[Tachycardia-induced syncopes]

In 50% of the patients presenting with a syncope, the cause is cardiac. The incidence of sudden death with 24% is high in this group. Since most of the tachycardia-induced syncopes are due to ventricular tachycardia (VT), a careful diagnostic approach must be used. The possibility of a VT to end in a fibrillation is great, especially in the presence of a organic heart disease, which leads to a bad prognosis in such patients. The aim of a careful anamnesis and clinical history is to establish the presence of a cardiac disease. A Wolff-Parkinson-White syndrome, a long QT, an old myocardial infarction or a coronary artery disease (CAD) can be assessed by echocardiography (ECG). Stress testing is useful in evaluating a CAD and can possibly lead to a diagnosis when a VT or a supraventricular tachycardia (SVT) is induced. ECG is used to assess the cardiac ejection fraction and in the evaluation of a suspected right or left cardiomyopathy. The ambulatory ECG allow a diagnosis only in 2 to 3% of the cases. Nevertheless, the presence of more than 10 PVC/h and/or asymptomatic nonsustained VT is a predictor for sudden death in syncopy patients. Detection of late potentials has a sensitivity of 50 to 83% and a sensibility of 89 to 91% for the prediction of inducible sustained VT during electrophysiological studies (EPS) in patients with syncope. However, the usefulness of this technique is not fully established, since there is no significant difference in survival or recurrence of syncope between patients with and without late potentials. The EPS is an invasive technique and therefore used at the end of the investigations. The cardiovascular mortality is low (4%) in patients with a negative EPS. A treatment is mandatory in tachycardia-induced syncopes even when the cause is a SVT. Antiarrhythmic drugs are useful for the treatment of SVT. However, radiofrequency ablation of the accessory pathway is preferable, since the success rate is over 90%, and the side effects of chronic ingestion of antiarrhythmic drugs can therefore be avoided. Some VT can be treated successfully with drugs under the control of an EPS, but most of the patients must have the implantation of an internal cardiac defibrillator (ICD).