AUTONOMIC MODULATION OF QT INTERVALS IN POSTMYOCARDIAL INFARCTION PATIENTS WITH AND WITHOUT VENTRICULAR-FIBRILLATION

The autonomic nervous system plays an important role in the genesis of sudden cardiac death. The aim of this study was to evaluate spatial a utonomic QT interval modulation at the myocardial level. Circadian pat terns of QT intervals and heart rate variability (HRV) components and their hourly linear correlations were determined by Halter recordings in 15 healthy subjects (controls), in 15 post-myocardial infarction (M I) patients resuscitated from ventricular fibrillation (VF) (VF group) , and in 15 matched infarction patients without a history of arrhythmi a events (MI group). QT intervals were measured in modified leads V-1 and V-5 individually at same stable heart rates during each hour and r elated to hourly measures of HRV. Controls had highly significant corr elations between QT intervals and the high-frequency component of HRV (parasympathetic modulation), and between QT intervals and low- to hig h-frequency ratio (sympathetic modulation) uniformly in both leads (r from 0.62 to 0,81, p <0,001), The MI group had impaired sympathetic mo dulation in VS (r = 0,34, p = NS), but had uniform and exaggerated sen sitivity to parasympathetic modulation, In the Vf: group the QT differ ence between V1 and Vg leads correlated with parasympathetic modulatio n (r = 0,401, p <0.05) and sympathetic modulation (r = 0.446, p <0,05) , Thus, normal subjects exhibit spatially uniform autonomic QT modulat ion. Myocardial damage can result in abolished, exaggerated, or region ally discordant QT modulation, and this may generate arrhythmic vulner ability. (C) 1998 by Excerpta Medico, Inc.