Is a QTcB (QT interval corrected by Bazett's formula) interval of 465 ms initially and 447 ms two months later within normal limits for a female?

From the Guidelines

A QTcB interval of 465 ms initially and 447 ms two months later is considered prolonged and potentially concerning for a female, as normal QTc intervals for women are typically below 460 ms. According to the American Heart Association electrocardiography and arrhythmias committee, council on clinical cardiology, the normal limits for QT-interval prolongation and shortening in adult men and women are: prolonged QT: women, 460 ms or longer; men, longer than 450 ms 1. While the decrease from 465 ms to 447 ms shows improvement, the current value remains in a borderline prolonged range.

Some key points to consider:

• The QT interval is longer in young and middle-aged females than in males, with a gender difference that appears during adolescence and becomes small after 40 years of age 1.
• QT prolongation is important to monitor because it can increase the risk of a dangerous heart rhythm called Torsades de Pointes, and other factors that can affect QT interval include electrolyte abnormalities, thyroid disorders, and certain genetic conditions.
• The woman should inform her doctor about any symptoms like dizziness, fainting, palpitations, or seizures, and regular ECG monitoring would be appropriate to ensure the QT interval doesn't increase again.
• The FDA guidelines for industry recommend that 3 severity levels for rate-corrected QT be reported when considering possible QT-prolonging effects of drugs: longer than 350 ms, longer than 480 ms, and longer than 500 ms 1.

It is essential to discuss this with a healthcare provider, especially if the woman is taking medications known to prolong QT interval, such as certain antidepressants, antipsychotics, antibiotics, or antiarrhythmics, to determine the best course of action and ensure the woman's safety.

From the Research

QTcB Interval Evaluation

• A QTcB interval of 465 ms initially and 447 ms two months later can be evaluated based on normal QTc intervals, which are typically <450 ms for men and <460 ms for women 2.
• Given that the individual is female, the initial QTcB interval of 465 ms is slightly above the normal limit, while the second measurement of 447 ms is within the normal limit.
• It is essential to consider that for every 10 ms increase in QTc interval, there is a ~5% increase in the risk of arrhythmic events 2.

Comparison of QTcB and QTcFri

• The Bazett formula (QTcB) is commonly used to correct the QT interval, but it may lack reliability, especially at heart rates above or below 60 beats per minute (bpm) 3.
• The Fridericia formula (QTcFri) is an alternative correction method that may provide more accurate results, particularly in certain patient populations 3.
• However, the provided QTcB intervals do not necessitate a comparison with QTcFri, as the primary concern is evaluating the QTcB intervals against normal limits.

Clinical Implications

• The initial QTcB interval of 465 ms may indicate a slightly increased risk of arrhythmic events, but the second measurement of 447 ms suggests a decreased risk 2.
• It is crucial to consider patient-related risk factors, such as female sex, age, and uncorrected electrolyte disturbances, when evaluating QTc intervals 2, 4.
• Close monitoring of electrocardiography (EKG) and electrolytes is necessary to prevent Torsades de Pointes (TdP), a potentially life-threatening cardiac arrhythmia 4.