Case
Hi, I’m calling from the ER. We have an 11-year old who “collapsed” while at the park with his family. The family called 911, started CPR, but by the time the ambulance came he improved, and they did not have to do CPR or shock him. He looks OK now but his ECG computer read says his QT is prolonged. Please help.
What am I thinking?
A computer read that says prolonged QT is a cause for concern, but the computer can make glaring mistakes sometimes. A diagnosis of long QT syndrome is a life-changing one and has to be made with care and consideration. The computer read has to be confirmed by manual measurement. That said, in this specific case, the index of suspicion that this is a true case of long QT is high because of the presentation with collapse.
Long QT syndrome is an inherited channelopathy (a disorder of the cardiac ion channels) making the patient vulnerable to episodes of an unusual form of ventricular tachycardia called Torsades des pointes (TdP) (see Fig. 24.1 ). TdP can cause death, and a shock can successfully restore sinus rhythm. However, patients can have nonsustained self-terminated episodes of TdP and therefore may spontaneously recover from a “collapse” without a shock. Another confounding presentation is the likelihood of presenting with a “seizure.” A TdP episode causes brain anoxia and, as a result, the patient has an anoxic seizure. When the TdP ceases, the blood supply to the brain resumes, the seizure stops, and the patient wakes up. In such an instance, it is easy to overlook the heart and go full tilt investigating the neurologic system.
A big confounder in teens and preteens is vasovagal syncope that is so much more common in this age group. Vasovagal syncope is a fainting episode with transient loss of consciousness due to transient low blood pressure. Studies have shown that 99% of faints in teens and preteens are due to vasovagal syncope (see Chapter 16 ). So, on the one hand, we have a rare life-threatening disorder (long QT) and, on the other hand, we have a benign condition that is common and almost never causes life-threatening consequences. Making a mistake either way could have terrible consequences for this child. Disregarding long QT put his life in danger, but mistakenly diagnosing long QT gives him a bad medical label to carry that can be hard to remove.
The history of the event that happened can be one of the most important aspects. If the “collapse” happened while he was running or actively playing and excited, the bias tilts toward a lethal condition like long QT and away from vasovagal syncope. A family history of someone else in the immediate family who died in a “sudden” or “unexplained” or “inadequately explained” manner further increases the index of suspicion. Family history of a “seizure-disorder” is also suspicious due to the factors discussed above.
TdP in long QT is often brought about during exercise or during a sudden alarming event, especially sudden noise such as a wakeup alarm or a fire alarm. Long QT also has a predisposition to swimming and unexplained drownings. A specific question to ask is whether there is a family history of deafness. A rare form of long QT called the Jervell and Lange-Nielsen syndrome is associated with deafness.
The ECG obtained is a crucial piece of evidence. The QT should be measured and then corrected using a formula (Bazett’s formula). A QTC >460 ms in boys and >480 ms in girls is considered abnormal. It is important to also look at the “shape” of the T waves. They can be bizarre in long QT syndrome (see Figs. 24.2–24.4 ).
