What does a heart block do to impulse transmission in the hearts?
A heart block refers to a disturbance or interruption in the electrical conduction system of the heart, which affects the transmission of electrical impulses between the heart's chambers. This can disrupt the coordinated contractions of the heart, leading to abnormal heart rhythms and potentially serious health consequences.
Effects of a Heart Block on Impulse Transmission:
1. Sinoatrial (SA) Block:
- Occurs when the electrical impulse from the sinoatrial node (SA node), which generates the regular heart rhythm, is blocked or delayed before reaching the atrioventricular (AV) node.
- The heart rate slows down, causing bradycardia, and the heart's contractions become irregular.
2. Atrioventricular (AV) Block:
- This is the most common type of heart block and occurs at the level of the AV node, which normally relays electrical signals from the atria to the ventricles.
- First-degree AV block: The delay in impulse transmission through the AV node is prolonged but still allows all impulses to reach the ventricles. No symptoms are typically experienced.
- Second-degree AV block (Mobitz type I or type II): Some electrical impulses are blocked from the atria to the ventricles, causing an irregular heart rhythm with dropped heartbeats.
- Third-degree AV block (complete heart block): All electrical impulses are blocked from the atria to the ventricles. The ventricles establish their own intrinsic escape rhythm, which is usually much slower than the normal sinus rhythm. This can cause severe bradycardia and symptoms like dizziness, fainting, or heart failure.
3. Bundle Branch Block:
- Occurs when the electrical impulses are blocked or slowed down in the bundle branches, which carry the electrical signals from the bundle of His to the left and right ventricles.
- This can result in abnormal conduction patterns in the ventricles, leading to changes in the timing and coordination of ventricular contractions.
4. Fascicular Block:
- This type of heart block affects the fascicles that divide the bundle branches into smaller fibers, causing delays or disruptions in the electrical conduction within the ventricles.
- Depending on the location of the block, it can result in either left or right bundle branch block or more complex conduction disturbances.
Each type of heart block can have different consequences on the heart's rhythm and function. The severity of a heart block and its impact on impulse transmission determine the appropriate treatment approach, ranging from medications to implanting a pacemaker to correct the conduction abnormality and ensure a regular heart rhythm.