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--- wikitox:ecg_changes [2024/04/24 01:29] – kharris
+++ wikitox:ecg_changes [2025/02/24 21:20] (current) – kharris
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- <font 36px/inherit;;#c12b04;;inherit>ECG</font>
+====== ECG ======
 ----
@@ Line 43: / Line 43: @@
 ===== QT Prolongation =====
-The QT interval is measured from the initiation of the QRS complex to the end of the T wave and largely represents ventricular repolarisation.  Prolongation of the QT interval is important clinically as it is associated with life threatening Torsades de Pointes (TdP).  QT Prolongation can be due to congenital or acquired causes.  Of the acquired causes, drugs are a common culprit – with the usual mechanism being blockade of the inward rectifying potassium channel.
+The QT interval is measured from the initiation of the QRS complex to the end of the T wave and largely represents ventricular repolarisation. Prolongation of the QT interval is important clinically as it is associated with life threatening Torsades de Pointes (TdP). QT Prolongation can be due to congenital or acquired causes. Of the acquired causes, drugs are a common culprit – with the usual mechanism being blockade of the inward rectifying potassium channel.
 \\
-In the poisoned patient, you should consider QT prolongation in any exposure to a QT prolonging agent.  Drugs associated with QT prolongation and TdP are listed below (this list is not exhaustive):
+In the poisoned patient, you should consider QT prolongation in any exposure to a QT prolonging agent. Drugs associated with QT prolongation and TdP are listed below (this list is not exhaustive):
 {{  :wikitox:qtpro_list.png?direct&400  }}
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   * Congenital QT prolongation
- A previous ECG maybe helpful in these cases. \\
+A previous ECG maybe helpful in these cases.
 ==== Measuring the QT & plotting on the nomogram ====
-The best approach to measuring the QT is to measure the QT interval in multiple leads and take the median value.  Be mindful that computer generated QT calculation is unreliable and should not be used.
+The best approach to measuring the QT is to measure the QT interval in multiple leads and take the median value. Be mindful that computer generated QT calculation is unreliable and should not be used.
 {{  :wikitox:qtmeasurepic.png?direct&400  }}
-Plot the QT on the QT nomogram to determine risk of TdP.  Values above the line are at risk of TdP and warrant closer observation.
+Plot the QT on the QT nomogram to determine risk of TdP. Values above the line are at risk of TdP and warrant closer observation.
 {{  :wikitox:qtnomogram.png?direct&550  }}
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 The QT nomogram has a sensitivity of 97% and specificity of 99% for predicting TdP following toxicological ingestions and has been found to be more accurate in predicting TdP than using Bazett’s QTc of 440ms or 500ms.
- \\
+{{  :wikitox:falseqt_ecg.png?direct&600  }}
-===== REFERENCE =====
+For the above ECG example, the measured QT in leads I, II aVF, V2, V4, V6 are 320, 340, 320, 300, 340 and 320 respectively. This gives a median QT of 320ms. Note the computer-generated QT is longer at 360ms, correcting with Bazett’s formula to 485. However, plotting this on the nomogram shows a level which is well below the risk line.
-Bruccoleri RE, Burns MM. A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening. J Med Toxicol. 2016 Mar;12(1):121-9. doi: 10.1007/s13181-015-0483-y. PMID: 26159649; PMCID: PMC4781799.
+Bazett’s QTc overcorrects in tachycardia and under-corrects for slow heart rates and should not be used in toxicology patients to determine overall risk of TdP.
-Isbister G and Page C.  “Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practive.  Brit J Clin Pharmacol 2012; 76(1):48-57
+==== Management of prolonged QT ====
-Thomas S and Behr E.  “Pharmacological treatment of acquired QT prolongation and torsades de pointes.” Br J Clin Pharmacol 2015; 81(3):420-7
+Observe patients with prolonged QT in a monitored environment with continuous telemetry. Review ECGs q4h to follow progression.
+Correct modifiable risk factors for TdP:
+  * Hypoxia
+  * Hypokalaemia (aim for K+ > 4.5)
+  * Hypomagnesaemia (aim for Mg2+ > 1.0)
+  * Hypocalcaemia: (aim for iCa > 1.2)
+==== Management of Torsades de Pointes ====
+Manage as above plus give **magnesium sulphate 10mmol (0.1mmol/kg paediatrics) over 10 min**, repeat as required. Consider chemical or mechanical overdrive pacing for ongoing stabilisation.
+Electrical cardioversion may be required in prolonged cases of TdP – although most cases are self-terminating bursts.
+----
+===== Further Reading =====
+  - Bruccoleri RE, Burns MM. A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening. J Med Toxicol. 2016 Mar;12(1):121-9. doi: 10.1007/s13181-015-0483-y. PMID: 26159649; PMCID: PMC4781799. {{:wikitox:bruccoleri_j_med_tox_2016_bicarb_for_qrs_widening.pdf|PDF}}
+  - Isbister G and Page C. “Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practive. Brit J Clin Pharmacol 2012; 76(1):48-57. {{:wikitox:isbister_-_drug_induced_qt.pdf|PDF}}
+  - Thomas S and Behr E. “Pharmacological treatment of acquired QT prolongation and torsades de pointes.” Br J Clin Pharmacol 2015; 81(3):420-7. {{:wikitox:thomas_-_qt_treatment.pdf|PDF}}