Determining the Pathophysiological Role of Slow Conduction Channels Identified by Ripple Mapping of the Ventricular Scar.

In patients with a previous heart attack, the scar formed in the left ventricle (bottom chamber of the heart) consists of dead tissue mixed with strands of live tissue which form "conduction channels" (CC's). These Conduction channels can cause dangerous heart rhythms such as Ventricular Tachycardia (VT). This can lead to symptoms such as shortness of breath, dizziness, blackouts, and, in some, sudden death.

Patients at risk of sudden death receive special implanted devices called implantable cardioverter defibrillators (ICD) and can present with recurrent painful and debilitating ICD therapies consisting of internal shocks. Patients experiencing frequent ICD shocks due recurrent VT usually undergo a procedure to burn (ablate) the area of scar within the heart thought to be the source of the VT. This involves catheters (plastic tubes) inserted into the heart via the groin vessels allowing the cardiac electrophysiologists to obtain information about the scar. Scar tissue has low electrical voltage. By measuring the electrical voltage of the tissue in the heart, areas of scar as well as areas of live, healthy tissue can be identified and mapped. By burning (ablation) these abnormal channels of live tissue within scar (conduction channels), this can effectively reduce the episodes of VT a patient experiences, thereby reducing the frequency of shocks they experience and improve their quality of life.

In any one patient, more than 1 conduction channel and hence source of VT can be found. Current mapping technologies are incapable of providing electrophysiologists with the information that is required to locate all these conduction channels. Therefore ablation strategies have shifted from ablating in a single location in the scar, to extensive ablation within the scar in the hope that ALL conduction channels will be burnt. However, this extensive ablation strategy has no globally agreed consensus with several techniques used worldwide.

The disadvantage of this extensive ablation strategy is that the potential regions which can be responsible for VT can be large, requiring extensive ablation and therefore prolonged procedure times in sick patients who are unable to tolerate such lengthy procedures. In its current state, VT ablation by any strategy is technically challenging and time consuming with procedural times as long as 8 hours. In addition, although acute procedural success ranges from 77% to 95%, recurrence rates remain high - up to 50%.

Therefore, identification of ALL conduction channels within scar is a desirable goal for catheter ablation therapy in VT. Ripple Mapping (RM) is a novel mapping program which allows simultaneous display of "voltage" and "activation" data of the underlying ventricular tissue. RM therefore has the potential to display more detailed information of the functional properties of the underlying scar including any interspersed live tissue channels. Investigators at Imperial College have demonstrated the proof of concept of RM and validated the program in a series of abnormal heart rhythms that arise within the upper heart chambers (the atria) where RM was found to have a superior diagnostic yield as well as aiding the operator in reaching a diagnosis in shorter time when compared with conventional mapping systems. The Investigators subsequently performed a retrospective analysis of 21 patients undergoing post infarct VT ablation. All documented locations with concealed entrainment or perfect pace matches to the induced or clinical VT coincided with Ripple Mapping Conduction Channels (RMCC). In patients where ablation lesions overlapped all identified RMCCs, these patients remained free of VT recurrence for >2 year follow up interval.