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Dysrhythmiassuefall08

Dysrhythmiassuefall08 - ECG Interpretation and Dysrhythmias...

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ECG Interpretation and Dysrhythmias Susan Hampson Fall 2008
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Electrocardiogram (ECG) Graphic representation of the heart’s electrical activity Wave forms produced by movement of ions into and out of the cardiac cell membranes Commonly use Lead II and MCL: show P waves and QRS clearly
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Cardiac Cells Properties: Automaticity -create an impulse Excitability -cardiac muscle to respond to stimulus Conductivity -receive impulse and conduct to adjoining cells Contractility -muscle cells shorten in response to impulse
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60-100 bpm 40-60 bpm 20-40 bpm connection.lww.com/Products/smeltzer10e/Ch26.asp
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ECG Paper Standard speed 25mm/sec Vertical axis is amplitude/ voltage Horizontal axis is time Use squares to determine HR and intervals between ECG complexes
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ECG Waveform
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P Waves Impulse initiated in SA node, pass thru atria Atrial depolarization and contraction Characteristics: Should be present Usually round Upright deflection from baseline 1:1 ratio with QRS complex
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P-R Interval Beginning of P wave to beginning of QRS complex Time impulse takes to spread thru atria, AV node, Bundle of His, to the Bundle Branches Isoelectric Duration: 0.12 - 0.20 seconds
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QRS Complex Ventricular depolarization and ventricular contraction Duration: 0.06 - 0.10 sec 3 distinct waves Q-wave: first downward deflection, below baseline Usually small, < 0.04 sec duration Wider/deeper than normal indicates pathology-infarct May or may not show early, serial ECGs
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QRS Complex R-wave: Upward deflection, above baseline Triangular S-wave: Upward deflection, back toward base line R and S: simultaneous depolarization of R and L ventricles
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T Wave Ventricular repolarization, recovery If stimulated before repolarized completely d/t ectopic impulse, lethal dysrhythmia can occur-vulnerable period of cardiac cycle Characteristic: Round, upright, usually asymmetric No > 5mm tall Elevated: high K+, MI, or ischemia
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S-T Segment Time between ventricular depolarization and the beginning of ventricular repolarization From end of QRS complex to beginning of T wave Characteristics: Isoelectric (not > 1mm above or below ) Elevation: acute MI Depression: low K+, or ischemia
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Q-T Interval Time for entire electrical depolarization/repolarization of ventricles Beginning of QRS complex to end of T wave Usually 0.36 – 0.44 sec Duration varies with age, gender and heart rate Medication and electrolyte imbalances can prolong, lengthens relative refractory period, increased vulnerability
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Interpretation of ECG Calculate HR Count the number of complexes in 6-sec period then multiply by 10. Atrial rate: count P waves Ventricular rate: count R waves More than 50% of complex in the 6-sec interval, count as full complex
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Interpretation of ECG Assess rhythm How regular do the complexes occur Artial: determine regularity of P waves
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