-E93.

Key words: electroanatomical mapping, arrhythmia, electrophysiology

A 52-year-old man with previous mitral valve replacement, cavotricuspid isthmus (CTI), and left-sided roof-line ablation for previous typical atrial flutter and tachycardia presented with recurrence of symptoms with an atrial tachycardia (AT) measuring 260 ms cycle length (CL) on electrocardiogram. Rhythmia electroanatomical mapping (Boston Scientific) was performed to understand the mechanism of arrhythmia and to guide ablative treatment.

A decapolar catheter was inserted in the coronary sinus (CS) and an Orion basket catheter was used to create a map of the right atrium (RA) (14,494 points). The intracardiac activation sequence on the CS catheter is shown in Figure 1, and a counter-clockwise activation sequence around the RA was observed during the tachycardia (Figure 2 and Video 1). Previous studies in this patient indicated that entrainment attempts would likely terminate the tachycardia, and guided the decision to not perform this maneuver at this point. From this, has CTI reconnection been re-established and how would you proceed?

Confirmation of a CTI-dependent flutter circuit could be performed following successful entrainment by pacing at a rate slightly faster than the tachycardia CL anywhere along the CTI,1 although this risks termination and the possibility of producing a different AT on re-induction. If in sinus rhythm, the differential pacing maneuver would quickly establish the presence of bidirectional CTI block.2 A proximal to distal or distal to proximal CS activation sequence would have also helped differentiate between a right-sided or left-sided AT, but was not useful in this case given indeterminate activation sequence (Figure 1).

Alternatively, closer inspection on the septal aspect of the CTI line showed that the earliest activity appeared to originate from the septal wall with a bidirectional wavefront – one up the septal wall to the roof of the RA and the other toward the CTI terminating at the previous line of ablation (Figure 3 and Video 2). This not only demonstrated the presence of CTI line block, but suggested an AT of left-sided origin with earliest point of breakthrough occurring via the CS ostium just medial to the CTI line. Following a transseptal puncture and mapping of the left atria, three macro-reentrant tachycardia circuits were identified and promptly ablated with non-inducibility demonstrated thereafter. 

This case highlights a potential pitfall in interpreting RA activation maps with previous CTI block during a tachyarrhythmia and underscores the need for careful inspection and/or the acquiring of more data points in the septal region medial to the CTI line, especially when using other electroanatomical navigation systems that do not readily provide high-density mapping.

Videos available here


1.    Waldo AL. Atrial flutter: entrainment characteristics. J Cardiovasc Electrophysiol. 1997;8:337-352.

2.    Shah DC, Haıssaguerre M, Takahashi A, Jaıs P, Hocini M, Clementy J. Differential pacing for distinguishing block from persistent conduction through an ablation line. Circulation. 2000;102:1517-1522.

From 1Imperial College Healthcare NHS Trust, Du Cane Road, London, United Kingdom; and 2Boston Scientific, Ltd, United Kingdom.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Lim reports honoraria and research grants from Boston Scientific. The remaining authors report no conflicts of interest regarding the content herein.

Manuscript accepted January 23, 2017.

Address for correspondence: Dr Phang Boon Lim, Imperial College Healthcare NHS Trust, Department of Cardiology, Block B, Hammersmith Hospital, Du Cane Road, London W12 0HS, United Kingdom. Email: