Clinical, echocardiographic, and pacing parameters affecting atrial fibrillation burden in patients with tachycardia-bradycardia syndrome

Background: The influence of various factors on atrial fibrillation (AF) development in the population of tachycardia-bradycardia syndrome (TBS) patients remains unclear. There are no data on the impact of different right ventricular pacing percentage (RVp%) profiles. Aim: The purpose of the study was to evaluate the relationship between the AF burden (AFB) and various clinical, echocardiographic, and pacing parameters in TBS patients. Methods: We performed a prospective, one-year registry of TBS patients with documented AF referred for dual-chamber pacemaker (DDD) implantation. Results: The data of 65 patients were analysed. The median 12-month RVp% and AFB was 9.4% and 1.0%, respectively. During the follow-up 14% of patients had no AF (p = 0.003), and the withdrawal of AF symptoms was observed in 49% of patients (p < 0.0001). The AFB was related to the left atrium diameter (r = 0.31, p = 0.02), especially in the subjects with left ventricular ejection fraction < 60% (r = 0.44, p = 0.04). Based on the relative change of RVp%, three groups of various RVp% profile were established: stable, decreasing, and increasing RVp%. In the stable RVp% group (n = 21) there was a quadratic correlation between the 12-month RVp% and AFB (r = 0.71, p = 0.0003). In the stable RVp% > 20% subgroup there was a significant increase of AFB in comparison to the RVp% ≤ 20% subgroup (ΔAFB 1.8% vs. 0.0%, p = 0.03, respectively). In the increasing RVp% group (n = 28) the AFB increased whereas in the decreasing RVp% (n = 16) it remained stable (ΔAFB 0.67% vs. 0.0%, p = 0.034, respectively). Conclusions: DDD implantation in TBS patients is related to a significant reduction in AF symptoms, and left atrial diameter correlates with cumulative AFB in the mid-term observation. Stable RVp% > 20% is associated with AF progression whereas lower stable RVp% may stabilise AF development. Increasing RVp% may be associated with the AFB increase in comparison to the decreasing RVp% subgroup in which AFB remains stable.Background: The influence of various factors on atrial fibrillation (AF) development in the population of tachycardia-bradycardia syndrome (TBS) patients remains unclear. There are no data on the impact of different right ventricular pacing percentage (RVp%) profiles. Aim: The purpose of the study was to evaluate the relationship between the AF burden (AFB) and various clinical, echocardiographic, and pacing parameters in TBS patients. Methods: We performed a prospective, one-year registry of TBS patients with documented AF referred for dual-chamber pacemaker (DDD) implantation. Results: The data of 65 patients were analysed. The median 12-month RVp% and AFB was 9.4% and 1.0%, respectively. During the follow-up 14% of patients had no AF (p = 0.003), and the withdrawal of AF symptoms was observed in 49% of patients (p < 0.0001). The AFB was related to the left atrium diameter (r = 0.31, p = 0.02), especially in the subjects with left ventricular ejection fraction < 60% (r = 0.44, p = 0.04). Based on the relative change of RVp%, three groups of various RVp% profile were established: stable, decreasing, and increasing RVp%. In the stable RVp% group (n = 21) there was a quadratic correlation between the 12-month RVp% and AFB (r = 0.71, p = 0.0003). In the stable RVp% > 20% subgroup there was a significant increase of AFB in comparison to the RVp% ≤ 20% subgroup (ΔAFB 1.8% vs. 0.0%, p = 0.03, respectively). In the increasing RVp% group (n = 28) the AFB increased whereas in the decreasing RVp% (n = 16) it remained stable (ΔAFB 0.67% vs. 0.0%, p = 0.034, respectively). Conclusions: DDD implantation in TBS patients is related to a significant reduction in AF symptoms, and left atrial diameter correlates with cumulative AFB in the mid-term observation. Stable RVp% > 20% is associated with AF progression whereas lower stable RVp% may stabilise AF development. Increasing RVp% may be associated with the AFB increase in comparison to the decreasing RVp% subgroup in which AFB remains stable

Characterization of Porphyrin-Co(III)-'Nitrene Radical' Species Relevant in Catalytic Nitrene Transfer Reactions

To fully characterize the Co-III-'nitrene radical' species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV-vis, IR, VCD, UHR-ESI-MS, and XANES/XAFS measurements. Reactions of cobalt(II) porphyrins 1(P1) (P1 = meso-tetraphenylporphyrin (TPP)) and 1(P2) (P2 = 3,5-Di(t)Bu-ChenPhyrin) with organic azides 2(Ns) (NsN(3)), 2(Ts) (TsN3), and 2(Troc) (TrocN(3)) led to the formation of mono-nitrene species 3(Ns)(P1), 3(Ts)(P2), and 3(Troc)(P2), respectively, which are best described as [Co-III(por)(NR ''(center dot-))] nitrene radicals (imidyl radicals) resulting from single electron transfer from the cobalt(II) porphyrin to the 'nitrene' moiety (Ns: R '' = -SO2-p-C6H5NO2; Ts: R '' = -SO2C6H6; Troc: R '' = -C(O)OCH2CCl3). Remarkably, the reaction of 1(P1) with N-nosyl iminoiodane (PhI=NNs) 4(Ns) led to the formation of a bis-nitrene species 5(Ns)(P1). This species is best described as a triple-radical complex [(por ''(center dot-))Co-III(NR ''(center dot-))(2)] containing three ligand-centered unpaired electrons: two nitrene radicals (NR?(-)) and one oxidized porphyrin radical (por(center dot-)). Thus, the formation of the second nitrene radical involves another intramolecular one-electron transfer to the "nitrene" moiety, but now from the porphyrin ring instead of the metal center. Interestingly, this bis-nitrene species is observed only on reacting 4(Ns) with 1(P1). Reaction of the more bulky 1(P2) with 4(Ns) results again in formation of mainly mono-nitrene species 3(Ns)(P2) according to EPR and ESI-MS spectroscopic studies. The mono- and bis-nitrene species were initially expected to be five- and six-coordinate species, respectively, but XANES data revealed that both mono- and bis-nitrene species are six-coordinate Oh species. The nature of the sixth ligand bound to cobalt(III) in the mono-nitrene case remains elusive, but some plausible candidates are NH3, NH2-, NsNH(-), and OH-; NsNH(-) being the most plausible. Conversion of mono-nitrene species 3(Ns)(P1) into bis-nitrene species 5(Ns)(P1) upon reaction with 4(Ns) was demonstrated. Solutions containing 3(Ns)(P1) and 5(Ns)(P1) proved to be still active in catalytic aziridination of styrene, consistent with their proposed key involvement in nitrene transfer reactions mediated by cobalt(II) porphyrins