Increased Transient Outward Current in the Subepicardial Region Is
Sufficient to Explain the Slurring of the QRS. A Simulation Study.
A.D. Corlan1, B. Amuzescu2, I. Milicin3,
L. De Ambroggi 4
1University Emergency Hospital - Bucharest - Romania,
2University of Bucharest - Bucharest - Romania,
3Scalacalc Laboratory, Quattro Electronic Design - Bucharest - Romania,
4IRCCS Policlinico San Donato, University of Milan - San Donato Milanese - Italy,
36-th Congress of the International Society of Cardiology, Wroclaw, 24-27 Jun 2009
Background QRS slurring was statistically associated with a recent
history of sudden death and malignant arrhythmias. Clarification
and differentiation between possible mechanisms of this easily detectable
feature is needed to increase its predictive value.
Methods We built a finite element model of the ventricles with 27000
elements organised in six myocardial strata for both the left and
right ventricle (figure 1). The shape of the action potential was computed for
the elements in each stratum using a modified Luo Rudy dynamic model
that includes parameters extracted from the literature for the human
myocardium. Activation times were assigned with a cellular automaton
model and tuned to reproduce the well known recordings of Durrer D. at al.
Electrograms were computed for 370 electrodes positioned on a surface
with the shape of a human thorax in a uniform volume conductor around
the ventricle (electrode positions were kindly provided by R. Macleod
from University of Utah, USA).
A pair of simulations were compared, one without an
Ito current and one with a maximum transient outward conductance \gto
assigned randomly in the 0.076--0.190 nS/pF interval in the
subepicardial layer. All other parameters were identical between
the two simulations.
The J point was taken as the instant where activation ended
in the simulated myocardium. It was identical for all simulations,
as activation was identical.
QRS slurring was measured by considering the
decrease of the second derivative of the electrical potential in time
on each lead at the instant when the last myocardial element was
activated between the \gto=0 and the \gto $>$ 0 cases.
1000 such pairs of simulations were run, with maximal
conductances for the rapid and slow K, the ATP-dependent K, plateau K,
T and L-type Ca, Na/Ca exchanger currents in a range of 40--160\% of
the reference value from the literature.
Adding the Ito current produced a QRS slurring effect
in 322±2.4 of the 370 leads.
The QRS slurring aspect on the electrocardiogram
could be obtained by the isolated increase in the maximum density
of the transient outward current in the subepicardial region.