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PVCs and Fusion Beats



Starting from the left, there is a sinus beat, then a PVC, another sinus beat,
another almost but not quite identical PVC, then a fusion beat.  This is a beat
that has two initiating impulses: there are two separate pacemakers for this
single beat.  There is a P-wave, seen best in the V-lead, that would have given
rise to a sinus beat like the preceding ones, but an ectopic impulse occurs
at almost the same moment, and the two waves of depolarization meet and
fuse, producing this QRS that resembles a PVC.  We know that that P-wave is
not a retrograde wave as sometimes seen with a PVC because the waveform
is the same and the P-waves march.  There follow three sinus beats and then
another, differently shaped fusion beat occurs.  The P-wave contributing to
the formation of this fusion beat is best seen in lead II.