NONUNIFORM ANISOTROPY IS RESPONSIBLE FOR AGE-RELATED SLOWING OF ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

Introduction: AV nodal reentrant tachycardia cycle length has been sho wn to be longer in the elderly population. Microfibrosis associated wi th aging producing nonuniform anisotropic conduction or changes in mem brane ionic properties could explain this finding. Methods and Results : Forty-five patients (33 women and 12 men) with typical AV nodal reen trant tachycardia were studied to analyze the effects of age on electr ophysiologic characteristics of the tachycardia using high-density cat heter mapping of the triangle of Koch. We classified patients into gro up A (age less than or equal to 45 years, mean [+/- SD] 32.7 +/- 8.8, n = 27) and group B (age > 45 years, mean [+/- SD] 61.1 +/- 10.2, n = 18), Retrograde atrial activation was recorded during tachycardia by m eans of a 2-mm decapolar catheter at the His bundle, a quadripolar cat heter at the high right atrium, a multipolar catheter (6 to 10 poles) in the coronary sinus, and a deflectable quadripolar catheter at the p osterior triangle of Koch, The AH interval at the AV junction as well as HA intervals at several atrial sites were measured during tachycard ia. HA intervals at all atrial recording sites except in the posterior triangle of Koch were significantly longer in group B, as well as the tachycardia cycle length (362 vs 329 msec, P = 0.01). The mean AH int erval was prolonged by 24 msec in group B, but this difference did not reach statistical significance. A sequential pattern of retrograde at rial activation during tachycardia was more frequently recorded in gro up B. Conclusions: Since the delayed activation to the atrium was hete rogeneous, transverse nonuniform anisotropic conduction is a likely ex planation of these age-related modifications of AV nodal reentrant tac hycardia characteristics.