[Factors related to the QT prolongation in chronic renal failure]

QT prolongation, a risk factor for arrhythmia and cardiac death, is observed in uremic patients. Though hypocalcemia, autonomic nerve dysfunction and cardiac hypertrophy are assumed to cause the uremic QT prolongation, the exact mechanism remains unspecified. We therefore examined factors related to the QT interval in chronic renal failure (CRF). Corrected QT interval (QTc) was significantly prolonged in CRF just before the induction of dialysis therapy (group A) compared with nephrotic syndrome with the intact or mildly impaired renal function (group B). QTc was also prolonged in acute renal failure (group C). Cardio-thoracic ratio, serum albumin and Ca correlated with QTc in group A, but not in B or C. A single HD session in group A failed to shorten QTc, despite a significant increase in serum Ca++. Autonomic dysfunction did not appear to be a major determinant of QT prolongation, since QTc was not different between diabetics and non-diabetics in group A and in chronic HD patients (group D). In group D, QTc did not correlate with SV1 + RV5 on ECG or left ventricular wall thickness (LVWT) on echocardiography. In another group of chronic HD patients (group E), there was no significant correlation between QTc and the parameters of left ventricular mass, plasma brain natriuretic peptide (BNP). However, in the patients subjected to repeated echocardiography in group D, QTc and LVWT changed in parallel. In a retrospective analysis of QTc in group D, QTc was maximally prolonged at the time of starting HD therapy, and gradually improved in the following 1-5 years in both diabetics and non-diabetics. In contrast, chronic CAPD patients (group F) revealed no improvement of QTc. Thus, uremic QT prolongation cannot be explained simply by any of the previously assumed factors, but appears to be affected by multiple factors, which are partially correctable by chronic HD therapy.