Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. From 1980 to 2000, the annual incidence of AF in the US increased from 3.03 to 3.68 per 1000 persons.1 It is important to determine the risk factors for the development of AF. Metabolic syndrome (MetS) is characterized by a cluster of atherosclerosis risk factors including obesity, insulin resistance, hypertension, dyslipidemia and high levels of inflammatory factors, many of which are risk factors of new-onset AF. It has been shown that the trend of prevalence of MetS and AF is similar.2 Recent studies have indicated that MetS and AF are closely related,3,4 and MetS was an independent predictor of recurrence after catheter ablation of AF.5,6 There have been many studies about the distribution of MetS in patients with coronary heart disease,7 however, there are few studies about MetS in patients with AF. In this study, we investigated the prevalence of MetS in patients with AF in the absence of structural heart disease prior to catheter ablation from a tertiary hospital in China.
From January 2005 to November 2007, 857 inpatients with AF referring to Beijing Anzhen Hospital prior to catheter ablation of AF were retrospectively recruited. Patients with structural heart disease (including valvular heart disease, dilated, hypertrophic or ischemic cardiomyopathy, heart failure) were excluded, the remaining 741 patients were enrolled. Among the enrolled patients, 588 (79.4%) had paroxysmal AF and 153 (20.6%) had persistent/permanent AF. Paroxysmal AF was defined when the arrhythmia terminated spontaneously and the duration was less than 7 days. When it sustained beyond 7 days and terminated with pharmacological therapy or direct-current cardioversion, AF was considered persistent. Permanent AF was designated if there was no indication of cardioversion or failed cardioversion.8
Definition of MetS
MetS was defined according to the guidelines issued by the Society of Diabetology of the Chinese Medical Association and the National Cholesterol Education Program Third Adult Treatment Panel (NCEP-ATP III).9-11 According to the baseline characteristics, MetS was diagnosed when at least 3 of the following criteria were met: (1) body mass index equal to or greater than 25.0 kg/m2, which was calculated by dividing weight in kilograms by the square of the height in meters; (2) elevated blood pressure (systolic blood pressure ≥130 mmHg, diastolic blood pressure ≥85 mmHg, and/or a history of treated hypertension); (3) elevated blood glucose (≥5.6 mmol/L) and/or a history of diabetes mellitus; (4) elevated triglycerides (≥1.69 mmol/L); and (5) low high-density lipoprotein cholesterol (<1.03 mmol/L in men, <1.29 mmol/L in women).
Continuous variables were presented as mean ± standard deviation (SD). Student's t test was employed for continuous data between the two groups. The chi-square test was employed for categorical variables. The prevalence of MetS in this study was compared with the data derived from the literatures by the chi-square test.7,12 The value of P <0.05 was considered statistically significant. Statistical analyses were performed with SPSS 13.0.
The age of the patients with AF was (55.8±11.6) (17-79) years. Of the 741 patients, 426 (57.5%) were male; 399 (53.8%) were overweight or obese, and 588 (79.4%) had paroxysmal AF. The duration of AF was (6.6±6.2) years.
Other characteristics are listed in Table. The patients with MetS had a higher proportion of diabetes mellitus, hypertension, as well as larger left atrial diameter, larger left ventricular end diastolic diameter, larger left ventricular end systolic diameter, higher body mass index, higher blood glucose level, higher triglycerides and lower high-density lipoprotein cholesterol than those without MetS. The gender proportion and AF duration were not different significantly between paroxymal AF and persistent/permanent AF. The patients with paroxymal AF were older than those with persistent/permanent AF ((56.3±11.6) vs (54.1±11.6) years, P=0.040).
Distribution of MetS and its components
Among the 741 patients, 343 (46.3%) had MetS (200 male, 143 female). The prevalence of MetS in AF patients was significantly higher than that in Chinese adults12 (46.3% vs 16.5%, P <0.001). There was no significant difference in MetS prevalence between the patients with AF and those with coronary artery disease in our hospital7 (46.3% vs 49.3%, P=0.130). According to the definition of MetS, there was a significant difference in the prevalences of hypertension, overweight/obesity, hyperglycemia, hypertriglyceridemia and low high-density lipoprotein cholesterol between the MetS group and the non-MetS group. Zero, 1, 2, 3, 4, 5 components of MetS were found in 59 (8.0%), 140 (18.9%), 199 (26.9%), 203 (27.4%), 103 (13.9%) and 37 (5.0%) patients, respectively. The prevalences of overweight/obesity, high blood pressure, high glucose level, high triglyceride level and low high density lipoproteins cholesterol level were 53.8%, 47.6%, 23.2%, 40.6% and 72.1%, respectively.
AF and MetS
The prevalence of MetS was not significantly different between the paroxysmal AF group and the persistent/permanent AF group (44.6% vs 52.9%, P=0.064). The proportions of paroxysmal AF were 9.4%, 19.4%, 26.7%, 26.7%, 12.6%, 5.3% from zero to five MetS components, respectively (Figure 1). While the proportions of persistent/permanent AF were 2.6%, 17.0%, 27.5%, 30.1%, 19.0%, 3.9% from zero to five MetS components respectively. The prevalence of different MetS components in different AF type is shown in Figure 2. The prevalence of overweight/obesity was significantly higher in persistent/permanent AF patients than in paroxysmal AF patients (69.3% vs 49.8%, P <0.001). The prevalence of the other four MetS components was not significantly different between the paroxysmal AF group and the persistent/permanent AF group. Left atrial enlargement is an important characteristic of atrial remodeling in AF patients. The diameter of the left atrium in the MetS group was significantly larger than that in the non-MetS group ((39.5±5.8) mm vs (36.5±5.7) mm, P <0.001) (Table). Subgroup analysis indicated that the diameter of the left atrium in the MetS group was also significantly greater than that in the non-MetS group both in patients with paroxysmal AF ((38.6±5.7) mm vs (35.7±5.3) mm, P <0.001) and in patients with persistent/permanent AF ((42.5±5.2) mm vs (40.4±6.2) mm, P=0.029). The diameters of the left atrium in patients with 0, 1, 2, 3, 4, 5 components of MetS were (34.1±5.1) mm, (36.2±6.1) mm, (37.4±5.4) mm, (38.7±5.4) mm, (41.0±6.7) mm, (39.7±4.5) mm, respectively (P <0.001).
The association between AF and MetS has been proposed in recent years. A follow-up of 592 patients without obvious organic heart disease3 showed that the prevalence of new-onset AF/atrial flutter in MetS subjects was 9%, which was significantly higher than that in non-MetS subjects (4%). The effect of MetS on AF/AFL was independent of age and the diameter of the left atrium. A prospective study4 showed that MetS was an independent predictor after a 4.5-year follow-up of 28 449 patients. Among the five components of MetS, overweight, abnormal glucose metabolism, hypertension and hypertriglyceridemia markedly increased the risk for AF. Different from the aforementioned studies, this study sought to survey the prevalence of MetS in patients with AF in absence of structural heart disease in a tertiary hospital. The prevalence of MetS (46.3%) in AF patients was significantly higher than that in general people.
MetS is a syndrome which includes obesity, insulin resistance, hypertension, dyslipidemia and high level of inflammatory factors. Its multiple components are remarkably related to AF. A research13 demonstrated that the incidence of AF in 43 673 patients with diabetes was 14.9%, which was significantly higher than that in 57 077 patients without diabetes (10.3%, P <0.0001). Diabetes was an independent correlated risk factor of AF. The Framingham heart study,14 including a 38-year follow-up of 4731 subjects, showed that hypertension was significantly associated with risk for AF in both genders (odds ratio, 1.5 for men and 1.4 for women). A prospective Framingham cohort study demonstrated that AF developed in 265 subjects.15 Compared with individuals with normal body mass index, overweight/obesity was related to the risk of new-onset AF. According to the result of another research,16 which included a total of 8051 consecutive patients who had undergone cardiac surgery, obesity was an independent predictor of new-onset AF after the surgery. The potential mechanism of AF associated with obesity was not understood. Some related factors may be the pathophysiological basis such as elevated plasma volume, ventricular diastolic dysfunction, enhanced neuro-hormonal activation, structural and electrophysiological abnormality of the myocardium resulted from fat itself.15,16 This study demonstrated that the percentage of overweight/obesity in AF subjects was 53.8%. And the prevalence of overweight/obesity in patients with persistent/permanent AF was significantly higher than that in patients with paroxysmal AF. It is indicated that metabolic disorder may be more important in the pathogenesis of persistent/permanent AF, which may be one of the reasons why the success rate of catheter ablation is low in patients with persistent/permanent AF.5
MetS is related to atrial remodeling. Umetani et al3 demonstrated that the diameter of the left atrium in patients with MetS was greater than that in patients without MetS. The number of components fulfilled for MetS was correlated with cardiac structural abnormity including the diameter of the left atrium as revealed by Azevedo et al.17 The diameter of the left atrium notably increased with the number of MetS components, which was in agreement with the reports in the literature. We also found that the diameter of the left atrium in the MetS group was significantly greater than that in the non-MetS group both in patients with paroxysmal AF and in those with persistent/permanent AF.
This study was based on the data from inpatients with AF prior to catheter ablation in a single center. The economic conditions and awareness of AF among the patients prior to catheter ablation might be different from those of other patients with AF. This study could not represent the prevalence of MetS in the general AF population because of sample selection bias. However, it provided important clinical data for the prevalence of MetS in patients with AF prior to catheter ablation. MetS accounts for a large proportion in the AF population. In clinical practice, we should pay more attention to the patients with AF and MetS. The effect of MetS on the ventricular rate control, the rhythm control as well as the anticoagulation of AF patients remains to be further investigated.
1. Miyasaka Y, Barnes ME, Gersh BJ, Cha SS, Bailey KR, Abhayaratna WP, et al. Secular trends in incidence of atrial fibrillation
in Olmsted County, Minnesota, 1980 to 2000, and implications on the projections for future prevalence. Circulation 2006; 114: 119-125.
2. Ford ES, Giles WH, Dietz WH. Prevalence of the metabolic syndrome
among US adults: findings from the third National Health and Nutrition Examination Survey. JAMA 2002; 287: 356-359.
3. Umetani K, Kodama Y, Nakamura T, Mende A, Kitta Y, Kawabata K, et al. High prevalence of paroxysmal atrial fibrillation
and/or atrial flutter in metabolic syndrome
. Circ J 2007; 71: 252-255.
4. Watanabe H, Tanabe N, Watanabe T, Darbar D, Roden DM, Sasaki S, et al. Metabolic syndrome
and risk of development of atrial fibrillation
: the Niigata preventive medicine study. Circulation 2008; 117: 1255-1260.
5. Tang RB, Dong JZ, Liu XP, Long DY, Yu RH, Kalifa J, et al. Metabolic syndrome
and risk of recurrence of atrial fibrillation
after catheter ablation
. Circ J 2009; 73: 438-443.
6. Chang SL, Tuan TC, Tai CT, Lin YJ, Lo LW, Hu YF, et al. Comparison of outcome in catheter ablation
of atrial fibrillation
in patients with versus without the metabolic syndrome
. Am J Cardiol 2009; 103: 67-72.
7. Hu R, Ma CS, Nie SP, Lu Q, Kang JP, Du X, et al. Effect of metabolic syndrome
on prognosis and clinical characteristics of revascularization in patients with coronary artery disease. Chin Med J 2006; 119: 1871-1876.
8. Fuster V, Ryden LE, Cannom DS, Crijns HJ, Curtis AB, Ellenbogen KA, et al. ACC/AHA/ESC 2006 Guidelines for the Management of Patients with Atrial Fibrillation
: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation
): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation 2006; 114: e257-e354.
9. Lu YH, Lu JM, Wang SY, Li CL, Liu LS, Zheng RP, et al. Comparison of the diagnostic criteria of metabolic syndrome
by International Diabetes Federation and that by Chinese Medical Association Diabetes Branch. Natl Med J China (Chin) 2006; 86: 386-389.
10. Grundy SM, Cleeman JI, Daniels SR, Donato KA, Eckel RH, Franklin BA, et al. Diagnosis and management of the metabolic syndrome
: an American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement. Circulation 2005; 112: 2735-2752.
11. Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report. Circulation 2002; 106: 3143-3421.
12. Gu DF, Reynolds K, Yang WJ, Chen SF, Wu XG, Duan XF, et al. The prevalence of metabolic syndrome
in Chinese adult. Chin J Diabetes (Chin) 2005; 13: 181-186.
13. Movahed MR, Hashemzadeh M, Jamal MM. Diabetes mellitus is a strong, independent risk for atrial fibrillation
and flutter in addition to other cardiovascular disease. Int J Cardiol 2005; 105: 315-318.
14. Benjamin EJ, Levy D, Vaziri SM, D'Agostino RB, Belanger AJ, Wolf PA. Independent risk factors for atrial fibrillation
in a population-based cohort. The Framingham Heart Study. JAMA 1994; 271: 840-844.
15. Wang TJ, Parise H, Levy D, D'Agostino RB Sr, Wolf PA, Vasan RS, et al. Obesity and the risk of new-onset atrial fibrillation
. JAMA 2004; 292: 2471-2477.
16. Zacharias A, Schwann TA, Riordan CJ, Durham SJ, Shah AS, Habib RH. Obesity and risk of new — onset atrial fibrillation
after cardiac surgery. Circulation 2005; 112: 3247-3255.
17. Azevedo A, Bettencourt P, Almeida PB, Santos AC, Abreu-Lima C, Hense HW, et al. Increasing number of components of the metabolic syndrome
and cardiac structural and functional abnormalities - cross-sectional study of the general population. BMC Cardiovasc Disord 2007; 7: 17.
Keywords:© 2009 Chinese Medical Association
metabolic syndrome; atrial fibrillation; catheter ablation