Influence of age, the autonomic nervous system and anxiety on QT-interval variability

As QT variability increases and heart rate variability diminishes, the QT v ariability index (QTVI) - a non-invasive measure of beat-to-beat fluctuatio ns in QT interval on a single ECG lead - shows a trend towards positive val ues. Increased QT variability is a risk factor for sudden death. Aging leng thens the QT interval and reduces RR-Interval variability. In the present s tudy we investigated the influence of aging and the autonomic nervous syste m on QT-interval variability in healthy subjects. We studied 143 healthy su bjects, and divided them into two age ranges (younger and older than 65 yea rs). For each subject we measured two QTVIs: from the q wave to the end of the T wave (QTeVI) and to the apex of the T wave (QTaVI). Both indexes were calculated at baseline and after sympathetic stress. In 10 non-elderly sub jects, both QTVIs were determined after beta -adrenoreceptor blockade induc ed by intravenous infusion of propranolol or sotalol. The QTVI was higher i n elderly than in younger subjects (P < 0.001). QTVIs obtained during sympa thetic stress remained unchanged in the elderly, but became more negative i n the younger group (P < 0.05). QTeVI and QTaVI at baseline were correlated positively with age (P < 0.01) and anxiety scores (P < 0.05), but inversel y with the low-frequency spectral power of RR-interval variability (P < 0.0 01). QTVIs were higher in subjects with higher anxiety scores. In younger s ubjects, sotalol infusion increased both QTVIs significantly, whereas propr anolol infusion did not. In conclusion, aging increases QT-Interval variabi lity. Whether this change is associated with an increased risk of sudden de ath remains unclear. The association of abnormal QT-interval variability wi th anxiety and with reduced low-frequency spectral power of heart rate vari ability merits specific investigation. In healthy non-elderly subjects, acu te sympathetic stress (tilt) decreases the QTVI. beta -Adrenoreceptor block ade inhibits this negative trend, thus showing its sympathetic origin. Beca use a negative trend in QTVI induced by sympathetic stress increases only i n younger subjects, it could represent a protective mechanism that is lost with aging.