for the REPLACE Registry InvestigatorsBackground-Prospective studies defining the risk associated with pacemaker or implantable cardioverter-defibrillator replacement surgeries do not exist. These procedures are generally considered low risk despite results from recent retrospective series reporting higher rates. Methods and Results-We prospectively assessed predefined procedure-related complication rates associated with elective pacemaker or implantable cardioverter-defibrillator generator replacements over 6 months of follow-up. Two groups were studied: those without (cohort 1) and those with (cohort 2) a planned transvenous lead addition for replacement or upgrade to a device capable of additional therapies. Complications were adjudicated by an independent events committee. Seventy-two US academic and private practice centers participated. Major complications occurred in 4.0% (95% confidence interval, 2.9 to 5.4) of 1031 cohort 1 patients and 15.3% (95% confidence interval, 12.7 to 18.1) of 713 cohort 2 patients. In both cohorts, major complications were higher with implantable cardioverter-defibrillator compared with pacemaker generator replacements. Complications were highest in patients who had an upgrade to or a revised cardiac resynchronization therapy device (18.7%; 95% confidence interval, 15.1 to 22.6). No periprocedural deaths occurred in either cohort, although 8 later procedure-related deaths occurred in cohort 2. The 6-month infection rates were 1.4% (95% confidence interval, 0.7 to 2.3) and 1.1% (95% confidence interval, 0.5 to 2.2) for cohorts 1 and 2, respectively. Conclusions-Pacemaker and implantable cardioverter-defibrillator generator replacements are associated with a notable complication risk, particularly those with lead additions. These data support careful decision making before device replacement, when managing device advisories, and when considering upgrades to more complex systems. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT00395447.

Atrial electrical remodeling develops quickly, is progressive, and may be persistent. Shifts in autonomic tone, atrial stretch, or depletion of high-energy phosphates do not contribute significantly to the phenomenon. Results of the study suggest that atrial electrical remodeling is mediated by rate-induced intracellular calcium overload.

Background— In the arterial endothelium, laminar flow and cyclical stretch induce expression of NO synthase (NOS). We hypothesized that atrial fibrillation (AF) causes a downregulation of atrial endocardial NOS expression and NO · production. Because NO · has antithrombotic properties, this may contribute to thromboembolism in AF. Methods and Results— In pigs, AF was produced with rapid atrial pacing at 600 bpm for 1 week, whereas controls had atrial pacing at 100 bpm. All animals had catheter ablation of the AV junction and ventricular pacing at 100 bpm. NO · production from freshly isolated tissue was measured by a NO · -specific microelectrode. Left atrial basal and stimulated NO · production was decreased in AF by 73% and 71% ( P <0.01). Endocardial NOS expression, determined by Western analysis, was also significantly decreased by 46%. Expression of the prothombotic protein plasminogen activator inhibitor 1 (PAI-1) is known to be regulated by NO · and was increased in the left atrium by 1.8-fold in AF ( P <0.05). NO · concentration was decreased in the left atrial appendage, although NOS expression was not affected. Neither NOS concentration, NO · levels, nor PAI-1 expression were altered in the aortas or right atria of animals with AF. Conclusions— AF is associated with a marked decrease in endocardial NOS expression and NO · bioavailability and an increase in PAI-1 expression in the left atrium. These data suggest that organized atrial contraction is needed to maintain normal endocardial expression of NOS. It is likely that loss of this antithrombotic enzyme contributes to the thromboembolic phenomena commonly observed in AF.

Background— Atrial fibrillation (AF) is associated with an increased risk of stroke due almost exclusively to emboli from left atrial appendage (LAA) thrombi. Recently, we reported that AF was associated with endocardial dysfunction, limited to the left atrium (LA) and LAA and manifest as reduced nitric oxide (NO · ) production and increased expression of plasminogen activator inhibitor-1. We hypothesized that reduced LAA NO · levels observed in AF may be associated with increased superoxide (O 2 ·− ) production. Methods and Results— After a week of AF induced by rapid atrial pacing in pigs, O 2 ·− production from acutely isolated heart tissue was measured by 2 independent techniques, electron spin resonance and superoxide dismutase–inhibitable cytochrome C reduction assays. Compared with control animals with equivalent ventricular heart rates, basal O 2 ·− production was increased 2.7-fold ( P <0.01) and 3.0-fold ( P <0.02) in the LA and LAA, respectively. A similar 3.0-fold ( P <0.01) increase in LAA O 2 ·− production was observed using a cytochrome C reduction assay. The increases could not be explained by changes in atrial total superoxide dismutase activity. Addition of either apocyanin or oxypurinol reduced LAA O 2 ·− , implying that NADPH and xanthine oxidases both contributed to increased O 2 ·− production in AF. Enzyme assays of atrial tissue homogenates confirmed increases in LAA NAD(P)H oxidase ( P =0.04) and xanthine oxidase ( P =0.01) activities. Although there were no changes in expression of the NADPH oxidase subunits, the increase in superoxide production was accompanied by an increase in GTP-loaded Rac1, an activator of the NADPH oxidase. Conclusions— AF increased O 2 ·− production in both the LA and LAA. Increased NAD(P)H oxidase and xanthine oxidase activities contributed to the observed increase in LAA O 2 ·− production. This increase in O 2 ·− and its reactive metabolites may contribute to the pathological consequences of AF such as thrombosis, inflammation, and tissue remodeling.