Objective When radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia, the distance from ablation catheter to His bundle was measuremented in X-ray images of different position (right anterior oblique 30 degree + foot position 0 to 15 degrees), in order to finding the best targets under which the image position furthest to improve surgical safety,reduce the incidence of complications such as atrioventricular block.

Methods Among 30 patients with AVNRT undergoing catheter ablation, 25 cases of slow/fast type, slow/slow type 4 cases, 1 case of speed/slow type, atrial and ventricular stimulation or incremental S1S2, S1S2S3 procedures stimulation can induce AVNRT. Send the coronary sinus (CS) catheter to the coronary sinus in X-ray exposure in left anterior oblique 45° position and adjust CS_9–10 at the lowest point of the curvature (CS ostium); send His catheter to His bundle district and it can record to clear HIS site (ideal site for the HISd records small HIS and large V; HISm records to small A, HIS and large V; HISp records to a larger A, HIS and large V). Then send ablation (ABL) catheter to the classic slow pathway area in X-ray exposure in RAO30° + CAUD10°, by measuring the distance from ABL to His catheter. The end points of ablation were that eliminating the 1:1 antegrade slow pathway conduction in any forms of AVNRT, the retrograde slow pathway conduction in fast/slow form and uninducibility of any form of AVNRT.

Results By measuring the 30 patients' distance from ABL to His bundle (ABL-his) and Height triangle of Koch (CSo-His) in different X-ray, application of linear correlation and regression methods, ABL-His distance is the dependent variable, reflecting the patient characteristics of each index – gender, age, height, weight, body mass index as independent variables, to obtained ABL-His distance was positively correlated with CSo-His distance, gender, age, height, weight , body mass index no relevance; According cardiothoracic ratio (0.5 for the sector) are divided into two groups to compare ABL-His and CSo-His distance in different X-ray whether the differences between the two groups using random design data comparing variance analysis results:① patients' cardiothoracic ratio ≥ 0.5 recommended radiofrequency ablation of slow pathway of AVNRT in RAO30° + CAUD15° X-ray; ② patients' cardiothoracic ratio < 0.5 is recommended to radiofrequency ablation of slow pathway of AVNRT in RAO30° + CAUD10° X-ray. Patients were followed up for 6 months to 1 year, all patients had no AVNRT recurrence, no symptoms after surgery.

Conclusions ABL-His distance was positively correlated with CSo-His distance, gender, age, height, weight, body mass index no relevance. patients' cardiothoracic ratio ≥ 0.5 recommended radiofrequency ablation of slow pathway of AVNRT in RAO30° + CAUD15° X-ray. Patients' cardiothoracic ratio < 0.5 is recommended to radiofrequency ablation of slow pathway of AVNRT in RAO30° + CAUD10° X-ray.