Child with Syncope

Name: RSL, 3yo, masculine, Caucasian, been born in Santo André, São Paulo, Brazil. Second son of an offspring of two.
Chief complaints: his Mother refer that three days ago he had an event manifested by fainting spells (syncope) triggers by an exposure to loud noises auditory stimuli (telephone ring).

Common childhood diseases absent. like, gastro-intestinal infections, respiratory illness, diabetes, jaundice, ingestion or inhalation of foreign bodies or others.
Prenatal History: without important intrauterine, or perinatal events, there is no history of drug intake, x-ray exposure and viruses during first trimester or pregnancy.

Parents not related by blood.
Natal History: full term normal delivery supervised by doctor, child cried immediately after birth and was pink in colour.
Post Natal History: 3,5kg to the birth, 49cm high, Normal Apgar score (8.). There is no history of cyanosis, jaundice. Refer two episodes of Seizures the last Month without explanation. Normal developmental history related to gross motor, fine, language.
Family history: Positivev family history of cardiac arrest and sudden death, at a young age, in his major brother at 9 yo.
Socio economic status: Low
Dietary History: Normal. Normal duration of breast feeding,
Physical: Normal. Only excessive bradycardia for his age.