3.2 Electrophysiology of the Heart

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Fig. 3.23: Oscillator model with SA and AV nodes of the heart according to Equation 3.26 ana-

log [89]: The model includes a delay τSA−AV = 1.2 from the SA to the AV node, which satisfies con-

duction. The factors kSA−AV and kAV−AV describe the attenuation from the sinusoid to the AV node

and the feedback from the output to the input of the AV node. Both have the value 1 here. Both the

sinus node and the AV node are represented in the model as blocks symbolising separate networks.

The network for the AV node is shown in Figure 3.24. The sinus node has a network with an identical

structure but modified parameters.

Fig. 3.24: Network for the AV node in Figure 3.29: It corresponds in structure to that of the sine node,

but has a different value for the parameter e. According to the information in [89], the parameters

vAV1 = 1, vAV2 = −1, dAV = 3, eAV = 7, fAV = 3 were used for the AV node, αAV = 5 and for the sinus

node the parameters vSA1 = 1, vSA2 = −1, dSA = 3, eSA = 12, fSA = 3, αSA = 5 were chosen.

oscillate with their natural frequencies (see Figure 3.25). In this case, each of these two

oscillators can react to external influences like a single oscillator, i.e. also with partial

or complete suspension of the oscillation (cf. Figure 3.21 and Figure 3.22). However,

if the coupling factor kSA−AV from the sine node to the AV node is stronger, the signal

from the sine node will have a large influence on the AV node:

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If the natural frequency of the AV node is not much lower than that of the sine

node, the signal of the sine node can "trigger" the AV node so that both nodes

oscillate at the same frequency (see Figure 3.26).

–

If the natural frequency of the AV node is too low to follow the signal of the sine

node, dropouts will occur (see Figure 3.26).

–

In the worst case, if the natural frequencies of the SA and AV nodes are too dif-

ferent, it is particularly dramatic. Then, after a few arrhythmic oscillations of the

AV node, excitation soon stops completely; the heart thus stops beating (see Fig-

ure 3.28).