Figure 2. Schematic diagram of the appearance of VA conduction with different VA intervals. The retrograde P waves were marked by black triangles. (A) There was no retrograde P-wave in a sequence of sinus P-wave or relatively long-coupling PAC followed by normal BVP. (B) PVC with a VA interval of 200 ms. (C) VA intervals following LVPepi were prolonged to 320 ms due to the transmural conduction delay from epicardium to endocardium. (D) LVPepi captured partial ventricle myocardium and delayed VA conduction from PVC, so that VA interval following PVC in RRVAS was prolonged to about 240 ms. Endo = endocardium; Epi = epicardium; LBB = left bundle branch; RBB = right bundle branch. LVPepi = epicardial left ventricular pacing; RVPendo = endocardial right ventricular pacing; RPmyo = refractory period of atrial myocardium. LOC = loss of capture.