User manual

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precaution against the blood’s reflux from the ventricles to the atriums, but also as electrical

insulation. In a healthy heart, the transmission of an electrical impulse via this insulation is

only possible via the atrioventricular - AV node, which stimulates the ventricles with a delay

against the SA node.

The electrical impulse spreads further from the AV node alongside the ventricular

septum via a bundle of His, which verges into the right and the left bundle branches, and

further to fine Purkyně (Purkynje) fibres. These fibres pass it on to the myocardium cells. In a

supraliminal stimulus, the impulse is thus spread throughout the heart; see Fig. 2.3. Spread

velocity differs in each structure. The slowest conduction is in the SA and AV nodes in 0.05

m/s, the working myocardium in 0.3 - 1 m/s, and the conduction system in the ventricles in 1-

4 m/s (the fastest being the bundle of His, and the slowest being the Purkyně (Purkynje)

fibres). The value for the heart rate in a resting state, if the SA node is the pacemaker, is 70

beats per minute; if the pacemaker is the AV node, it is 50 - 60 beats per minute, and if the

ventricular structures are the pacemaker, the rate is 25 - 45 beats per minute.

Disorders of the conduction system in a form of the electrical stimulus transmission

blockades or malfunctions of any of its parts form grounds for implanting a cardiostimulator,

a cardioverter-defibrillator, or a biventricular cardioverter-defibrillator. This intervention does

not heal the disorder, but significantly increases the quality and length of the patient’s life.

Catheter ablation represents another possible treatment [2.1], [2.2], [2.3], [2.4].

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Restingandactionmembranepotential

 The ability of depolarization and repolarization is the essential quality of excitable

cells. The resting membrane potential equals to -50 to -90 mV (depending on the cell’s

function) - the cell is polarized. The negative sign expresses the fact that the inside of the cell

is negatively charged as opposed to the outside of the cell. This state is given by the uneven

spreading of ions on the opposite sides of the cell membrane. The main intracellular ion of the

heart cells, just like in all other cells, is K

, and the main extracellular ions are Na

, Ca

and

. The cell membrane in a non-irritated state is better permeable for the potassium ions than

for the others. As the K

ions’ concentration inside the cell is approximately 30-times higher

as opposed to the outside, they are transported out of the cell on their concentration gradient.

That, together with the presence of natrium and calcium ions outside the cell causes an excess

of positive ions in the extracellular area. The Cl

ions move through the membrane almost

exclusively passively, i.e. they only pass through the membrane as a result of the movement

of the cations.