[Prolongation of the Q-T interval of the ECG: classification and clinical significance].

The extension of the Q-T interval of ECG can be accompanied by loss of consciousness and even sudden death. A unified approach is required to assess the normal duration of the Q-T interval. A table of maximum normal limits of the Q-T interval is given calculated with Bazett's formula with the coefficient K equal to 0.42. It is suggested to subdivide the extensions of the Q-T intervals according to the clinical manifestations with attacks of loss of consciousness and without them and also according to aetiology: congenital syndrome Jarvel-Lange-Nielsen and that of Romano-Ward, the acquired acute (intoxications, disorders of electrolyte balance, lesions of the central nervous system, myocardial infarction, myocarditis, medicinal reactions) and the acquired chronic (diffuse lesions of the myocardium, of the brain etc.). Personal observations of syndromes of extended Q-T intervals of different aetiology are given with attacks of ventricular tachycardia of the "torsade de pointes" type and ventricular fibrillation.