From the Guidelines
The normal QT interval for an elderly woman is considered to be 460 ms or longer, as suggested by the American Heart Association and the American College of Cardiology Foundation 1. This interval represents the time from the beginning of ventricular depolarization to the end of ventricular repolarization in the heart's electrical cycle. Age-related changes in cardiac tissue and slower repolarization naturally extend the QT interval in older individuals. Women generally have longer QT intervals than men by about 10-20 ms due to hormonal influences on cardiac ion channels. When evaluating an ECG in clinical practice, it's essential to use the corrected QT interval (QTc), which adjusts for heart rate variations. A QTc greater than 470 ms in elderly women may indicate prolonged QT syndrome, which increases the risk for dangerous arrhythmias like torsades de pointes. Certain medications (including some antiarrhythmics, antipsychotics, antibiotics, and antihistamines), electrolyte abnormalities (particularly low potassium, magnesium, or calcium), and structural heart disease can further prolong the QT interval in elderly patients, as noted in a study on the risk of arrhythmia induced by psychotropic medications 2. It's also important to consider that the risk of torsade de pointes increases exponentially with the duration of the QT interval, with a QTc >500 ms associated with a 2- to 3-fold higher risk for TdP, as indicated by a scientific statement from the American Heart Association and the American College of Cardiology Foundation 3. Key points to consider when evaluating the QT interval in elderly women include:
- The normal upper QTc value in women is 460 ms 1
- QTc values from 440 to 470 ms are considered a 'grey zone' due to a considerable overlap between affected and controls in this range 2
- A QTc greater than 470 ms may indicate prolonged QT syndrome and increase the risk for torsades de pointes 1, 3
From the Research
Normal QT Duration for an Elderly Woman
- The normal QT duration for an elderly woman can be determined based on age- and sex-specific criteria, as established by a study published in the International Journal of Cardiology 4.
- According to this study, the criteria for prolonged QTc are: + Age ≥ 70 years: men 455 ms, women 460 ms
- Therefore, a normal QT duration for an elderly woman would be less than 460 ms.
- It is essential to use age- and sex-specific criteria for evaluation of QT prolongation, as upper normal limits for QTc vary substantially by age and sex 4.
- Other studies have focused on the risks of QT interval prolongation associated with various drugs, including antiarrhythmic agents, antimicrobial drugs, and other cardiovascular agents 5, 6, 7, 8.