Abstract Brugada syndrome is an inherited arrhythmia disorder that predisposes to sudden cardiac death. It is characterized by its distinct ECG pattern. The purpose of this thesis was to study the phenotype and genotype characteristics of subjects with Brugada syndrome type ECG.

The first study population consisted of 2479 young male Air Force applicants and 542 healthy middle-aged subjects. The 12-lead ECG was analyzed to assess the prevalence and prognosis of Brugada pattern in Finnish population. The second population consisted of 168 patients with AF. The ECGs of the patients with family history of lone AF were analysed in order to characterize the ECG features of familial AF. The third population consisted of 200 patients with Brugada syndrome and their ECGs were analyzed for detection of distinct ECG characteristics. In a substudy, the H558R variant was genotyped and the clinical presentation of this variant was evaluated. The clinical characteristics were collected of 47 patients with induced Brugada ECG during fever or medication.

The prevalence of type 2 or 3 Brugada ECG was 0.61% in the young population and 0.55% in the middle-aged Finnish population. In a retrospective analysis, none of the Brugada ECG carriers had died. In the AF study, the prevalence of type 2 or 3 Brugada ECG was significantly higher among the subjects with lone AF compared to the healthy controls (p < 0.001). Many of the Brugada ECG carriers had a family history (> 30% of first-degree relatives) of AF. In patients with Brugada syndrome, the prolonged QRS duration was associated with previous symptoms. The R allele carriers in H558R variant had a trend towards less symptoms (p = 0.067) and had less conduction disturbances in 12-lead ECG than the HH genotype carriers (p < 0.05 in all ECG analysis). Among the subjects with induced Brugada ECG, 51% exhibited arrhythmic symptoms during the medical condition that had provoked the ECG pattern.

In conclusion, type 2 and 3 Brugada ECGs were found to be benign in the Finnish population since no mortality occurred during an extensive follow-up period. On the other hand, these ECG abnormalities seem to be a marker of familial AF. Among patients with the Brugada syndrome, a prolongation of QRS is associated with prior symptoms. The variant H558R R allele seems to be a protecting genetic modulator. Induced Brugada ECG is a medical emergency since the patients are at high risk of sudden cardiac death.