Causes and Risk Factors

What causes the heart to beat too slowly?

There are two common causes.

  • A problem with the specialized tissue called the sinoatrial or S-A node. This tissue acts as the heart’s “natural pacemaker”
  • Heart block

This can mean that your brain and other organs might not get enough oxygen.

It may help to picture how a car works. If the accelerator is broken, the engine can’t get enough gas to move the car very fast. Similarly, if your heart's electrical system is not working normally, your body may not get the fuel it needs to take a brisk walk.

This condition is often associated with heart disease. So the things that increase your risk of heart disease can also increase the risk of bradycardia.

Problems with the sinus (S-A) node

The sinus node may not be sending electrical impulses slower than normal, not sending them often enough or sending signals that are blocked.

These types of rhythms are called sick sinus syndrome.

Sinus node problems node can also show up with a heart rate that is not matched to the work you are doing. This is called chronotropic incompetence. This can cause you to feel tired when you are doing activities because your heartbeat that is late or not fast enough to give your body the oxygen-rich blood it needs.

Heart block

  • There may be problems with the electrical pathway between the upper and lower heart.
  • The electrical signals may be slowed (the mildest form).
  • Or the signals may not reach the ventricles all together (complete heart block).

The lower heart has a natural standby system that can produce its own heartbeat. But this heartbeat is often too slow and unreliable. As a result, heart block often means that the ventricles pump too slowly even though the sinus may be sending out faster signals because they’re trying to speed up the heart rate.

If the timing of contractions between the upper and lower heart is poor, the ventricles may not fill with enough blood before pumping. This is called asynchrony.