Specific reaction to para-Hisian pacing in the presence of a concealed nodoventricular pathway

Figures

• 

  Figure 1. 12-lead electrocardiogram: Normal sinus rhythm (A) and tachycardia (B).

• 

  Figure 2. A: Extra pacing at 500/320 ms from the atrium. SVT was induced, showing an A-H-A pattern with infra-Hisian block. B: PVC from the RV apex at the His-refractory period during SVT. PVC reset the next atrial potential with delay, and SVT terminated with the HA block pattern. The third QRS complex is the fusion beat of SVT and PVC, excluding the nodofascicular pathway. PVC = premature ventricular contraction; RV = right ventricle; SVT = supraventricular tachycardia

• 

  Figure 3. Responses to PHPs in 2 different locations. A: Because of the difference in pacing output, the first and second beats showed wide and narrow QRS, respectively. The different HA intervals, regardless of the identical VA intervals, indicate that HB is not contained in the pathway from stimulation to the atrium, indicating the AP pattern. B: PHP at the ventricular side showed a different response. Although the first narrower beat resulted in a VA of 112 ms, the second wider beat resulted in a prolonged VA interval, indicating an AVN pattern. The lower schemes represent the presumed mechanism of the different responses. At site A, a normal AP pattern of PHP was observed because the pacing site was close enough to the NVP to conduct through the NVP. At site B, conduction through the HB is faster than conduction through the NVP because of the separation of the NVP and the pacing site. AP = accessory pathway; AVN = atrioventricular node; HB = His bundle; NVP = nodoventricular pathway; PHP = para-Hisian pacing; SP = slow pathway.