Cryoablation of ventricular tachycardia guided by return cycle mapping after entrainment

Background: Although the implantable cardioverter-defibrillator effectively prevents sudden cardiac death, patients are still prone to recurrence of v entricular tachyarrhythmias. Electrophysiologically guided surgery is the m ost effective modality in abolishing ventricular tachycardia, having a lowe r recurrence rate than pharmacologic therapy or catheter ablation, Return c ycle mapping after entrainment has been shown to localize the central commo n pathway, which is the target region for ablation, without pacing at the p athway or recording the potentials from the pathway. Methods: To determine the accuracy and usefulness of return cycle mapping i n surgery for ventricular tachycardia, we cryoablated 8 morphologies of ven tricular tachycardia induced in postinfarction dogs with the guidance of re turn cycle mapping. The ventricular tachycardia was entrained from 3 to 5 d ifferent epicardial sites at a paced cycle length 10 to 20 ms shorter than the ventricular tachycardia cycle length and the epicardium was mapped with 61 unipolar electrodes during cessation of entrainment to construct return cycle maps. The return cycle was determined by subtracting the first activ ation time from the second activation time after the last stimulus in each electrode location, and the maps were then displayed on a computer. Results: The total analysis process was completed within 3 minutes by means of a computer with custom-made programs. The activation map during ventric ular tachycardia did not localize the central common pathway in any morphol ogy of ventricular tachycardia, because the pattern of activation was conce ntric and diastolic potentials were not recorded. Cryoablation of the regio n where the isotemporal lines of the return cycle equal to the ventricular tachycardia cycle length intersected resulted in termination of ventricular tachycardia in all morphologies. The intersection was 26 +/- 9 mm from the earliest activation site. Epicardial mapping with 253 electrodes during cr yothermia showed that the region localized by return cycle mapping was the central common pathway sandwiched between the lines of conduction block and that the cryolesion connected the lines of block, blocked the rotating wav e front, and resulted in termination of the ventricular tachycardia. Conclusion: Return cycle mapping provides an accurate and rapid means of lo calizing the central common pathway without the need for recording potentia ls from the pathway or pacing at the pathway in ablation for ventricular ta chycardia.