Figure 206-5

Determination of cardiac refractory periods during atriat pacing (A through C).
During a basic cyclelength pacing at 600 ms (S1S1 or A1A1), atrial premature stimulation (S2 or A2) at progressively shorter coupling intervals (S1S2 or A1A2) is depicted. The definition of the effective refractory period (ERP) of the His-Purkinje system (HPS), atrioventricular node, and atrium are Labeled. ANT RP = antegrade refractory period.

(From Akhtar.11 Reproduced with permission from the publisher and authors.)