Segment by segment linear ablation with an articulated bilimb catheter: initial experimental results

Transcatheter radiofrequency (RF) ablation of atrial fibrillation or flutter requires the creation of linear lesions. However, conventional catheters are not predictably effective because of poor endocardial contact, and limited lesion size and penetration. The purpose of the study was to assess in the right atrium, the efficacy and safety of a new catheter designed to create long myocardial tissue lesions using RF energy. The main characteristics of this 8 Fr deflectable RF ablation catheter were: (1) a perpendicularly contacting articulated bilimb electrodes ensuring stable and firm endocardial firm contact; and (2) an irrigated planar interface. Three different electrode prototypes were tested. Fourteen anesthetized sheep weighing 61 +/- 7 kg underwent RF ablation in the right atrium using three incremental power levels (25 to 45, 50, 55 to 75 W) with the aim of creating fully transmural (FT) lesions, defined as continuous and complete epicardial and endocardial lesion imprints. The animals were euthanized 1 hour later for macroscopic and histologic examinations. Forty-three of the 80 right atrial lesions created, in smooth as well as in trabeculated areas, were FT. The percentage of FT lesions increased with the applied power from 37% with 25-45 W, to 49% with 50 W, and up to 86% for 55-75 W. In all but two cases, histologic examination showed no discontinuity between FT lesions produced by both limbs resulting in 19 coalescent linear lesions with an average size of 25 x 6 x 4 mm (length x width x depth). In situ bipolar electrograms after ablation in the FT group showed split potentials and/or a marked decrease in amplitude from 2.85 +/- 1.79 to 0.33 +/- 0.14 mV (P = 0.001) accompanied by near complete disappearance of unipolar electrograms. There was no perforation due to RF ablation. In conclusion, continuous and FT lesions can be achieved in various areas of sheep atria, including the trabecular right atrium, with a perpendicularly contacting bilimb electrode catheter. It represents a promising tool for catheter ablation of atrial fibrillation and flutter.

Effect of catheter tip length and position on lesion volume in temperature controlled RF ablation in canine tricuspid valve annulus

BACKGROUND

Radiofrequency (RF) energy has been delivered to the tricuspid valve annulus (TVA) in humans with both 4 mm and 8 mm long catheter tip electrodes to treat atrial flutter. However, lesion volume with temperature controlled RF delivery systems has not been previously characterized.

METHODS

In 10 anesthetized canines, a single pulse of temperature controlled RF energy at a 70 degrees C set point, 30 second duration was delivered with either a 7 Fr/4 mm tip or a 7 Fr/8 mm tip electrode in a position both anterolateral and posteroseptal to the tricuspid valve annulus (TVA). Surface echocardiogram was obtained prior and after ablation. The animals were sacrificed after ablation and the lesions underwent gross and histological examination.

RESULTS

Lesion size, tip temperature and power were related to tip electrode surface area (SA). Eight mm tips (SA = 59 mm2) tended to create significantly larger lesions than 4 mm tips (SA = 29 mm2). Median lesion volume was 22 vs. 1.5 mm3, respectively. Eight mm tips were also associated with higher power requirements and lower temperatures than 4 mm tips. Posteroseptal TVA lesions tended to be larger than anterolateral lesions. No significant complications were noted.

CONCLUSIONS

Using temperature controlled RF ablation, large lesions may be safely created on the canine TVA using 7 Fr catheters with 8 mm long tips.

Temperature controlled RF ablation in canine ventricle and coronary sinus using 7 Fr or 5 Fr ablation electrodes

The safety and lesion volume of temperature controlled radiofrequency ablation (TCRFA) in the right ventricle (RV), left ventricle (LV), and coronary sinus (CS) comparing long 5 Fr to standard tip electrodes have not been previously reported. In 10 canines, TCRFA was delivered at a 70 degrees C set point for 30 seconds. Lateral and septal RV lesions were made with either a 5 Fr/5 mm or 7 Fr/4 mm tip. Lateral and septal LV lesions were made with either a 5 Fr/7 mm or 7 Fr/4 mm tip. Proximal and distal CS lesions were made with either a 7 Fr/4 mm, 5 Fr/5 mm or 5 Fr/7 mm tip. Gross and histologic examination of the lesions was completed. Lesion size, tip temperature and power required are related to electrode surface area (SA) when ablating in the RV, LV or CS. 5 Fr/7 mm tips (SA = 36 mm2) tended to create larger lesions than 7 Fr/4 mm tips (SA = 29 mm2) in the LV. 7 Fr4 mm tips tended to create larger lesions than 5 Fr/5 mm tips (SA = 26 mm2) in the RV. 7 Fr/4 LV lesions exceeded 7 Fr/4 mm RV lesions due to thicker LV walls. In the CS, 5 Fr/7 mm tips tended to create the largest lesions. In the RV, LV and CS, tips with larger SA tended to have lower temperatures and require higher power. No high temperature or high impedance shut-downs were observed. In conclusion, varying 5 Fr tip length can safely produce larger or smaller lesions compared to those created with 7 Fr/4 mm tips.

A comparison of bronchial drainage treatments in cystic fibrosis

We compared standard chest physical therapy and postural drainage (CPT/PD) with a new airway clearance therapy called high-frequency chest wall oscillation (HFCWO) in a group of stable cystic fibrosis (CF) patients. In this crossover trial, 29 CF patients (15 males, 14 females), aged 7-47 years that met the inclusion criteria were randomly assigned to alternate CPT/PD and HFCWO, on a daily basis, over a 4 day period. Each patient received 2 days of each form of therapy; treatment frequency and the length of treatment were the same for both techniques. Expectorated secretions were collected during each 30 minute therapy session and for 15 minutes following treatment. The wet and dry weights of collected secretions were determined gravimetrically, and the therapy methods were compared. Significantly more sputum was expectorated during HFCWO than during CPT/PD as determined by both the wet (P < 0.001) and the dry (P < 0.01) measurements. This study suggests that HFCWO is at least as effective as manual CPT/PD in clearing secretions from the airways in patients with cystic fibrosis.

A national survey of cigarette smoking in fourth-form school children in New Zealand

AIMS

To determine the prevalence of cigarette smoking in 14 and 15 year old school children in New Zealand and to examine associated risk factors.

METHODS

Nationwide cross-sectional survey of fourth-form school children in New Zealand by means of an anonymous self administered questionnaire in November 1992.

RESULTS

Questionnaires from 14,097 fourteen and fifteen year-olds were analysed. 65.6% had tried smoking, and 36.1% regarded themselves as smokers. Females and Maori had significantly higher prevalence rates. Of Maori females 44.6% were current smokers (more than one per month) compared to 24.0% for the whole group, and 33.0% were daily smokers. Pacific Island students, who have similar socioeconomic disadvantage to Maori, have a lower relative risk of smoking (RR) 0.79, (95% confidence interval (CI) 0.68, 0.91), than Europeans. Major independent risk factors were identified and population attributable risk was calculated for parental smoking (22.9%), poor knowledge of adverse health effects (7.3%) and watching televised sports (13.4%). These three modifiable factors accounted for 36.1% of the total smoking prevalence in these children.

CONCLUSION

The continued high prevalence of smoking in New Zealand children, especially in Maori and in females, prove current public health measures to be inadequate. Our results suggest that strategies aimed at decreasing parental smoking, improving student knowledge of adverse health effects and preventing tobacco sponsorship of television sports could greatly decrease the smoking prevalence in this age group.