Click on image to view larger version.

Figure 1 Recordings from case 8 showing variation of P-QRS relation with changes in AH, HA and AH/HA ratio at the initiation of slow-fast atrioventricular node reentry tachycardia following delivery of two atrial extrastimuli during sinus rhythm. The sinus cycle length was 655 ms and the coupling interval of the first extrastimulus was 320 ms. (A) The coupling interval of the second extrastimulus was 280 ms, and was 260 ms in (B). Note that the HA interval of the first echo beat was the longest and a progressive shortening of HA interval associated with changes in AH interval, AH/HA ratio and the cycle length of the tachycardia was observed after initiation of the tachycardia. The atrial activation sequence was unchanged, and the earliest atrial activation was registered from the orifice of the coronary sinus. Note also that the HA interval of the first echo beat was longer in (A) when the tachycardia was induced at a longer coupling interval (A₂A₃) with a shorter AH interval (A₃H₃) as compared to that in (B). I, aVF and V₁ = ECG leads I, aVF and V₁; HRA, CSd, CSp and HBE = bipolar electrograms recorded from the high right atrium, the distal two electrodes of coronary sinus catheter, the proximal two electrodes of the coronary sinus catheter, and the His bundle recording catheter; CL = cycle length; S₂ and S₃ = stimulus artifact of the first and the second extrastimulus; A₁, A₂ and A₃ = atrial responses to the basic sinus or driven beat, the first extrastimulus and the second extrastimulus; H₁, H₂ and H₃ = His bundle responses to the basic sinus or driven beat, the first extrastimulus and the second extrastimulus; Ae and He = atrial and His bundle responses during atrioventricular node reentry echoes or tachycardia. The cycle lengths of the tachycardia, AeHe and HeAe intervals are listed.