Long QT Syndrome
- Episodes of syncope and asyncope may occur, possibly accompanied by seizures
- May be asymptomatic
- Patients with LQTS type 1 have symptoms with exercise and type 2 have symptoms with emotion triggers
- Most cases in the general population are acquired but in the case of athletes, the main risk factor is genetics
- 17 known genetic causes of Long QT syndrome (as of 2019), the specific etiologies are broad and involve ion channel defects
- Acquired long QT is more common in the general population and may co-exist with congenital long QT syndrome in the athlete population
- Certain medications can prolong the QT interval as well as hypokalemia, hypomagnesemia and hypothermia.
- ECG evaluation is the first step to assessing long QT syndrome
- The QT interval is calculated into the QTc (to adjust for heart rate) with one of several formulas, of which Bazzet's is the most common
- A normal QTc is <440ms in men and <460ms in women but the upper limit of normal can be up to 470ms or 480ms.
- The Schwartz criteria exists to thoroughly assess Long QT syndrome.
- QTc greater than 480ms = 3 points
- QTc 460 to 479mc = 2 points
- QTc 450 to 459 (male) = 1 point
- QTc greater than 480ms after 4th minute of exercise = 1 point
- Torsades de pointes = 2 points
- T wave alternans = 1 point
- Notched T wave in 3 leads = 1 point
- Clinical bradycardia = 1 point
- Syncope with stress or exertion = 2 points
- Syncope at rest = 1 point
- Congenital deafness = 0.5 points
- Family members with diagnosed Long QT syndrome = 1 point
- Unexplained sudden death under age 30 among immediate family members = 0.5 points
- Result evaluation
- A score of less than or equal to 1 is equal to low probability
- A score of 2 to 3 is equal to intermediate probability
- A score greater than 3.5 is equal to a high probability of congenital long QT syndrome.
- Depending on the score and clinical suspicion, then genetic testing may be considered.
- 17 types of Long QT syndrome exist
- The first 3 types make up over 90% of cases.
- A beta blocker is commonly prescribed to diagnosed cases of Long QT syndrome
- Other options include sodium channel blocking drugs and for severe cases, an ICD.
- Supplementation of potassium and magnesium is common
- Avoiding exercise is highly debatable and is a decision best made between the patient and physician.
- Drug induced cases are best treated with discontinuation of the offending medication.
- Long QT syndrome can lead to torsades de pointes, a type of polymorphic ventricular tachycardia
- This is an unstable and often pulseless rhythm which can lead to ventricular defibrillation and sudden death
- Patients who are silent carriers and have QTc <500ms are less likely to have episodes of sudden cardiac death