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An "abnormal" QTc in males is a QTc above 450 ms; and, in females, above 470 ms. [17] 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.
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]
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.
Those affected by short QT syndrome (SQT) have an increased risk of developing abnormal heart rhythms. [3] These abnormal heart rhythms often occur at a young age. They may take relatively benign forms such as atrial fibrillation, leading to symptoms of palpitations, breathlessness, or fatigue. [3]
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.
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Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemistry (also known as "clinical biochemistry", "chemical pathology" or "pure blood chemistry"), the ...
The electrical axis of the heart is the net direction in which the wave of depolarization travels. It is measured using an electrocardiogram (ECG).Normally, this begins at the sinoatrial node (SA node); from here the wave of depolarisation travels down to the apex of the heart.