How does this QTc calculator work?
This is a handy health tool that can estimate the QT corrected interval by using the heart rate expressed in beats per minute and QT interval expressed either in seconds or milliseconds. The QT values can be obtained from the ECG test.
This QTc calculator is designed to show the QT corrected interval for heart rate extremes because it returns the estimations by 4 different equations as presented below:
QT corrected interval:
■ by Bazett’s formula: QTc = QT/√(RR in seconds)
■ by Fridericia’s formula: QTc = QT/(RR^0.33)
■ by Framingham’s formula: QTc = QT + 0.154(1-RR)
■ by Hodges’s formula: QTc = QT + 1.75(HR — 60)
Where:
RR interval = 60 / HR
HR = Heart rate in beats per minute.
Moreover it returns the QT corrected interval expressed in both seconds and milliseconds.
As agreed upon by ACC / HRS the normal QTc interval is below 450 milliseconds for men and below 460 milliseconds for women.
No gender specific, any QTc greater than 500 milliseconds is considered highly abnormal, while any value of QTc smaller than 340 milliseconds may indicate short QT syndrome.
Please remember that this QTc calculator should NOT be considered as a substitute for any medical professional service.
Example calculation
For a heart rate/ Pulse of 72 beats per minute and a QT interval of 0.42 seconds the result is:
■ QTc Interval by Bazett’s method = 0.460 sec OR 460 msec
■ QTc Interval by Fridericia’s equation = 0.446 sec OR 446 msec
■ QTc Interval by Framingham’s algorithm = 0.446 sec OR 446 msec
■ QTc Interval by Hodges’s equation = 0.441 sec OR 441 msec
■ RR Interval = 0.833 sec OR 833 msec
What is the short QT syndrome?
This is a condition that can cause arrhythmia which is a disruption in the heart’s normal rhythm because the QT interval shortening means that the heart takes less time to recharge/ relax between beats but there is no underlying structural anomaly of the heart.
This is a relatively new discovery of the 21st century medicine and there haven’t been numerous cases documented. It can be detected through EKG (electrocardiogram) that measures the electrical activity of the heart.
This condition that appears at any age, if left untreated leads to syncope which is fainting, feelings of dizziness and even to cardiac arrest and sudden death. On the other hand there are people, generally healthy that have shortened QT but don’t display any symptoms.
What if the QT is higher than normal?
The long QT syndrome is an uncommon condition, also put under arrhythmias and can pose a serious threat as the electrical activity of the heart is disrupted. There are also some individuals that have QT intervals longer but don’t develop serious arrhythmia while others experience moments in which their heart suddenly beats faster for no particular reason and this disruption of rhythm leads to the brain not being oxygenated properly and then fainting.
It is discussed that there is an inheritance pattern for this anomaly and that there are higher chances for it to appear to individuals that have cases of heart disease in the family.
Источник: www.thecalculator.co
Здравствуйте, у ребёнка 9 лет 80% времени увеличенный интервал корр qt 460-500.
Плюс тахикардия.
Пьёт магний, кудесан.
Очень переживаю
Вот заключение Холтера :
Мониторирование ЭКГ в 12 отведениях проведено в течение 21 ч. 55 мин. (пригодно для анализа 21 ч. 55
мин.), из которых 3 ч.
мин. занимала физическая активность (53 мин.- интенсивная типа "ходьба",
интеграл активности за время наблюдения 30433 mg), 8 ч. 28 мин. — сон.
ЧСС ср.дневная – 92 уд/мин (норма 93 уд/мин), макс. ЧСС 144 уд/мин (14:28 — прогулка)
ЧСС ср.ночная — 69 уд/мин (норма 75 уд/мин), мин. ЧСС 60 уд/мин (0:50 — сон)
ЧСС ср.суточная — 83 уд/мин (норма 84 уд/мин)
Значения ЧСС получены при периоде расчета 60 с.
ЦИ – 1,33
В дневное время регистрируется синусовый ритм с ЧСС в пределах возрастной нормы, во время сна —
незначительная синусовая брадикардия. Правильный циркадный профиль сердечного ритма.
В течение суток регистрируется частая миграция водителя ритма по предсердиям, частые эпизоды (во время
сна периоды) замещающего и единичные эпизоды ускоренного предсердного ритма с ЧСС до 93 уд/мин
(представленность предсердного ритма около 20-25%, преобладает ночной циркадный тип аритми).
Транзиторное замедление атриовентрикулярной проводимости (интервал PQ до 168 мс, преимущественно во
время сна, представленность около 15-20%).
В течение суток регистрируется транзиторное удлинение интервала QT. Эпизоды нарушения процесса
реполяризации (в период бодрствования отрицательные зубцы Т в отведениях III, aVF (больше на фоне
повышения ЧСС), во время сна — в V1-V3). Ишемических изменений ST-T не выявлено.
Максимальная пауза ритма за счет синусовой аритми 1348 мс (норма при ХМ не более 1300 мс).
Продолжительность интервала QT составляет 296 мс при максимальной ЧСС 144 уд/мин (QTc 459 мс), 444 мс
при минимальной ЧСС 60 уд/мин (QTc 444 мс)-(норма QT при ХМ до 480 мс, QTc до 440 мс).
Автоматический анализ интервала QT: максимальный QT 453 мс (норма QT до 480 мс), максимальный QTc
503 мс (вручную макс.
c 522 мс при ЧСС 129 уд/мин)-(норма QTc до 440 мс), средний QTc 463 мс (норма
400-450 мс), дисперсия средняя/максимальная — 18/93 мс (норма до 40 мс). Превышение QTc свыше 450 мс в
течение 92% времени записи (доступно для анализа около 98% времени записи). QT-динамика в пределах
нормальных значений.
Вариабельность ритма сердца: основной уровень функционирования синусового узла в норме.
Функции разброса ослаблена. Функция концентрации ритма усилена.
Уровень парасимпатических влияний на ритм сердца в пределах нормы.
Возраст: 9
Источник: sprosivracha.com
Tangent method
To determine the end of the T-wave by the tangent method, you first take the tangent on the steepest point of the terminal limb of the T-wave. There were the tangent intersects with the isoelectric baseline, is the end of the T-wave (Figure).
Threshold method
To determine the end of the T-wave by the threshold method, you take the intersection of the terminal limb of the T-wave with the isoelectric baseline (Figure). When a U-wave interrupted the T-wave before it returned to baseline, the end of the T-wave is than the nadir between the T- and U-wave.
Both manual methods for measuring the QT-interval, require the determination of the isoelectric baseline:
Isoelectric baseline
The isoelectric baseline can be obtained by connecting the TP-segment (the segment between T-wave and P-wave) of the complex in which you measured the QT-interval, with the TP-segment of the preceding complex (Figure).
The QT-interval is corrected for the RR-interval or heart rate. It is important that the RR-interval (or heart rate) between the measured and the preceding complex was used to obtain the QTc-interval (figure). The QT-interval can then be corrected for the RR-interval/heart rate with several correction formulas as shown in the QTcalculator.
1. Bazett: QTcB=QT/RR1/2
2. Fridericia: QTcFri=QT/RR1/3
3. Framingham: QTcFra=QT+0.154 (1−RR)
4. Rautaharju: QTcR=QT−0.185 (RR−1)+k
(k=+0.006 seconds for men and +0 seconds for women and children <12years)
5. Hodges: QTc=QT+(1,75*(HR-60))
The QT-interval is preferably measured during stable sinus rhythm. However, in some occasions you are challenged with extra systoles, overt sinus arrhythmia or even atrial fibrillation. Extra systoles and the beat directly following an extra systole should preferably not be included in the measurement of the QT-interval but may provide a lot of information; those patients with decreased repolarization reserve will show aberrant QT-intervals or even giant T-U waves after the sudden change in heart rate initiated by the extra systole.
sinus arrhythmia, especially apparent in (young) children, the varying RR-intervals result in so much variation in the QTc-interval that the probability for an erroneous diagnosis of a prolonged QT-interval is increased. The QT-interval should be measured in complexes without a marked sinus arrhythmia when possible. In atrial fibrillation, the QT-interval is difficult to determine and the irregular RR-intervals/heart rate also effects the QTc-interval. Therefore, the QT-interval is preferably determined during stable sinus rhythm, while QTc-intervals values derived from ECGs with arrhythmias should be interpreted with caution.
Looking at conduction disorders, the largest problem is the influence of the QRS-duration on the QT-interval. If the QRS-complex duration is increased, it will mostly result in an increase in QT-interval. Prolonged QT-intervals in individuals with wide QRS-complex can be associated with normal repolarization or prolonged repolarization times and can therefore be non-specific. Since the QT-interval prolongs in ventricular conduction defects, an adjustment for QRS duration becomes necessary. This can be accomplished best by using the JT interval (QT-interval minus the QRS-duration), which then would need dedicated reference values (not currently available). There are several correction formulas for QT-interval assessment in bundle branch block, e.g. Bogossian et al, Heart Rhythm 2015.
Please note that the reference values used for this calculator were determined in patients without the use of QT prolonging drugs or severe hypokalemia. In the case QTc prolongation with severe hypokalemia and/or the use of QT prolonging drugs, we advise to determine the QTc again after correction of these elements.
Источник: www.qtcalculator.org
