CVS Anatomy 2 Conduction System
Ectopic pacemakers and their triggers
A site other than the SA node that develops abnormal excitability, producing extra beats or pacing the heart for a period of time. Triggers: caffeine, nicotine, electrolyte imbalances, hypoxia, toxic reactions to drugs (digitalis)
Where does the AV bundle divides into right and left bundle branches?
At the junction of the membranous and muscular parts of the septum
Define atrial and ventricular fibrillation
Atrial fibrillation - common; impulses begin and spread through the atria, competing for a chance to travel through the AV node -> loss of coordinated contraction Ventricular fibrillation - disorganized firing of impulses from ventricles results in ventricular quivering -> heart is unable to pump blood to the body
Why does the heart continue to beat after it has been removed from the body?
Autorhythmic cells are self excitable, need no stimulation from CNS Functions of autorhythmic cells: Pacemaker for the heart - sets the rhythm Form the conduction system - the route for spreading action potentials throughout the heart in sequence.
What is the route of the blood and what is the route of the cardiac conduction system?
Blood: vena cavae -> right atrium -> right ventricle -> pulmonary trunk/artery ->lungs -> pulmonary veins -> left atrium -> left ventricle -> aorta The route of the cardiac conduction system is within the muscle itself: SA node -> AV node -> bundle of His-> right and left bundle branches -> Purkinje fibers
What do each of the following indicate? Increased P-Q interval Elevated S-T interval Depressed S-T interval Increased Q-T interval
Increased P-Q interval - indicates coronary artery disease or scar tissue resulting from rheumatic fever Elevated S-T interval indicates acute MI (myocardial infarction = heart attack) Depressed S-T interval indicates hypoxia Increased Q-T interval indicates myocardial damage (previous heart attack), coronary ischemia, conduction abnormalities
What do each of the following indicate? Large P-wave Enlarged Q-wave Enlarged R segment Flat T-wave Elevated T-wave
Large P-wave indicates enlargement of an atrium Enlarged Q-wave indicates MI Enlarged R segment indicates enlarged ventricles Flat T-wave indicates heart is receiving decreased oxygen Elevated T-wave may indicate hyperkalemia (too much blood potassium)
Propagation of action potentials through the heart (5)
Sinoatrial node (SA node) Atrioventricular node (AV node) Atrioventricular bundle or Bundle of His Right and left bundle branches Purkinje fibers
What are the subendocardial branches?
The Purkinje fibers, which are the extension of the right and left bundle branches, extend into the walls of the respective ventricles. The subendocardial branches of the right bundle stimulate the muscle of the IV septum, the anterior papillary muscle (through the septomarginal trabecula), and the wall of the right ventricle. The subendocardial branches of the left bundle stimulate the IV septum, the anterior and posterior papillary muscles, and the wall of the left ventricle.
The SA Node
The SA node, the pacemaker of the heart, is located anterolaterally just deep to the epicardium at the junction of the SVC and right atrium near the superior end of the sulcus terminalis
The AV node
a smaller collection of nodal tissue located in the posteroinferior region of the interatrial septum near the opening of the coronary sinus. The signal generated by the SA node passes through the walls of the right atrium propagated by the cardiac muscle (myogenic conduction), which transmits the signal rapidly from the SA node to the AV node.
The AV bundle
the only bridge of conduction between the atrial and the ventricular myocardium, passes from the AV node through the fibrous skeleton of the heart and along the membranous part of the IV septum
