Table 1.
Demographic, clinical, and laboratory characteristics of patients and comparison of variables in subjects with and without long QT syndrome on admission
| Variable | Patients (n = 243) | Patients with LQTSa (n = 89) | Patients without LQTSa (n = 154) | p valueb |
|---|---|---|---|---|
| Age, years | 79.65 ± 8.27 | 81.79 ± 8.40 | 78.42 ± 7.96 | 0.002 |
| Males | 121 (49.8) | 55 (61.8) | 66 (27.8) | 0.004 |
| Body mass index | 25.32 ± 4.79 | 24.28 ± 3.22 | 25.92 ± 5.41 | 0.005 |
| Total number of drugs | 7.10 ± 3.04 | 7.62 ± 2.92 | 6.80 ± 3.07 | 0.043 |
| QT-prolonging drug usersc | 218 (89.7) | 84 (94.4) | 134 (87.0) | 0.069 |
| Number of QT-prolonging drugs | 2.04 ± 1.27 | 2.35 ± 1.25 | 1.86 ± 1.25 | 0.004 |
| > 1 QT-prolonging drug usersc | 156 (64.2) | 65 (73.0) | 91 (59.1) | 0.029 |
| > 2 QT-prolonging drugs usersc | 82 (33.7) | 40 (44.9) | 42 (27.3) | 0.005 |
| Chronic QT-prolonging drugs usersc | 165 (67.9) | 70 (78.6) | 95 (61.7) | 0.006 |
| List 1c drug users | 74 (30.5) | 32 (35.9) | 42 (27.3) | 0.157 |
| List 2c drug users | 25 (10.3) | 13 (14.6) | 12 (7.8) | 0.092 |
| List 3c drug users | 206 (84.8) | 79 (88.8) | 127 (82.5) | 0.188 |
| Serum potassium (mEq/L)d | 4.11 ± 0.58 | 3.96 ± 0.56 | 4.20 ± 0.58 | 0.002 |
| Serum calcium (mg/dL)d | 8.30 ± 0.81 | 8.13 ± 0.97 | 8.40 ± 0.69 | 0.013 |
| Serum magnesium (mg/dL)d | 1.91 ± 0.32 | 1.90 ± 0.38 | 1.92 ± 0.28 | 0.550 |
| Creatinine (mg/dL), median (IQR) | 1.21 ± 0.84 | 1.10 (0.75–1.61) | 0.88 (0.67–1.29) | 0.009 |
| Bradycardia (heart rate < 60 bpm) | 28 (11.5) | 10 (11.2) | 18 (11.3) | 0.915 |
| Hypokalemiad (< 3.5 mEq/L) | 23 (9.7) | 10 (11.2) | 13 (8.4) | 0.450 |
| Hypocalcemiad(< 8.0 mg/dL) | 63 (26.8) | 31 (34.8) | 32 (20.8) | 0.015 |
| Hypomagnesemiad (< 1.5 mg/dL) | 18 (7.9) | 9 (10.1) | 9 (5.8) | 0.222 |
| Hypercreatininemia (> 1.2 mg/dL) | 99 (40.7) | 43 (48.3) | 56 (36.4) | 0.068 |
| Hypertension | 152 (63.0) | 59 (66.3) | 94 (61.0) | 0.414 |
| Hypothyroidism | 18 (7.4) | 12 (13.5) | 6 (3.9) | 0.006 |
| Type 2 diabetes mellitus | 60 (24.7) | 24 (27.0) | 36 (22.6) | 0.532 |
| Acute coronary syndrome | 3 (1.2) | 2 (2.2) | 1 (0.6) | 0.556 |
| Dilated cardiomyopathy/heart failure | 34 (14.0) | 21 (21.8) | 13 (8.9) | 0.001 |
| Chronic ischemic cardiopathy | 43 (17.7) | 20 (22.5) | 23 (14.5) | 0.138 |
| Left ventricular hypertrophy | 52 (21.4) | 24 (27.0) | 28 (17.6) | 0.108 |
Data are presented as mean ± standard deviation or n (%) unless otherwise indicated
IQR interquartile range, LQTS long QT syndrome, QTc corrected QT interval
aDefined as QTc interval QTc ≥ 450 ms in males and ≥ 470 ms in females using Bazett’s correction formula
bThe two-tailed independent t-test or the Mann–Whitney test (in case of non-normal distribution) were used for continuous variables, whereas the χ2 test or the Fisher exact test (in case of n < 5) were used for categorical variables
cDrugs on admission, from https://www.crediblemeds.org
dSerum potassium, calcium, and magnesium levels available in 237, 235, and 229 patients, respectively. Outcomes: LQTS,b n = 89 (36.6%); QTc > 500 ms, n = 29 (11.9%); uncorrected QT, 406.92 ± 49.09 ms; heart rate, 76.02 ± 13.28 beats/minute; QTc, 453.70 ± 43.77 ms