Complexities of the Dynamical Progression of 4:1 Atrioventricular Block in Atrial Flutter

Abstract

No previous studies have dealt with the dynamics of progression of 4: 1 atrioventricular block (AVB). In order to do this, we analyzed Holter recordings of 6 patients (receiving digoxin and beta blockers or calcium channel blockers) in whom atrial flutter with ‘stable’ (≥5 min) 4: 1 AVB increased to higher degrees of AVB. The ratios (ra) in each episode (ep) were expressed numerically as well as M (number of atrial deflections): N (number of ventricular complexes). In stage 1, 324 ep of 4: 1 AVB progressed (with letter representation in parentheses) to one (4N + 2:N) or several cycles of 6: 1 AVB and to one (4N + 4:N) or several cycles of 8: 1 AVB with subsequent regression to 4:1 AVB. In these ep, the ra between adjacent M:N and M’:N’ ra could be expressed as M + M’:N + N’ in the direct 4:1 to 6:1 or 4:1 to 8:1 steps of the so called devil's staircase. In the 398 ep of stage 2, these progressions of 4: 1 AVB also coexisted with increases to: a) 5: 1 to 6: 1: b) 5: 1 to ≥8:1; and c) 5:1 to 6:1 to 8: 1 AVB. The higher degrees of AVB did not regress to short cycles of 4:1 AVB for several, seconds. In summary: 1) 4: 1 AVB in atrial flutter could progress directly to 6: 1 and 8: 1 AVB, bypassing intermediate steps of the devil's staircase, and 2) 8: 1 AVB could also emerge directly from 5:1 and 6:1, but apparently not from 7: 1 AVB