Baseline characteristics of the cohort
| Characteristic | Overall (n=142) | Adult (n=58) | Paediatric/young (n=84) | P value |
| Clinical characteristics | ||||
| Female | 85 (59.9) | 38 (65.5) | 47 (56.0) | 0.298 |
| Onset age | 27±23 | 50±16 | 11±7 | <0.0001 |
| Current age | 34±23 | 58±16 | 18±10 | <0.0001 |
| Initial QTc interval | 504±44 | 507±51.2 | 501±38 | 0.510 |
| Family history of LQTS | 56 (39.4) | 21 (36.2) | 35 (41.7) | 0.601 |
| Family history of SCD | 22 (15.5) | 12 (20.7) | 10 (11.9) | 0.166 |
| Initial asymptomatic | 63 (44.4) | 24 (41.4) | 39 (46.4) | 0.608 |
| Initial syncope | 46 (32.4) | 13 (22.4) | 33 (39.3) | 0.045 |
| Initial VT/VF | 33 (23.2) | 21 (36.2) | 12 (14.3) | 0.004 |
| Syncope | 61 (43.0) | 24 (41.4) | 37 (44.0) | 0.863 |
| Syncope frequency | 0.96±1.44 | 0.81±1.25 | 1.06±1.56 | 0.519 |
| VT/VF | 52 (36.6) | 32 (41.4) | 20 (23.8) | <0.001 |
| Sustained VT/VF frequency | 2.3±13.0 | 2.6±9.7 | 2.1±14.9 | <0.001 |
| Annual VT/VF incidence rate | 0.6±2.6 | 0.6±1.6 | 0.5±3.1 | <0.001 |
| EPS | 6 (4.2) | 3 (5.2) | 3 (3.6) | 0.688 |
| Positive EPS | 4 (66.7) | 2 (66.7) | 2 (66.7) | 1.00 |
| ICD | 51 (35.9) | 33 (56.9) | 18 (21.4) | <0.0001 |
| Holter | 53 (35.9) | 14 (24.1) | 39 (46.4) | 0.008 |
| Arrhythmia in holter study | 33 (62.3) | 11 (78.6) | 22 (56.4) | 0.336 |
| Other arrhythmias | 29 (20.4) | 13 (22.4) | 16 (19.0) | 0.675 |
| Genetic test | 92 (64.8) | 23 (39.7) | 69 (82.1) | 0.069 |
| Positive genetic test | 77 (83.7) | 19 (82.6) | 58 (84.1) | 1.00 |
| Treadmill test | 48 (33.8) | 6 (10.3) | 42 (50.0) | <0.0001 |
| Positive treadmill test | 33 (68.8) | 3 (50.0) | 30 (71.4) | 0.112 |
| Schwartz score | 4.24±1.13 | 4.20±1.11 | 4.27±1.15 | 0.723 |
| Death | 9 (6.34) | 7 (12.1) | 2 (2.38) | 0.032 |
| Follow-up duration | 97.7±65.0 | 95.2±67.3 | 91.1±63.7 | 0.743 |
| Baseline ECG characteristics | ||||
| Heart rate | 76±24 | 70±19 | 82±27 | 0.041 |
| P-wave duration | 104±16 | 110±20 | 99±9 | 0.019 |
| PR interval | 161±30 | 169±28 | 155±30 | 0.005 |
| QRS interval | 97±22 | 104±26 | 90±15 | 0.004 |
| QT interval | 445±70 | 462±57 | 432±79 | 0.024 |
| QTc interval | 489±44 | 492±45 | 487±44 | 0.438 |
| P Axis | 55±41 | 66.7±49 | 44±30 | 0.005 |
| QRS axis | 56±59 | 48±73 | 65±39 | 0.012 |
| T axis | 53±55 | 68.1±69 | 39±32 | 0.090 |
| Lead V5 R wave amplitude | 1.17±0.65 | 1.15±0.82 | 1.18±0.42 | 0.361 |
| Lead V1 S wave amplitude | 0.70±0.42 | 0.65±0.42 | 0.74±0.42 | 0.298 |
| First degree AV block | 7 (4.9) | 5 (8.6) | 2 (2.4) | 0.236 |
| Interventricular delay | 17 (12.0) | 13 (22.4) | 4 (4.8) | 0.015 |
Bold values indicate P<0.05.
AV, atrioventricular; EPS, electrophysiological study; ICD, implantable cardioverter-defibrillator; LQTS, long QT syndrome; VT/VF, ventricular tachycardia/ventricular fibrillation.