Ventricular fibrillation: the mechanism of the arrhythmia conduction pathway

2021-05-31 03:50 PM

The first round of electrical stimulation causes depolarization waves to spread in all directions, leaving all myocardium in an inert state. After 25s. part of this muscle mass escapes inertness.

In ventricular fibrillation, there are multiple divisions and small excitation waves that spread simultaneously in different directions. Impulse re-acceptance in ventricular fibrillation is not simply a pulse moving in a loop, as shown in the figure.

Figure. The re-entry loop represents impulse suppression in the short path and continued impulse propagation in the long path.

Instead, they have decreased in the many previous waves that appeared in this chain reaction. One of the darkest ways to explain the increase in vibration is to suggest that the onset of vibration is with electric shock with 60Hz alternating current.

Vibration caused by 60 Hz alternating current.

 

Figure. A: Initiation of ventricular fibrillation when excitable muscle plaques are present. B: Continue to propagate vibrational impulses in the ventricles.

In the heart's ventricular center in Figure A, a current of 60Hz is used in the electrocardiogram. The first round of electrical stimulation causes depolarization waves to spread in all directions, leaving all myocardium in an inert state. After 25s. part of this muscle mass escapes inertness. Some positions exit inert before others. This situation is shown in figure A by many bright patches representing excitable areas and dark patches representing still inert muscle areas. At this point, continued electrical stimulation of 60Hz generates pulses that propagate in several directions only. Thus, in Figure A, several pulses travel short distances until they reach the refractory region of the heart and are blocked. However, there are several impulses that exit the inert region and continue to propagate to the same stimulus. These phenomena occur continuously in a short time, causing the heart muscle to continuously stimulate and exhibit vibration.

First, the block of impulses of some instructions traveling in several other directions creates one of the important conditions of "pulse re-acceptance": conduction of depolarized waves around the heart only in certain directions but not in other directions. other.

Second, tachycardia causes two changes in the myocardium, both of which lead to circular conduction: (1) The rate of contraction of the heart decreases. This allows a longer time for the pulse to circumnavigate the heart and (2) shortens the refractory period of the heart, allowing the pulse to be re-accepted in the first region that was previously stimulated.

Third, one of the most important points of vibration is the division of the pulse as shown in the figure. When the depolarization wave reaches the refractory region of the heart, it conducts in all directions around that inert region. As a result, a single pulse becomes 2 pulses, then these pulses again go to other inert regions and divide like that, and so on and on, etc. In this way, many new waves are formed in the heart and follow along. many directions in the heart. Furthermore, due to the way the pulse is separated, the intensity is not uniform, which causes many detours and conduction prolongation, which is one of the conditions that sustain vibration. It is also the result of a scattered distribution of inert regions in the heart.

One can easily see when this repetitive stimulus is encountered again: As more and more impulses are generated, these impulses cause more areas of inert muscle, these inert muscle regions cause the separation of impulses. And every time an area of ​​the myocardium escapes, the impulse is locked.

Figure B in the figure is the final state in vibration. People can see pulses going in all directions with some split pulses increasing the number of pulses, some blocked due to inert areas of the heart. In fact, simple electric shock during this period of injury can stabilize impulses that are travelling in multiple directions.