Optimal conditions for high-power, short-duration radiofrequency ablation using a novel, flexible-tipped, force-sensing catheter.

Background: High-power, short-duration (HPSD) radiofrequency ablation (RFA) reduces procedure time; however, safety and efficacy thresholds vary with catheter design. Objective: The study sought to determine optimal HPSD ablation conditions with a novel flexible-tipped, contact force-sensing RFA catheter. Methods: RFA lesions were created in thigh muscle (16 swine) over a range of conditions (51-82 W, 2-40 g, 8-40 mL/min irrigation). An intracardiac study was performed (12 swine) to characterize steam pop thresholds. Lesions were created in a second intracardiac study (14 swine, n = 290 pulmonary vein isolation [PVI] lesions) with combinations of radiofrequency power, duration, and contact force. PVI was tested, animals were sacrificed, and lesions were measured. Results: The likelihood of coagulation formation in the thigh model was <20% when power was ≤79 W, when contact force was ≤40 g, when duration was ≤11 seconds, and when irrigation rates were 8 to 40 mL/min. The impact of contact force on lesion safety and efficacy was more pronounced using HPSD (60 W/8 seconds) compared with conventional ablation (30 W/45 seconds) (P = .038). During PVI, focal atrial lesions ranged in width from 4.2 to 12.5 mm and were transmural 80.8% of the time. PVI was achieved in 13 of 14 veins. Logistic regression identified that the optimal parameters for radiofrequency application were 60 to 70 W with a duration <8 seconds and <15 g contact force. Conclusions: Optimal HPSD lesions with this this flexible-tipped, force-sensing RFA catheter were created at 60 to 70 W for <8 seconds with <15 g contact force. Chronic studies are ongoing to assess radiofrequency parameter refinements and long-term lesion durability using these conditions.

Continuous and discontinuous radiofrequency energy delivery on the atrial free wall: Lesion transmurality, width, and biophysical characteristics.

BACKGROUND: Although lesion transmurality is required for durable pulmonary vein isolation, excess ablation is associated with increased risk of complications. OBJECTIVE: We sought to understand the impact of interrupted radiofrequency (RF) delivery conditions on lesion characteristics in the atrial free wall. METHODS: Thirty-three (11 left atrial, 22 right atrial) RF ablation lesions were created in the atria of 6 swine using power control mode (25 W, target contact force 15 g) with 1 of 3 conditions: 15 seconds ablation (n = 8), 30 seconds ablation (n = 14), or 2 15-second ablations at the same site separated by a 2-minute interruption (15 seconds × 2) (n = 11). RESULTS: Thirty of 33 lesions were transmural. Rates of transmurality (P = .45) and endocardial lesion width (5.6 ± 1.2 mm, P = .70) were similar between conditions. Mean tissue thickness was 1.7 ± 0.8 mm for transmural lesions. Wide variability in bipolar electrogram attenuation was observed across and within conditions and there were no significant between-group differences. Although impedance reductions were numerically greater in the 30-second and 15-second × 2 conditions (-14.6 ± 6.6 ohms and -14.0 ± 4.4 ohms, respectively) compared to the 15-second condition (-10.3 ± 6.4 ohms), variability was large, and differences were not statistically significant (P = .243). Impedance changes after ablation were largely transient. CONCLUSION: A single 15-second ablation at 25 W (target contact force of 15 g) with good stability produced similarly sized lesions compared to 30-second ablations and 2 15-second ablations at the same site in atrial free wall tissue. These data suggest over-ablation in the atria is common, larger-diameter lesions may require greater power, and many clinically available parameters of lesion size may be unreliable on the posterior wall.

Impact of interruptions in radiofrequency energy delivery on lesion characteristics.

BACKGROUND: During catheter ablation, delivery of radiofrequency (RF) energy to a target site is sometimes interrupted by catheter instability and clinical factors. The impact of interruption of RF delivery on lesion characteristics has not been characterized. OBJECTIVE: The purpose of this study was to determine the impact of interruption of RF application on lesion size. METHODS: Forty-two RF ablation lesions (21 left ventricle, 21 right ventricle) were created in the ventricles of 6 swine using power control mode (30 W; target contact force 15g) with 1 of 3 conditions: 15-second ablation (15s), 30-second ablation (30s), or two 15-second ablations (15s×2) at the same site separated by a 2-minute pause. RESULTS: Lesion volume was significantly larger for 30s lesions (501 ± 146 mm3) compared to both 15s×2 (314 ± 98 mm3) and 15s (242 ± 104 mm3) lesions (P <.001 for both pairwise comparisons). Compared to 15s lesions, lesion volume was numerically greater for 15s×2 lesions, but this did not reach statistical significance (P = .087). Differences in lesion volume between 30s and 15s×2 lesions were driven mainly by differences in lesion width (10.7 ± 1.1 mm vs 9.1 ± 1.7 mm; P = .04) rather than depth (9 ± 1.2 mm vs 8.4 ± 1.2 mm; P = .29). There were no differences in mean contact force by group. There was no difference in total force-time integral for the 30s and 15s×2 lesion groups [median 444 (interquartile range 312) g∙s vs 380 (164) g∙s; P = 1]. CONCLUSION: Compared to lesions resulting from continuous RF ablation, lesions resulting from interrupted ablation have a smaller overall lesion volume, predominantly due to smaller lesion width. These data suggest that if disruption in energy delivery occurs, lesions may need closer spacing to avoid gaps.

Cytology and the cell block method in diagnostic characterization of canine lymphadenopathy and in the immunophenotyping of nodal lymphoma.

Minimally invasive techniques used to evaluate canine peripheral lymphadenopathy (PLN), including fine needle aspiration biopsy with cytological evaluation (FNAB-C) and flow cytometry (FC), have benefits and limitations. The cell block (CB) method is an alternate processing technique in which fine needle aspirate biopsy samples are concentrated, fixed, and embedded in paraffin for routine histological processing/staining. Utilizing three observers, we determined the diagnostic value of the CB in evaluating canine PLN across six categories (non-diagnostic, reactive, inflammatory/infectious, probable lymphoma and lymphoma, metastatic neoplasia) and correlated findings to immunophenotypic and clonal antigen receptor rearrangement results in canine nodal lymphoma. Eighty-five paired FNAB-C and CB samples were evaluated from canine patients presenting to the University of Minnesota Veterinary Oncology or Internal Medicine services. Diagnostic quality samples were obtained in 55/85 (65%) CB and 81/85 (95%) FNAB-C samples, respectively, and nodal pathology impacted CB diagnostic yield. Overall percent agreement between diagnostic-quality FNAB-C and CB samples was 86%, but increased to 95% if the categories of lymphoma and probable lymphoma were combined. There was 100% agreement for both the diagnoses of metastatic neoplasia and reactive lymph nodes and 92% agreement for the diagnosis of lymphoma/probable lymphoma. Using immunohistochemistry (IHC), CB samples correctly immunophenotyped 22/23 (96%) cases of B-cell lymphoma, but only 1/6 (17%) cases of T-cell lymphoma. IHC was not completed on nine cases of lymphoproliferative disease because of insufficient cellularity. When the CB method (CBM) yielded diagnostic quality samples there was good to excellent agreement with FNAB-C samples and CB samples were suitable for some IHC tests.

The presence of diatom algae in a tracheal wash from a German Wirehaired Pointer with aspiration pneumonia.

A 7-year-old spayed female German Wirehaired Pointer was presented with difficulty breathing after being found seizing in a water-filled drainage ditch while out hunting. Aspirates from a tracheal wash contained numerous degenerate neutrophils, fewer macrophages, some of which contained basophilic debris, low numbers of extracellular diatoms, and a single intracellular short bacterial rod. As the dog continued to clinically decline and could not be weaned from oxygen support, the owners chose euthanasia. The major necropsy finding was a severe granulomatous bronchopneumonia that was likely due to aspiration of foreign material based on the microscopic presence of plant-like material, bi-refringent crystalline material, non-cellular debris, and occasional fungal structures. Diatoms are a class of algae that live primarily in water. Diatom analysis has been used, with some controversy, in human forensics to assist in documenting drowning as the cause of death. In this case, given the clinical history, the presence of diatoms and inflammation in the tracheal wash were interpreted as a likely result of the aspiration of surface water. To our knowledge, this is the first reported case of diatoms observed in a cytologic specimen in a nonhuman mammal with aspiration pneumonia.

Performance of 2 microtiter canine Coombs' tests.

BACKGROUND: The Coombs' test, which detects immunoglobulin or complement on RBC surfaces, has long been the standard for laboratory confirmation of immune-mediated hemolytic anemia (IMHA), a common cause of hemolytic anemia in the dog. This test, however, suffers from relatively low sensitivity. Optimization of test sensitivity would lead to fewer discrepancies between laboratory results and clinical diagnoses, and in some cases institution of appropriate therapy in a timely manner. OBJECTIVES: The objectives of this study were to 1) characterize the sensitivity and specificity of 2 canine Coombs' tests for the detection of IMHA, 2) document the efficacy of using multiple antisera dilutions beyond what is directed by manufacturers, and 3) evaluate the necessity of monovalent antisera in the test protocol. METHODS: Sixty-five canine whole-blood samples submitted for Coombs' testing were evaluated. Patients were classified as IMHA positive or negative based on a set of predetermined criteria. IMHA classification was compared to Coombs' test results from 2 different Coombs' tests adapted to a microtiter-plate format. One Coombs' test (VMRD Coombs' test) utilized a single polyvalent antiserum (VMRD, Inc, Pullman, WA, USA), while a second Coombs' test (University of Minnesota [U of MN] Coombs' test) used both polyvalent and monovalent antisera. RESULTS: Sensitivity and specificity were 61% and 100% for the VMRD Coombs' test, and 82% and 95% for the U of MN Coombs' test. The use of multiple antisera dilutions resulted in 6 additional Coombs' positive test results. All positive Coombs' test results were positive by polyvalent antisera. CONCLUSIONS: When used in a microtiter-plate format, the U of MN Coombs' test was a more sensitive test for the detection of IMHA in canine patients when compared to the VMRD Coombs' test. The use of multiple antisera dilutions increased test sensitivity. Sensitivity, however, was not increased by the use of monovalent antisera in the Coombs' test protocol.