A study published online in the HeartRhythm Journal indicates that while the sodium channel blocker test has good prognostic value in symptomatic patients with non-diagnostic Brugada ECG (Br-ECG), it appears to have little value in asymptomatic patients.
The sodium channel blocker test is increasingly used in patients who have non-diagnostic type two or type three Br-ECG as the test (using a drug such as flecainide) can unmask type one Br-ECG, which is indicative of Brugada syndrome.
Alessandro Zorzi, Division of Cardiology, Department of Cardiac, Thoracic and Vascular Sciences, University of Padova, Italy, and co-authors wrote that data show that patients with drug-induced type one Br-ECG have a lower incidence of arrhythmic events than patients with spontaneous type one Br-ECG. However, they added that previous studies were not specifically designed to assess the outcome of patients with types two or three Br-ECG and also do not provide information about the protocol of the sodium channel blocker test used. Therefore, the aim of their study was to “specifically assess the prognostic value of a drug-induced type one Br-ECG for arrhythmic events during a long-term follow-up and, thus, the impact of sodium channel blocker test on risk stratification of individuals with non-diagnostic type two or three Br-ECG.”
Patients were recruited to the study if they had evidence of type two Br-ECG or type three Br-ECG on at least one ECG tracing and had no evidence of type one Br-ECG in more than five ECG tracings over time. The sodium channel blocker test was performed with intravenous administration of either flecainide to a target dose of 2mg/kg in five minutes or ajmaline to target dose of 1mg/kg in five to 10 minutes. Zorzi et al reported: “The test was considered diagnostic if a type two or three ECG converted to type one after administration of the drug, either in conventional leads V1–V3 or leads V1–V2 positioned over the third intercostal space.”
Of the 153 patients assessed, 76 (50%) developed type one Br-ECG during the test. Significantly more patients who experienced at least one arrhythmic event during follow-up (mean 59±33 months) had a positive sodium channel blocker test (p=0.02) and a history of cardiac arrest or syncope (p=0.002) than patients who had no events during follow-up.
Zorzi et al wrote that their study confirms that the sodium channel blocker test in symptomatic patients with type two or type three Br-ECG is “justified” because it predicts (if positive) an increased risk of arrhythmic events during follow-up and “enables appropriate work-up for risk assessment and therapeutic interventions.” However, they added that their study also indicates that the test does not provide additional prognostic value in asymptomatic patients with type two or type three Br-ECG. They stated: “A positive sodium channel blocker test in these individuals, though not useful for risk stratification, may have severe consequences in terms of psychological distress as well as further evaluation by programmed ventricular stimulation and placement of a prophylactic implantable cardioverter defibrillator.” They added that according to their results, asymptomatic patients with an incidental Br-ECG “may be reassured because of their good prognosis and just recommended to undergo ECG follow-up for detection of possible transient appearance of spontaneous type one Br-ECG unless new symptoms such as pre-syncope or syncope occur and require prompt risk re-evaluation.”
Domenico Corrado, an investigator in the study, from the Inherited Arrhythmogenic Cardiomyopathy Unit, Department of Cardiac Thoracic and Vascular Sciences, University of Padua Medical School, Italy, told Cardiac Rhythm News: “Our suggestion (not evidence based) is that individuals with a non-diagnostic Brugada ECG should undergo a repeat ECG (standard as well as with V1&V2 leads on third and second intercostal spaces) on a regular basis (every one to two years) to check for spontaneous type one Br-ECG.”
Zorzi et al concluded their study by saying that a prospective, validation study with larger number of patients and longer follow-up was needed before any final conclusions could be drawn on the value of the sodium channel blocker test.