Patients in peritoneal dialysis very often show elongation of the QTc interval. This can carry an arrhythmogenic risk that can be worsened by ischaemia or by electrolitic abnormalities.
We have measured the duration of the QTc interval and recorded a 24 h ECG Holter in 84 patients in peritoneal dialysis and we correlated the duration of QTc and the arrthymias with plasma levels of Ca++, PO4--, PTH, K+, Na+ and Mg++. Qtc was calculated on 12 leads surface ECG with the Bazzetts formula. Statistical analysis performed in SPSS version 10 for Windows (SPSS Inc., Chicago, IL, USA).
Mean QTc duration in dialyzed patients was 0.445+0.04 sec. 59 patients showed a long QTc (>0.45 sec).PTH was 344+25 pg/ml, Ca++ 9.27+0.11 mg/dl, PO4-- 5.5+1,5 mg/dl, Na+ 139,6+ 3,4 mMol, K+ 4.04+0.64 mMol/L,. Mg 2.52+043 mg/dl. We found at 24 h ECG Holter supraventricular arrhytmias in 41 patients, complex premature ventricular contractions in 45 patients, monomorphic premature ventricular contractions in 17 patients, non sustained ventricular tachycardia (NSVT) in 10 patients. We also found the following statistically significant positive correlations: QTc / P r= 0.045 p<0.05,QTc / PTH r= 0.077 p<0.02, QTc / Ca r= 0.076 p<0.02. 7 patients had sudden death and their QTc was 465+ 0,03 msec, 11 patients belonged to Lown class 4a or 4b and their QTc was 465+0,02 msec, 10 patients showed NSVT and their QTc was 464+0,03 msec. The 7 sudden death patients showed a NSTV and belonged to Lown class 4.
QTc is prolonged in the majority of patients with peritoneal dialysis. The QTc value is correlated with the plasma levels of PTH, PO4—and Ca++. To our knowledge this is the first study to examine the relationship between phosphorus and arrthymias in peritoneal dialysis patients. Long Qt seems to be correlated to increased prevalence of ventricular arrhytmias that may be in turn the cause of sudden cardiac death. The role of hyperparathyroidism and elevated levels of calcium and phosphates in the prolongation of QTc and in the alterations of ventricular repolarization has to be established with perspective studies.
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