Epidemiology and significance of atrial fibrillation

Incidence of chronic atrial fibrillation in general practice and its treatment pattern

The object of this article was to estimate the incidence rate of chronic atrial fibrillation (AF) in a general practice setting, to identify factors predisposing to its occurrence, and to describe treatment patterns in the year following the diagnosis. The method used was a population-based cohort study using the General Practice Research Database (GPRD) in the UK. We identified patients aged 40-89 years with a first ever recorded diagnosis of AF. The diagnosis was validated through a questionnaire sent to the general practitioners. A nested case-control analysis was performed to assess risk factors for AF using 1,035 confirmed incident cases of chronic AF and a random sample of 5,000 controls from the original source population. The incidence rate of chronic AF was 1.7 per 1,000 person-years, and increased markedly with age. The age adjusted rate ratio among males was 1.4 (95% CI 1.2-1.6). The major risk factors were age, high BMI, excessive alcohol consumption, and prior cardiovascular comorbidity, in particular, valvular heart disease and heart failure. Digoxin was used in close to 70% of the patients, and close to 15% did not receive any antiarrhythmic treatment. Close to 40% did not receive either warfarin or aspirin in the 3 months period after the diagnosis. Among the potential candidates for anticoagulation only 22% of those aged 70 years or older were prescribed warfarin in comparison to 49% among patients aged 40-69 years. Chronic AF is a disease of the elderly, with women presenting a lower incidence rate than men specially in young age. Age, weight, excessive alcohol consumption, and cardiovascular morbidity were the main independent risk factors for AF. Less than half of patients with chronic AF and no contraindications for anticoagulation received warfarin within the first trimester after the diagnosis.

New Bayesian discriminator for detection of atrial tachyarrhythmias

BACKGROUND

Accurate, rapid detection of atrial tachyarrhythmias has important implications in the use of implantable devices for treatment of cardiac arrhythmia. Currently available detection algorithms for atrial tachyarrhythmias, which use the single-index method, have limited sensitivity and specificity.

METHODS AND RESULTS

In this study, we evaluated the performance of a new Bayesian discriminator algorithm in the detection of atrial fibrillation (AF), atrial flutter (AFL), and sinus rhythm (SR). Bipolar recording of 364 rhythms (AF=156, AFL=88, SR=120) at the high right atrium were collected from 20 patients who underwent electrophysiological procedures. After initial signal processing, a column vector of 5 features for each rhythm were established, based on the regularity, rate, energy distribution, percent time of quiet interval, and baseline reaching of the rectified autocorrelation coefficient functions. Rhythm identification was obtained by use of Bayes decision rule and assumption of Gaussian distribution. For the new Bayesian discriminator, the overall sensitivity for detection of SR, AF, and AFL was 97%, 97%, and 94%, respectively; and the overall specificity for detection of SR, AF, and AFL was 98%, 98%, and 99%, respectively. The overall accuracy of detection of SR, AF, and AFL was 98%, 97% and 98%, respectively. Furthermore, sensitivity, specificity, and accuracy of this algorithm were not affected by a range of white Gaussian noises with different intensities.

CONCLUSIONS

This new Bayesian discriminator algorithm, based on Bayes decision of multiple features of atrial electrograms, allows rapid on-line and accurate (98%) detection of AF with robust anti-noise performance.

Hospitalizations for atrial fibrillation in the general male population: morbidity and risk factors

OBJECTIVES

To analyse the incidence, prevalence, aetiology, risk factors and prognosis of hospitalizations for atrial fibrillation.

SUBJECTS

A random population sample of 7495 men aged 47-55 years was first examined in 1970-73. During follow-up until 1996 (mean 25.2 years) 754 men were hospitalized with a diagnosis of atrial fibrillation.

RESULTS

In the age groups of 55-64, 65-74 and 75-79 years, the incidence rate was 2.0, 5.8 and 17.3 per 1000 person years, and the prevalence 1.2, 4.2 and 8.0%, respectively. Definite or possible coronary heart disease was diagnosed in 46.0%, heart failure in further 20.2% and valvular heart disease or cardiomyopathy in 4.5%. In bivariate analysis adjusted for age, the following factors were significantly associated with future hospitalization for fibrillation: a family history of myocardial infarction, stroke in mother, dyspnoea at entry, alcohol abuse, high body stature and body weight, high blood pressure but not diabetes, high serum cholesterol, high heart rate, smoking, coffee consumption or psychological stress. Significant risk factors in multivariate analysis were age, odds ratio (OR) [95% confidence interval (CI)] -1.11 (1.07, 1.16) per year, hospitalization for coronary heart disease or heart failure -6.77 (5.17, 8.87), stroke in mother - 1.49 (1.15, 1.93), high body stature -1.04 (1.03, 1.06) per cm, high body mass index (BMI) -1.07 (1.04, 1.10) per kg m(-2), as well as hypertension -1.33 (1.07, 1.65). After a diagnosis of atrial fibrillation, mortality was increased by 3.3 times.

CONCLUSION

In spite of a clinical association with coronary heart disease, risk factors for atrial fibrillation were only partly the same. Prevention includes avoidance of weight gain and control of blood pressure as well as prevention of myocardial infarction and heart failure.

Impaired myofibrillar energetics and oxidative injury during human atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with severe contractile dysfunction and structural and electrophysiological remodeling. Mechanisms responsible for impaired contractility are undefined, and current therapies do not address this dysfunction. We have found that myofibrillar creatine kinase (MM-CK), an important controller of myocyte contractility, is highly sensitive to oxidative injury, and we hypothesized that increased oxidative stress and energetic impairment during AF could contribute to contractile dysfunction. Methods and Results-- Right atrial appendages were obtained from AF patients undergoing the Maze procedure and from control patients who were in normal sinus rhythm and undergoing cardiac surgery. MM-CK activity was reduced in AF patients compared with controls (25.4+/-3.4 versus 18.2+/-3.8 micromol/mg of myofibrillar protein per minute; control versus AF; P<0.05). No reduction in total CK activity or myosin ATPase activity was detected. This selective reduction in MM-CK activity was associated with increased relative expression of the beta-myosin isoform (25+/-6 versus 63+/-5%beta, CTRL versus AF; P<0.05). Western blotting of AF myofibrillar isolates demonstrated no changes in protein composition but showed increased prevalence of protein oxidation as detected by Western blotting for 3-nitrotyrosine (peroxynitrite biomarker) and protein carbonyls (hydroxyl radical biomarker; P<0.05). Patterns of these oxidative markers were distinct, which suggests discrete chemical events and differential protein vulnerabilities in vivo. MM-CK inhibition was statistically correlated to extent of nitration (P<0.01) but not to carbonyl presence.

CONCLUSIONS

The present results provide novel evidence of oxidative damage in human AF that altered myofibrillar energetics may contribute to atrial contractile dysfunction and that protein nitration may be an important participant in this condition.

Trends and outcomes in the hospitalization of older Americans for cardiac conduction disorders or arrhythmias, 1991-1998

OBJECTIVE

To identify epidemiological trends and measure outcomes in elderly patients hospitalized for cardiac conduction disorders or arrhythmias.

DESIGN

Review of the standard 5% samples of the Medicare Provider Analysis and Review Files to characterize 144,512 discharges from 1991 through 1998 in which the principal diagnosis was a conduction disorder or arrhythmia, using the corresponding Enrollment Databases for denominator data.

SETTING

Short-stay hospitals in the United States.

PARTICIPANTS

Medicare beneficiaries age 65 and older in the standard 5% sample.

MEASUREMENTS

Diagnosis-specific trends and rates; discharges by year; cumulative age-, race-, and sex-specific discharge rates; mean length of stay in hospital and in intensive care; mean Medicare reimbursement to the hospital; case-fatality rate in hospital; discharge destinations of patients discharged alive.

RESULTS

Annual hospitalizations for sinoatrial node dysfunction, atrial flutter, atrial fibrillation, or ventricular fibrillation increased more rapidly than did the elderly Medicare beneficiary population. Hospitalizations with a principal diagnosis of ventricular extrasystoles or asystole showed steep secular declines. Discharge rates for sinoatrial node dysfunction, a group of rhythms with a nonsinus pacemaker, atrial fibrillation, Mobitz I, or complete atrioventricular block all increased steeply and continuously with patient age. In contrast, discharge rates for atrial flutter or ventricular tachycardia or fibrillation peaked among 75- to 84-year-old patients. White men were at uniquely high risk of hospitalization for atrial flutter or ventricular tachycardia or fibrillation, and, among the white majority, men had higher discharge rates than women for nine of the 11 commonest rubrics. Whites, particularly white women, had the highest discharge rates for atrial fibrillation. Blacks, especially black women, were at disproportionate risk for hospitalization for the group of nonsinus pacemaker rhythms. Diagnosis-specific mean resource costs were strongly correlated with each other and with mean Medicare reimbursement but not with case-fatality rate.

CONCLUSION

Medicare claims data demonstrated striking differences among and within diagnoses of heart blocks or arrhythmias in terms of the populations at greatest risk for hospitalization. This variation should be explored further to generate and test hypotheses about differential causation or delivery of care.

Atrial fibrillation in patients with heart failure: pharmacologic options

Atrial fibrillation is a common arrhythmia in patients with heart failure. The presence of atrial fibrillation deteriorates cardiac function and increases the risk of thromboembolic events. The management of patients with atrial fibrillation in association with heart failure should consist of ventricular rate control, prevention of thromboembolic events, and conversion to normal sinus rhythm. Traditionally, digoxin has been widely used in patients with heart failure and atrial fibrillation; however, it does very little to restore sinus rhythm and requires the addition of another rate-limiting agent to control ventricular rate. The likelihood of successful cardioversion is dependent on the duration of heart failure and the degree of neurohormonal activation. The initiation of antiarrhythmic drug therapy in patients with heart failure should be guided by safety issues as well as consideration of potential benefits vs. risks associated with therapy. Amiodarone has been evaluated in numerous clinical trials and appears to be safe and effective when used in low dosage. Treatment with dofetilide is another option. Comparative studies with oral dofetilide vs. amiodarone are needed to evaluate their efficacy in restoration and maintenance of sinus rhythm in patients with heart failure. Such trials will clearly define the role of dofetilide in the treatment of atrial fibrillation. Routine prophylactic use of antiarrhythmic drug therapy for chronic atrial fibrillation in the setting of heart failure is not recommended due to a low efficacy rate and high proarrhythmic risk. Anticoagulation with warfarin and rate control remain the standard therapy. (c)2001 by CHF, Inc.