What Is Borderline Prolonged QTc?
The word borderline means an indefinite area, something in-between. So borderline prolonged QTc also means, the value is more than the normal range but it does fall into the category of prolonged QTc. Falls into a category in-between.
Borderline prolonged QTc is when the patient’s QTc is slightly high than the normal value, but does not fall into the category of prolong QTc. The normal QTc for males is 0.36s – 0.44s, borderline values range from 0.44 – 0.47s, more than 0.47s is considered prolong QTc. The normal QTc for females is 0.36s -0.46s, borderline value range from 0.46s – 0.48s, more than 0.48s is considered prolong QTc. However the cutoff values does not have universal figure therefore the values can change slightly. The mentioned figures are a rough guideline. QTc more than 0.50s is considered dangerous in any age or gender. If you are diagnosed with borderline QTc your doctor will decide what further investigations are needed to diagnose prolong QT interval/LQTS.
The normal QTc range is taken as 0.36 – 0.44s according to most of the studies done on patients with normal QTc and prolongs QTc and even genetic studies done on individuals who are not affected by any genetic condition, which prolong the QTc report similar values. However there is a considerable overlap of QTc intervals between actually healthy individuals and patients affected by long QT syndrome (LQTS).
When the cut off value 0.44s is taken there is some percentage of patients who actually have LQTS, but their QTc interval fall in the normal range. Same way some people who are healthy sometimes fall into the category of LQTS because they have a prolong QTc interval.
Some studies have done to select the QTc cut off value as 0.43; it has 100% sensitivity but lacks specificity and this result in over diagnosis of 40% of healthy individuals. Genetic testing can be a solution to diagnose LQTS definitely, but genetic tests are expensive, sometimes it show a variant of unknown significance and detects mutations in about 75% of patients with a clear LQTS phenotype. Schwartz criteria identify patients with a high probability of LQTS but have a low sensitivity. However the criteria remain useful in identifying patients with LQTS.
Normal, Borderline And Prolonged QTc Values
|Normal QTc||Borderline QTc||Prolonged QTc|
|Male||0.36s – 0.44s||0.44 – 0.47s||> 0.47s|
|Female||0.36 – 0.46s||0.45 – 0.48s||> 0.48s|
There have been several debates on the cut off value of the normal QTc range. No proper agreed value has been established yet for normal QTc, borderline QTc and for prolonged QTc. Therefore, the above mentioned cut off values can change slightly. In the absence of rigorous cutoff values patients with QTc interval of >0.48s can have LQTS even in the absence of symptoms. Most of the patients with familial LQTS do not have symptoms. Patients with lesser QTc values may be considered in the borderline category. However, QTc >0.50s is considered as a dangerous level for any age or gender.
What If You Have A Borderline Prolonged QTc?
We are giving you a brief account on what your doctor will do in such a circumstance. But the actual decisions should be taken by your doctor after discussing it with you.
Can repeat the 12-lead ECG after sometime and check if the QTc prolongation still present in Lead II, V5, V6. If it is still present check the Lead I, III as well.
If the QTc was taken automatically by the machine, doctor should manually measure the QTc interval in Lead II, V5 and V6.
- Get a detail history about any symptoms, family history of LQTS.
- Do appropriate investigations to identify any acquired causes for prolong QTc.
- Additional provocative tests such as standing ECG or exercise stress ECG will be necessary to diagnose prolong QTc/LQTS.
- Genetic testing can be carried out if other tests do not give a proper diagnosis.
- Family screening can be considered if a patient is diagnosed with congenital LQTS.
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