Introduction: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia.
Methods and results: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His-bundle area and the base of the coronary sinus orifice (DHis-OS) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His-bundle recording site from the successful ablation site (DHis-Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis-Ab/DHis-Os) were determined. The mean DHis-Os and DHis-Ab were 25.9 +/- 7.9 and 13.4 +/- 3.8 mm, respectively. DHis-Os negatively correlated with patient age (r = -0.41, P < 0.0001) and body mass index (r = -0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis-Os was longer (27.2 +/- 6.6 vs 24.6 +/- 8.4 mm, P < 0.005), DHis-Ab was similar (12.9 +/- 3.1 vs 13.9 +/- 4.0, P > 0.05) and DHis-Ab/DHis-Os was smaller (0.48 +/- 0.04 vs 0.74 +/- 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 +/- 4 vs 4 +/- 3, P < 0.05).
Conclusion: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His-bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle; therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis-Os to avoid injury to AV node.