**7. Ablation**

#### **7.1. Radio-frequency ablation**

Radio-frequency ablation uses radio-frequency energy in the form of electrical current delivered from typically 4 to 8 mm catheter tip and collects it on an indifferent electrode patch which is commonly placed on the mid-spine in the lumbar region. The density of the current at the catheter tip causes an ablation lesion 4–6 mm deep in the cardiac tissue which interrupts electrical conduction. An 8 mm catheter tip is increasingly being used as the first choice in CTI ablation due to the length and depth of ablation line needed. Irrigated catheters with a shorter tip length of 3.5–4 mm are employed in redo cases where deeper ablation lesions are needed.

In the management of especially typical atrial flutter, ablation has evolved as the first-line treatment, even after a single episode of documented symptomatic atrial flutter above antiarrhythmic pharmacotherapy [27]. In this multicentric prospective randomised study, amiodarone and radio-frequency ablation were compared in 104 patients (aged 78 +/-5 years; 20 women) with atrial flutter. The recurrence of atrial flutter was 3.8 % versus 29.5 %, P<0.0001. Ablation therapy for atrial flutter has a success rate depending on the studies of ~90–95 % [28]. The other forms of atrial flutter generally also respond best to ablation if the circuit can be mapped and a line of conduction is performed.

The conventional method of CTI ablation was to make a linear ablation line along CTI as guided by electrograms; however recently, the 'maximum voltage-guided' technique using radiofrequency application has been studied as an alternative method and has demonstrated to be equivocal in achieving bidirectional cavo-tricuspid isthmus block. Ablation for atrial flutter using the "Maximum Voltage Guided" technique results in significantly less ablation appli‐ cations than the traditional approach, potentially by concentrating ablation lesions on the muscle bundles responsible for Trans-isthmus conduction [29, 30].

### **7.2. Complications**

During ablation, signs that can indicate that the catheter is ablating in a possibly unsafe position can include ventricular ectopy or a sharp increase in measured catheter tip impedance. Ventricular ectopy could indicate that the ablation catheter is in close proximity to the tricuspid annulus or right ventricle and potentially result in valve damage. A sharp impedance rise could indicate that the catheter has been pulled back into the IVC or wedged into a pouch on the isthmus which can create a sharp temperate increase and a possibility of a steam pop.

In patients who have had persistent atrial flutter, ablation can result in post-reversion asystole. This is commonly due to underlying sinus node disease. So one should always be ready to pace in either the atria (assuming normal AV node conduction) or ventricle (assuming a ventricular catheter is in place). Rarely, cavo-tricuspid isthmus ablation can lead to atrioven‐ tricular block or myocardial infarction if the right coronary artery or the artery to the atrio‐ ventricular node is occluded by an ablation lesion.

Other complications which can potentially occur during atrial flutter ablation include venous access/puncture (one in 100) such as hematoma, bruising and deep vein thrombosis, with or without pulmonary embolism. A small risk of stroke (1 in 500), pericardial effusion or death (1 in 1,000) remains with radio-frequency ablation method.

#### **7.3. Emerging trends and novel technologies**

Recently, the focus of atrial flutter ablation has been on emerging technology. There has been some promising data about the use of contact force catheter and its effectiveness at predicting the lesion size using the lesion size index (LSI). It is based on an algorithm which integrates contact force, radio-frequency power and ablation duration to make a key parameter, forcetime integral [31]. Contact force catheters are used for pulmonary vein isolation. Contact force parameters however have not yet been employed for atrial flutter ablation. We are currently involved in a research study of a contact force catheter, and the initial results have shown that the guidance of CTI ablation using novel CF parameters can be performed successfully. It is independent of traditional parameters and demonstrates excellent short- to medium-term results.
