1. Table 2: Baseline characteristics of patients by serum Mg levels
A Dose Relationship between Hypermagnesemia and QTc Interval Prolongation
© 2014 Mayo Foundation for Medical Education and Research
Chayakrit Krittanawong, M.D.1, Charat Thongprayoon, M.D.2, Thoetchai Peeraphatdit, M.D.1, Malcolm R Bell, M.B.B.S., F.RA.C.P1, Peter
Brady, M.B. Ch. B., M.D1, Vitaly Herasevich, M.D.2, PhD., Suraj Kapa, M.D.1, Samuel Asirvatham, M.D.1,3, Niyada Naksuk, M.D.1
1Department of Cardiovascular disease, 2Department of Anesthesiology, 3Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MN, USA
• Hypomagnesemia is thought to be
associated with acquired long QT
syndrome
• However, this association is based
only on a few small case series
• Objective: To evaluate quantitative
relationship between serum magnesium
(Mg) levels and QTc interval
Background
• A dose relationship between hypermagnesemia and
prolonged QTc interval was demonstrated
• Compared with the reference group, Serum Mg ≥2.4 and
2.2-<2.4 mg/dL were independently associated with a 2%
(OR 1.02, 95%CI 1.00-1.02) and a 1% (OR 1.01, 95%CI
1.01-1.03) increase in risk of lengthening QTc interval
• Compared with the reference group, Mg <1.8 and 1.8-<2.0
mg/dL were a protective factor (OR 0.98, 95%CI 0.97-0.98
and OR 0.99, 95%CI 0.98-0.99, respectively)
Mean serum magnesium levels, mg/dL
< 1.8 1.8-<2.0 2.0-<2.2 2.2-<2.4 ≥ 𝟐𝟐. 𝟒𝟒 P-value
Age, mean + SD, y 67+16 67+15 67+15 68+15 70+16 < 0.0001
Male, % 54 62 66 68 67 < 0.0001
White, % 86 85 84 84 84 0.44
Diabetes mellitus, % 32 27 26 28 35 < 0.0001
Hypertension, % 66 62 61 64 63 0.01
CKD, % 19 17 18 23 36 < 0.0001
CVA , % 7 7 6 5 6 0.54
AMI, % 50 55 51 48 35 < 0.0001
Cardiac arrest, % 8 10 9 7 10 0.08
Cardiogenic shock, % 7 9 9 9 12 0.01
ADHF, % 37 39 43 48 63 < 0.0001
K, mean + SD , mEq/L 4.1+0.4 4.1+0.4 4.2+0.4 4.3+0.4 4.4+0.6 < 0.0001
Ca, mean + SD, mg/dL 4.7+0.4 4.7+0.3 4.8+0.3 4.8+0.3 4.7+0.4 < 0.0001
Antiarrhythmic, % 22 27 30 29 33 < 0.0001
Beta-blockers, No. (%) 69 74 72 70 62 <0.001
Prolonged QTc meds, % 51 50 49 48 50 0.44
• Retrospective review of 8,512
consecutive patients who admitted to
the CCU at Mayo Clinic between
2004 and 2013 were included
• All patients had at least one Mg
level measurement during CCU
admission
• Mg levels of 2.0-<2.2 mg/dL were
the reference groups
• The primary outcome was the
association between levels of Mg and
the QTc interval
• Multivariable analysis adjusted for
age, sex, serum K and Ca levels,
antiarrhythmic and medications
known to cause QTc prolongation
was used to evaluate the association
between serum Mg levels and QTc
interval
Results
Methods
Figure 1: A dose relationship between mean serum Mg levels (mg/dL), mean serum
K levels (mg/dL), mean serum Ca levels (mg/dL) and mean QTc interval (ms)
Conclusions
• This finding suggests that hypomagnesemia was a protective
factor for QTc prolongation
• Contrary to conventional wisdom, we found a dose
relationship between hypermagnesemia and prolonged QTc
interval
• Further experimental studies of cardiac molecular physiology
between serum magnesium level and QTc interval are still
needed to verify our findings
Table 2: Baseline characteristics of patients by serum Mg levels