B. Murienne - Master Project Thesis - Infoscience - EPFL

Figure 3. Normal electrical conduction versus reentry [49].
In a normal tissue, as represented in the top image of Figure 3, the action potential generated
travels down along both branches 1 and 2 of the conducting pathway. The electrical impulses then
propagate into branch 3 towards opposite directions or cancel each other. In case of an abnormal
tissue, reentry may occur, as represented in the bottom image of Figure 3. This can be due to a
blocking element (grey region) within one branch, which allows the electrical propagation to
travel only in one direction, and to a difference in tissue excitability at the time of propagation.
As shown in the bottom image of Figure 3, no impulse can travel down through branch 2 because
of the blocking element and the only pathway for an impulse is down branch 1, through branch 3
and eventually up via branch 2. After crossing the blocking element, if the impulse finds excitable
tissue, it will continue its propagation and travel again via branch 1, describing a loop. If it finds
non-excitable tissue, meaning a tissue still in its refractory period, the impulse will die [49].
2.1.6 Stretch-activated ion channels
Stretch-activated channels (SACs) provide a simple mechanism to explain
mechanosensitivity, although it has not yet been proved in vivo. When a cell is mechanically
stimulated, SACs open as they are directly gated by mechanical stimulation and allow the
mechanical signal to be converted into an electrochemical flux [23]. All SACs found in the heart
are cation-selective and have been found in both ventricular and atrial cells, in both tissue-
cultured and freshly isolated cells. Most of them are non-selective channels which are weakly
selective to monovalent cations and permeable to divalent cations such as Ca2+ [23].
In stretched ventricular myocytes, the intracellular calcium concentration ([Ca2+]i) has
been shown to increase during rest. This increase in [Ca2+]i is potentially caused by either the
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