Hybrid radiofrequency and cryoablation device: preliminary results in an animal model.
OBJECTIVE
To determine whether the simultaneous application of combined bipolar radiofrequency (RF) ablation and cryoablation in a hybrid system produces larger ablation zones than RF or cryoablation alone.


METHODS
Multiple 15-minute ablations were performed in ex vivo bovine liver (n = 167) with a hybrid applicator system with RF ablation alone (0.3-0.7 A), cryoablation alone (3,500 psi, two freeze/thaw cycles), and combined RF/cryoablation (0.4-0.7 A, 1,000-3,500 psi) with use of a novel applicator consisting of two 2.5-cm active bipolar RF poles located on the same 18-gauge needle separated by two embedded cryoablation nozzles. Resultant coagulation diameters were compared with use of analysis of variance for more than three groups or Student t tests for two groups. Confirmation of the optimal parameters of combination RF/cryoablation was performed by reassessing a range of argon pressure (1,000-3,500 psi) and RF current (0.4-0.7 A) in in vivo porcine liver (n = 36). Arrays of two to four RF/cryoablation applicators were also assessed in ex vivo (n = 54) and in vivo (n = 12) liver.


RESULTS
In ex vivo liver, simultaneous RF/cryoablation (0.6 A, 3,000 psi) produced 3.6 cm +/- 0.4 of short-axis coagulation. This was significantly larger than that achieved with optimal RF alone or cryoablation alone (1.5 cm +/- 0.3 and 1.6 cm +/- 0.3, respectively; F = 95; P < .01). The coagulation diameter with simultaneous combination RF/cryoablation was related in parabolic fashion to argon pressure and current with a multivariate r(2) of 0.68. For in vivo liver, optimal combination RF/cryoablation achieved 3.3 cm +/- 0.2 of coagulation, which was significantly larger than that achieved with RF alone (1.1 cm +/- 0.1; P < .01) or cryoablation alone (1.1 cm +/- 0.1 and 1.3 cm +/- 0.1; F = 203; P < .01). The greatest contiguous coagulation was achieved with multiple-applicator arrays. For ex vivo liver, short-axis coagulation measured 5.3 cm +/- 0.1, 6.4 cm +/- 0.1, and 7.6 cm +/- 0.1 for two-, three-, and four-applicator arrays, respectively. For in vivo liver, two-, three-, and four-applicator arrays produced 5.1 cm +/- 0.2, 5.8 cm +/- 0.5, and 7.0 cm +/- 0.5 of confluent coagulation, respectively.


CONCLUSIONS
Simultaneous combination RF and cryoablation with use of a novel applicator design yielded significantly larger zones of coagulation than either modality alone. The large ablation diameters achieved warrant further investigation of the device.
Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 1 Deaconess Road, WCC 308B, Boston, Massachusetts 02215, USA.
Andrew
A
Hines-Peralta
C Yehuda
CY
Hollander
Stephanie
S
Solazzo
Clare
C
Horkan
Zheng-Jun
ZJ
Liu
S Nahum
SN
Goldberg
D000704:Analysis of Variance; D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D003452:Cryosurgery / Q000295:instrumentation*; D004867:Equipment Design; D066298:In Vitro Techniques; D008099:Liver / Q000473:pathology*; D012044:Regression Analysis; D013552:Swine