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Atrial Flutter example two



Notice that the progression of F-waves is very regular, but that the QRS complexes are not.  The atria are fluttering regularly at a rate of about 320 per minute, but conduction to the ventricles is irregular.  This is called variable capture.  Notice that the R-R intervals are not irregularly irregular; they are always either 0.41 or 0.72 seconds.  These intervals are not simple multiples of the F-F interval: they also include an AV nodal delay which varies according to the relative refractoriness of the AV node.