QT interval correction in patients with cirrhosis.

INTRODUCTION: QT interval prolongation is a common electrophysiological abnormality in patients with cirrhosis. As QT interval varies with the heart rate, many QT correction formulas have been proposed, the Bazett's one being the most criticized because it over-corrects the QT interval and may be misleading. This study focused on the QT-RR relationship in patients with cirrhosis to derive a population-specific QT correction formula.

METHODS: One hundred cirrhotic patients of different etiology and severity and 53 healthy controls comparable for age and sex were enrolled. The QT-RR relationship was analyzed in patients by five regression analysis models to derive the population-specific QT-RR equation. The QTc was calculated and compared with those calculated by four common QT correction formulas (Bazett, Fridericia, Framingham, and Hodges). The correlation coefficient QTc-RR was calculated as a measure of the independence of QTc from the original RR interval.

RESULTS: In patients the QT-RR relationship was best described by the power equation "QT = 453.65 x RR1/3.02" (R2 = 0.41), similar to the Fridericia's formula. Bazett's formula led to the longest QTc (P < 0.0001), which was still significantly influenced by the RR interval (R = -0.39; P < 0.0001), while the estimated equation led to a QTc value not influenced by RR (R = -0.014).

CONCLUSION: Bazett's correction should be avoided in patients with cirrhosis because it still provides a rate-dependent QTc value and might be misleading, particularly when assessing the overall preoperative cardiac risk and the effect of drugs affecting the QT interval. In its place, our formula or that of Fridericia can be confidently employed.