EKG - Basic EKG 3 Main Functions of the Heart Electrical...

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Basic EKG 3 Main Functions of the Heart Electrical conduction system of the heart Mechanical pumping ability of the heart (lub dub, lub dub ) Plumbing o coronary arteries that supply blood and nutrients to the heart/electrical system o coronary circulation consists of coronary arteries and veins o The right coronary artery (RCA) supplies blood to the Sinoatrial (SA) Node in about 60% of the  population If there is a lesion or blockage in the RCA, the patient will have a slowed heart rate o The RCA supplies blood to the AV node in about 85-90% of the population Cardiac Conduction Center 3 Characteristics that Account for the Coordination Between the Transmission of Electrical impulses and the contraction: Automaticity   ability of the cardiac pacemaker cells to create electrical impulses without being stimulated  from another source (initiation of impulse) Excitability   ability of cardiac pacemaker cells to respond to a stimulus Conductivity ability of cardiac pacemaker cells to receive an electrical stimulus and conduct it to an  adjoing cardiac cell Types of Cardiac Cells Myocardial cells  contain contractile filaments Pacemaker cells responsible for generating and conducting electrical impulses Cardiac Action Potential (electrical changes recorded within a single cell) Polarization o During the resting stage (PO phase), cardiac muscle cells are polarized, which means an electrical  difference exists between the negatively charged inside and positively charged outside of the membrane o The inside of the cell is more negative than the outside Depolarization o Electrical activation of a cell caused by influx of sodium into the cell while potassium ions exit the cell o As soon as the electrical impulse is initiated, depolarization occurs, follow by myocardial contraction Repolarization o Return of the cell to its resting state, when potassium moves back into the cell as sodium moves out  (restored to its original negative charge) o This corresponds to the relaxation of the heart muscle o After the rapid influx of sodium into the cell during depolarization, calcium enters the cell and is  released from intracellular calcium stores.  The increase in calcium, which occurs at the plateau phase  of repolarization is much slower than that of sodium and continues for a longer period Phases of Cardiac Action Potential Phase 0 1
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o QRS  cardiac contraction begins (rapid depolarization) as sodium moves into the cell and potassium  moves out of the cell o Calcium moves slowly into the cell Phase 1 o Early repolarization occurs as sodium channels slow and chloride enters the cells
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This note was uploaded on 05/04/2008 for the course NURS 130 taught by Professor Dupuy during the Spring '08 term at Lady of the Lake.

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EKG - Basic EKG 3 Main Functions of the Heart Electrical...

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