Bazett's QTc Prolongation as a Marker of Cardiac Autonomic Neuropathy in Diabetic Subjects.

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  • Kida Yasuo
    Department of Diabetes, Daini-Okamoto General Hospital

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  • 糖尿病心臓自律神経障害のマーカーとしてのＢａｚｅｔｔのＱＴｃ延長の問題点
  • トウニョウビョウ シンゾウ ジリツ シンケイ ショウガイ ノ マーカー ト シテ ノ Bazett ノ QTc エンチョウ ノ モンダイテン

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Abstract

Prolongation of the QT interval due to autonomic neuropathy has been considered a possible mechanism of sudden cardiac death in diabetic subjects, but the acuracy of QTc determined by Bazett's equation (BQTc) has come into question.Because significant inverse correlation between the BQTc and RR interval after conversion of QT by Bazett's equation (QT/RR1/2), alinear regression equation has been recomended in the Framingham heart study to determine QTc. Vagalneuropathy in diabetes tends to be associated withrelative tachycardia (RR interval shortening) and results in QTc overestimation when use BQTc in subjects with autonomic neuropathy. We determined QTc using a regression-based method (NQTc: QT+[1-RR]×143) as mentioned in the Framingham heart study. We compared the relationship of RR and QT and BQTc and NQTc between type-2 diabetes (group D) and age-matched controls (group N) with normal resting ECG. We also studied BQTc as a marker of diabetic cardiac autonomic neuropathy.(1) Theregression curve was linear and significantly positively correlated between QT and RR in both groups. On the contrary, the BQTc showed an inverse correlation with the RR in both groups. NQTc was independent of RR in both groups suggesting NQTc was appropriately adjusted for the heart rate (QT interval at 60 bpm).(2) NQTc is significantly longer in group D than in group N, and in women than in men.(3) Because of the significant correlation between.heart rate and RR-interval variation (CV) and orthostatic change in systolic blood pressure (ΔSBP), influence of these autonomic nerve functions on BQTc becomes less significant when adjusted to the heart rate. The relationship between NQTc and CV or ΔSBP is still consistent even after being adjusted for age, gender, and heart rate. This data indicates that previously reported QTc prolongation in subjects with autonomic neuropathy using Bazett's equation may be due, at least in part, to decreased RR interval induced overestimaiton of QTc. The simple measurement of NQTc based on the linear regresson curve could thus be a useful marker for evaluating QTc prolongation due to diabetic cardiac autonomic neuropathy.

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