Pacemaker or from impulse generation from an abnormal

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pacemaker or from impulse generation from an abnormal (ectopic) site Dysrhythmias initiated by three types of depolarizing mechanisms Abnormal automaticity Triggered activity from depolarization Reentrant circuits Automaticity Spontaneous generation of an action potential Major causes Failure to repolarize to normal resting membrane potential Plasma membrane leakiness to sodium or calcium ions at rest Hypokalemia Triggered Activity Occurs when an impulse is generated during or just after repolarization Due to depolarizing oscillation of the membrane potential Early occurs in phase 3
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Cardiac impulse continues to depolarize in a part of the heart after the main impulse has finished its path and the majority of the fibers have repolarized
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Dysrhythmia Analysis ECG recordings allow measurement of waveform amplitude, duration, and heart rate Standard ECG Strip Normal Sinus Rhythm Impulse rate between 60 and 100 beats/minute Regular rhythm Starts in the SA node and follows the normal pathway P wave precedes every QRS complex PR, QRS, QT intervals are of normal duration
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Normal Sinus Rhythm Sinus Tachycardia Abnormally fast heart rate of greater than 100 beats/minute Often a compensatory response to increased demand for CO or reduced SV Usually occurs from SNS activation Treatment aimed at correcting underlying cause; sympatholytic agents or calcium-channel blocking agents may be indicated Sinus Bradycardia Heart rate lower than 60 beats/minute May be normal in physically trained individuals with large resting SVs Usually from parasympathetic activation If slow HR precipitates low CO, treatment includes sympathomimetic or parasympatholytic drugs
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Sinus Bradycardia Sinus Arrhythmia Associated with fluctuations in autonomic influences and respiratory dynamics May be particularly pronounced in children Must be differentiated from sick sinus syndrome May need a pacemaker Sinus arrhythmia is normal and needs no treatment Sinus Arrhythmias vs. Sick Sinus Syndrome Sinus Arrest Absence of impulse initiation in the heart results in electrical asystole Escape rhythm: a slower pacemaker will generally begin to fire after several seconds of sinus arrest
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Pacemaker may be required Abnormal Site of Impulse Initiation Initiation of cardiac impulse at a site other than the SA node can occur with: SA node failure: allows a slower pacemaker to take over (escape rhythm) Enhanced excitability, triggered activity or reentrant circuits may cause a premature
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