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Cardiac conduction velocity

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Cardiac conduction velocity

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The conduction of the action potential in the mammalian heart is examined. The total time of action potential to reach from the sinoatrial (SA) node to the ventricles is estimated to be around 220 ms. However, it was noted that the action potential travels in certain areas of the heart faster than other areas. Which of the following represents the velocity of conduction of action potentials in the heart from the fastest to the slowest?  

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Contributors:

Tanner Marshall, MS

Cardiac conduction velocity is the velocity at which a depolarization wave moves through the myocardium, the muscular middle layer of the heart, and it’s measured in meters per second.

The depolarization wave travels through the sinoatrial node, or SA node, through both atria, down the atrioventricular or AV node, through the Bundle of His and the Purkinje fibers, and finally to all of the parts of the ventricles, all in about 220 milliseconds, which is less than a quarter of a second!

If we zoom in on the myocardium, the depolarization waves move across neighboring cells. It moves from one cell to the next when ions like calcium and sodium slip through gap junctions and trigger voltage-gated sodium channels in that cell over to open up, allowing a rush of more sodium into the cell and causing an action potential to occur.

That then results in more sodium and calcium leaking through to the next cell, triggering an action potential, which goes on to the next, and so on.

Ultimately these cellular processes determine how fast or slow a depolarization wave will move across different types of tissues.

More sodium channels and gap junctions speed up the depolarization wave, Fewer gap junctions and fewer sodium channels slow down the depolarization wave.

Alright so let’s break down the conduction velocities in the different parts of the heart, starting at the SA node,i the depolarization wave moves through the myocytes in the atria at about 1 meter per second, then goes through the AV node really slowly, roughly between 0.01 and 0.05 meters per second.

Summary

The cardiac conduction velocity is the speed at which the electrical signal travels through the heart muscle. This electrical signal is generated by the sinoatrial (SA) node, which is located in the right atrium. After getting propagated through booth atria, the signal travels down the atrioventricular (AV) node in the Bundle of His and the Purkinje fibers, and later to all of the parts of the heart ventricles. Cardiac conduction velocity is measured in meters per second (m/s).

The cardiac conduction velocity can be affected by several factors, including age, medications, electrolyte levels, and disease states. Older individuals generally have a slower cardiac conduction velocity, as do those taking certain medications (such as beta blockers). Electrolyte imbalances (such as low potassium levels) can also decrease cardiac conduction velocity. Finally, heart diseases (such as cardiomyopathies) can also result in a slower cardiac conduction velocity.

There are several ways to measure cardiac conduction velocity. The most common method is an electrocardiogram (ECG), which measures the electrical activity of the heart and can be used to determine the cardiac conduction velocity.

Sources
  1. "Physiology" Elsevier (2017)
  2. "Medical Physiology" Elsevier (2016)
  3. "Human Anatomy & Physiology" Pearson (2017)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Impact of Sarcoplasmic Reticulum Calcium Release on Calcium Dynamics and Action Potential Morphology in Human Atrial Myocytes: A Computational Study" PLoS Computational Biology (2011)
  6. "The Role of the Funny Current in Pacemaker Activity" Circulation Research (2010)