What will you learn?
- what is entrainment
- how to correctly interpret PPI
- what typical errors can be avoided during this simple maneuver
About this scenario
Entrainment is a common and straightforward pacing maneuver used during electrophysiology (EP) studies to assess reentrant tachycardia, including both supraventricular tachycardia (SVT) and ventricular tachycardia (VT). It involves pacing the heart from multiple locations during an episode of reentrant tachycardia at a cycle length that is typically 20–30 msec shorter than the tachycardia's cycle length.
Traditionally, entrainment is expected to produce fusion beats. This occurs because the paced impulse is sent in both directions along the reentrant circuit, and in the reverse direction, it collides with the impulse from the preceding cycle. Consequently, since part of the myocardium in the circuit receives depolarization signals from two different directions, fusion of the beats takes place. Concealed fusion, meaning that the paced morphology is identical with the native one, is a sign of pacing directly within the reentry circuit.
As the impulse can also collide with the propagation zone of the tachy a too aggressive (too short CL or extended period of pacing) can terminate tachycardia without any diagnostic conclusions.
The main product of entrainment is the post-pacing interval (PPI) which is defined as the time interval from the last paced beat (during an entrainment maneuver) to the return of the first spontaneous beat of the tachycardia.
Remember that PPI:
- Must be measured recorded from the same site where the pacing was delivered.
- If the PPI is very close to the TCL (usually within 20-30 milliseconds of the TCL), it suggests that the pacing site is within or very near to the critical part of the reentrant circuit.
- PPI can only be measured if the reentry was advanced by pacing (the CL shortened) and the tachycardia reoccurred as a first beat after the pacing stopped
