Introduction:

Linear ablation of the cavotricuspid isthmus (CTI) is the therapy of choice for common atrial flutter and usually a very straight forward approach. However sometimes CTI ablation can become a nightmare and bidirectional block of the CTI is hard to achieve. 

Case report:

We present the case of a 78 year old male patient, that presented with symptomatic atrial tachycardia with sawtooth waves in the surface ECG suggesting CTI-dependent atrial flutter. After informed consent and intraprocedural nearly perfect entrainment around the tricuspid anulus and proximal to distal activation pattern in the coronarysinus, we diagnosed CTI-dependent atrial flutter and performed linear ablation of the CTI that did not terminate the tachycardia. After repeated and broadened linear ablation, the tachycardia cycle length was still unaltered. We then decided to perform electric cardioversion and check for CTI-block, which revealed a conducting CTI without a significant delay. A point-by-point three-dimensional map using the ablation catheter under continuous proximal CS-stimulation revealed in the bipolar voltage map a broad scar area with healthy myocardium on both sides (Fig. 1). The activation map showed a block line in the ablated area and a distinct focal activation pattern originating from a site about 2cm lateral of the ablation lines as shown and clear collision at the ablated site (Fig. 2). At the breakthrough site we found the earliest signals lateral of the CTI line and unipolar signals were monophasic negativ without an R-wave (Fig. 3). Focal ablation at this site lead to immediate successful bidirectional CTI block.

Discussion:

Linear ablation of CTI is well established in patients with common atrial flutter but difficulties in the creation of the blockline can be encountered. Besides insufficient lesion formation due to a variety of reasons such as poor catheter-tissue contact, pouches or insufficient contact force. Another explanation proposed by some scientific papers is an epicardial, possibly fat-isolated conducting musclefiber that might be immune to RF-ablation at the chosen linear ablation site.

The prevalence of epicardial-side conduction in the course of CTI was investigated by a japanese working group using a non-contact mapping system. In this study, 61% of the patients had epicardial-side conduction which led to a significantly higher number of RF-applications needed to achieve bidirectional CTI block (9.6 +/− 5.9 vs. 17.2 +/− 10.3, p<0.01), with an overall low number of patients in which bidirectional CTI block could not be achieved by extensive ablation (Nakajima et al; Circulation. 2009;120;S644).

Fig. 1

Fig. 2

Fig. 3