Biomedical Engineering Reference
In-Depth Information
Chapter 8
Formal Logic Based Heart-Model
Abstract A closed-loop model of a system is considered as a de facto standard in
the area of system engineering for validating a system model. Cardiac pacemak-
ers and implantable cardioverter-defibrillators (ICDs) are the most critical of these
medical devices, requiring closed-loop modelling (integrated system and environ-
ment modelling) for verification purposes before obtaining a certificate from the
certification bodies. This chapter presents a methodology for modelling a biological
system, such as the heart, to enable modelling in a biological environment. The heart
model is based mainly on electrocardiography analysis, which models the heart sys-
tem at the cellular level. This heart model will be used for modelling the closed-loop
system of a cardiac pacemaker.
8.1 Introduction
The human heart is well known as a mechanical device of amazing efficiency that
pumps blood via the circulatory system continuously throughout the person's life-
time. It is one of the most complex and important biological systems, providing oxy-
gen and nutrients to the body to sustain life [ 30 ]. The regular impulses generated by
the heart result in rhythmic contractions through a sequence of muscles in the heart,
beginning at the natural pacemaker known as the sinoatrial (SA) node, which pro-
duces an action potential that travels across the atrioventricular (AV) node, the bun-
dle of His and the Purkinje fibres distributed throughout the ventricles. The pattern
and the timing of these impulses determine the heart rhythm. Variable time inter-
vals and conduction speeds during the heartbeat generate abnormal heart rhythms,
which are also known as heart rhythm impairments. Heart rhythm impairment is the
principal source of several diseases. Electrocardiography analysis is frequently used
to diagnose various types of heart disease [ 24 ] by presenting the timing properties
of the electrical system of the heart. These are the most fundamental properties of
the heart.
Cardiac pacemakers and ICDs are the two main types among the remarkable
range of medical and technological devices recommended by doctors in cases of
abnormal heart rhythm. These devices are used to maintain the heart rhythm, and
are life-saving in many instances. In the last few years, the use of cardiac pace-
makers and cardioverter-defibrillators has increased. However, these devices may
 
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