THE UTILITY AND INCREMENTAL VALUE OF THE SIGNAL AVERAGED ECG: A NOVEL MODEL FOR STRATIFYING PATIENTS WITH SUSPECTED BRUGADA SYNDROME

Abstract

Patients with suspected Brugada syndrome often undergo a procainamide challenge to stratify their risk for sudden death and arrhythmic events. Patients that develop a Type 1 Brugada pattern during procainamide infusion are at greater risk for cardiac arrest. The signal-averaged ECG (SAECG) can detect late potentials in Brugada syndrome, which may have prognostic significance. We used historical and clinical features, and the SAECG to predict the yield of the procainamide and ajmaline tests in patients with suspected Brugada syndrome. 251 patients were enrolled across Canada with a procainamide challenge and standard, high precordial, and signal-averaged ECGs. A second cohort of 97 patients were enrolled in the United Kingdom, undergoing ajmaline challenge. We evaluated 6 variables including: sex, syncope, palpitations, previous cardiac arrest, baseline ST-elevation (STE; Type 2 or 3 Brugada pattern), and abnormal SAECG. We derived and validated a parsimonious model to predict the outcome of the sodium channel blocker challenge. The average age was 43±15 years (61% male). 100 patients (40%) had a cardiac arrest, 54 (22%) had syncope, and 24 (10%) had palpitations prior to assessment. 83 patients (33%) had baseline STE and 20 patients (8%) had a positive procainamide challenge. Univariate and multivariate analysis identified baseline STE (OR 50.7) and SAECG (OR 1.84 per parameter) to be associated with a positive procainamide challenge (see Table). A simple 2-factor, 6-point model derived using baseline STE (3 points) and SAECG (1 point per parameter) was strongly predictive of the procainamide challenge (AUC 0.876). This model was validated in a second cohort, and found to be moderately predictive of the ajmaline challenge (AUC 0.730). Patients that scored 0 were unlikely to have a positive test (100% sensitivity), and patients that scored 6 were very likely to have a positive test (93% specificity). In this combined cohort of 348 patients, we derived and validated a simple 2-factor, 6-point score that can be effectively used to triage the role of the procainamide and ajmaline challenge in patients with suspected Brugada syndrome. Our findings also highlight the utility and incremental value of the SAECG in stratifying patients with suspected Brugada syndrome, prior to a sodium channel blocker test. We identified two populations where the sodium channel blocker test could be avoided to prevent adverse events and ensure appropriate use of resources.