Have you ever wondered how the heart beats? In order for the heart to beat and pump blood to the different parts of our body, it operates through the heart’s so-called electrical conduction system.
In this article we will briefly explain what the human heart looks like and how it works, what the heart’s electrical conduction system consists of and how it operates . Finally, we will talk about arrhythmias, a disorder that occurs when this system fails.
Before we talk about the heart’s electrical conduction system, and how it works, let’s briefly explain what the heart is and what its functions are.
The word heart comes from the Latin cor, and is the main organ of the circulatory system . The circulatory system serves to transport internally the different substances that we need as living beings to live: hormones, nutrients, oxygen, carbon dioxide…
As for its characteristics, the heart is a hollow muscular organ. It works like a pump, propelling the blood through the arteries , in order to distribute it throughout our body. Its size is that of a fist, and its weight is between 250 and 300 grams (in women) and 300 and 350 grams (in men). This is approximately 0.4% of our body weight. Anatomically, the heart is located in the center of the chest cavity, between the lungs.
Thus, the heart is the pump of the muscle tissue, which is pumping blood through the body. On the other hand, the electrical conduction system of the heart coordinates the contraction of the different chambers of the heart.
What structures are part of the heart, and therefore the heart’s electrical conduction system? There are 4 of them:
- Right atrium (AD)
- Right ventricle (DV)
- Left atrium (AI)
- Left ventricle (LV)
Now, let’s see how the heart’s electrical conduction system works.
Electrical conduction system of the heart
The heart’s electrical conduction system has the main function of allowing blood pumped by the heart to be distributed throughout the body (i.e. pumped throughout the body). It coordinates the contractions of the chambers of the heart so that the heart can beat properly.
More specifically, it is a system that allows the impulse generated by a node of the heart, the sinus node, to spread and stimulate an important heart muscle, the myocardium. In this way, the latter contracts.
Thus, this system involves a series of coordinates of the myocardium, which makes the heart contract effectively , and, as we said, so the blood is pumped throughout the body.
Components, location and operation
The main components of the heart’s electrical conduction system are two, the sinoatrial (SA) or sinus node and the atrioventricular (AV) node. Let’s explain what each is, and how the heart’s electrical conduction system operates through these nodes (i.e., how the heart beats):
1. Sinoatrial Node (SA)
You could say that the sinoatrial node is the natural pacemaker of the heart. This module is also called other names, such as sinus node, Keith and Flack node or heart pacemaker . Anatomically, the SA is located in the upper back of the right atrium of the heart, just at the entrance to the superior vena cava.
In terms of its characteristics, it is the largest heart pacemaker, and its shape is oval. It is in this node where the electrical impulse is born, which moves and spreads through the atria . It does so through pathways called internodal pathways, causing the atria to contract.
In healthy adults, the sinus node discharges at a rate of 60 pulses per minute (60 contractions per minute); that is, the electrical stimulus is regularly generated between 60 and 100 times per minute.
2. Atrioventricular (AV) node
This is when the electrical impulse reaches the next node, the atrioventricular node (also called the Aschoff-Tawara node). It is about 40% the size of the previous node, the sinus node. It is oval in shape, and is located on the left side of the right atrium , specifically in a structure called the atrial septum.
Almost always (in 90% of cases), the atrioventricular node is irrigated by a branch located in the right coronary artery. This node has two types of innervations: sympathetic and parasympathetic .
It is in the atrioventricular node that the electrical impulse (or electrical wave) stops for less than 1 second (specifically, for 0.13 seconds).
And then what…?
After this pause in the electrical impulse in the atrioventricular node, the impulse spreads through the bundle of His, a bundle of fibers that acts as a bridge between the node and the branches of the ventricles.
This beam is divided into two more branches: the right and the left. On the left is another division: the left anterior fascicle, the left posterior fascicle and the middle or septal fascicle. From this last instalment, the electrical impulse is distributed to the ventricles, through the Purkinje fibres , fibres which allow ventricular contraction.
Abnormal functioning of the heart’s electrical conduction system
We have talked about how the heart’s electrical conduction system works under normal or healthy conditions, that is, when our heart beats normally and the different parts of the body receive the pumping of blood normally.
But… what happens when there’s a malfunction? Then situations or phenomena like arrhythmias occur.
An arrhythmia is a disorder of the heart rate or rhythm ; in these cases, it can happen that the heart beats faster than usual (so we talk about tachycardia), that it beats too slow (bradycardia) or that it beats irregularly.
That is, arrhythmias involve abnormal beating of our heart. The arrhythmias themselves may not be harmful, although sometimes they are a sign of underlying problems , or of an imminent danger to our health.
When and why do arrhythmias occur? They can occur in different cases and situations. The three most frequent are as follows:
- When another part of the heart acts as a pacemaker (i.e. takes over this role).
- When our heart’s natural pacemaker (i.e., the sinus node) produces an abnormal rhythm (frequency)
- When the normal driving route is interrupted for some reason.
As we can see, when the heart’s electrical conduction system fails, arrhythmias can occur. But, what symptoms does this disorder or alteration of the heart’s rhythm produce? Arrhythmias mainly produce 4 symptoms: feeling of lack of air, dizziness, fainting and palpitations.
To evaluate this problem, we use the electrocardiogram (ECG) , which allows us to determine and analyse the rhythm of our heart. An ECG consists of a painless test that allows the recording of the heart’s electrical activity, through different electrodes placed on the chest.
Sometimes, when the electrical rhythm is not normal, medication or surgery may even be needed. A specialist should always be called in to evaluate and treat our case.
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- Harrison. (2006). Principles of Internal Medicine 16th edition. Electrocardiography. Harrison online in Spanish. McGraw-Hill.
- Stanford Children’s Health. (2019). Anatomy and functions of the electrical system.