ECG-I Targeted Ablation for Persistent AF Not Responding to Pulmonary Vein Isolation Results of a Two Staged Strategy. (TARGET-AF2)

Atrial Fibrillation (AF) is the commonest heart rhythm disturbance and is associated with significant morbidity and mortality. Catheter ablation (CA) is a procedure where catheters (leads) are passed into the heart and energy is used to disrupt and isolate (by freezing or cauterising) heart tissue causing AF. CA is an established therapy for AF. Success rates for CA for paroxysmal AF lies in the region of 70% or better. However, success rates for persistent AF is much lower and estimates lie in the region of 30-60%.

Current CA protocols for AF centre on isolating the pulmonary veins (the pulmonary veins drain into the left atrium) which have been proven to trigger AF. Pulmonary Vein Isolation (PVI) ablation alone seems sufficient to remove the trigger for the vast majority of patients with paroxysmal AF. However, in patients with persistent AF it is common for AF to continue after the pulmonary veins have been electrically isolated.

The difference in success rates between the paroxysmal and persistent form of AF is thought to be due to changes within the heart atria after AF has been established for some time. In persistent AF the atria dilate and remodel structurally and electrically, and therefore the maintenance of persistent AF differs from paroxysmal AF.

Persistent AF is thought to be maintained by focal sources, whether rotors or sites of radial activation. Currently, targeting other sites within the atria in addition to PVI such as fractionated electrograms (areas of electrical activity) are thought to be imprecise and require extensive ablation. Often AF will persist despite targeting additional sites within the atria.

One particular challenge is to select patients likely to benefit from CA. CA carries an approximate less than 1% risk of life threatening complication. Therefore being able to select suitable patients is desirable in order to prevent unnecessary procedures.

Currently clinical characteristics of patients or structural imaging have limited accuracy in selecting patients likely to benefit from CA. Mapping studies have shown that patients with persistent AF who have higher frequency signals near the pulmonary veins than being distributed in the left atrial body are more likely to terminate to sinus rhythm (normal heart rhythm) with PVI alone and to maintain sinus rhythm.

Studies have suggested that patients undergoing standard PVI ablation procedures for persistent AF who have coincidental interruption of drivers have a far better long term outcome. This suggests that the characteristics of atrial heart tissue and electrical activation patterns maintaining AF are likely to determine the response to ablation therefore it may be possible to determine more directly and accurately the likelihood of success by performing non-invasive mapping of the atria using the ECG-I.

ECG-I is able to localise the drivers of AF and one of the objectives is to study the electrical characteristics of the tissue. ECG-I is currently being used in research into AF. A recently published a study using ECG-I to identify targets of ablation in 103 patients. The on-going multicentre AFACART study has published early data to suggest that ECG-I can identify the drivers of AF and improve CA success rates.

PHENOTYPE AF is an ongoing clinical trial in which 100 patients with persistent AF are receiving cryoballoon pulmonary vein isolation for persistent AF (NCT03394404). Patients with recurrent AF or atrial tachycardia within 1 year following pulmonary vein isolation for AF within this trial will be recruited into this study. Up to 50 such patients who have failed Pulmonary Vein Isolation will be enrolled. These patients will undergo a second procedure at which time participants will undergo catheter ablation of drivers of AF and will then be followed up for 12 months.