Tachycardia's (fast heart rhythms) can lead to troublesome palpitations, dizziness, blackouts and breathlessness. They are caused either by a cluster of abnormal cells within the heart, or an electrical short circuit which rotates rapidly around the heart. Sometimes these can be controlled with tablets, though owing to side effects many patients want something else. Many tachycardia's can be cured by a procedure known as an "ablation". In essence, either the focus of abnormal cells or the narrowest point of the short circuit causing the abnormal heart rhythm (the source) is electrically destroyed (burnt) resulting in restoration of the normal heart beat.

One form of tachycardia is known is Atrial Tachycardia (AT). These arise from the top two chambers of the heart (the atrium). Interestingly, this problem is frequently seen in patients who have previously undergone an ablation or surgical procedure for a condition called Atrial Fibrillation. In others the reason for its occurrence is unknown. Current strategies to find the "source" during an ablation procedure are technically challenging resulting in long procedure times. Sometimes the wrong source is found resulting in ablation at the incorrect site.

Ripple Mapping (RM) is a novel system that Investigators at Imperial College are looking to study. RM displays electrical information within the heart as a series of bars coming out of the chamber, with each bar representing signals travelling down the heart. By seeing the pattern of electrical information, they believe it will show the pattern of the tachycardia better than conventional techniques. In a previous retrospective study that they conducted, RM found the source of the tachycardia in 80% of the maps, compared to only 50% with the current system. Investigators at Imperial College have identified why they did not get 100% and they believe that, in future, RM will find the source of the tachycardia first time, and every time.

Conventional mapping strategies used to find the "source" of "atrial tachycardia" within the heart are technically challenging resulting in long procedure times. Sometimes the wrong source is found resulting in ablation at the incorrect site.

In a retrospective study conducted by investigators at Imperial College, Ripple Mapping (RM) found the source of the tachycardia 80% of the time, compared to only 50% with conventional maps (known as local activation time maps). They have since studied the reasons why did not achieve 100%, but could not improve matters with a retrospective data-set. They believe that, in future, Ripple mapping will find the source of the tachycardia first time, and every time. The purpose of this study is to prospectively test whether Ripple Mapping is better at finding the source of the "atrial tachycardia" (AT) than conventional local activation time mapping.

Patients referred for clinically indicated AT ablation by their electro-physiologist will be recruited. For each patient recruited to the study, they will be block randomized into 2 arms: Ripple Mapping guided AT ablation, or Conventional AT guided Ablation (local activation time mapping). Following explanation of the study the patients will be allowed time to decide on whether they would like to participate.

Following completion of the consent procedure the patient will undergo the electrophysiology study as is routine standard practice. This is usually performed by inserting plastic tubes (catheters) into the heart using the vessels in the groin. Once the catheter is in the atrium (top chambers of the heart) the catheter will be moved to different locations in the chamber to gather the electrical information of the tissue. Using "CARTO3v4 ConfiDENSE", a 3-Dimensional map of the geometry of the heart chambers will be constructed.

Patient randomized to RM will proceed as follows: Once sufficient points have been collected, the Ripple Map will be played in order to diagnose the source of the tachycardia. In the context of a clear diagnosis, the operator can proceed to ablation at the defined source from the Ripple map. Termination of the tachycardia with ablation will be used to confirm the diagnosis was correct. A single entrainment is permissible where the diagnosis is unclear.

Patients randomized to conventional local activation time (LAT) mapping will proceed according to standard practice of the operator. When the operator is satisfied adequate number of points have been collected, the operator can proceed to ablation if the diagnosis is clear. A single entrainment is permissible where the diagnosis is unclear. The endpoints measured will include:

1. Tachycardia change or termination following first series of ablations with Ripple Mapping vs local activation time mapping.
2. The reliance on entrainment.

Inclusion Criteria:

1. Patients undergoing clinically indicated ablation for atrial tachycardia using 3D mapping.

Exclusion Criteria:

1. Patients with typical flutter.

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