Background A combination of clinical and electrocardiographic risk factors is used for risk stratification in Brugada syndrome. In this study, we tested the hypothesis that the incorporation of latent variables between variables using nonnegative matrix factorization can improve risk stratification compared with logistic regression. Methods and Results This was a retrospective cohort study of patients presented with Brugada electrocardiographic patterns between 2000 and 2016 from Hong Kong, China. The primary outcome was spontaneous ventricular tachycardia/ventricular fibrillation. The external validation cohort included patients from 3 countries. A total of 149 patients with Brugada syndrome (84% males, median age of presentation 50 [38–61] years) were included. Compared with the nonarrhythmic group (n=117, 79%), the spontaneous ventricular tachycardia/ ventricular fibrillation group (n=32, 21%) were more likely to suffer from syncope (69% versus 37%, P =0.001) and atrial fibrillation (16% versus 4%, P =0.023) as well as displayed longer QTc intervals (424 [399–449] versus 408 [386–425]; P =0.020). No difference in QRS interval was observed (108 [98–114] versus 102 [95–110], P =0.104). Logistic regression found that syncope (odds ratio, 3.79; 95% CI, 1.64–8.74; P =0.002), atrial fibrillation (odds ratio, 4.15; 95% CI, 1.12–15.36; P =0.033), QRS duration (odds ratio, 1.03; 95% CI, 1.002–1.06; P =0.037) and QTc interval (odds ratio, 1.02; 95% CI, 1.01–1.03; P =0.009) were significant predictors of spontaneous ventricular tachycardia/ventricular fibrillation. Increasing the number of latent variables of these electrocardiographic indices incorporated from n=0 (logistic regression) to n=6 by nonnegative matrix factorization improved the area under the curve of the receiving operating characteristics curve from 0.71 to 0.80. The model improves area under the curve of external validation cohort (n=227) from 0.64 to 0.71. Conclusions Nonnegative matrix factorization improves the predictive performance of arrhythmic outcomes by extracting latent features between different variables.

Introduction Electronatomical mapping allows direct and accurate visualization of myocardial abnormalities. This study investigated whether high‐density endocardial bipolar voltage mapping of the right ventricular outflow tract (RVOT) during sinus rhythm may guide catheter ablation of idiopathic ventricular arrhythmias (VAs). Methods and Results Forty‐four patients (18 males, mean age: 38.1 ± 13.8 years) with idiopathic RVOT VAs and negative cardiac magnetic resonance imaging underwent a stepwise mapping approach for the identification of the site of origin (SOO). High‐density electronatomical mapping (1096.6 ± 322.3 points) was performed during sinus rhythm and identified at least two low bipolar voltage areas less than 1 mV (mean amplitude of 0.20 ± 0.10 mV) in 39 of 44 patients. The mean low‐voltage surface area was 1.4 ± 0.8 cm2. Group 1 consisted of 28 patients exhibiting low‐voltage areas and high‐arrhythmia burden during the procedure. Pace match to the clinical VAs was produced in one of these low‐voltage areas. Activation mapping established the SOO at these sites in 27 of 28 cases. Group 2 comprised 11 patients exhibiting abnormal electroanatomical mapping, but very low‐arrhythmia burden during the procedure. Pace mapping produced a near‐perfect or perfect match to the clinical VAs in one of these areas in 9 of 11 patients which was marked as potential SOO and targeted for ablation. During the follow‐up period, 25 of 28 patients from group 1 (89%) and 7 of 9 patients from group 2 (78%) were free from VAs. Conclusions Small but detectable very low‐voltage areas during mapping in sinus rhythm characterize the arrhythmogenic substrate of idiopathic RVOT VAs and may guide successful catheter ablation.

Aims Risk stratification in Brugada syndrome (BrS) still represents an unsettled issue. In this multicentre study, we aimed to evaluate the clinical characteristics and the long-term clinical course of patients with BrS. Methods and results A total of 111 consecutive patients (86 males; aged 45.3 ± 13.3 years) diagnosed with BrS were included and followed-up in a prospective fashion. Thirty-seven patients (33.3%) were symptomatic at enrolment (arrhythmic syncope). An electrophysiological study (EPS) was performed in 59 patients (53.2%), and ventricular arrhythmias were induced in 32 (54.2%). A cardioverter defibrillator was implanted in 34 cases (30.6%). During a mean follow-up period of 4.6 ± 3.5 years, appropriate device therapies occurred in seven patients. Event-free survival analysis (log-rank test) showed that spontaneous type-1 electrocardiogram pattern (P = 0.008), symptoms at presentation (syncope) (P = 0.012), family history of sudden cardiac death (P < 0.001), positive EPS (P = 0.024), fragmented QRS (P = 0.004), and QRS duration in lead V2 > 113 ms (P < 0.001) are predictors of future arrhythmic events. Event rates were 0%, 4%, and 60% among patients with 0–1 risk factor, 2–3 risk factors, and 4–5 risk factors, respectively (P < 0.001). Current multiparametric score models exhibit an excellent negative predictive value and perform well in risk stratification of BrS patients. Conclusions Multiparametric models including common risk factors appear to provide better risk stratification of BrS patients than single factors alone.

Aims An incomplete understanding of the mechanism of atrial tachycardia (AT) is a major determinant of ablation failure. We systematically evaluated the mechanisms of AT using ultra-high-resolution mapping in a large cohort of patients. Methods and results We included 107 consecutive patients (mean age: 65.7 ± 9.2 years, males: 81 patients) with documented endocardial gap-related AT after left atrial ablation for persistent atrial fibrillation (AF). We analysed the mechanism of 134 AT (94 macro-re-entries and 40 localized re-entries) using high-resolution activation mapping in combination with high-density voltage and entrainment mapping. Voltage in the conducting channels may be extremely low, even &lt;0.1 mV (0.14 ± 0.095 mV, 51 of 134 AT, 41%), and almost always &lt;0.5 mV (0.03–0.5 mV, 133 of 134 AT, 99.3%). The use of multipolar Orion, HDGrid, and Pentaray catheters improved our accuracy in delineating ultra-low-voltage areas critical for maintenance of the circuit of endocardial gap-related AT. Conventional ablation catheters often do not detect any signal (noise level) even using adequate contact force, and only multipolar catheters of small electrodes and shorter interelectrode space can detect clear fractionated low-amplitude and high frequency signals, critical for re-entry maintenance. We performed a diagnosis in 112 out of 134 AT (83.6%) using only activation mapping and in 134 out of 134 AT (100%) using the combination of activation and entrainment mapping. Conclusion  High-resolution activation mapping in combination with high-density voltage and entrainment mapping is the ideal strategy to delineate the critical part of the circuit in endocardial gap-related re-entrant AT after AF ablation.

Outflow tract (OT) premature ventricular complexes (PVCs) are being recognized as a common and often troubling, clinical electrocardiographic finding. The OT areas consist of the Right Ventricular Outflow Tract (RVOT), the Left Ventricular Outflow Tract (LVOT), the Aortomitral Continuity (AMC), the aortic cusps and the Left Ventricular (LV) summit. By definition, all OT PVCs will exhibit an inferior QRS axis, defined as positive net forces in leads II, III and aVF. Activation mapping using the contemporary 3D mapping systems followed by pace mapping is the cornerstone strategy of every ablation procedure in these patients. In this mini review we discuss in brief all the modern mapping and ablation modalities for successful elimination of OT PVCs, along with the potential advantages and disadvantages of each ablation technique.