Effect of botulinum toxin on inducibility and maintenance of atrial fibrillation in ovine myocardial tissue.

BACKGROUND: Aberrant vagal stimulation may promote the generation and propagation of atrial fibrillation (AF). Researchers have suggested that botulinum toxin (BTX), a neurotoxin that decreases neural vagal stimulation, may decrease the incidence of postoperative AF. The exact electrophysiologic mechanism underlying the observations and histopathologic alterations associated with BTX are unclear. OBJECTIVE: To investigate the electrophysiologic, functional, and histopathologic effects of BTX on fibrillation induction in ovine atria. METHODS: Eight sheep underwent BTX injections into their pulmonary veins, atrial fat pads, and ventricular walls. Electrophysiology with pacing was performed at baseline and 7 days after injection to evaluate the atrial effective refractory period (ERP) and vulnerability to AF with and without vagal stimulation. Echocardiography was performed at baseline and day 7. After euthanasia, histopathologic analysis was performed. RESULTS: Seven sheep completed the study. For both atria, there was significant shortening in the ERP with vagal stimulation versus no stimulation on day 0 but not on day 7. More aggressive pacing was required to induce AF in the left atrium on day 7 than on day 0. Echocardiography on day 7 showed no significant changes in ejection fraction or new wall-motion abnormalities of the left and right ventricle. Histopathologic analysis showed no significant adverse effects. CONCLUSION: The subacute BTX effect reduced the vulnerability of atrial tissue to AF induction and reduced the vagal influence on atrial ERP shortening compared to baseline levels. Direct BTX injection did not cause myocardial dysfunction or histologic adverse effects.

Contact-force recovery can predict cardiac perforation during radiofrequency ablation.

BACKGROUND: During radiofrequency ablation (RFA), the ability to know whether a steam pop has led to cardiac perforation (CP) would be of profound clinical significance. We aimed to determine whether catheter contact-force characteristics can predict whether a steam pop during RFA causes CP. METHODS: We used a 7.5F Thermocool® Smarttouch™ force-sensing catheter (Biosense Webster Inc., Diamond Bar, CA, USA) to perform open-chest left atrial RFA under direct visualization in four sheep. We measured the contact force and its direction every 50 ms during RFA. At each steam pop, we noted whether CP occurred. We then analyzed the contact-force signals to determine whether specific features predicted the presence (+) or absence (-) of CP. RESULTS: A total of 24 steam pops occurred; 10 were CP+ and 14 were CP-. At the time of CP+ and CP- events, the contact force was 50 ± 25 and 40 ± 15 g, respectively (P = 0.146). All steam-pop events were associated with a rapid drop-off in contact force, but 10 of the 14 CP- events showed an immediate contact-force rebound, whereas none of the CP+ events did. This rebound presumably occurred as the catheter tip resumed contact with the left atrial wall. The average contact-force rebound equaled 80-100% of the contact-force drop-off. CONCLUSIONS: The ability to measure catheter contact force during RFA is a valuable asset, as contact-force recovery may be used to predict CP. Further studies are warranted to validate our findings in the clinical setting.

Endovascular Treatment of Superior Vena Cava Syndrome via Balloon-in-Balloon Catheter Technique with a Palmaz Stent.

Superior vena cava syndrome is a well-known disease entity that carries substantial rates of morbidity and mortality. Although most cases of superior vena cava syndrome are secondary to a malignant process, additional causes (such as mediastinal fibrosis, pacemaker lead implantation, or central venous catheter placement) have been reported. Multiple treatment options include percutaneous transluminal angioplasty, stent implantation, thrombolysis, mechanical thrombectomy, and venous grafting. We present a case of superior vena cava syndrome in a symptomatic 30-year-old woman who obtained complete relief of obstruction and marked symptomatic improvement through venoplasty and stenting, aided by our use of a balloon-in-balloon catheter system.