QRS amplitude and volume changes during hemodialysis

Background: According to several studies the QRS amplitude of the ECG incre ases during hemodialysis. The detailed background to this phenomenon has no t been defined. Two main mechanisms have been suggested: myocardial ischemi a and volume changes. New noninvasive technologies make possible a comparis on of ORS complex changes synchronously with myocardial ischemia and extrac ellular water (ECW)/blood volume (BV) changes during hemodialysis. Methods: In this study hemodialysis-related changes in body weight, biochemical blo od variables, BV, ECW, ST segment and QRS complex were analyzed in 15 patie nts (age 36-76, time on dialysis 0-6 years) undergoing chronic hemodialysis treatment. QRS complex and ST segment changes were measured using a dynami c vectorcardiographic monitoring system. The ECG parameters measured were Q RS vector difference (QRS-VD) and ST vector magnitude (ST-VM6). Bioimpedanc e analysis was used to detect changes in the ECW. Continuous measurement of BV changes was implemented using an on-line optical reflection method base d on the reflection of infrared light by erythrocyte membranes. Blood hemog lobin (B-Hb), hematocrit (B-Hcr), plasma sodium (P-Na), chloride (P-CI), ma gnesium (P-Mg), potassium (P-K), ionized calcium (P-iCa), phosphate (P-PI), creatinine (P-Crea) and urea (S-Urea) were monitored. Results: The mean QR S-VD increase during the dialysis session was almost fourfold (372 +/- 300% ) from 4.16 +/- 2.40 to 15.60 +/- 7.0 mu Vs (p < 0.001). This change was du e to a change in amplitude, since the duration of the QRS complex did not a lter significantly. The correlation between the changes in QRS-VD and body weight from the start to the end of the dialysis session was moderate and s tatistically significant (r = -0.55, p < 0.05). The correlation between the changes in QRS-VD and ECW varied from r = -0.67 to -0.97, being statistica lly significant in all patients (p < 0.001). The correlation between BV and QRS-VD was assessed at one minute intervals during the dialysis and varied from r = -0.22 to -0.98, being significant in 14 of the 15 patients (p < 0 .001). Significant ST segments alterations (ST-VM6 elevation > 100 mu V) di d not occur during dialysis. Laboratory parameters reflecting volume and os motic changes during hemodialysis correlated with QRS-VD change: B-Hcr(r = 0.56, p < 0.05), B-Hb (r = 0.63, p < 0.05), P-Na (r = 0.62, p < 0.05) and S -Urea (r = -0.62, p < 0.05). Conclusions: The increase in QRS complex ampli tude during hemodialysis is correlated to reduced ECW. The mechanism involv ed is most probably augmentation of electrical resistance of the tissues ar ound the heart caused by loss of interstitial fluid.