Invasive cardiac ablation techniques for the treatment of arrhythmias are well known in the art. For example, U.S. Pat. Nos. 5,443,489 and 5,480,422, whose disclosures are incorporated herein by reference, describe systems for ablating cardiac tissue by application of radio-frequency (RF) energy to the tissue through a catheter.
In a cardiac ablation procedure, it is important to apply sufficient energy to create a lesion that will block undesired conduction, while minimizing collateral damage to surrounding tissues. Various methods have been proposed for monitoring ablation procedures for this purpose. For example, U.S. Pat. No. 6,743,225, whose disclosure is incorporated herein by reference, proposes to measure electrical activity of the cardiac tissue proximate a lesion site during an ablation treatment, and then to compare the measurements in order to determine whether the lesion is clinically efficacious so as to be able to block myocardial propagation. The electrical activity can include electrical signals corresponding to the local electrogram signal, pacing threshold value, and the like.
As another example, U.S. Patent Application Publication 2007/0198007, whose disclosure is incorporated herein by reference, describes methods and devices for monitoring intracardiac ablation progress in near real time, by evaluating capture of a pacing signal while ablation energy is concurrently directed to a target site. Sufficiency of ablation is indicated by failure of signal capture at a maximum predetermined pacing voltage. An electrode in a cardiac catheter is simultaneously used to test pacing capture and to deliver ablation energy.