The effect of a residual isthmus of surviving tissue on conduction after linear ablation in atrial myocardium

The aim of this study was to determine the relationship between the size of discontinuities in lines of ablation and wavefront propagation. Discontinu ities in linear radiofrequency lesions used for the treatment of atrial fib rillation may be proarrhythmic and a major clinical problem. A better under standing of the electrophysiological properties of these discontinuities (i sthmuses) may assist in their detection and treatment. Linear lesions were made in the right atrial free wall using a Nd:YAG laser in 12 dogs. Conduct ion properties across the discontinuities were studied by pacing from eithe r side of the lesion. Two of the three isthmuses less than 0.8 mm(2) in cro ss section (smallest 0.2 mm(2)) conducted at extrastimulus intervals of 300 ms. All three failed to conduct at cycle lengths close to the atrial effec tive refractory period. Isthmuses above 0.8 mm(2) (n = 8) conducted at all cycle lengths. Conduction slowing (mean slowest conduction 0.5 +/- 0.3 m/s) occurred in the region of the isthmus but the overall delay was only 6 +/- 6 ms where propagation through the isthmus occurred. The effect on conduct ion of small discontinuities in Linear lesions is dependent on the size of the residual isthmus. All but the very smallest of discontinuities in linea r lesions conduct and therefore have the potential to participate in reentr ant arrhythmias. Efforts should be directed toward the development of ablat ion techniques that reliably produce continuous transmural linear lesions f or cure of atrial fibrillation and flutter.