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The dimensionally correct form of Bazett's formula is: Q T c B = Q T R R 1 s {\displaystyle QTc_{B}={QT \over {\sqrt {RR \over 1{\text{ s}}}}}} where QTc B is the QT interval corrected for heart rate, and RR is the interval from the onset of one QRS complex to the onset of the next QRS complex.
The value for a normal QT interval is similar in males and females from birth up to adolescence. During infancy, a normal QTc is defined as 400 ± 20 milliseconds. Before puberty, the 99th percentile of QTc values is 460 milliseconds. After puberty, this value increases to 470 milliseconds in males and 480 milliseconds in females. [citation needed]
Torsades de pointes, torsade de pointes or torsades des pointes (TdP; also called torsades) (/ t ɔːr ˌ s ɑː d d ə ˈ p w æ̃ t /, [2] French: [tɔʁsad də pwɛ̃t̪], translated as "twisting of peaks") is a specific type of abnormal heart rhythm that can lead to sudden cardiac death.
The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. LQTS is suggested if the QTc is longer than these cutoffs. However, as 5% of normal people also fall into this category, some suggest cutoffs of 470 and 480 ms for males and females respectively, corresponding with the 99th centiles of normal values.
Quinidine, a class Ia antiarrhythmic agent, has been shown to partially correct the QT interval and make the heart more resilient to artificially-induced abnormal heart rhythms, [3] [14] although it is still uncertain at present whether this translates to a lower risk of sudden death.
The hexaxial reference system is a diagram that is used to determine the heart's electrical axis in the frontal plane.. In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°.
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In 2001, the FDA changed the labeling requirements for droperidol injection to include a Black Box Warning, citing concerns of QT prolongation and torsades de pointes.The evidence for this is disputed, with 9 reported cases of torsades in 30 years and all of those having received doses in excess of 5 mg. [9] QT prolongation is a dose-related effect, [10] and it appears that droperidol is not a ...