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Monday, October 23, 2017

The marked variability of subclinical atrial fibrillation makes risk assessment difficult

A post  hoc analysis (1) of the TRENDS study concluded "significant temporal variability of AF burden exists when measured continuously with an implantable CRMD ( cardiac rhythm management device)."

The authors examined data from 394 patients who had a mean CHAD2DS.Vasc score of 3.7 (average) and divided AF burden into three categories: 1) No AF, 2) Low AF (less than 5.5 hours per day on any given day) and 3) High AF (greater than or equal to 5.5 hours per day).

They then determined how often that classification changed over time. What category in which the patient was placed was dependent on the time period over which the sampling was analyzed. One day they might have " no AF" another day be placed in the high AF category of greater than 5.5 hours per day.

So to what extent do these data invalidate the conclusion of the TRENDS study? Certainly  one at least has to be much  more skeptical of the findings. If a significant number of patients were considered to have no AF and then developed into either category 2 or 3 the calculation of the relative risk for  stroke would likely be an underestimation of risk .So how good is the data regarding the question of  the degree to which  AF burden is an indicator of stroke risk at all?

The authors concluded: "The burden of AF is highly variable over time and cannot be accurately assessed by short-term monitoring. If burden of AF is shown to be an important variable to be considered when making decisions regarding long-term anticoagulation, perhaps continuous monitoring should be employed to follow changes in AF burden over time."

1 Kaplan RM et al Atrial Fibrillation variability on long term monitoring of implantable cardiac rhythm management devices. Clinical Cardiology 2017: 1-5 March June

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