Syncope is a common presentation in the Pediatric ED. While often it will be due to a benign etiology (ex, Hair Grooming Syncope), we know that there are many concerning conditions that we must consider. In the course of our contemplations, we rightfully scrutinize the ECG for possible subtle clues to the mystery. Is there evidence of the delta waves of WPW? Is there signs of Brugada or HOCM (dagger Q waves)? Maybe there is evidence of right heart strain concerning for a pulmonary embolism. Naturally, we look at the ST segments for evidence of ischemia and the PR segments for evidence of AV blocks. Oh, and let us not overlook that all important QT interval. Yes… prolonged QT can be problematic (like causing submersion injuries). While prolonged QT deserves our respect, do not let its shorter sibling be dismissed as being less important. Let us take a minute to consider the potential impact of Short QT Syndrome in Children:

Short QT Syndrome: Basics

Short QT Syndrome is a malignant cardiac electrical disorder [Pereira, 2017; Villafane, 2013]
- Associated with channelopathies that affect repolarization.
- Shorter myocardial repolarization creates opportunity for atrial and ventricular tachyarrhythmias.

Ventricular Tachyarrhythmias develop and lead to:
- Sudden Cardiac Death or
- Syncope

There is a genetic component Short QT Syndrome. [Pereira, 2017; Villafane, 2013]
- 6 specific mutations identified thus far.
- There is a male predominance
  - Higher testosterone plasma levels may lead to shorter QT…
  - Or perhaps estrogen is protective.
  - Short QT Syndrome does still, however, occur in women.
- Unfortunately, ~40% of families will not have a identifiable genetic cause.

Age of presentation: [Pereira, 2017; Guerrier, 2015; Mazzanti, 2014]
- Median age at diagnosis = 30 years, but ranges from 4 – 80 years of age.
- Prevalence in adult population = 0.02 – 0.1%
- Prevalence in pediatric population = 0.05%
- Two peaks in at high risk for Sudden Cardiac Death: [Mazzanti, 2014]
  - 1st year of life
  - 20 – 40 years of age
  - Probability of cardiac arrest in patients with Short QT Syndrome is 4% in 1st year of life and then 1.3% per year between 20 and 40 years of age.

Presenting Symptoms: [Pereira, 2017]
- Cardiac Arrest (28%) – never good when the initial symptom is death
- Syncope (24%)
- “Dizziness”
- Palpitations / Arrhythmias – most common arrhythmias in children with short QT syndrome are:
  - Atrial Fibrillation
  - Supraventricular Tachycardia
  - Polymorphic Ventricular Tachycardia
  - Ventricular Fibrillation
- Asymptomatic – found in patients due to family members having the diagnosis.

Short QT Syndrome: Management

The diagnostic criteria for Short QT Syndrome is debated and there are several criterion: [Pereira, 2017; Mazzanti, 2014; Villafane, 2013]
- A short QT measurement in isolation is not always indicative of Short QT Syndrome.
- Symptoms, family history, and genotyping also play a role.
- There are different guidelines available, so be aware that one cardiologist’s reference may differ from another’s:
  - QTc measurements (QTc </= 340 ms) is used by some, </= 320 ms is used by others.
  - Longer durations (QTc </= 360 ms) with at least one additional risk factor is also considered worrisome:
    - Pathogenic Mutation
    - Family history of Short QT Syndrome
    - Family history of Sudden Death before 40 years of age
    - Survival of V-Tach/V-fib episode in absence of heart disease
  - There is also shortening of the J-point to T-Point interval (< 120 ms) that has been found to be associated with Short QT Syndrome.
  - A “Scoring” scheme for Short QT Syndrome has been proposed by Gollob, et al. that has yet to be validated.
    - Points given for length of QT segment and other risk factors.
    - Some evidence that higher scores were associated with greater risk for events. [Villafane, 2013]

Patients who develop symptoms are at high risk of having recurrent arrhythmic events. [Pereira, 2017]

Given the presentation can be of devastating significance (sudden death), conservative strategies are often employed. [Pereira, 2017; Mazzanti, 2017; Mazzanti, 2014]
- Implantable Cardioverter-Defibrillator (ICD) is 1st line therapy
  - Upside = effective at preventing death from sudden arrhythmia!
  - Downside = surgery (potentially at a very young age), inappropriate shocks due to over sensing tall T waves.
- Hydroquinidine prophylaxis has also been used to prolong the QT in some patients.
  - Upside = no surgery!
  - Downside = may not work for all genotypes of Short QT Syndrome
  - Can also be used with ICD to help reduce number of shocks.

Moral of the Morsel

Once again, size matters. Both Long and Short QTc Syndromes are problematic!
Genetics matter also! For that patient with syncope or “Dizziness,” ask about family history of sudden death in person < 40 years of age (or other odd syncope that has been poorly explained).
Measurements matter, but so does the rest of the story. Pay attention to the QT duration, but consider the other risk factors when you are discussing the case with Cardiology.