The Dependence Of Pacing Frequency On The Atrial Input And Output Of The Atrioventricular Nodal Fast Pathway In Humans

Objectives:The purpose of this study was to investigate the dependence of pacing frequency on the atrial input and output of the atrioventricular nodal fast pathway to map the the earliest retrograde atrial activation site of fast pathway during slow/fast AVNRT in humans.Methods:The study populatin consisted of 15 patients (10 men, mean age of 39±15 years) without structural heart diseases underwent radio-frequency catheter ablation of supraventricular tachycardia or idiopathic left ventricular tachycardia who presented both good 1:1 antegrade and retrograde AV nodal fast pathway conduction before and after successful ablation. Electrophysiological programmed study was performed before ablation of slow/fast AVNRT in 3 patients and after ablation in the other 12 non-AVNRT patients. The right-sided and left-sided His bundle recording catheters were positioned by venious and rentrograde aortic approaches in all the 15 patients. The right atrium, left atrium (different sites of coronary sinus) and right ventricle were paced at different cycle lengthes, and the corresponding antegrade and retrograde atrial activation sequence and timing recorded at both the right and left His bundle sites were measured and compared. In addition, the atrial activation sequence and the earliest retrograde atrial activation site by AV nodal fast pathway conduction were also mapped during slow/fast AVNRT.Result:During pacing from the right atrium and the left atrium (at different sites of the coronary sinus) with 1:1 fast pathway conduction, the AHis recorded at the left side was earlier than the AHis at the right side at the same pacing cycle length in most of the patients, for exemple (A-H)cs 1-2 preceding (A-H)RA by (-5.9±10.7ms). During pacing from the right ventricle with 1:1 retrograde fast pathway conduction, the relationships between the A cs and the A RA could be divided into three different forms:⑴In 9 (60%) patients, the A His recorded from the right side was earlier than the A His recorded from the left side at a longer pacing cycle length, but reversing the earlier site from the right-sided A His to the left-sided when the pacing cycle length gradually getting shorter and shorter. (2)In 5 (33%) patients, the A His recorded from the left side was always earlier than the A His recorded from the right side at different pacing cycle lengthes, and the advantage became more significant when the pacing cycle length getting shorter.(3)In 1 (7%) patient, the A His recorded from the right side was always earlier than the A His recorded from the left side at different pacing cycle lengthes, although the advantage became less significant when the pacing cycle length getting shorter.In all the 3 patients with slow/fast AVNRT, the earliest atrial activation site by the retrograde fast pathway conduction during AVNRT was near the left-sided His bundle recording site.Pacing the left atrium (the coronary sinus electrode) and the high right atrial with circumference 10-50ms decreasing and maintaining 1:1 anterior conduction, meanwhile we would record the His potential at the left and right side of the septum. First, through pacing the distal coronary sinus (CS1-2) with the different circumference, we measured the AH interval of the left and right sides, and calculated the difference between the two, the statistical correlation analysis carried out showed that the two variables showed a zero correlation. These results indicated that two variables seem unrelated, but specific to each individual sample showed that the absolute difference increased gradually with the pacing frequency increased. The left atrium to the atrioventricular node conduction time relative to the right atrium to the atrioventricular node conduction time was gradually shortened. The possible reasons were the different population of individual, as well as age, gender, autonomic nervous system effects of different individuals of this stimulus was not exactly the same region, but also overlap, such as no distinction would be discussed for all the individual samples together. Its inter-relationship between variables would be concealed, could not reach the right conclusion.Conclusion:In most patients at this study, the AV nodal fast pathway has a atrial input and output conduction priority of the left-sided atrial septum to the right-sided atrial septum, especially during pacing at a short cycle length and pacing from the left atrium. During slow/fast AVNRT, the earliest retrograde atrial activation site by the fast pathway conduction was near the left-sided His bundle recording site.