The qt interval should be measured in either lead ii

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The QT interval should be measured in either lead II or V5-6 QT Interval 101
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Several successive beats should be measured, with the maximum interval taken . Large U waves (> 1mm) that are fused to the T wave should be included in the measurement . Smaller U waves and those that are separate from the T wave should be excluded. The maximum slope intercept method is used to define the end of the T wave. How to measure QT 102
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Normal QTc values :- QTc is prolonged if > 440ms in men or > 460ms in women QTc > 500 is associated with increased risk of torsades de pointes QTc is abnormally short if < 350ms 103
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Causes of a prolonged QTc (>440ms) :- Hypokalaemia Hypomagnesaemia Hypocalcaemia Hypothermia Myocardial ischemia Post-cardiac arrest Raised intracranial pressure Congenital long QT syndrome 104
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Causes of a short QTc (<350ms) Hypercalcaemia Congenital short QT syndrome Digoxin effect 105
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Normal QTc values 106
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ECG IN ELECTROLYTE ABNORMALITIES 107
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Potassium is vital for regulating the normal electrical activity of the heart. Decreased extracellular potassium causes myocardial hyperexcitability with the potential to develop re- entrant arrhythmias. Hypokalaemia is defined as a potassium level < 3.5 mmol/L Moderate hypokalaemia is a serum level of < 3.0 mmol/L Severe hypokalaemia is defined as a level < 2.5 mmol/L Hypokalaemia 108
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Changes appear when K+ < 2.7 mmol/l Increased amplitude and width of the P wave Prolongation of the PR interval T wave flattening and inversion ST depression Prominent U waves (best seen in the precordial leads) Apparent long QT interval due to fusion of the T and U waves Effects of hypokalaemia on the ECG 109
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ST depression. T wave inversion. Prominent U waves. Long QU interval 110
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Increased extracellular potassium reduces myocardial excitability , with depression of both pacemaking and conducting tissues. Progressively worsening hyperkalaemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system , 1. Resulting in bradycardia and 2. Conduction blocks and 3. Ultimately cardiac arrest. Hyperkalaemia 111
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Hyperkalaemia is defined as a potassium level > 5.5 mEq/L Moderate hyperkalaemia is a serum potassium > 6.0 mEq/L Severe hyperkalaemia is a serum potassium > 7.0 mE/L. Serum potassium > 5.5 mEq/L is associated with repolarization abnormalities 112
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Peaked T waves (usually the earliest sign of hyperkalaemia) - > 5.5 mEq/L P wave widens and flattens PR segment lengthens P waves eventually disappear > 6.5mEq/L Prolonged QRS interval with bizarre QRS morphology Sinus bradycardia or slow AF >7.0 mEq/L Serum potassium level of > 9.0 mEq/L causes cardiac arrest 113
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Tall, symmetrically peaked T waves.
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  • Winter '16
  • jean grey
  • Cardiac electrophysiology, QRS, Rate

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