Because humoral alterations have been implicated in the generation and perpetuation of atrial fibrillation (AF), we aimed to elucidate possible abnormalities in atrial endocrine function in the setting of lone AF. Levels of plasma apelin and amino terminal fragment of the brain natriuretic peptide prohormone (NT–pro-BNP) were measured in 40 patients with persistent AF, before and 1 month after electrical cardioversion, and in 15 controls in sinus rhythm (SR). All patients were successfully cardioverted to SR, although in 9 of them AF recurred. Baseline apelin levels were lower and NT–pro-BNP levels higher in patients with AF compared to controls (380 ± 186 vs 700 ± 151 pg/ml, p <0.001, and 615 ± 611 vs 50 ± 28 pg/ml, p <0.001, respectively). Maintenance of SR resulted in an increase of apelin and a decrease of NT–pro-BNP levels during the postcardioversion follow-up period compared to baseline (497 ± 170 vs 368 ± 178 pg/ml, p <0.001, and 206 ± 106 vs 398 ± 269 pg/ml, p <0.001 respectively). Patients who developed AF recurrence by the end of the follow-up period had similar values of apelin and NT–pro-BNP on final and initial evaluations (444 ± 142 vs 422 ± 217 pg/ml, p = 0.62, and 1,328 ± 714 vs 1,362 ± 862 pg/ml, p = 0.74, respectively). Stepwise logistic regression analysis showed that left atrial diameter (b =−0.49, p = 0.05), and baseline NT–pro-BNP (b = 0.006, p = 0.022), but not apelin, were independent predictors for AF recurrence. In conclusion, this study suggests that endocrine heart function, as judged from apelin and NT–pro-BNP levels, is reversibly modified in the setting of lone AF. This could influence systemic hemodynamics and pharmacologic measures designed to treat this arrhythmia.
Atrial fibrillation (AF) has a progressive nature. It has been increasingly recognized that there is a tendency for AF to become sustained over time and more resistant to cardioversion. Recent studies have shown that, in addition to electrical and structural remodeling, an atrial autocrine or paracrine system, which potentially regulates heart function, is involved in the course of AF. Apelin is an endogenous peptide ligand of the previously orphaned G-protein–coupled receptor, apelin–angiotensin receptor-like 1 (APJ), and has recently emerged as an important regulator of cardiovascular homeostasis with direct effects on cardiomyocyte contractility and perhaps electrophysiology. The purpose of the present study was to elucidate possible abnormalities in atrial endocrine function in the setting of AF, by assessing levels of plasma amino terminal fragment of the brain natriuretic peptide prohormone (NT–pro-BNP) and apelin in healthy subjects and in patients with persistent AF, and to evaluate alterations in cardiac hormonal activity reflected by the course of NT–pro-BNP and apelin levels in patients with persistent AF, just before and 1 month after electrical cardioversion.
Methods
The ethics committee of the University Hospital of Heraklion (Heraklion, Crete, Greece) approved the study. This investigation conformed to the principles outlined in the Declaration of Helsinki. Signed informed written consent was obtained from all subjects before their participation in the study.
The study population consisted of 40 patients who had from persistent, lone AF, defined as AF without clinical or echocardiographic evidence of cardiopulmonary disease, including hypertension, and had been referred to the cardiology department of the University Hospital of Heraklion for cardioversion. A diagnosis of AF was based on the following electrocardiographic criteria: (1) fluctuation of baseline of isoelectric line without regular P or F waves and (2) totally irregular RR intervals. Arrhythmia was considered persistent when it was documented on sequential 12-lead electrocardiograms, without any intervening periods of sinus rhythm (SR). All patients underwent repeat electrocardiography immediately before electrical cardioversion to confirm the persistence of AF. Fifteen healthy subjects in SR with no history of atrial arrhythmias, selected from our hospital and medical school staff, served as a control group. Subjects were excluded if they had any history of coronary artery disease, significant valvular disease, cardiomyopathy, or hyperthyroidism that preceded the history of AF. Patients who were >80 years old, had diabetes, chronic liver disease or hepatic dysfunction, or renal impairment and those with a pacemaker/implantable cardioverter–defibrillator were also excluded.
All subjects underwent a comprehensive clinical evaluation, which included medical history, physical examination, routine laboratory tests, thyroid function tests, and chest x-ray on their entry into the study. Maximal left atrial diameter and left ventricular ejection fraction were also assessed in all participants by 2-dimensional echocardiography, before cardioversion. Using a case–control study design, plasma levels of apelin and NT–pro-BNP in a group of patients with lone, persistent AF were compared to corresponding values in a control group of healthy subjects in SR. To evaluate alterations in apelin and NT–pro-BNP levels after cardioversion, blood samples were drawn immediately before sedation for cardioversion and at the end of the 1-month follow-up period. Patients were prospectively followed for recurrence of AF up to 1 month after cardioversion through telephone interviews and weekly clinic visits. When arrhythmia recurrence was suspected, it had to be confirmed by a physician’s examination and electrocardiographic documentation.
Electrical conversion to SR was attempted after patients with AF were properly anticoagulated by oral treatment with acenocoumarol that resulted in an international normalized ratio from 2.0 to 3.0 for ≥4 weeks. Anticoagulation had to be continued for ≥1 month after the procedure, regardless of its outcome. Cardioversion was performed in the electrophysiology laboratory under short-lasting general anesthesia with intravenous propofol, using a biphasic defibrillator with single synchronized shock energy of 200 J in the anteroposterior paddle position. The electrocardiograph was monitored continuously throughout the procedure and the recordings were stored on an optical disk (EP Laboratory Quinton, Inc., Quinton, Oklahoma).
Blood samples obtained from all participants after 30 minutes of supine rest were immediately placed on ice and centrifuged within 1 hour. Plasma samples were stored at −80°C until analysis. Plasma apelin-12 levels were determined using a commercially available enzyme immunoassay without extraction (Phoenix Pharmaceuticals, Inc., Burlingame, California) according to the manufacturer’s instructions. Values were normalized to a standard curve. Commercially available assay kits (Biomedica, Vienna, Austria) were also used for determination of NT–pro-BNP by enzyme-linked immunosorbent assay. Measurements were performed by personnel blinded to the clinical trial.
Summary descriptive data are presented as mean ± SD or count (percentage), as appropriate. Categorical variables were compared between groups with Fisher’s exact or chi-square tests, as appropriate. Continuous variables were compared between the relapsed and nonrelapsed groups with t test or Mann-Whitney test, and changes within groups were assessed by paired t test. Stepwise logistic regression was used to determine independent predictors for relapse. Thresholds for entry into and removal from the model were 5% and 10%, respectively. All tests were carried out at the 5% level of significance. SPPS 16 (SPSS, Inc., Chicago, Illinois) was used for statistical analysis.
Results
The patients included 26 men and 14 women, 48 to 74 years old (61 ± 8), who had persistent, lone AF lasting >3 months, with no known underlying disease. All subjects had normal left ventricular ejection fraction, as assessed by 2-dimensional echocardiography. Diltiazem and β blockers were allowed for ventricular rate control and all patients with AF received the indicated antithrombotic treatment according to international guidelines.
There were no significant differences in the age, gender, body mass index, and diastolic blood pressure between controls and patients. Subjects in SR had a significantly smaller left atrium and borderline lower systolic blood pressure compared to patients with persistent AF (37 ± 3 vs 43 ± 6 mm, p <0.001, and 131 ± 10 vs 138 ± 12 mm Hg, p = 0.05, respectively). In addition, baseline apelin, and NT–pro-BNP levels differed significantly between patients with AF and controls ( Figures 1 and 2 ). Specifically, baseline mean apelin levels were lower, whereas baseline mean NT–pro-BNP levels were higher in patients with AF compared to controls (380 ± 186 vs 700 ± 151 pg/ml, p <0.001, and 615 ± 611 vs 50 ± 28 pg/ml, p <0.001, respectively).
Of the 40 patients with persistent AF who participated in the study, all were successfully cardioverted to SR, but arrhythmia recurred immediately in 1. AF recurred within the study period in another 8 patients (total recurrence rate 22.5%). All patients tolerated the procedures well without developing any complication during follow-up. Clinical characteristics of patients who developed AF relapse compared to those who remained in SR are listed in Table 1 . Age, gender, body mass index, left ventricular ejection fraction, and systolic and diastolic blood pressures were similar in these 2 groups. However, patients who maintained SR during the follow-up period had larger left atrial diameters than those in whom AF recurred (44 ± 5 vs 39 ± 7 mm, respectively, p = 0.026).
| AF Recurrence | p Value | ||
|---|---|---|---|
| No | Yes | ||
| (n = 31) | (n = 9) | ||
| Age (years) | 61 ± 8 | 60 ± 7 | 0.71 |
| Men | 20 (64.5%) | 6 (66.7%) | 0.99 |
| Left ventricular ejection fraction (%) | 56 ± 9 | 61 ± 6 | 0.18 |
| Left atrial diameter (mm) | 44 ± 5 | 39 ± 7 | 0.026 |
| Body mass index (kg/m 2 ) | 27 ± 2 | 27 ± 2 | 0.24 |
| Systolic blood pressure (mm Hg) | 140 ± 12 | 133 ± 9 | 0.11 |
| Diastolic blood pressure (mm Hg) | 84 ± 4 | 83 ± 4 | 0.89 |
| Apelin (pg/ml) | 368 ± 178 | 422 ± 217 | 0.44 |
| NT–pro-BNP (pg/ml) | 398 ± 268 | 1,362 ± 862 | <0.001 |
In patients with AF, baseline apelin levels, determined before cardioversion, were comparable in patients still in SR 30 days after cardioversion and in those who had relapse of AF (368 ± 178 vs 422 ± 217 pg/ml, respectively, p = 0.44; Figure 3 ). However, baseline NT–pro-BNP levels were significantly higher in patients with AF on final evaluation compared to those who remained in SR after cardioversion (1,362 ± 862 vs 398 ± 268 pg/ml, respectively, p <0.001; Figure 3 ). In addition, NT–pro-BNP levels determined at the final evaluation were lower in patients who maintained SR during the follow-up period than in those with AF recurrence (206 ± 106 vs 1,328 ± 714 pg/ml, respectively, p <0.001; Figure 3 ). Stepwise logistic regression analysis revealed that baseline NT–pro-BNP (b = 0.006, p = 0.022) followed by left atrium (b = −0.49, p = 0.05) were independent predictors for AF recurrence within 1 month after cardioversion to SR ( Table 2 ).
