Characterization of a long linear thermolesion in rabbit atria by high density mapping

A major problem in radiofrequency ablation is to evaluate if linear atrial lesions are transmural and continuous. Characteristics of the atrial electrograms recorded from these lesions might be useful to determine the completeness of linear atrial lesions. In seven isolated perfused rabbit atria, a long transmural linear lesion was made with a hot needle (perfused with water of 80 degrees C) (width 2 +/- 0.2 mm). The lesion extended from the orifice of the superior caval vein to the A V ring. High density mapping (240 electrodes, 7.5 x 7.5 mm) of the right atrium was performed before and after the lesion. Complete bidirectional conduction block was confirmed by pacing close at either side of the lesion. No change in conduction or electrogram characteristics occurred outside the lesion. From the center of the lesion, low amplitude double potentials were recorded. The conduction delay around the lesion and the width of the double potentials showed a high correlation (R2 = 0.99) and were both dependent of the site of pacing. From the boundaries of the lesion towards its center, the amplitude and slope of the unipolar electrograms decreased exponentially by 72 +/- 5 and 85 +/- 3%. From the decay of these electrotonic potentials a space constant (lambda of 0.79 +/- 0.04 mm) could be calculated for the lesion. Unipolar electrograms recorded from a complete and transmural linear atrial lesion are electrotonic in nature. Their characteristics could be used to evaluate the width and depth of the lesion.