Cryosurgical ablation of atrioventricular nodal reentry: histologic localization of the proximal common pathway.

A method using cryosurgery has been previously described to selectively ablate atrioventricular nodal reentry tachycardia while preserving intact atrioventricular conduction. The purpose of the present study was to define the histologic features of the cryolesions in relationship to the specialized conduction system. In 12 adult dogs a series of nine discrete cryolesions was placed along the perimeter of the triangle of Koch while continuously monitoring the His bundle electrogram. All animals survived the operation and maintained intact atrioventricular conduction. At 14 weeks after surgery the hearts were sectioned and examined. In all 12 animals there was a confluent mass of dense fibrous tissue present in the lower atrial septum that was in immediate proximity to but did not involve the atrioventricular node-His bundle. The ablation of perinodal tissue with preservation of the specialized conduction system with the use of this cryosurgical technique was confirmed. It is likely that the cryoablated perinodal tissue represents the proximal common pathway of the circuit for atrioventricular nodal reentry tachycardia.

Cardiac cryosurgery: regional myocardial blood flow of ventricular cryolesions.

Cryosurgery is one of three methods introduced recently for the treatment of ventricular tachyarrhythmias. Cryothermic exposure ablates arrhythmogenic ventricular myocardium, and produces a dense fibrous scar with a sharp border to histologically normal tissue. Myocardial blood flow in the region of the cryolesion, however, has not been quantitated. The purpose of this study was to measure regional blood flow within and around the cryolesion in an attempt to identify ischemic zones that might become arrhythmogenic. Left ventricular cryolesions were created in eleven adult dogs. Two weeks later, the animals underwent radioactive tracer microsphere injection for quantitation of regional myocardial blood flow. The fibrotic cryolesion demonstrated a significantly depressed blood flow (0.44 +/- 0.07 ml/min/g) compared to blood flow in control tissue (1.36 +/- 0.12 ml/min/g) (P less than 0.001). A 1-mm strip of myocardium immediately adjacent to the cryolesion, as well as other myocardium surrounding and subjacent to the cryolesion, did not show a significant decrease in regional blood flow. The border between the fibrotic cryolesion and the surrounding myocardium is, therefore, sharply defined not only in terms of histology but also in regards to regional blood flow. These data lend further support to the safe clinical use of cryothermia in the treatment of refractory ventricular tachycardia.

Cryosurgical modification of retrograde atrioventricular conduction. Implications for the surgical treatment of atrioventricular nodal reentry tachycardia.

Paroxysmal supraventricular tachycardia resulting from atrioventricular nodal reentry is a common arrhythmia that usually responds to medical therapy. When atrioventricular nodal reentry tachycardia is refractory to medical therapy, cryoablation or endocardial catheter ablation of the His bundle has been employed to protect the ventricles from the tachycardia. However, these techniques necessitate implantation of a permanent ventricular pacemaker. A cryosurgical procedure that ablates the anatomic-electrophysiologic substrate for atrioventricular nodal reentry tachycardia while preserving antegrade atrioventricular conduction has been described. The purpose of the present study was to determine the effects of this procedure on retrograde atrioventricular conduction and on the ventricular echo phenomenon in particular. Thirty adult mongrel dogs underwent either the cryosurgical procedure (n = 20) or a sham operation (n = 10). The animals were studied either immediately postoperatively (acute cryosurgery group and control group, n = 10 for each group) or 14 weeks postoperatively (chronic cryosurgery group, n = 10). Decremental ventricular pacing and programmed premature ventricular pacing protocols were used to determine the retrograde atrioventricular nodal conduction time, Wenckebach point, atrioventricular nodal refractory periods, and ventricular echo reflection time. No electrophysiologic alterations were noted in the sham-operated group. In the acute cryosurgery group, the retrograde Wenckebach point, atrioventricular nodal conduction time, functional refractory period of the atrioventricular node, effective refractory period of the atrioventricular node, and ventricular echo reflection time were all significantly prolonged. In the chronic cryosurgery group, no significant change in ventriculoatrial conduction was noted, but the ventricular echo phenomenon was eliminated in all but one animal. These data further document that this cryosurgical procedure is capable of ablating the anatomic-electrophysiologic substrate necessary for atrioventricular nodal reentry tachycardia while preserving atrioventricular conduction.

Alteration of antegrade atrioventricular conduction by cryoablation of peri-atrioventricular nodal tissue. Implications for the surgical treatment of atrioventricular nodal reentry tachycardia.

Paroxysmal supraventricular tachycardia due to atrioventricular nodal reentry is a common arrhythmia that usually responds to medical therapy. When atrioventricular nodal reentry tachycardia is refractory to medical therapy, surgical cryoablation or endocardial catheter ablation of the His bundle has been employed to protect the ventricles from the tachycardia. However, these techniques necessitate implantation of a permanent ventricular pacemaker. The purpose of the present study was to develop a cryosurgical procedure capable of ablating the anatomic-electrophysiological substrate of atrioventricular nodal reentry by modifying, rather than ablating, atrioventricular conduction. Thirty-three adult mongrel dogs underwent either the cryosurgical procedure (n = 23) or a sham operation (n = 10). All animals were restudied immediately postoperatively (acute cryosurgery group [n = 12) and sham group [n = 10]), and 11 animals (chronic cryosurgery group) subjected to cryosurgery were studied 14 weeks postoperatively. Decremental atrial pacing and programmed premature atrial stimulation protocols were utilized to determine atrioventricular nodal conduction time, atrioventricular nodal refractory period, and the Wenckebach point before and after operation in all animals. No electrophysiological alterations were noted in the sham-operated group. In the cryosurgery groups, atrioventricular nodal conduction time, functional refractory period of the atrioventricular node, and the Wenckebach point were all significantly prolonged in the immediate postoperative period, but only atrioventricular nodal conduction time remained prolonged 14 weeks postoperatively. The potential application of the new cryosurgical procedure for the treatment of atrioventricular nodal reentry tachycardia was demonstrated in three animals that exhibited dual atrioventricular nodal conduction preoperatively but had monophasic atrioventricular conduction curves postoperatively. The results in these animals documented that the cryosurgical procedure is capable of ablating the anatomic-electrophysiological substrate necessary for atrioventricular nodal reentry tachycardia.

The electrophysiologic effects of discrete cryosurgery for the treatment of supraventricular tachycardia due to AV nodal reentry.

The electrophysiologic effects of multiple cryosurgical lesions along the circumference of Koch's triangle were evaluated as a treatment of AV nodal reentrant tachycardia in 31 dogs. These animals were divided into a control group (n = 8) and a cryosurgical group (n = 23), and were studied using incremental atrial pacing and programmed atrial premature stimulation. In the cryosurgical group, significant prolongation of AV nodal conduction time, initiation of Wenckebach periodicity at a slower atrial pacing rate, and an increase in the functional refractory period of the AV node were documented postoperatively. In contrast, there were no significant differences between preoperative and postoperative AV node conduction characteristics in the control group. Four dogs in which the effective refractory period of the AV node could be measured showed an increase of 28-104 msec following cryosurgery. In 2 dogs, discontinuous conduction curves (i.e., dual AV nodal pathways) were demonstrated preoperatively. Postoperatively, a uniform conduction curve was demonstrated. In conclusion, these results strongly suggest that this new cyrosurgical method is an effective surgical procedure for the interruption of the reentrant circuit responsible for AV nodal reentry while preserving AV conduction.

Elective prolongation of atrioventricular conduction by multiple discrete cryolesions: a new technique for the treatment of paroxysmal supraventricular tachycardia.

The present study describes a surgical method for the permanent prolongation of atrioventricular (AV) conduction. In 22 dogs, a series of nine discrete cryolesions were placed along the perimeter of the triangle of Koch while the His bundle electrogram was being monitored continuously. Ten dogs underwent a sham operation to control for the effects of cardiopulmonary bypass and atriotomy on AV conduction. The conduction time through the AV nodal region was significantly (p less than 0.01) prolonged acutely (3 hours postoperatively) and chronically (14 weeks postoperatively) in the animals subjected to cryosurgery. Thus selective cryosurgery in the AV nodal region produces a permanent alteration in AV conduction. This cryosurgical technique may result in ablation of the electrophysiological substrate required for paroxysmal supraventricular tachycardia resulting from AV nodal reentry.