Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: When the clock strikes: Modeling the relation between circadian rhythms
  and cardiac arrhythmias   It has recently been observed that the occurrence of sudden cardiac death has
a close statistical relationship with the time of day, viz., ventricular
fibrillation is most likely to occur between 12 am-6 am, with 6 pm-12 am being
the next most likely period. Consequently there has been significant interest
in understanding how cardiac activity is influenced by the circadian clock,
i.e., temporal oscillations in physiological activity with a period close to 24
hours and synchronized with the day-night cycle. Although studies have
identified the genetic basis of circadian rhythms at the intracellular level,
the mechanisms by which they influence cardiac pathologies are not yet fully
understood. Evidence has suggested that diurnal variations in the conductance
properties of ion channel proteins that govern the excitation dynamics of
cardiac cells may provide the crucial link. In this paper, we investigate the
relationship between the circadian rhythm as manifested in modulations of ion
channel properties and the susceptibility to cardiac arrhythmias by using a
mathematical model that describes electrical activity in ventricular tissue. We
show that changes in the channel conductance that lead to extreme values for
the duration of action potentials in cardiac cells can result either in
abnormally high-frequency reentrant activity or spontaneous conduction block of
excitation waves. Both phenomena increase the likelihood of wavebreaks that are
known to initiate potentially life-threatening arrhythmias. Thus, disruptive
cardiac excitation dynamics are most likely to occur in time-intervals of the
day-night cycle during which the channel properties are closest to these
extreme values, providing an intriguing relation between circadian rhythms and
cardiac pathologies.

13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph