Brugada, sudden unexplained nocturnal death syndromes more common in Asians
Compared to Western populations, the prevalence rates of Brugada syndrome and of sudden unexplained nocturnal death syndrome (SUNDS) are higher in Asia, particularly in the Philippines, reports Dr Giselle Gervacio in the recently concluded 2018 Congress of the Asian Pacific Society of Cardiology (APSC 2018) in Taipei, Taiwan.
“In Asia, our prevalence of the Brugada ECG (electrocardiography) pattern is many times-fold than that in the West,” she said.
Citing the 2003 National Nutrition and Health Survey (NNHeS), Dr Gervacio showed that the prevalence rates of type 1 and 2 Brugada ECG patterns were 0.18 percent (n=7 of 3,907) and 1.7 percent (n=70 of 3,907), respectively. The survey included 3,907 households all over the country selected through a two-step stratified randomized sampling method. [Phil J Internal Medicine 2005;43:103-115]
In the same survey, the incidence of SUNDS was found to be 0.043 percent. “This is 40 times more common than the incidence reported in the West,” Dr Gervacio said.
Notably, there is also a stark difference between Western and Asian populations in terms of the demographics of SUNDS, she added. Structural heart diseases account for only 30 percent of SUNDS cases in Asia, including the Philippines, while 70 percent of the cases are unexplained. In Western populations, the opposite is true (70 percent structural heart diseases, 30 percent unexplained). [Circ Arrhythm Electrophysiol 2010;3:96-104; Heart Asia 2014;6:11-16]
A subsequent 2015 cohort, including 3,702 participants recruited via convenience sampling across four Philippine provinces, showed that the prevalence rates of type 1 and 2 Brugada ECG type were 0.46 percent (n=14) and 5.3 percent (n=163), respectively. [Heart Asia 2018;10:e010969]
“Most of these are young, healthy, asymptomatic individuals,” said Dr Gerpacio. “And we followed these guys that were identified with the type 1 [Brugada ECG] for 5 years to try to see how many of them would develop a cardiac event within that 5-year timespan.”
Of the seven individuals with asymptomatic type 1 Brugada syndrome in the 2003 NNHeS, three had developed cardiac events, defined as arrhythmic syncope, arrhythmic types of seizure and unexplained vehicular accidents. [Am J Cardiol 2011;107:714-716]
In comparison, three out of 14 type 1 Brugada participants developed cardiac events in the more recent 2015 cohort. The corresponding cardiac event rate was 12 percent in 4 years or 3 percent per year. [Heart Asia 2018;10:e010969]
Overall, the current prevalence rate of the Brugada ECG type in the Philippines is 2 percent, most of which are initially asymptomatic, according to Dr Gervacio. On the other hand, the conversion rates appear to be high at 3 percent per year for cardiac events and 1 percent per year for sudden death.
While the exact mechanisms underlying conversion are still unknown, various environmental factors play important roles. Particularly, “hyperthermia and/or alcohol [may] facilitate the occurrence of sudden death,” said Dr Gervacio, noting that these factors may account for the elevated event rates observed in the Philippines.
Moreover, shared genetic factors may potentially account for the differences in Brugada syndrome and SUNDS patterns between Western and Asian populations, though these are still undetermined.
“That will be the subject of the next Philippine Bangungut Project, where we will be conducting not only genetic studies but also molecular autopsies among victims of SUNDS,” said Dr Gervacio.