Because of relatively long coupling interval, this type of VPC occurs just before the expected sinus beat.

  This may result in the appearance of
- a coincidental P wave preceding the VPC (not directly related to the VPC).
- a fusion wave due to ventricular depolarization partially by the VPC and partially by the conducted supraventricular impulse.




ECG 1. An end diastolic VPC resulting in the formation of a fusion beat is seen in the 3-channel Holter recording above.
It's a fusion beat since its configuration is different than that of the partially seen VPC at the right end of the tracing.
Its coupling interval (671 ms) is also longer that of the VPC (390 ms) at the right end of the tracing.
The P wave preceding the VPC is not causally related to it.
(The PR interval is so short that the formation of this wide QRS complex (this VPC can not be explained by this P wave)

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ECG 2. End-diastolic VPC in a patient with prolonged PR interval (1st degree AV block).

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