Third-degree atrioventricular (AV) block, also referred to as third-degree heart block or complete heart block, is an abnormal heart rhythm where the heart’s electrical signal cannot move from the upper heart chambers (atria) to the lower heart chambers (ventricles). This results in the P waves (atrial contraction) being completely unrelated to the QRS complexes (ventricular contraction) ― meaning the P waves and QRS complexes have no correlations.
How to Spot Complete Heart Block on Your Watch ECG
Third-degree AV block (complete heart block) exists when there are more P waves than QRS complexes, and there is no relationship between them.
The following characteristics help identify this rhythm:
- Regular P-P interval
- Regular R-R interval
- Lack of an apparent relationship between the P waves and QRS complexes
- More P waves are present than QRS complexes
Common Symptoms of Complete Heart Block
Complete heart block has a wide range of symptoms. Occasionally, people are asymptomatic or have only minimal symptoms related to hypoperfusion. In these situations, symptoms include the following:
- Impaired exercise tolerance
- Chest pain
More commonly, however, people are profoundly symptomatic, especially if a wide QRS complex is present, indicating that the origin of the impulse is below the His bundle (ventricle). In such cases, symptoms can include the following:
- Severe chest pain
- Sudden death
Because an acute myocardial infarction (MI) can cause complete heart block, people who concurrently experience an MI can have associated symptoms from the MI, including chest pain, dyspnea, nausea or vomiting, and diaphoresis.
People who have a history of cardiac disease may be on medications that affect the conduction system through the AV node, including:
- Calcium channel blockers
- Digitalis cardioglycosides
Any Cause for Concern?
Complete heart block is the most severe type of AV heart block and is often first discovered during an emergency. This can affect the blood flow to your body and brain, resulting in no pulse or a very slow pulse.
As always, if you show signs of complete heart block, contact your healthcare provider immediately.
Still Not Sure How to Spot Complete Heart Block on Your Watch ECG?
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