Ja. Abildskov et Rl. Lux, Simulated torsade de pointes - The role of conduction defects and mechanism of QRS rotation, J ELCARDIOL, 33(1), 2000, pp. 55-64
A possible mechanism of torsade de pointes consisting of moving sites of re
entry in the presence of disparate recovery of excitability has been previo
usly proposed. This study evaluates the role of conduction defects in that
mechanism. A computer model that simulated propagation, cycle length depend
ent recovery of excitability, and slow propagation during incomplete recove
ry and in conduction defects was used. Localized conduction defects consist
ing of slow propagation were shown to allow reentry at changing locations i
n the presence of uniform recovery properties. Later activation within defe
cts resulted in later recovery, which permitted independent antegrade propa
gation adjacent to the defects. Retrograde propagation in the defects then
resulted in reentry. The location of serial reentry changed because retrogr
ade propagation and antegrade recovery had opposing directions and met dist
al to the origin of antegrade excitation. This mechanism was similar to tha
t produced by disparate recovery and the combination of conduction defects
and disparate recovery permitted the mechanism to occur with less marked di
sparity than otherwise required. The study also showed bidirectional serial
reentry around a localized conduction defect or region of disparate recove
ry which resulted in relation of QRS peaks around the isoelectric line. The
study provided evidence that either conduction defects or disparate recove
ry of excitability may be a substrate for torsade de pointes. It also indic
ated that combination of these factors might permit torsade de pointes when
neither alone does so. This provides a possible explanation for the specia
l propensity of quinidine and other drugs that slow conduction as well as p
rolong recovery to result in torsade de pointes. Findings also suggested a
more explicit mechanism for rotation of QRS peaks about the electrocardiogr
am baseline than was previously available.