Biomedical Engineering Reference
In-Depth Information
veloping expertise, it is likely that at least over the next decade there will be
increasingly realistic and computationally expensive models of electrical and
mechanical wave propagation in human heart. Although most studies to date
have focused on ventricular tachycardia, ventricular fibrillation, and atrial fibril-
lation, realistic models should be able to incorporate anatomical and physiologi-
cal abnormalities that are associated with other arrhythmias, and consequently it
is likely that mathematical models of other arrhythmias will likewise be gener-
ated.
In parallel with the development of models of arrhythmias, I anticipate
work will be carried out on the mathematical analysis and modeling of arrhyth-
mias in people. Although there is a large clinical literature describing various
arrhythmias, there is still lots of room for theoreticians to dive into this literature
to develop testable models of arrhythmia. One aspect that such models will nec-
essarily have to deal with is the often paroxysmal starting and stopping of ar-
rhythmia. In some cases, if it were possible to predict the onset of the arrhythmia
before it occurred, then it might be possible to take corrective steps to avert the
arrhythmia. I feel certain that if more theoreticians took time to examine the
records of patients experiencing arrhythmias, they would find the data compel-
ling. To understand the clinical data, it will be necessary to examine experimen-
tal and mathematical models of the heart in which there is a spontaneous
initiation of arrhythmia, in contrast to most current mathematical models in
which arrhythmia is induced by delivering a stimulus or series of stimuli to the
heart.
Tissue cultures of cardiac cells grown in various geometries often exhibit
the spontaneous generation of reentrant arrhythmias (36-39). Figure 3 shows an
example of a burst of activity in tissue culture. Mathematical models that incor-
porate spontaneous activity, excitability, heterogeneity, and a decrease of excit-
ability following rapid activation typically show a range of parameter values in
which there is spontaneous initiation and termination of reentrant activity (36)
similar to the paroxysmal rhythms observed clinically. Moreover, in heteroge-
neous excitable media, plane waves may spontaneously break up into spiral
waves over intermediate ranges of coupling between the cells (40). Therefore,
this approach gives insight into how complex cardiac rhythms may spontane-
ously arise as a consequence of physiological and anatomical changes that re-
duce excitability and/or increase heterogeneity. I expect that an ability to
manipulate the geometry combined with the potential to manipulate the ionic
components of cells using molecular biology techniques, and the use of optical
methods to record rhythms over extended spatial areas for extended periods of
time, should make tissue cultures an excellent preparation for future studies of
complex arrhythmia.
The treatment of cardiac patients has undergone a remarkable development
and evolution over the past two decades. The advances are due to many factors,
including medications to better control hypertension and blood lipids; a variety
