In entrainment mapping of a flutter circuit, PPI minus TCL should be within how many milliseconds?

• A. 10
• B. 20
• C. 30
• D. 40

Answer: (C)

Entrainment mapping uses how the post-pacing interval compares to the tachycardia cycle length to know if your pacing site is inside the flutter circuit. The post-pacing interval (PPI) is the time from the last stimulus to the next return beat, while the tachycardia cycle length (TCL) is the intrinsic loop time of the flutter. If you pace from within the circuit, the impulse travels around the same loop and returns with almost the same timing as the ongoing tachycardia, so PPI is very close to TCL. The difference PPI minus TCL thus reflects how far you are from the actual circuit path. A threshold of 30 milliseconds is commonly used: if PPI minus TCL is within 30 ms, the pacing site is considered to be within or on the circuit; if it’s larger, the site is outside the circuit. That’s why the guideline value here is 30 ms.