Biomedical subjects

W J Rittman

Publications and source records attributed to W J Rittman.

6 recordsLinked to original sources

PubMed1996

Radiofrequency tissue ablation: increased lesion diameter with a perfusion electrode.

RATIONALE AND OBJECTIVES: We sought to induce large zones of coagulation necrosis using radiofrequency (RF) with perfusion electrodes and to define optimal parameters for this system. METHODS: We developed RF electrodes with internal cannulas to enable tip perfusion. Lesions were created with monopolar RF in ex vivo and in vivo liver and muscle tissue with and without perfusion of the electrode tip using 0 degree C saline. In separate experiments, wattage, current, procedure duration, tip exposure, and perfused tip temperatures were studied. RESULTS: In ex vivo liver tissue, a maximum lesion diameter of 3.1 cm without charring occurred with perfusion at 12 min and 50 W. In in vivo liver tissue with perfusion (tip temperature = 25-35 degrees C) and a 3-cm tip exposure, 80 W were deposited in muscle tissue and 65 W in liver tissue for 12 min without inducing charring. Lesion diameters were 4.5 cm and 2.4 cm, respectively. By comparison, without perfusion a maximum of 20 W could be deposited into either tissue type, resulting in 1.8-cm muscle lesions and 1.2-cm liver lesions. Tip temperatures between 45 degrees C and 55 degrees C resulted in charring. Smaller but predictable lesion diameters were created with a lower power, a shorter tip exposure, or both. Of all the parameters, diameter correlated best with the current applied. CONCLUSION: Perfusion of RF electrodes with chilled saline allows for increased power deposition without tissue charring, increasing the volume of coagulation necrosis created with a single electrode insertion. Perfusion electrodes therefore might decrease the number of probe insertions required for percutaneous tumor ablation therapy or allow for the treatment of larger lesions.

Animals↗

PubMed1996

Radiofrequency tissue ablation: importance of local temperature along the electrode tip exposure in determining lesion shape and size.

RATIONALE AND OBJECTIVES: We determined whether heat distribution along a radiofrequency (RF) electrode would be uniform when longer tip exposures are used and whether local temperature effects would influence the shape of induced tissue coagulation. METHODS: Thermistors were embedded within 18-gauge RF electrodes at both ends and in the middle of the exposed tip. The length of tip exposure varied from 1 to 7 cm. RF was applied in vitro to pig liver for 6 min using a constant tip temperature, which was varied in 10 degrees C increments from 60 degrees C to 110 degrees C. Experiments were performed in triplicate. The 3- and 5-cm probes were used at a 90 degrees C tip temperature to create lesions in live pig liver and muscle using similar parameters. Temperature was measured throughout the procedure. Observable coagulation necrosis was measured at the end of the treatment. Regression analysis was used to evaluate the local temperature-lesion diameter relationship. RESULTS: Temperatures were not uniform along the tip exposure for any given trial. Temperature variation increased with higher tip temperatures and longer tip exposures. The diameter of local coagulation necrosis was a function of the local mean temperature. For in vitro trials, no coagulation was seen when the local temperature was less than 50 degrees C. Temperatures above this threshold resulted in progressively greater lesion diameter, with a minimum of 1 cm of necrosis occurring at 71 degrees C. Additional increases in lesion diameter (1.4-1.6 cm) were observed at approximately 90 degrees C. Mathematical modeling demonstrated a best-fit curve: lesion diameter (in cm) = ¿1.4 + 0.03 (tip exposure)¿ ¿1 - e [-0.067(local temp - 49.5 degrees C)]¿, r2 = .986, SD = 0.14 cm for each curve. In living tissue, less uniformity in the shape of coagulation necrosis was seen around the electrodes. Local temperature-lesion diameter data fit the same logarithmic relation, but the threshold for coagulation necrosis was 8.5 degrees C higher than for in vitro specimens. CONCLUSION: Using a single-probe technique for RF-induced tissue necrosis, the diameter of tissue coagulation may be predicted by the local temperature along the exposed electrode. The uniformity of temperature decreases with increased tip exposures. This effect may be partially corrected by creating lesions at higher tip temperatures, where necrosis diameter is increased. Because effects are more pronounced in vivo, uniform volumes of tissue necrosis are limited to tip exposures of 3 cm or less.

Animals↗

PubMed1995

Tissue ablation with radiofrequency: effect of probe size, gauge, duration, and temperature on lesion volume.

RATIONALE AND OBJECTIVES: We evaluated the parameters affecting the size and distribution of thermal tissue damage produced by radiofrequency electrodes. METHODS: Thermal lesions were produced by electrodes connected to a radiofrequency generator in specimens of liver (n = 143) and muscle (n = 20). Various combinations of probe tip exposure (0.5-8 cm), gauge (12-24 gauge), duration of treatment (0.5-12 min), and temperature (80-90 degrees C) were studied. The resulting volumes of tissue coagulation were measured and compared. RESULTS: Lesions equal to or less than 1.6 cm in diameter were symmetrically distributed around the electrode. Lesion diameter (but not length) increased with probe gauge and duration of treatment to a maximum of 6 min. However, lesions with mean diameters larger than 1.6 cm could not be produced using a single probe with any technique. Lesion length correlated with probe tip exposure from 1 to 8 cm (r2 = .996). Over the limited range investigated, increased temperature had minimal effects, except for tip exposures greater than 5 cm, in which larger and more uniform lesions resulted. Lesions varied equal to or less than 3 mm in diameter and equal to or less than 5 mm in length for each combination of variables. CONCLUSION: Radiofrequency ablation can accurately and reproducibly cause coagulative tissue necrosis. Necrosed tissue volume increases with length of exposed probe tip, larger probes, and sessions lasting at least 6 min.

Animals↗

PubMed1995

Tissue ablation with radiofrequency using multiprobe arrays.

RATIONALE AND OBJECTIVES: We studied the feasibility of increasing the volume of tissue destroyed by radiofrequency tissue coagulation using multiprobe arrays and defined parameters that determine lesion size and shape. METHODS: Radiofrequency was applied to ex vivo calf liver using arrays of two to five 18-gauge probes for 6 min at 70-90 degrees C. Probe spacing (1-3 cm) and arrangement, as well as the method of radiofrequency application (simultaneous or sequential), were varied. The resulting areas of tissue coagulation were measured and compared. RESULTS: Uniform tissue necrosis was observed with simultaneous radiofrequency application for probes 1.5 cm or less apart. At 1.5 cm, arrays of three equidistant probes produced spheroid lesions approximately 3.0 +/- 0.2 cm in diameter. Arrays of four equidistant probes produced cuboid lesions of 3.2 +/- 0.1 cm per side. However, probes placed 2 cm or more apart produced independent lesions 1.4 cm in diameter, with incomplete necrosis between probes. In the trials using five-probe arrays, a central region 4mm in diameter showed no visible evidence of tissue necrosis. With each array, lesion size varied less than 3 mm in any direction. Greater necrosis was accomplished when radiofrequency was applied simultaneously rather than sequentially. CONCLUSION: Multiprobe radiofrequency arrays permit the destruction of more tissue in a single treatment session than is possible with multiple individual probes operating alone. Probes spaced 1.5 cm or less apart act synergistically, producing a total volume of coagulated tissue that is greater than when the individual probes are operated sequentially.

Animals↗

PubMed1994

Temperature-guided radiofrequency catheter ablation of closed-chest ventricular myocardium with a novel thermistor-tipped catheter.

Successful lesion formation using radiofrequency energy requires adequate tissue heating. Temperature monitoring during ablation may thus improve the efficiency of radiofrequency catheter ablation. Each of five anesthetized, closed-chest adult mongrel dogs weighing 19 to 24 kg received a single pulsed ablation at four left ventricular and two right ventricular sites using a thermistor-tipped 2 mm electrode catheter. The maximum temperature at the electrode-tissue interface was preset at 90 degrees C and current delivered for 40 seconds (method A) or at 70 degrees C for 40 seconds (method B1) or 80 seconds (method B2). With method C, the temperature was set at 90 degrees C for 20 seconds, after which the temperature setting was turned off and ablation continued until impedance increased or the temperature reached > or = 100 degrees C. The size of the resultant lesion was greater with method A than with methods B1, B2 or C (mean length x width x depth, 5.6 x 4.8 x 6.5 vs 4.1 x 4.0 x 5.1 vs 4.2 x 4.0 x 5.2 vs 5.0 x 4.3 x 5.7 mm, respectively; p < 0.01). There was no significant difference in lesion size between pulse durations of 40 seconds (group B1) and 80 seconds (group B2). Only two ablations, both in the anteroapical right ventricle, resulted in a marked rise in impedance without the temperature reaching > or = 100 degrees C. We conclude that temperature (and thus impedance) monitoring improves control and efficacy of lesion formation during radiofrequency catheter ablation.

Analysis of Variance↗

PubMed1988

Radiofrequency lesion generation and its effect on tissue impedance.

The method of radiofrequency heat lesion generation is reviewed with specific reference to the dorsal root entry zone. Experimental data on the impedance of electrolytic media as a function of temperature are reported, and their relation to what should be observed during radiofrequency lesioning in the body is commented upon. The future utility of impedance monitoring is discussed as well as possible implications of bipolar lesion electrode systems.

Animals↗