Background: Patients with syncope or near syncope of unknown etiology represen t a great challenge to cardiologists. An initial symptomatic episode triggers a series of diagnostic analysis which remain unsatisfactory when negative. More in vasive tools such as electrophysiologic testing yield only partial answers to ri sk stratification while the complementary implantable holter diagnostics are not usually considered until a recurrent episode is documented. Objective: This stu dy targets predictors of significant cardiac rhythmic events in patients with a reported episode of syncope or near syncope presenting with negative diagnostics and electrophysiologic study results(EPS). A significant cardiac rhythmic event was defined as a combined end-point of(1) symptomatic AV block;(2) symptomatic conduction abnormalities requiring pacemaker therapy;(3) symptomatic sustained ventricular arrhythmia; and(4) sudden death.Methods: All patients undergoing EPS after a first episode of syncope or presyncope between January 1997 and Decembe r 2001 were included for analysis. The study population consisted of 329 pts(42. 6%women), 21 to 96 years old(mean 70±15 years) referred for an EP study for sy ncope or near syncope. Results: Of the 329 patients who underwent EPS, 305(92.7 %) had follow-up data. The population, mean age 70(±15 years) and composed of 42%women, presented with hypertension(51.5%), diabetes mellitus(14.4%), hype rcholesterolemia(30%), tobacco use(35%), a familial history of coronary heart disease(22%), history of stroke(4%), history of MI(12%), history of atrial fi brillation(10%), structural heart disease(17.4%), left ventricular ejection fr action 61(±11%) and ECG abnormalities(37%). These anomalies included right(RB BB) or left(LBBB) bundle branch blocks, left anterior fascicular block(LAFB), le ft posterior fascicular block(LPFB), bifascicular block(RBBB +LAFB) and traces of myocardial in farction. The mean follow-up was 31±20 months with 5%of patients recording significant cardiac rhythmic events(15 /305): AV block requiring pacemaker thera py in 7 patients, sinus dysfunction in 4, sudden death in 3 and ventricular tach ycardia in 1. Univariate analysis reveals structural heart disease, ECG abnormal ities and LVEF associated with the risk of significant cardiac rhythmic events d efined by the combined end-point. Multivariate analysis using a Cox model found that the only independent predictor of events was an ECG abnormality. The long -term risk of significant event in the subset with ECG abnormalities is of 10.6 %(12/113). If unexplained syncope recurrence was included in the combined end- point, ECG abnormality and LVEF were both determinants with a 13.3%(15/113) ris k of a arrhythmic events analysis in the subset of patients presenting with ECG abnormalities and Cox model found ECG abnormality as the only independent predic tor of event. Conclusions: This study demonstrated that an ECG abnormality is th e only predictive variable associated with a significant arrhythmic event in pat ients with a lone episode of syncope or near syncope and a negative EPS. Background: Patients with syncope or near syncope of unknown etiology represen ta great challenge to cardiologists. An initial symptomatic episode triggers a series of diagnostic analysis which remain unsatisfactory when negative. More in vasive tools such as electrophysiologic testing yield only partial answers to ri sk stratification while the complementary implantable holter diagnostics are not usually considered until a recurrent episode is documented. Objective: This stu dy targets predictors of significant cardiac rhythmic events in patients with a reported episode of syncope or near syncope presenting with negative diagnostics and electrophysiologic study results (EPS A significant cardiac rhythmic event was defined as a combined end-point of (1) symptomatic conduction abnormalities requiring pacemaker therapy; (3) symptomatic sustained ventricular arrhythmia; and (4) sudden death. Methods: All patients undergoing EPS after a first episode of syncope or pr esyncope between January 1997 and Decembe r 2001 were included for analysis. The study population consisted of 329 pts (42.6% women), 21 to 96 years old (mean 70 ± 15 years) referred for an EP study for sycope or near The population, mean age 70 (± 15 years) and composed of 42% women, presented with hypertension (51.5%), diabetes (51.7%), had follow-up data history of coronary heart disease (22%), history of stroke (4%), history of MI (12%), history of MI (14%), hypercholesterolemia Atrial fi brillation (10%), structural heart disease (17.4%), left ventricular ejection fr action 61 (± 11%) and ECG abnormalities (37%). These anomalies included right (RB BB) or left blocks, left anterior fascicular block (LAFB), le ft posterior fascicular block (LPFB), bifascicular block (RBBB + LAFB) and traces of myocardial in farction. The mean follow-up was 31 ± 20 months with 5% of patients reco rdingi cardiac cardiac dysfunction in 4, sudden death in 3 and ventricular tach ycardia in 1. Univariate analysis reveals structural heart disease, ECG abnormal ities and LVEF associated with the risk of significant cardiac rhythmic events d efined by the combined end-point. Multivariate analysis using a Cox model found that the only independent predictor of events was an ECG abnormality. The long -term risk of significant event in the subset with ECG abnormalities is unexplained syncope recurrence was included in the combined end-point, ECG abnormality and LVEF were both determinants with a 13.3% (15/113) ris k of a arrhythmic events analysis in the subset of patients presenting with ECG abnormalities and Cox model found ECG abnormality as the only independent predic tor of event. Conclusions: This study demonstrates that an ECG abnormality is th e only predictive variable associa ted with a significant arrhythmic event in pat ients with a lone episode of syncope or near syncope and a negative EPS.