The Effect of Different Dialysate Magnesium Concentrations on QTc Dispersion in Hemodialysis Patients

Figures & data

Table 1. Baseline characteristics of the study patients.

Variables	Study subjects
Age (years)	53.7 ± 18.0
Male (%)	6 (27.3)
Black race (%)	9 (40.9)
Hb (low Mg session)	12.0 ± 1.0
Hb (normal Mg session)	12.1 ± 1.0
Kt/V (low Mg session)	1.5 ± 0.2
Kt/V (normal Mg session)	1.5 ± 0.3
Antihypertensive medications
Beta-blockers (%)	15 (68.2)
Loop diuretics (%)	4 (18.2)
Calcium channel blockers (%)	4 (18.2)
Alpha-blocker (%)	1 (4.5)
Comorbid conditions
Hypertension (%)	21 (95.5)
Diabetes (%)	9 (40.9)
Coronary artery disease (%)	4 (18.2)
Congestive heart failure (%)	3 (13.6)

Table 2. Changes of blood pressure, weight, electrolytes, and QT intervals before and after hemodialysis in low and normal dialysate magnesium concentrations.

	Low magnesium bath			Normal magnesium bath
	Before	After		Before	After
Variables	Mean ± SD	Mean ± SD	p-Value	Mean ± SD	Mean ± SD	p-Value
SBP (mmHg)	147.7 ± 21.8	125.0 ± 18.8	<0.001	143.8 ± 12.8	123.8 ± 13.4	<0.001
DBP (mmHg)	76.6 ± 10.0	68.7 ± 11.1	<0.001	76.1 ± 10.6	65.9 ± 11.0	<0.001
Heart rate (per min)	71.1 ± 9.0	82.3 ± 15.7	0.002	71.4 ± 8.8	82.8 ± 16.0	0.002
Weight (kg)	78.2 ± 14.3	76.0 ± 14.1	<0.001	78.4 ± 14.3	74.2 ± 11.7	<0.001
Na (mmol/L)	138.9 ± 2.7	139.5 ± 2.1	0.234	138.4 ± 2.3	139.2 ± 1.6	0.143
K (mmol/L)	4.8 ± 0.5	3.5 ± 0.4	<0.001	4.9 ± 0.8	3.4 ± 0.3	<0.001
Mg (mg/dL)	1.8 ± 0.2	1.2 ± 0.1	<0.001	1.8 ± 0.2	1.6 ± 0.1	<0.001
iCa (mEq/L)	2.4 ± 0.2	2.5 ± 0.2	0.117	2.5 ± 0.2	2.5 ± 0.1	0.134
HCO3 (mmol/L)	23.7 ± 3.3	26.7 ± 2.3	<0.001	22.7 ± 3.0	28.3 ± 2.4	<0.001
QTcd (ms)	76.3 ± 31.4	67.0 ± 24.9	0.145	65.9 ± 21.0	75.4 ± 21.7	0.120
QTc (ms)	444.2 ± 26.3	460.9 ± 26.8	<0.001	446.0 ± 32.9	460.0 ± 27.3	0.049

Note: SBP, systolic blood pressure; DBP, diastolic blood pressure; Na, sodium; K, potassium; Mg, magnesium; iCa, ionized serum calcium; HCO₃, bicarbonate; QTcd, corrected QT dispersion; QTc, corrected QT interval.

Table 3. Bivariate correlation coefficient of change in QTc and QTc dispersion with age and changes of blood pressure and electrolytes before and after dialysis in low and normal magnesium dialysate concentrations.

	Low magnesium bath				Normal magnesium bath
	ΔQTcd		ΔQTc		ΔQTcd		ΔQTc
Variables	r	p-Value	r	p-Value	r	p-Value	r	p-Value
Age (years)	0.07	0.75	0.28	0.20	0.12	0.60	0.01	0.97
ΔSBP (mmHg)	0.22	0.33	0.05	0.10	−0.25	0.26	0.31	0.17
ΔDBP (mmHg)	0.04	0.85	0.17	0.46	−0.26	0.24	0.38	0.08
ΔWeight (kg)	−0.12	0.59	−0.12	0.60	0.29	0.21	0.26	0.27
ΔNa (mmol/L)	0.34	0.13	0.02	0.94	0.15	0.49	0.01	0.95
ΔK (mmol/L)	0.03	0.89	0.25	0.26	−0.16	0.49	0.15	0.50
ΔiCa (mEq/L)	−0.08	0.74	0.15	0.52	0.05	0.82	−0.26	0.23
ΔMg (mg/dL)	−0.12	0.59	0.20	0.38	−0.14	0.55	0.23	0.31
ΔHCO3 (mmol/L)	−0.08	0.72	0.17	0.17	0.42	0.06	−0.33	0.15
Beta-blocker use^a	−0.05	0.84	0.02	0.92	−0.03	0.89	−0.34	0.08

Notes: Δ is the product of before minus after dialysis; SBP, systolic blood pressure; DBP, diastolic blood pressure; Na, sodium; K, potassium; iCa, ionized serum calcium; Mg, magnesium; HCO₃, bicarbonate.

^aCorrelation coefficient for beta-blocker is Spearman correlation coefficient.