atrioventricular (AV) node

Examples of atrioventricular (AV) node in the following topics:

• Electrical Events

  • The heart's activity is dependent on the electrical impulses from the sinoatrial (SA) node and atrioventricular (AV) node, which form the intrinsic conduction system of the heart.
  • The SA node impulses also travel to the AV node, which stimulates ventricular contraction.
  • The AV node slightly slows the neural impulse from the SA node, which causes a delay between depolarization of the atria and the ventricles.
  • The normal firing rate in the AV node is lower than that of the SA node because it slows the rate of neural impulses.
  • Certain types of autonomic nervous stimulation alter the rate of firing in the AV node.

• Anatomy of the Heart

  • The sinoatrial (SA) and atrioventricular (AV) nodes are bundles of nerve fibers that form this conduction system.
  • These nodes can send impulses to the heart without central nervous system stimulation, but may be influenced by nervous stimulation to alter heart rate.
  • Cardiac muscle tissue is distinct from skeletal or smooth muscle because it pumps involuntarily based on conduction from the AV and SA nodes.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • An action potential, induced by the pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes, is conducted to contractile cardiomyocytes through gap junctions.

• Agonists, Antagonists, and Drugs

  • ACh binds to muscarinic receptors (M2) that are found principally on cells comprising the sinoatrial (SA) and atrioventricular (AV) nodes.
  • Increases in vagal activity to the SA node decreases the firing rate of the pacemaker cells by decreasing the slope of the pacemaker potential decreasing heart rate.
  • Similar electrophysiological effects also occur at the AV node.
  • However, in this tissue, these changes are manifested as a reduction in impulse conduction velocity through the AV node.
  • Working as a nonselective muscarinic acetylcholinergic antagonist, atropine increases firing of the sinoatrial node (SA) and conduction through the atrioventricular node (AV) of the heart, opposes the actions of the vagus nerve, blocks acetylcholine receptor sites, and decreases bronchial secretions.

• Cardiac Output

  • The heart rate is determined by spontaneous action potential generation in the sinoatrial (SA) node and conduction in the atrioventricular (AV) node.
  • Sympathetic nervous system activation will stimulate the SA and AV nodes to increase the heart rate, which will increase cardiac output.
  • Parasympathetic nervous system activation will conversely act on the SA and AV nodes to decrease the heart rate, which will decrease cardiac output.
  • For the SA node, the rate of depolarization is altered, while the AV node's rate of conduction is altered by autonomic nerve stimulation.

• Arrhythmia

  • These cells are found in the conduction system of the heart and include the SA node, AV node, Bundle of His, and Purkinje fibers.
  • The impulse initially causes both atria to contract, then activates the atrioventricular (or AV) node which is normally the only electrical connection between the atria and the ventricles (main pumping chambers).
  • Arrythmias arising from pathologies at the AV node (AV blocks): First degree heart block, which manifests as PR prolongation, Second degree heart block, and Third degree heart block, also known as complete heart block.
  • Electrical mpulse arising in SA node, traversing atria to AV node, then entering ventricle.
  • Rhythm originating at or above AV node constitutes supraventricular tachycardia (SVT).

• Operation of Atrioventricular Valves

  • The atrioventricular valves separate the atria from the ventricles and prevent backflow from the ventricles into the atria during systole.
  • The atrioventricular (AV) valves separate the atria from the ventricles on each side of the heart and prevent backflow of blood from the ventricles into the atria during systole.
  • The subvalvular apparatus describes the structures beneath the AV valves that prevent the valves prom prolapsing.
  • The AV valves are anchored to the wall of the ventricle by chordae tendineae (heartstrings), small tendons that prevent backflow by stopping the valve leaflets from inverting.
  • Describe the operation of the atrioventricular valves: bicuspid (mitral) and tricuspid

• Fibrous Skeleton of the Heart

  • It also surrounds the coronary arteries and AV node.
  • It also surrounds the coronary arteries and AV node.
  • The sinoatrial (SA) node lies on the top of the heart, while the AV node is located at the center of the fibrous skeleton, the only path by which electricity can flow through the heart.
  • The separation allows the AV node and AV bundle to delay the wave of depolarization so that the atria can contract and assist in ventricular filling before the ventricles themselves depolarize and contract.

• Layers of the Heart Walls

  • During ventricular contraction, the wave of depolarization from the SA and AV nodes moves from within the endocardial wall through the myocardial layer to the epicardial surface of the heart.
  • The Purkinje fibers are located just beneath the endocardium and send nervous impulses from the SA and AV nodes outside of the heart into the myocardial tissues.

• Electrocardiogram and Correlation of ECG Waves with Systole

  • The P wave is the first wave on the ECG because the action potential for the heart is generated in the sinoatrial (SA) node, located on the atria, which sends action potentials directly through Bachmann's bundle to depolarize the atrial muscle cells.
  • The QRS complex represents action potentials moving from the AV node, through the bundle of His and left and right branches and Purkinje fibers into the ventricular muscle tissue.
  • It generally occurs with myocardial infarcations and heart failure, and is thought to be caused by action potentials that re-enter the AV nodes from the muscle tissue and induce rapid, irregular, weak contractions of the heart that fail to pump blood.