Ventricular tachycardia (VT) is considered as the main cause for syncope after myocardial infarction (MI). Multiple other causes have been reported. When left ventricular ejection fraction (LVEF) is low (35%), the implantation of a defibrillator (ICD) is recommended. The mortality of these patients (pts) remains relatively high. The purpose of study was to evaluate the main causes implicated in syncope after MI and the clinical factors associated with the diagnosis.

363 pts, 307 men, 56 women, consecutively admitted for syncope and history of MI (> 1 month), without VT underwent echocardiography, Holter monitoring, head-up tilt-test, exercise testing, signal-averaged ECG, electrophysiological study (EPS) and evaluation of coronary status. They were followed 4 ± 2 years.

The presumed cause of syncope was attributed after EPS to a ventricular arrhythmia in 151 pts (monomorphic VT 88, ventricular flutter or fibrillation (VF) 63), to a supraventricular tachyarrhythmia (SVT) in 39 pts, to conduction disturbances in 24 pts; 57 pts had several electrophysiological abnormalities: 26 had inducible VT or SVT and coronary ischemia; hypervagotonia was noted in 8 pts with induced VT or SVT. In the case of negative EPS, coronary ischemia alone was identified in 41 pts, hypervagotonia in 27pts. All studies were negative and syncope remains unexplained in 86 pts (24%), mainly women (p<0.001)(27% vs 20%***). Male gender (90% vs 80%**), a longer QRS duration (139 ± 31 vs 115 ± 28 ms**), a lower LVEF (36 ± 11.5 vs 46 ± 12%***) and grade IVa,b of Lown on Holter ECG (53 vs 31.5%***) were associated with VT induction. LVEF < 40% and VT/VF induction were predictors of cardiac mortality, VT predictor of sudden death, low LVEF and advanced age predictors of death by heart failure.

Several causes were frequently implicated; therefore complete evaluation remains necessary. Coronary ischemia was present in 18% of patients with syncope after myocardial infarction; it was the sole cause in 11% of our population. Syncope remained unexplained more frequently in women than in men. Hypervagotonia explains syncope in only 8% of our population.