Increased QTc dispersion is related to blunted circadian blood pressure variation in normoalbuminuric type 1 diabetic patients

A reduced nocturnal fall in blood pressure (BP) and increased QT dispersion both predict an increased risk of cardiovascular events in diabetic as wel l as nondiabetic subjects. The relationship between these two parameters re mains unclear. The role of diabetic autonomic neuropathy in both QT dispers ion and circadian BP variation has been proposed, but data have been confli cting. The aim of the present study was to describe associations between QT dispersion and circadian BP variation as well as autonomic function in typ e 1 diabetic patients. In 106 normoalbuminuric (urinary albumin excretion < 20 <mu>g/min) normotensive patients, we performed 24-h ambulatory BP (Space labs 90207) and short-term (three times in 5 min) power spectral analysis o f RR interval oscillations, as well as cardiovascular reflex tests (deep br eathing test, postural heart rate, and BP response). No patient had receive d (or had earlier received) antihypertensive or other medical treatment apa rt from insulin. In a resting 12-lead electrocardiogram, the QT interval wa s measured by the tangent method in all leads with well-defined T-waves. Th e measurement was made by one observer blinded to other data. The QT interv al was corrected for heart rate using Bazett's formula. The QTc dispersion was defined as the difference between the maximum and the minimum QTc inter val in any of the 12 leads. When comparing patients with QTc dispersion bel ow and above the median (43 ms), the latter had significantly higher night BP (114/67 vs. 109/62 mmHg, P < 0.003/P < 0.001), whereas day BP was compar able (129/81 vs. 127/79 mmHg). Diurnal BP variation was blunted in the grou p with QTc dispersion >43 ms with significantly higher night/day ratio, bot h for systolic (88.8 vs. 86.2%, P < 0.01) and diastolic (83.1 vs. 79.5%, P < 0.01) BP. The association between QTc dispersion and diastolic night BP p ersisted after controlling for potential confounders such as sex, age, dura tion of diabetes, urinary albumin excretion, and HbA(1c). Power spectral an alysis suggested an altered sympathovagal balance in patients with QTc disp ersion above the median (ratio of low-frequency/high-frequency power: 1.0 v s. 0.85, P < 0.01). In normoalbuminuric type 1 diabetic patients, increased QTc dispersion is associated with reduced nocturnal fall in BP and an alte red sympathovagal balance. This coexistence may be operative in the ability of these parameters to predict cardiovascular events.