The Electrical System of The Heart
Most of the movements in our body are done through muscles. These muscles are connected to the brain through the equivalent of electrical wires in our machines - neurons. These muscles can then be controlled through our voluntary thoughts. However, the heart must continue beating when you are awake or asleep, or even conscious, to ensure that you stay alive. As a fail-safe, your heart has developed its conduction system that provides a steady heart rhythm and coordination between different parts of the heart on its own. However, your brain exerts some influence over the functioning of the heart through a separate system called the autonomic nervous system. This is why your heart reacts to emotional stress or even the anticipation of activity.
The heart's conduction system comprises specialised muscle fibres that generate pulses at specific intervals. The incoming nerve fibres into these cells help guide the rate at which these pulses are generated. However, even if the connection from the parts preceding a cell is cut off, it will continue to create impulses at its inherent rhythm. Although this is a fail-safe and most cases, it can also lead to a lack of coordination between different parts of the beating heart leading to low pumping efficiency.
How does the heart beat?
Your heartbeat is a complicated and intricate process involving the sequential contraction and relaxation of different parts of your heart in a coordinated fashion; through the sequence of contractions and a series of valves, ensuring your blood travels across your body within a minute. In each heartbeat, the atria or the upper chambers of your heart fill up with fluid first and contract to push the fluid at pressure into the ventricles or the lower chambers of your heart. The ventricles then function with a forceful contraction pushing out your blood into the lungs from your right ventricle and throughout the body from the left ventricle. The blood that the right ventricle pumps out in one contraction is received back by the left side of the heart in the subsequent contraction.
If this perfectly coordinated rhythm is broken and the atria contract without being in sync with the ventricles, with every heartbeat, the ventricles are not filled correctly. Suppose the right and left sides of your heart are not well coordinated. In that case, this also reduces the volume of blood that passes through the lungs from the right side to the left side of the heart, causing inefficiencies in cardiac pumping.
What are the parts of the heart's conduction system?
- Sino-Atrial or SA Node
This small cluster of cells acts like a natural pacemaker for your heart. The cells are located as a bunch in the wall of the right upper chamber of your heart. When the signal is generated, the heart muscles nearby - the atrial walls begin contracting.
- Atrioventricular or AV node
The AV node is located between the walls of the atria upper Chambers of your heart. This node is smaller but similar to the SA node. However, they are slower to conduct electricity, which provides unnecessary breaking to ensure the ventricles contract after a pause, giving them time to fill.
- Bundle of His
This is a bundle of cells that extend outward from the AV node and travel towards the centre of your heart. These fibres conduct electricity much faster than the surrounding tissue. This bundle enhances conductivity by ensuring that the electrical signal is propagated to the heart's centre more quickly than it can spread through walls. This, in turn, ensures a contractile motion that enables sudden and consistent squeezing from all sides.
- Right Bundle Branch and Left Bundle Branch
The bundle of his splits up into two branches - the right bundle branch and the left bundle branch. The split up into the right and left bundle branch happens at the junction of the atria and ventricles. These branches help conduct the signals faster to the right and left ventricles.
- Purkinje Fibers
This bundle branches for the split path into a network of conducting fibres known as Purkinje fibres. Together with the Bundle of His and the bundle branches, it takes the shape of an upside-down open umbrella. These fibres quickly conduct the signal to the bottom of the heart and then help them spread upward and outward along the walls of the ventricles. This allows the ventricles to pump upward and outward to ensure maximum blood is ejected with every contraction.
What are the standard conditions affecting the heart's conduction system?
As we have seen above, the heart's conduction is a very intricate process and has to happen in a specific sequence. A problem with the sequence, either through defects in the heart valves or damage caused due to infections on myocardial infarction, leads to rhythm problems and, sometimes, symptoms of inefficient cardiac output.
Abnormal heart rhythms caused due to problems with conductivity are known as arrhythmias. They mainly occur in two types. Bradycardia, or slowing the heart rate, usually occurs due to damage or scarring of the heart's electrical system, stopping the signal's flow. Tachycardia or faster heartbeats often happen because it is similar to a short circuit that causes an abnormal signal to return to the system and trigger another series of contractions where there should be none.
What are the common symptoms of problems with the heart's electrical system?
When the arrhythmia becomes significant enough to affect the functioning of the heart, it can start causing symptoms such as:
- Lightheadedness or fainting
- Unpleasant thumping heartbeats, known as palpitations
- Shortness of breath or dyspnea
- Pain in the chest or discomfort