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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]
If there is not a very high or low heart rate, the upper limits of QT can roughly be estimated by taking QT = QTc at a heart rate of 60 beats per minute (bpm), and subtracting 0.02 s from QT for every 10 bpm increase in heart rate. For example, taking normal QTc ≤ 0.42 s, QT would be expected to be 0.42 s or less at a heart rate of 60 bpm.
Sedation is very common, and extrapyramidal side effects are common and include restlessness, dystonic reactions, pseudoparkinsonism, and akathisia; the extrapyramidal symptoms can affect 2% of people at low doses, whereas higher doses may affect as many as 40% of people. [18] [19]
The cardiac features of JLNS can be diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. In those with Jervell and Lange-Nielsen syndrome the QTc is typically greater than 500 ms. [8]
The resting heart rate in children is much faster. In athletes, however, the resting heart rate can be as slow as 40 beats per minute, and be considered normal. [citation needed] The term sinus arrhythmia [26] refers to a normal phenomenon of alternating mild acceleration and slowing of the heart rate that occurs with breathing in and out ...
The normal range has since been revised in textbooks to 50–90 bpm for a human at total rest. Setting a lower threshold for bradycardia prevents misclassification of fit individuals as having a pathologic heart rate. The normal heart rate number can vary as children and adolescents tend to have faster heart rates than average adults.
Since these agents do not affect the sodium channel, conduction velocity is not decreased. The prolongation of the action potential duration and refractory period, combined with the maintenance of normal conduction velocity, prevent re-entrant arrhythmias. (The re-entrant rhythm is less likely to interact with tissue that has become refractory).
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