Summary – Risk Stratification in the Brugada Syndrome – Current Status and Future Diretions
Whereas the diagnosis of the BrS is relatively straightforward with currently available ECG-based methods, the identification of high risk patients who need prophylactic ICD implantation is still an unresolved issue. Currently the only class I indications for ICD implantation in patients diagnosed with the BrS endorsed by the 2013 HRS/EHRA/ APHRS Expert Consensus Statement7 is history of aborted cardiac arrest or documented spontaneous sustained VT, whereas syncope judged to be likely of arrhythmic origin is only a Class IIa indication which mainly reflects the difficulty of excluding a non-cardiac origin of syncope. The guidelines of the Japanese Cardiac Society of 2011 accept practically the same Class I indications whereas for Class IIa indication they require the presence of at least two of the following risk factors: history of syncope, family history of sudden cardiac death and inducible VF during EPS.104 Obviously, these guidelines do not offer solution to the problem of identifying the high risk asymptomatic patients with the BrS. Strict adherence to the HRS/EHRA/APHRS guidelines means that each year in the UK alone, approximately 40 asymptomatic BrS patients are likely to experience their first and potentially lethal arrhythmic event without ICD protection (assuming 0.5 % annual rate in asymptomatic patients [approximately 2/3 of all BrS patients] × estimated 12,600 (2 per 10,000) BrS patients in the UK). Clearly, there is a pressing need to develop novel, easily applicable (e.g. ECG based) risk stratifiers (or combinations thereof) and to confirm prospectively the value of the most promising available ones (e.g. QRS fractionation, infero-lateral ER, possibly others).
Obvious obstacles along the path to this goal are the low rate of arrhythmic events (i.e. end-point events in prospective studies), the small number of patients in the individual centres (since the prevalence of the disease outside South-East Asia is generally low), difficult organisation of big multicentre prospective studies and, possibly, inherent differences between various patient populations (e.g. Western vs Japanese).66 Less appreciated obstacle is the fact that currently ECG research studies (as well as everyday clinical practice) still use mainly 12-lead paper ECGs (or digital ECG images) which are amenable only to visual assessment and simple manual measurement. Computerised mathematical methods for quantitative assessment of QRS and ST-T wave abnormalities have been developed and successfully tested in various cardiac diseases105,106 but they require the availability of digital ECGs (digital files containing the raw ECG signal and not just digital image files). Finally, the development of sustained VT/VF in the BrS is likely a complex event resulting from interaction between the arrhythmic substrate (repolarisation and depolarisation abnormalities) and various triggering and modifying factors (e.g. ventricular ectopic beats, atrial arrhythmias, autonomic modulations such as vagal surge, fever, etc.).14,107,108 Therefore a successful ECG-based risk stratification in BrS should likely involve the combined quantitative assessment of several most important elements of arrhythmogenesis.