Atrioventricular Node AV

Historically and romantically, the heartbeat is recognized as the quintessential hallmark of life. Normally, the heart beats at 60-100 beats per minute (bpm), with each beat yielding a ventricular contraction that ejects blood out to the body. Each heartbeat is an electrical event that originates from a collection of electrically excitable cells within the heart called the sinoatrial node (SA), anatomically located at the upper pole of the heart. The sinoatrial node is the primary pacemaker of the heart. The electrical impulse generated in the sinoatrial node spreads rapidly downward from the atria chambers of the heart and reaches the atrioventricular node (AV), a collection of electrically excitable cells that constitutes the electrical interface between the atria and ventricles of the heart. Erom the AV node, the impulse propagates throughout the ventricles via an electrical conduction system referred to as the His-Purkinje system. The electrical transmission... 

Class Ic agent that prolongs refractoriness and slows conduction in the atria, atrioventricular node (AV-node), His-Purkinje system, ventricles and accessory pathways. Predominantly blocks sodium channels in the activated state with rate-dependent block (40). 

The sinoatrial node (SA), consisting of spindle-shaped cells, initiates the electrical activity of the heart. From its location in the right atrium in proximity to the superior vena cava, the electrical activity spreads to the atria whose cells are larger than those of the SA. The pulse from the atria spreads to the atrioventricular node (AV), the gateway to the ventricles. The atria and the ventricles are electrically isolated. The AV node also slows down the electrical activity giving the atria time to fill. The bundle of His is the upper end of the electrical path, which through the Purkinje fibers allows the electrical signal to activate the ventricles and thus to pump the blood. 

In the normal heart, the process of contraction is initiated at the sino-auricular node (SA node) and spreads over the auricles which discharge their contents to the ventricles. In seriatum, the atrioventricular node (AV node) next continues the process and the ventricles contract, discharging blood into the lesser circulation (pulmonary vessels) and greater circulation (systemic arteries). This process is then repeated with a normal repetition rate (pulse rate) of about 70 per minute. The process of contraction is termed systole relaxation, diastole. 

As discussed previously, the P wave represents the depolarisation of both the left and right atria. The initial half of the P wave represents depolarisation of the right atria as the electrical impulse travels from the Sinoatrial node (SAN) to the right atrium and then the left. The impulse reaches the Atrioventricular node (AV) at the... 

Cardiovascular conditions - Cholinesterase inhibitors have vagotonic effects on the sinoatrial and atrioventricular nodes, leading to bradycardia and AV block. These actions may be particularly important to patients with supraventricular cardiac conduction disorders or to patients taking other drugs concomitantly that significantly slow heart rate. Consider all patients to be at risk for adverse effects on cardiac conduction. 

Figure 5.8. The conduction system of the heart, a Anatomy, b Electrical rhythm in the sinoatrial node (top), atrioventricular node (center), and the heart muscle (bottom). The dotted line inb (center) represents the own rhythm of the AV node that normally gets overridden by the faster sinoatrial rhythm (solid line).

AO Aorta MPA Main pulmonary artery RSCV Right superior vena cava TV Tricuspid valve MV Mitral valve PV Pulmonary valve AV Aortic valve RA Right atrium LAA Left atrial appendage RV Right ventricle LV Left ventricle LV-PM Left ventricle, muscle IVS Interventricular septum CR Crista supraventricularis SN sinus node AVN + B Atrioventricular node LBB Left bundle branch. 

Atrioventricular node Increase in automaticity and conduction velocity++ ft>ft Decrease in conduction velocity AV block+++ M3 M3... 

ABBREVIATIONS PLC, phospholipase C IP3, inositol-1,4,5-trisphosphate DAG, diacylglycerol PLD2, phospholipase D AA, arachidonic acid PL A, phospholipase A cAMP, cyclic AMP SA node, sinoatrial node AV node, atrioventricular node HR, heart rate PTX, pertussis toxin VTA, ventral tegmentum area. 

This is the failure of the Atrioventricular node to conduct an impulse. AV blocks can be classified as 1st, 2nd and 3rd degree AV blocks. These blocks can be temporary or permanent. 

The antimuscarinic drug atropine, and its derivative ipratropiumbromide, can also be used for antiarrhyth-mic treatment. Muscarinic receptors (M2 subtype) are mainly present in supraventricular tissue and in the AV node. They inhibit adenylylcyclase via G proteins and thereby reduce intracellular cAMP. On the other hand, activation of the M2 receptor leads to opening of hyperpolarizing Ik.acii and inhibits the pacemaker current If probably via the (3y-subunit of the Gi protein associated with this receptor. The results are hyperpolarization and slower spontaneous depolarization. Muscarinic receptor antagonists like atropine lead to increased heart rate and accelerated atrioventricular conduction. There are no or only slight effects on the ventricular electrophysiology. 

Supraventricular tachycardia is a heart condition characterised by fast arrhythmias involving the atrioventricular (AV) node. 

Decreases the conduction velocity through the atrioventricular (AV) and sinoatrial (SA) nodes in the heart... 

Sympathetic (sympatholytic) Heart Sinus node Atrioventricular (AV node) Slowing Increased refractory period Bradycardia Dysrhythmias, conduction block... 

An internodal conduction pathway also extends from the SA node and transmits the impulse directly to the atrioventricular (AV) node. This node is located at the base of the right atrium near the interventricular septum, which is the wall of myocardium separating the two ventricles. Because the atria and ventricles are separated from each other by fibrous connective tissue, the electrical impulse cannot spread directly to the ventricles. Instead, the AV node serves as the only pathway through which the impulse can be transmitted to the ventricles. The speed of conduction through the AV node is slowed, resulting in a slight delay (0.1 sec). The cause of this AV nodal delay is partly due to the smaller fibers of the AV node. More importantly, however, fewer gap junctions exist between the cells of the node, which... 

Figure 13.3 Route of excitation and conduction in the heart. The heart beat is initiated in the sinoatrial (SA) node, or the pacemaker, in the right atrium of the heart. The electrical impulse is transmitted to the left atrium through the interatrial conduction pathway and to the atrioventricular (AV) node through the intemodal pathway. From the AV node, the electrical impulse enters the ventricles and is conducted through the AV bundle, the left and right bundle branches, and, finally, the Purkinje fibers, which terminate on the true cardiac muscle cells of the ventricles.

The electrical impulse for contraction (propagated action potential p. 136) originates in pacemaker cells of the sinoatrial node and spreads through the atria, atrioventricular (AV) node, and adjoining parts of the His-Purkinje fiber system to the ventricles (A). Irregularities of heart rhythm can interfere dangerously with cardiac pumping func-tioa... 

I. Drugs for selective control of sinoatrial and AV nodes. In some forms of arrhythmia, certain drugs can be used that are capable of selectively facilitating and inhibiting (green and red arrows, respectively) the pacemaker function of sinoatrial or atrioventricular cells. 

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