CH7 Critical Care.docx

CH7 Critical Care.docx - Book Notes Ch 7 Dysrhythmia...

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Book Notes Ch. 7 Dysrhythmia Interpretation & Management Cardiac Cycle Begins with an impulse that is generated from a small, concentrated are of pacemaker cells high in the right atrium called the sinoatrial (SA) node or sinus node. o SA node has the fastest rate of discharge therefore it is the dominant pacemaker of the heart. o The sinus impulse quickly passes through the intermodal conduction tracts and the Bachmann bundle, conductive fibers in the right and left atria o The impulse quickly reaches the AV node located in an area called the AV junction, between the atria and ventricles. Here the impulse is slowed to allow time for ventricular filling during relaxation or ventricle diastole. AV node has pacemaker properties & can discharge an impulse if the SA node fails. o The electrical impulse is then rapidly conducted through the bundle of His to the ventricles via the L/R bundle branches. L bundle branch further divides in the left anterior fascicle and the left posterior fascicle. They divide into smaller and smaller branches, finally terminating in tiny fibers called Purkinje fevers that reach the myocardial muscle cells of myocytes. o The ventricles have pacemaker capabilities if the sinus or AV nodes cease to generate impulses. The electrical signal stimulates the atrial muscle, called atrial systole, and causes the atria to contract simultaneously and eject their blood volume into the ventricles. o Simultaneously, the ventricles fill with blood during ventricular diastole.
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o During atrial systole, a bolus of atrial blood is ejected into the ventricles and the inflow or AV valves close b/c of the increasing pressure of the blood volume in the ventricles. o By this time the electrical impulse reaches the Purkinje fibers, and the muscle cells have become stimulate and cause ventricular contractions. The aortic and pulmonic valves open b/c the increase pressure and volume in the ventricles, allowing for ejection of ventricular blood, ventricular systole. At the same time ventricular systole is occurring, atrial diastole, or filling is occurring. Atria are relaxed and filling with blood from periphery (deoxygenated) and the lungs (oxygenated). Then, because of the rhythmic pacing of the heart, the muscle cells are again stimulated, the atria contact, and atrial blood is ejected once again into the ventricles. Cardiac electrophysiology Specialized cardiac pacemaker cells possess the property of automaticity and can generate an electrical impulse on their own Non-pacemaker or muscle cells must receive and outside stimulus in normal circumstances to generate a response.
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Response generated by pacemaker or muscle cells once stimulated is called the action potential.
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