Table 4.
Longitudinal associations of serum calcium and ionized calcium with QTc interval in 146 incident dialysis patients after simultaneously adjusting for serum potassium, and the interaction between each serum calcium measure and serum potassium
| Variables | Multivariable* | Interaction | |
|---|---|---|---|
| QTc difference (95% CI), ms | P | P** | |
| Serum calcium and potassium in one model | |||
| Total calcium, per 1 SD decrease | + 0.12 (−0.008, 0.25) | 0.07 | 0.29 |
| Potassium, per 1 SD decrease | + 0.14 (0.04, 0.23) | 0.004 | |
| Ionized calcium and potassium in one model | |||
| Ionized calcium, per 1 SD decrease | + 0.21 (0.10, 0.32) | < 0.001 | 0.18 |
| Potassium, per 1 SD decrease | + 0.13 (0.04, 0.22) | 0.003 | |
| Serum calcium and magnesium in one model | |||
| Serum calcium, per 1 SD decrease | + 0.12 (−0.02, 0.25) | 0.08 | 0.19 |
| Magnesium, per 1 SD decrease | −0.02 (− 0.15, 0.12) | 0.82 | |
| Ionized calcium and magnesium in one model | |||
| Ionized calcium, per 1 SD decrease | + 0.21 (0.10, 0.31) | < 0.001 | 0.87 |
| Magnesium, per 1 SD decrease | + 0.01 (−0.13, 0.14) | 0.91 | |
| Serum potassium and magnesium in one model | |||
| Serum potassium, per 1 SD decrease | + 0.13 (0.04, 0.23) | 0.006 | 0.84 |
| Magnesium, per 1 SD decrease | −0.02 (−0.15, 0.12) | 0.79 | |
*Includes main exposures (calcium, potassium, or magnesium), age, sex, ethnicity, Charlson comorbidity index, non-dialysis systolic blood pressure, left ventricular mass index, and use of beta-blocker, renin-angiotensin-aldosterone system blockade, cinacalcet, and QT-prolonging medication. Model with ionized calcium also includes serum pH
**Interaction between calcium and potassium tested in a separate model