Cardiac Repolarisation- Long and Short of It

How many times we have read that apparently healthy children and young adults die without warning. Even fit atheletes die.

The long-QT syndrome is foremost among responsible causes, and is known to be the consequence of mutations in genes encoding ion channel function. Previously thought to be rare , its prevalence is now estimated as one in 2000.

LQT1 is the most common type, and events are typically triggered by exercise, including swimming, and emotion. The child found unconscious at the bottom of the swimming pool may well have LQT1. Events may occur with exercise or at rest in LQT2 and also, characteristically, with loud noises such as being awakened by a telephone call. LQT3 has been linked to death during sleep or inactivity, with a lower likelihood of events, but increased mortality.

What are the implications for physicans and general practitioners?

Fainting is common, most often vasovagally mediated, and benign. How do we decide otherwise? The key is to be mindful of possible long-QT syndrome when checking the history; fainting or a seizure during exercise, or when upset or angry, and premature death (including drownings or accidents) in family members should ring alarm bells and trigger detailed exploration of the family history, close scrutiny of ECGs and appropriate referral. In such settings, a corrected QT (QTc) interval > 0.45 seconds in males and > 0.47 seconds in females makes the diagnosis virtually certain.

ECG showing LONG QT

With diagnosis comes the dual responsibility of triaging individual patient risk and screening the wider family. The most important factor determining individual risk is the length of the QT interval - long intervals (QTc ≥ 0.5 seconds) equal high risk.
If you want to learn Molecular Physiology of Cardiac Repolarization please click here..( It is a large 50 page PDF file) he he.