1. Cluster analysis of a population of patients with atrial fibrillation (AF) identified four unique phenotypes using variables not traditionally associated with AF classification.
2. The four phenotypic AF groups were associated with differences in treatment strategies and clinical outcomes.
Evidence Rating Level: 3 (Average)
Study Rundown: Atrial fibrillation is the most common cardiac arrhythmia and is associated with significant morbidity. Traditional classification systems have characterized patients based on duration or thromboembolic risk. The current classification systems may not capture the full extent of diversity of AF patients and could fail to encapsulate important variables for disease course. The current study sought to re-evaluate clinical phenotypes of AF by evaluating a study population with cluster variable analysis and determine the connection between phenotype and treatment and clinical outcomes. The analysis determined four phenotypic groupings: a low comorbidity group, young patients with comorbid behavioral disorders, patients requiring device implantation, and those with atherosclerotic disease comorbidities. The study found adverse cardiovascular and neurologic events were more common amongst the 3-comorbidity groups, and major bleeding was more common in the behavioral comorbidity, and device implantation groups.
The study has important significance as it applies a novel statistical approach to describe phenotypic groups of patients with AF which may prove more meaningful that current classification systems. Factors that comprise the current classification of AF were not determined to be significant in the cluster analysis. The study has a large population and was also externally validated in a second large population. The main limitations of the study include the reliance on a set number of available variables, and the influence of existing patterns of care on clinical outcomes.
Click to read the study in JAMA Cardiology
In-Depth [prospective cohort]: This study used data from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry and included patients 18 years and older with electrographically confirmed AF. Patients with identified reversible causes of AF or life expectancy less than 6 months were excluded. Data on comorbidity and adverse clinical outcomes were obtained at baseline, and then every 6-months up to 2 years. The primary outcome includes a composite of cardiovascular death, myocardial infarction, stroke/non CNS systemic embolism, or transient ischemic attack. Cluster analysis was performed using 60 baseline variables and resulted in the 4-cluster model as described before. External validation was performed using a mutually excluded ORBIT-AF II Registry.
In analysis of treatment patters, patients in the device implantation cluster were more likely to be managed with rate control. Patients in the low comorbidity cluster were more likely to be on a Class 1c antiarrhythmic agent. Compared to the low-comorbidity cluster, the primary outcome was more common in the behavioural (hazard ratio [HR], 1.49; 95%CI, 1.10-2.00), device implantation (HR, 1.39; 95%CI, 1.15-1.68), and atherosclerotic clusters (HR, 1.59; 95%CI, 1.31-1.92). Major bleeding was more common in the behavioural (HR, 1.35; 95%CI, 1.05-1.73), and device implantation clusters (HR, 1.24; 95%CI, 1.05-1.47).
Image: PD
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