QT interval and drug therapy
BMJ 2016; 353 doi: https://doi.org/10.1136/bmj.i2732 (Published 22 June 2016) Cite this as: BMJ 2016;353:i2732
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The formula given for the Fridericia correction is incorrect. The Fridericia method divides the QT by the cube root of the RR interval.
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I read with interest the article on QT interval and drug therapy which is very useful. In box 2 antibiotics seem to have been classified with "other cardiac drugs". Levofloxacin and moxifloxacin are, I think, fluoroquinolones. Also it may be worth mentioning other antibiotics that prolong the QT interval such as clofazamine, bedaquiline and delaminid.
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Dear Editor,
I would like to thank you for publishing the article on QT interval and drug therapy. It is a well written and on a topical subject. Cardiologists are often asked to comment on ECGs from other health professionals regarding QT intervals and whether this abnormality precludes them from taking certain drugs. On other occasions the ECG abnormalities queried are a result of the ECG being incorrectly recorded.
I would like to make reference to the picture used to illustrate the article. I realise this is only an illustration but it shows poor placement of the chest leads. Leads V1 and V2 are meant to be positioned either side of the sternum in the 4th intercostal space. V3 - V6 follow the fifth intercostal space with V4 being in the mid-clavicular line and V3 being between V2 and V4. V5 should be in the anterior axillary line and V6 in the mid axillary line.
The abnormally high positions on V1 and V2 give an abnormal appearance to these leads, especially in the ST segment, leading to the false suggestion of the Brugada syndrome.
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Re: QT interval and drug therapy
In our article, QT interval and drug therapy, the Fridericia formula for correcting the QT interval for heart rate [QTc=QT/(RR/3)] was taken from a review paper. Although the formula was reproduced directly from the paper, it is incorrect. The Fridericia method was derived from a cube root relationship. The full details are attached in a separate document.
Competing interests: No competing interests