Abstract
Background Myeloperoxidase (MPO) has been associated with the development of atrial fibrillation (AF), but its impact on the recurrence of AF after catheter ablation has not been explored. This study investigated the effect of plasma MPO on recurrence after catheter ablation of paroxysmal AF.
Methods and Results Two hundred eighty-eight consecutive patients with paroxysmal AF and who underwent circumferential pulmonary vein isolation were prospectively enrolled. After a mean ± SD follow-up of 516 ± 204 (91–910) days, the recurrence rates were 16.9%, 25.7%, 29.7%, and 38.0% from the lowest MPO quartile to the highest MPO quartile, respectively (P = 0.023). After adjustment for age, sex, left atrial diameter, high-sensitivity C-reactive protein, and pulmonary vein isolation, there was an increased risk of recurrence in the subjects with the highest MPO quartile compared with those with the lowest quartile (hazard ratio, 3.18; 95% confidence interval, 2.12–5.23; P = 0.024). As a continuous variable, MPO was also an independent predictor of recurrence (hazard ratio, 2.12; 95% confidence interval, 1.71–3.27; P = 0.032).
Conclusions Patients with high MPO levels were at an increased risk of AF recurrence after catheter ablation.
Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice, with the highest prevalence observed among population older than age 60.1Atrial fibrillation is associated with cardiovascular mortality, including stroke, congestive heart failure, and cardiomyopathy.2,3Many risk factors are associated with AF, including hypertension, coronary artery disease, metabolic function, and inflammation, which lead to atrial structural remodeling and induce persistent AF.
Atrial structural remodeling is strongly connected with the fibrotic process and the subsequent disturbances in extracellular matrix (ECM) turnover. Matrix metalloproteinases (MMPs), a multigene family of structurally and functionally homogeneous proteolytic enzymes, regulate ECM turnover and are proposed to have a determinant role in atrial structural remodeling involved in the development of AF.4–9Notably, the activity of MMPs is regulated by redox reactions. Recent reports suggest that the leukocyte-derived heme enzyme myeloperoxidase (MPO), by generating hypochlorous acid (HOCl), is a crucial regulatory switch-modulating MMP activity.10,11It would be expected that MPO is an independent risk factor of AF recurrence after ablation. We tested the hypothesis that the high MPO levels in patients with paroxysmal AF predict arrhythmia recurrence after AF catheter ablation.
MATERIALS AND METHODS
Study Population
Two hundred eighty-eight consecutive patients with refractory symptomatic paroxysmal AF who were hospitalized in the First Affiliated Hospital of Zhengzhou University for index circumferential pulmonary vein (PV) radiofrequency ablation from January 2010 to July 2012 were prospectively enrolled. Exclusion criteria included left atrial (LA)/LA appendage thrombus, previous catheter ablation, previous cardiac surgery, infections, renal failure or hemodialysis, and unsuccessful radiofrequency ablation. Informed consent was obtained from all participants, and the study was approved by the local ethics committee. Transesophageal and transthoracic echocardiography images were obtained before ablation to measure the LA anteroposterior diameter, left ventricular (LV) end-diastolic diameter, LV end-systolic diameter, and LV ejection fraction, and to exclude the presence of intra-atrial thrombus.
Pulmonary Vein Isolation Procedure
The ablation procedure was performed in postabsorptive state under conscious sedation.12All antiarrhythmic drugs, with the exception of amiodarone, had been discontinued for at least 5 half-lives. We used the technique of circumferential PV ablation guided by 3-dimensional LA mapping, which had been described previously in detail.13Briefly, left atrium was explored using a transseptal approach. Left atrial geometry was reconstructed with a 3.5-mm tip ablation catheter (Navi-Star ThermoCool, Biosense-Webster; Diamond Bar, CA) in a CARTO system. A continuous irrigated radio frequency ablation was performed along each PV antrum to encircle the ipsilateral PVs (target temperature, 43°C; maximum power, 35 W; infusion rate, 17 mL/min). Procedural end points were completeness of continuous circular lesions and electrical isolation of all PVs identified by a decapolar circumferential mapping catheter (Lasso, Biosense-Webster). If a typical atrial flutter had been documented before the procedure, the tricuspid isthmus responsible for this tachycardia was identified and ablated.
Clinical Measurements
The baseline and clinical characteristics of all participants were determined. The details of age, sex, AF duration, history of smoking, and the weight and height were obtained, with the body mass index calculated as the body weight in kilogram divided by the height in meters squared. The laboratory measurements were carried out after overnight fasting. Blood was collected at baseline for white blood cell count (Beckman Coulter LH750, Shanghai, China), creatinine (Jaffe method, Roche Diagnostics, Shanghai, China), total cholesterol, triglycerides, high-density lipoprotein cholesterol low-density lipoprotein cholesterol (enzymatic method, Roche Diagnostics, Shanghai, China), and high-sensitivity C-reactive protein (hsCRP; immunoturbidimetric assay, Abbott Diagnostics, Shanghai, China).
MPO Concentration Assay
Blood samples were collected from each patient into a tube containing potassium EDTA as anticoagulant before procedure on the day of ablation; and within an hour after collection, they were centrifuged at 4000 rpm for 10 minutes at a temperature of approximately 4°C. The plasma was separated into aliquots and was stored in −70°C until personnel blinded to the patients’ clinical information performed the assay analysis. Furthermore, smoking had been paused for 3 months before taking blood samples. Plasma MPO levels were determined using a chemiluminescent microparticle immunoassay on an Architect i2000SR instrument (Abbott Diagnostics). According to the manufacturer, this assay has a dynamic range of 0 to 10,000 pmol/L with a limit of detection of less than 20.0 pmol/L and a functional sensitivity of less than 50.0 pmol/L. The validation of the Architect MPO assay in our laboratory revealed intra-assay and interassay coefficients of variation between 2.6% and 4.2%.
Postablation Management and Follow-Up
After the procedure, all patients received antiarrhythmic drugs if there were neither contraindications nor intolerance. If no recurrent atrial tachyarrhythmia occurred after 2 or 3 months, the drug treatment was discontinued. All asymptomatic patients were followed up with a 12-lead electrocardiogram and 24-hour Holter recordings before discharge and at 1, 3, 6, and 12 months after the ablative procedure. If the patient was symptomatic, a new electrocardiogram was obtained. Additionally, telephone interviews were conducted monthly in all patients by a physician, and transtelephonic event recorders (Life Care Networks, China) were performed in patients who accepted this monitoring after the physician’s recommendation. Recurrence was defined as the occurrence of confirmed atrial tachyarrhythmia (documented by electrocardiogram or Holter recordings) beyond 3 months after the index catheter ablation.
Statistical Analysis
Continuous data are presented as mean ± standard deviation and were compared by Student t test or 1-way analysis of variance. If variables were not in normal distribution, the Mann-Whitney U test was performed. Categorical variables were compared by χ2 analysis. Plasma MPO level was categorized into quartiles and a Kaplan-Meier estimation with a log-rank test served for the unadjusted analysis of the effect of MPO on the recurrence of catheter ablation of AF. A Cox proportional hazards model was used to estimate the relationship between MPO and the recurrence of AF. Age, sex, LA diameter, hsCRP, and PV isolation (PVI) were adjusted in the Cox analysis. All analyses were performed with SPSS software version 15.0. All probability values were 2-sided, and P < 0.05 was considered statistically significant.
RESULTS
The characteristics of the recurrence and non-recurrence groups are shown in Table 1. The level of plasma MPO (382 ± 179 pmol/L vs 457 ± 165 pmol/L, P = 0.017) and hsCRP (1.12 ± 0.59 mg/dL vs 3.23 ± 1.14 mg/dL, P = 0.031) were significantly higher in the recurrence group than in the non-recurrence group. There was significant difference in the prevalence of MPO quartiles between the recurrence group and the non-recurrence group. The patients with the larger LA diameter was significantly higher recurrence rate (36.2 ± 6.8 vs 41.7 ± 5.9 mm, P = 0.048). There were no differences in age, gender, body mass index, heart rate prior to the procedure, history of smoking, AF duration, LV end-diastolic diameter, LV end-systolic diameter, LV ejection fraction, white blood cell count, creatinine, or plasma lipids levels between the 2 groups. The prevalence of diabetes mellitus, hypertension, structural heart disease (including valvular heart disease, dilated, hypertrophic or ischemic cardiomyopathy, heart failure, coronary artery disease), medications (antiarrhythmic medications, β-receptor blockers, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, or statins) did not differ significantly between the 2 groups. There were no significant differences in procedure time, fluoroscopy time, or the PVI rate between the 2 groups.
The patients’ characteristics according to MPO quartile are listed in Table 2. From the lowest to the highest MPO quartile, the mean ± SD LA diameters were 35.6 ± 6.0, 35.5 ± 6.3, 36.3 ± 7.1, and 39.8 ± 6.8 mm, respectively (P = 0.037); and the mean ± SD hsCRPs were 1.01 ± 0.6, 1.61 ± 1.1, 2.69 ± 0.7, and 3.51 ± 2.1 mg/dL, respectively (P = 0.027). However, statistically significant differences of other variables were not found among the quartiles. As shown in Figure 1, from the lowest MPO quartile to the highest quartile, the recurrence rates were 16.9%, 25.7%, 29.7%, and 38.0%, respectively (P = 0.023).
Considering MPO as a category variate in model 1 (Table 3), after adjustment for age, sex, LA diameter, hsCRP, and PVI, there was an increased risk of recurrence in the subjects in the highest quartile of MPO after catheter ablation of AF compared with the subjects in the lowest quartile (hazard ratio, 3.18; 95% confidence interval, 2.12–5.23; P = 0.024). Considering MPO as a continuous variate in model 2 (Table 3), after adjustment for age, sex, LA diameter, hsCRP, and PVI, Cox analysis revealed that MPO was also an independent predictor of recurrence (hazard ratio, 2.12; 95% confidence interval, 1.71–3.27; P = 0.032).
DISCUSSION
This study is the largest to date to evaluate the relationship between MPO and the recurrent risk after ablation of paroxysmal AF. A main finding in our study is that in patients with paroxysmal AF, MPO correlates with AF and is a strong and independent predictor of recurrence after AF ablation.
The pathophysiological mechanism that underlies the development of electrophysiological and structural substrate that promotes AF maintenance and recurrence has been named “atrial remodelling”.14Rudolph et al.15demonstrate that MPO is a crucial prerequisite for structural remodeling of the myocardium, leading to an increased vulnerability to atrial fibrillation. Myeloperoxidase is a crucial regulatory switch-modulating MMP activity by generating HOCl.10,11Active MMPs regulate ECM turnover and are proposed to have a determinant role in atrial structural remodeling involved in the development of AF.4–9Friedrichs et al.16elucidate MPO catalyzes the generation of reactive species like HOCl, which affect intracellular signaling cascades in various cells and advance activation of pro-MMPs and deposition of atrial collagen resulting in atrial arrhythmias. Thus, MPO effectively promotes atrial structural remodeling and importantly contributes to the initiation and the occurrence of atrial fibrillation.
Currently, there is an increasing research interest on the role of inflammation and oxidative stress in the pathophysiologic effects of AF.17–19It has also been speculated that these processes are interrelated and contribute to the atrial remodeling.17,19The atrial oxidative damage experienced during AF alters myofibrillar energetics and can lead to myocyte necrosis. Apoptosis and necrosis induce low-grade inflammation, paving the way for structural alterations. The histologic substrate of these processes are inflammatory and fibrotic changes of the atrial myocardium.20Inflammation can thus perpetuate adverse electrical and structural remodeling and promote disease chronicity. Myeloperoxidase, a hemoprotein produced by polymorphonuclear neutrophils and macrophages that functions to catalyze the conversion of chloride and hydrogen peroxide to hypochlorite,21is a recently identified and potentially useful plasma inflammatory biomarker for cardiovascular diseases.22Myeloperoxidase is released into the extracellular fluid and general circulation during inflammatory conditions. Myeloperoxidase acts as a catalytically active protein, which depletes anti-inflammatory molecules such as NO and generates pro-oxidants such as HOCl, tyrosyl radicals or NO2, MPO has been recently shown to elicit proinflammatory cell-activating properties, which proved to be independent of the catalytical properties of this enzyme. Myeloperoxidase binding to CD11b/CD18 integrins initiated the activation of intracellular signaling cascades, which translated to increased superoxide generation, degranulation, and integrin expression.23Specifically, binding of MPO to antineutrophil cytoplasmic antibodies has been linked to the generation of reactive oxygen species, degranulation and release of proteolytic enzymes, and increased production of inflammatory chemokines and cytokines such as IL-1 and IL-8.24,25Furthermore, our findings showed that the level of plasma hsCRP was higher in the recurrence group than in the nonrecurrence group. These data were in line with previous research,26and there was a linear rise from the lowest to the highest MPO quartile.
The aforementioned findings supported the hypothesis that higher MPO level confers a higher risk of AF. It was reasonable to believe that a high level of MPO would lower the success rate of catheter ablation of AF. In this study, we sought to address the outcome of catheter ablation of AF in a subgroup of patients. To the best of our knowledge, our data show for the first time that a high level of MPO correlates with the incidence of recurrence after catheter ablation of paroxysmal AF in both univariate and multivariate analysis. Several potential mechanisms could cause this effect of MPO on recurrence of AF, including oxidative damage, atrial remodeling, and ischemia resulting from coronary atherosclerosis.27According to the study by Fazio et al.,28increased LA pressure should be a mechanism of increasing the LA diameter. The present study also showed that patients in the highest quartile of MPO had the largest LA diameter. The LA diameter is a well-known predictor of recurrence after catheter ablation of AF.29,30Nevertheless, after adjusting for LA size, a high level of MPO became an independent predictor of recurrence.
Study Limitations
It is unclear whether elevated MPO participates actively in the atrial remodeling or it simply is a result of increased atrial remodeling. For this reason, further outcome-directed prospective studies would clarify this point. Patients with early AF recurrence were excluded from the study because we do not really consider that early AF disappears at a successful radiofrequency ablation but myocardial swelling by ablation.
CONCLUSION
To the best of our knowledge, this study provides the first evidence that high MPO level is an independent predictor of AF recurrence after catheter ablation.