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Frequency of Cardiac Rhythm Abnormalities in a Half Million Adults

Key findings

  • Abnormalities of cardiac rhythm are prevalent and affect >2% of middle-aged and older adults
  • Incident cardiac rhythm abnormalities occur at a rate of about 0.5% per year, similar to rates of stroke, myocardial infarction and heart failure
  • Risk factors for rhythm abnormalities include older age, male sex, traditional cardiac risk factors, chronic kidney disease and heart failure

Most studies of cardiac arrhythmias have focused on specific conditions such as atrial fibrillation and bradyarrhythmias. However, a contemporary survey of the frequency of heart rhythm disorders across multiple arrhythmia categories in a large adult population has been lacking, likely due to the challenge of obtaining baseline and follow-up health data in a large cohort. Such a cohort does exist in the United Kingdom. From 2006 to 2010, over nine million middle-aged and older adults in the UK were invited to participate in the UK Biobank, a prospective cohort study. Over 500k volunteers agreed to participate and provided access to their health information as well as other detailed measures of health.

Steven Lubitz, MD, cardiac electrophysiologist, and colleagues at Massachusetts General Hospital recently published the results of their analysis of arrhythmias in the UK Biobank in Circulation. At enrollment in the UK Biobank, physical measurements, biological samples, demographic and life-style information were collected along with baseline health assessments including factors relevant to arrhythmias. Of the 502,627 individuals who were enrolled in the study, the median age was 58 years, 94.1% were white, and 54.4% were women.

Follow-up data were derived from hospital and other national registry resources, with a median follow-up of approximately seven years. The Mass General Hospital team classified heart rhythm disorders into major clinical categories of atrial fibrillation, bradyarrhythmias, conduction system diseases, supraventricular arrhythmias and ventricular arrhythmias. They assessed the baseline prevalence of these arrhythmia conditions, the incidence of new arrhythmias, and the relations between risk factors and arrhythmia development using multivariable models.

They observed that at baseline, 2.35% (95% CI: 2.31–2.39) of the total cohort had a rhythm abnormality, with a prevalence of 0.96% in the in the <55 years of age group (95% CI: 0.91-1.00) and 4.84% (95% CI: 4.71-5.00) for those aged ≥ 65 years. Among those with no reported arrhythmias at baseline, nearly 16,000 new rhythm disorders developed during follow-up corresponding to a rate of 4.72 cases per 1000 person-years (95% CI: 4.65-4.80). The five arrhythmia categories studied had the following incidence rates:

  • Atrial fibrillation: 3.11 (95% CI: 3.05-3.17)
  • Bradyarrhythmias: 0.89 (95% CI: 0.86-0.92)
  • Conduction system diseases: 1.06 (95% CI: 1.02-1.09)
  • Supraventricular arrhythmias: 0.51 (95% CI: 0.48-0.53)
  • Ventricular arrhythmias: 0.57 (95% CI: 0.55-0.60)

In all five arrhythmia categories in all three age strata, prevalence and incidence was greater among males. The associations between arrhythmias and established risk factors such as age, sex and hypertension are consistent with previous reports.

This study offers several new insights into the epidemiology of heart rhythm disorders. First, the current report demonstrates that arrhythmias are common among adults and that most are atrial fibrillation. Second, the current study indicates that increasing age is a common factor associated with the development of arrhythmias. Third, the findings illustrate that many common risk factors are related to arrhythmia onset, including hypertension, coronary artery disease and heart failure. Moreover, frequent alcohol consumption was associated with increased risk of atrial fibrillation whereas active smokers were at greater risk for ventricular arrhythmias.

Limitations of this study include unidentified confounding factors and relatively short-term follow-up data on the cohort. The results provide contemporary frequencies of major arrhythmia categories in a large, prospective sample, and demonstrate the relative effect sizes of a broad array of risk factors. This is an important step in for quantifying the morbidity and economic costs attributed to arrhythmias, and ultimately for directing interventions to improve health outcomes.

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Patrick Ellinor, MD, PhD, director of Mass General’s Cardiac Arrhythmia Service, discusses his team’s recent work leveraging genome-wide association studies to identify over 100 different genetic determinants of atrial fibrillation, and his hope of using those variants to develop new drugs to treat atrial fibrillation in the years to come.

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