Diagnostic criteria LQTS—1993 Schwartz

• QTc ≥480 ms 3 points, 460–479 ms 2 points, 450–459 ms (in males) 1 point, TdP 2 points, T wave alternans 1 point, Notched T wave in three leads 1 point, Low heart rate for age 0.5 point, Congenital deafness 0.5 point, Family members with definite LQTS 1 point, Unexplained sudden cardiac death below age 30 among immediate family members 0.5 point

• QTc calculated by Bazett's formula, where QTc = QT/√ RR.

• 2–3 points, intermediate probability of LQTS; ≥4 points, high probability of LQTS

Common Types of Inherited LQTS:

• LQT1: Usually physical exercise can trigger arrhythmias. Repolarization is abnormal just in sympathetic activation. About 50% of LQTS cases.

• LQT2: Usually surprise and startling can cause arrhythmias. Repolarization could be abnormal in long time periods. About 30% of LQTS cases.
• LQT3: Arrhythmias during sleep or rest, caused by a slow heart rate. Repolarization is abnormal in bradycardia. About 5% of LQTS cases.

When LQTS is suspected

• Holter is important to examine the QT-time in deferent pulse rates and T-wave morphology.

• Exercise test: In recovery phase normally QT-time is shorter than exercise phase with the same pulse rate. But in LQT1 and LQT2, the QT-time in recovery phase with 100-110/min pulse rate, is often longer than the QT-time in exercise phase with the same pulse rate. In LQT3 the QT-time in exercise phase will be shortened exceptionally much.

• It is recommended to check also other family member ECGs, because a long QT time in another member of family will confirm the diagnosis in your patient.

Treatment

• The treatment is Bisoprolol or Propranolol.

• If there is bradycardia with Betablockers, then DDD-pacemaker implantation is needed.

• If patient has had syncope during treatment with Betablockers, then ICD implantation is needed.

• It is important to forbid drugs which prolong qt interval.

Long QT syndrome patients may faint due to neurocardiogenic syncope. (Toft E1, ..., Kanters JK. Europace. 2003 Oct;5(4):367-70.)

Syncope in long QT syndrome (LQTS) is expected to be due to Torsades de Pointes ventricular tachycardia (TdP). Often these patients faint in situations with emotional stress. The aim of the present study was to evaluate whether neurocardiogenic syncope occurs in LQTS.

METHODS AND RESULTS: Ten untreated consecutive LQTS patients (age 11-72 years, median 37.5 years, five males and five females from five different families (one KvLQT1 mutation, two HERG mutations in three families and one without established genetic background)) were examined by a head-up tilt-table test (HUT). If syncope did not occur within 25 min, the patient received 0.25 mg nitroglycerine sublingually and the HUT was continued for 20 min. Nine out of 10 patients had a positive HUT. The syncope resulted from a combined vasodepressor and bradycardiac response. There were no cases of TdP. No syncope occurred in a 42-year-old asymptomatic male LQTS patient with a borderline prolonged QTc of 0.45 s and a HERG mutation. In 11 of 21 patients referred for syncope without LQTS a positive HUT was found (P < 0.10).

CONCLUSION: Syncope in LQTS can be of neurocardiogenic origin and is not necessarily due to TdP. The reason for neurocardiogenic syncope in LQTS is unknown, but involvement of the autonomic nervous system outside the heart is possible.

Compilation by Dr. Samad Ali Moradi, According to Duodecim Finnish cardiology reference book & author work experience.