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Heme oxygenase 2 (HO-2), which synthesizes carbon monoxide (CO), has been localized by immunohistochemistry to endothelial cells and adventitial nerves of blood vessels. HO-2 is also localized to neurons in autonomic ganglia, including the petrosal, superior cervical, and nodose ganglia, as well as ganglia in the myenteric plexus of the intestine. Enzyme studies demonstrated that tin protoporphyrin-9 is a selective inhibitor of HO with approximately 10-fold selectivity for HO over endothelial nitric oxide synthase (NOS) and soluble guanylyl cyclase. Inhibition of HO activity by tin protoporphyrin 9 reverses the component of endothelial-derived relaxation of porcine distal pulmonary arteries not reversed by an inhibitor of NOS. Thus, CO, like NO, may have endothelial-derived relaxing activity. The similarity of NOS and HO-2 localizations and functions in blood vessels and the autonomic nervous system implies complementary and possibly coordinated physiologic roles for these two mediators.

We sought to evaluate the relationship between arrhythmia recurrence following catheter ablation and the electrode temperature at successful ablation sites. 347 patients were studied; (184 F, 163 M. 38 ± 22 yrs). Ablation targets included AVNRT (131 pts), the AV junction (46 pts), and 178 accessory pathways (AP). Catheter ablation was performed with the Atakr ablation system incorporating a thermister in the distal electrode. RF output was automatically varied to achieve a target temperature of ≥70°C. Results Thirty-one patients (9%) developed a recurrence. The relationship between the incidence of recurrence, electrode temperature, and ablation target are shown below: Target AVNRT AP AV junction P Recurrence 7/131 (5%) 23/178 (13%) 1/46 (2%) 0.01 Temp Rec °C 58 ± 9 62 ± 9 50°C Temp No Rec °C 60 ± 9 62 ± 10 67 ± 7 P Value 0.5 0.9 N/A In conclusion, recurrence of conduction following catheter ablation is related to the ablation target but not to the electrode temperature. The incidence of recurrence is highest during ablation of accessory pathways and lowest during ablation of AVNRT and the AV junction.