Comparison of left ventricular cryolesions created by liquid nitrogen and nitrous oxide.

OBJECTIVES. This study was designed to compare the cryosurgical lesions produced by liquid nitrogen (-196 degrees C) and nitrous oxide (-76 degrees C). BACKGROUND. Cryosurgical ablation is a useful method of arrhythmia surgery, but information on the dimensions of cardiac lesions produced by modifying cryoprobe temperature is limited. METHODS. We compared the dimensions, volumes and electrophysiologic effects of cryolesions created by a liquid nitrogen cryoprobe (Group I) and a nitrous oxide cryoprobe (Group II) on the left ventricular myocardium in the beating canine heart. Exposure time was compared at 1, 2, 3 and 4 min. In each of 18 dogs, two to four lesions were created on the left ventricle and analyzed: 35 lesions created with use of the nitrous oxide cryoprobe and 30 lesions created with the liquid nitrogen cryoprobe. Lesions were measured at the time of induced death 6 weeks postoperatively and assessed by tissue staining with the Masson trichrome technique. RESULTS. The volumes (mm3) of the cryolesions created by the liquid nitrogen cryoprobe were significantly larger (p < 0.05) than those of lesions created by nitrous oxide: 826 +/- 163 versus 493 +/- 197 at 1 min; 1,101 +/- 327 versus 666 +/- 185 at 2 min; 1,356 +/- 318 versus 787 +/- 258 at 3 min and 1,735 +/- 534 versus 923 +/- 376 at 4 min. CONCLUSIONS. Decreasing the temperature of the cryoprobe by using liquid nitrogen increases the volume of the lesions. Programmed electrical stimulation before and 6 weeks after cryoablation indicated no arrhythmogenicity.