An Atypical “Isthmus”-Dependent Atrial Flutter Case

Introduction

Cavotricuspid isthmus-dependent atrial flutter may be one of the best examples for which there is a high correlation between electrocardiogram morphology and circuit mechanism/location. Nevertheless, some important variations may be observed in the presence of modified or complex anatomies (eg, enlarged right atrium, scarred atrium).

In those situations, a three-dimensional mapping system may be useful to define the exact location of the circuit, after having understood its mechanism.

Case Description

We report the case of a 45-year-old patient who was referred for recurrent palpitations. His past medical history included a D-transposition of the great vessels with a Blalock-Hanlon (associated pulmonary stenosis) procedure, and then a Mustard intervention (atrial switch) at the age of 2. In 1986, the patient was implanted with a pacemaker due to sick sinus syndrome, with a battery replacement in 1995. In 2007, a lead dysfunction was noticed, and an attempt to implant a new lead was tried but failed in the presence of a superior vena cava occlusion.

The arrhythmia occurred, despite antiarrhythmic (80 mg sotalol daily) and antithrombotic (rivaroxaban 20 mg daily) drug therapy. The ECG on admission is represented in Figure 1. It shows a broad QRS and regular tachycardia (150 beats per minute) with right bundle morphology and right axis deviation. No capture or fusion beat is visible on the tracing. It is important to note that patients with transposition of the great arteries may experience ventricular tachycardia during follow-up, with a sudden death incidence of approximately 0.48% per year.¹

A carotid compression was then performed, revealing an atrial flutter with negative F waves in the inferior leads but also in V1, with a measured cycle length of 300 msec, and a 4:1 atrioventricular transmission, with the same complete right bundle branch block and axis deviation (Figure 2). The morphology of this flutter was not compatible with a classical isthmus-dependent atrial flutter circuit.²

After having performed a cardiac CT scan for 3D reconstruction, an EP study was proposed. A decapolar catheter was inserted in the systemic venous atrium after ultrasound-guided right femoral vein puncture,³ and entrainment maneuvers confirmed that the flutter circuit was not located in this chamber. An activation map was performed (atrial flutter cycle length of 240 msec) using a 3D electroanatomical mapping system (CARTO 3, Biosense Webster, Inc., a Johnson & Johnson company) via right femoral artery access. Because of the complex anatomy, a magnetic catheter was chosen for mapping (NAVISTAR RMT THERMOCOOL, Biosense Webster, Inc.) using the Niobe Robotic Magnetic Navigation System (Stereotaxis). The retrograde approach was chosen because of the absence of any baffle leak visible on echocardiography, and the ablation catheter progressed from the aorta towards the right ventricle, and then from the pulmonary vein atrium through the tricuspid valve (Figure 3). Next, an image integration with the CT scan was performed (Figure 4). Entrainment maneuvers confirmed the macroreentrant nature of the circuit, which was dependent on an isthmus located between the tricuspid valve anteriorly and the pulmonary vein atrium posteriorly. An ablation line was created that allowed atrial flutter termination (Figure 5) with confirmation of bidirectional block, which persisted after 30 minutes.

The patient was discharged the next day, and after 14 months of follow-up, he was free from any recurrent atrial arrhythmia without any antiarrhythmic drugs.

Discussion

Our case illustrates the importance of defining the exact location of the critical isthmus involved in the circuit, especially in the presence of complex or modified anatomy.⁴ The advantages of using magnetic navigation for complex anatomies were previously reported by Ernst et al in their series of arrhythmia ablations in congenital heart disease.^5,6 Their initial experience reported 77% successful ablation in a series of 9 patients with transposition of the great arteries using remote magnetic navigation and an exclusive retrograde arterial approach. The chamber of interest was the pulmonary vein atrium in most cases. In our case, because of the absence of a baffle leak, we decided not to perform a transbaffle puncture since the rigidity of the material might render the puncture technically challenging, although still feasible in some cases.⁷

Conclusion

Atrial flutter ablation may be challenging in the presence of modified/complex anatomy. It is mandatory to precisely define the critical isthmus for those procedures. In this purpose, image integration gives a roadmap before starting the procedure, and remote magnetic navigation may be helpful as well in these complex anatomies. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein.

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