An AV block, also known as an atrioventricular block, is a type of heart conduction disorder that affects the normal electrical impulses that coordinate the heart's pumping action. The heart has a specialized conduction system that sends electrical signals to control the rhythm and rate of the heartbeats. The AV node is a crucial part of this system, responsible for transmitting electrical impulses from the atria (upper chambers) to the ventricles (lower chambers) of the heart.
In an AV block, there is a disruption or delay in the transmission of these electrical signals from the atria to the ventricles. Depending on the severity of the block, the heart may skip beats or beat at a slower rate than normal. This can have several effects on the delivery of oxygen to the body's tissues:
Reduced heart rate: An AV block can lead to a slower heart rate (bradycardia) because the electrical signals are not passing through the AV node as quickly as they should. With a slower heart rate, the heart pumps less blood per minute, which can reduce the amount of oxygen-rich blood delivered to the tissues.
Inadequate cardiac output: Since the ventricles are responsible for pumping blood to the rest of the body, a significant AV block can reduce the cardiac output. Cardiac output is the amount of blood pumped by the heart in one minute. With reduced cardiac output, less oxygenated blood reaches the tissues, leading to potential oxygen deprivation.
Exercise intolerance: Individuals with AV blocks may experience exercise intolerance or difficulty performing physical activities. During exercise, the body's oxygen demands increase, and the heart needs to pump more blood to meet those demands. In the presence of an AV block, the heart may struggle to keep up with the increased demand, leading to symptoms like fatigue, dizziness, and shortness of breath.
Impaired organ function: Vital organs such as the brain, kidneys, and muscles require a continuous supply of oxygen to function correctly. With an AV block and reduced cardiac output, these organs may not receive enough oxygen, potentially causing various symptoms, including cognitive impairment, dizziness, and muscle weakness.
The severity of the impact on oxygen delivery depends on the degree of the AV block. First-degree AV block, which involves a slight delay in conduction but normal impulse transmission, may have little to no effect on oxygen delivery. However, more severe blocks, such as third-degree AV block (complete heart block), can lead to significant consequences and may require medical intervention, such as a pacemaker, to regulate the heart's rhythm and ensure adequate oxygen delivery to the body's tissues.