ECG criteria
- Measure QT from the beginning of the QRS complex to the end of the T wave in the lead with the clearest T-wave boundary (usually II or V5–V6), but check other leads as well and take the longest reliably measured value; if the end of the T wave is unclear, use the tangent method, and do not include a clearly separated U wave in the measurement.
- Calculate QTc using Bazett's formula: QTc = QT / √RR (RR in seconds); in cases of pronounced tachycardia or bradycardia, additionally rely on Fridericia's formula.
- In the absence of secondary (acquired) causes of QT prolongation, evaluate QTc using the revised Schwartz score: QTc ≥480 ms on repeat 12-lead ECGs = 3.5 points, 460–479 ms = 2 points, 450–459 ms (in men) = 1 point; a clinical diagnosis of LQTS is supported by a total score of ≥3.5 points taking into account symptoms and family history.
- Keep in mind that values of 470 ms (men) and 480 ms (women) in some normative tables denote the upper limit of normal / 99th percentile rather than an independent diagnostic threshold — evaluation is always performed using the Schwartz score, symptoms, and family history.
- QTc ≥500 ms is a marker of a substantially increased risk of torsades de pointes regardless of sex, especially in the presence of additional risk factors (bradycardia, electrolyte disturbances, medications); it does not mean that arrhythmia is inevitable in a particular patient.
- Evaluate T-wave morphology: broad, rounded, fused with the onset (LQT1); low-amplitude, broad, notched, or biphasic (LQT2); normal shape with a late onset following a long isoelectric ST segment (LQT3) — morphology is only roughly correlated with genotype and does not replace genetic testing.
- Exclude acquired causes of QT prolongation (hypokalemia, hypomagnesemia, hypocalcemia, QT-prolonging drugs, marked bradycardia) before interpreting it as a congenital syndrome.
- Compare the ECG with the history (syncope, seizures, family history of sudden death) and hearing (preserved in Romano–Ward syndrome, unlike Jervell and Lange-Nielsen syndrome).
What it looks like on ECG
The basis of diagnosis is a prolonged QT interval corrected for heart rate (QTc). QT is measured from the beginning of the QRS complex to the end of the T wave in the lead where the T-wave boundary is most distinct — usually II or V5–V6, but it is worth checking several leads and using the longest reliably measured value. If the end of the T wave is unclear or the T wave is fused with a U wave, the tangent method is used (a tangent to the steepest part of the descending limb of the T wave to the intersection with the isoelectric line); a clearly separated U wave is not included in the measurement.
Correction using Bazett's formula: QTc = QT / √RR. In tachycardia, Bazett's formula overestimates QTc, and in bradycardia, it underestimates it; therefore, in doubtful cases, Fridericia's formula is additionally used as a guide.
T-wave morphology is only roughly associated with genotype, frequently overlaps between subtypes, and does not replace genetic testing:
| Genotype | T-wave morphology | Arrhythmia trigger |
|---|---|---|
| LQT1 (KCNQ1) | broad, rounded, fused with the onset | physical exertion, swimming |
| LQT2 (KCNH2) | low-amplitude, broad, notched, or biphasic | sudden sounds and emotional stimuli; increased risk in the postpartum period |
| LQT3 (SCN5A) | normal shape, but late onset following a long isoelectric ST segment | sleep, rest, bradycardia |
The rhythm is usually sinus, and moderate sinus bradycardia for age is possible. T-wave alternans is recorded in some patients — a rare nonspecific marker of electrical instability; its absence does not rule out the diagnosis, and its independent prognostic value is limited. When a prolonged QT interval is detected in the setting of syncope, episodes of polymorphic VT such as torsades de pointes are sought on prior tracings or Holter monitoring.
Mechanism
The underlying cause is mutations in cardiomyocyte ion channel genes, most commonly potassium genes (KCNQ1 — LQT1, KCNH2/HERG — LQT2) or a sodium gene (SCN5A — LQT3). A reduction in repolarizing potassium currents (IKs in LQT1, IKr in LQT2) predominantly slows phase 3 of the action potential, while an increase in late sodium current in LQT3 disrupts the plateau phase; in both cases, the action potential and QT interval are prolonged, and the exact contribution depends on the specific channel and LQTS subtype. Prolongation of repolarization promotes early afterdepolarizations (triggered activity) and repolarization dispersion between myocardial layers, which creates conditions for triggering torsades de pointes; the contribution of re-entry to the maintenance of arrhythmia is debated and should not be presented as the sole mechanism. Romano–Ward syndrome typically involves a heterozygous pathogenic variant causing LQTS without congenital deafness; biallelic variants, especially in KCNQ1 or KCNE1, can lead to Jervell and Lange-Nielsen syndrome with sensorineural deafness. Inheritance in Romano–Ward syndrome is autosomal dominant.
Causes
- Mutations in the KCNQ1 gene (LQT1) are the most frequent genotype
- Mutations in the KCNH2/HERG gene (LQT2)
- Mutations in the SCN5A gene (LQT3)
- The majority of genetically confirmed cases are associated precisely with these three genes; other, rarer confirmed forms have also been described, as well as candidate genes with limited or debatable evidence of association with LQTS
- A negative genetic panel test result does not rule out LQTS
- Autosomal dominant inheritance, incomplete penetrance — some mutation carriers have a normal QTc at rest
Differential diagnosis
- Acquired QT prolongation (due to medications, electrolyte disturbances, bradyarrhythmias) — a reversible cause is sought; hearing impairment and family history are not characteristic
- Jervell and Lange-Nielsen syndrome — prolonged QT plus congenital sensorineural deafness, autosomal recessive inheritance (or biallelic variants of KCNQ1/KCNE1)
- Short QT syndrome — QTc is shortened rather than prolonged
- A borderline QTc in an asymptomatic young woman does not automatically allow a diagnosis of LQTS, but it should not be called a normal variant without evaluating repeat ECGs, medications, electrolytes, family history, and the Schwartz score.
- Pseudo-QT prolongation due to T-wave fusion with a U wave — in T–U fusion, QT is measured to the end of the T wave using the tangent method, multiple leads are compared, and if necessary, the ECG is repeated or expert assessment is sought; a distinct U wave is not included in the measurement.
Clinical significance and management
Romano–Ward syndrome is dangerous due to the development of polymorphic ventricular tachycardia of the torsades de pointes type, which can progress to ventricular fibrillation and lead to syncope or sudden cardiac death, especially in young people during physical or emotional exertion.
When a prolonged QTc is detected, the physician must: exclude acquired causes (electrolytes — potassium, magnesium, calcium; QT-prolonging drugs), take a family history of syncope and sudden death, assess the probability using the Schwartz score on repeat ECGs, and examine first-degree relatives (cascade ECG screening). Genetic counseling and testing are recommended when LQTS is suspected, but a negative result does not rule out the diagnosis, and testing is not mandatory for clinical diagnosis — the diagnosis can be established based on repeat ECGs and the Schwartz score.
Further management falls within the competence of a cardiologist-arrhythmologist. Beta-blockers are the baseline therapy in most patients with a clinical diagnosis of LQTS. Implantable cardioverter-defibrillator (ICD) implantation is considered primarily after a survived cardiac arrest or ventricular fibrillation, as well as in recurrent life-threatening ventricular arrhythmias despite therapy; recommendations for physical activity and avoiding specific triggers are individualized based on the genotype and clinical picture, without tying to specific doses within the scope of a reference article.
Common interpretation errors
- Measuring QT in a lead with a low-amplitude or U-wave-fused T wave instead of the lead with the clearest T-wave boundary
- Using only Bazett's formula without correction for tachycardia or bradycardia
- Diagnosing LQTS based on a single borderline ECG without repeat recordings and evaluation of the Schwartz score
- Omitting acquired causes of QT prolongation (hypokalemia, medications) before interpreting it as a congenital syndrome
- Requiring genetic confirmation as a mandatory condition for diagnosis
1. Which feature distinguishes Romano–Ward syndrome from Jervell and Lange-Nielsen syndrome?
Jervell and Lange-Nielsen syndrome features congenital deafness (biallelic variants), whereas Romano-Ward syndrome preserves hearing.
2. Which QT measurement method is preferred when the T-wave end is indistinct or fused with a U wave?
When the T-wave boundary is indistinct, the tangent method is used—drawing a tangent to the downward slope of the T wave to its intersection with the isoelectric line, excluding a separate U wave.
3. How many points on the revised Schwartz score are awarded for a QTc ≥480 ms on repeat ECGs in the absence of secondary causes?
A QTc ≥480 ms on repeat ECGs without secondary causes corresponds to 3.5 points on the revised Schwartz score, which supports the clinical diagnosis of LQTS.
Frequently asked questions
How does Romano-Ward syndrome differ from Jervell and Lange-Nielsen syndrome?
Both are congenital long QT syndromes, but Romano-Ward syndrome has preserved hearing and an autosomal dominant inheritance pattern (heterozygous variant), whereas Jervell and Lange-Nielsen syndrome features congenital deafness and autosomal recessive inheritance, frequently due to biallelic variants in KCNQ1 or KCNE1.
What QTc is considered pathological in Romano-Ward syndrome?
In the absence of secondary causes, a QTc ≥480 ms on repeat ECGs awards 3.5 points on the revised Schwartz score, supporting the clinical diagnosis of LQTS. Values of 460–479 ms require taking into account symptoms, family history, and other score components. Thresholds of 470/480 ms in several normative tables denote the upper limit of normal rather than a universal diagnostic criterion by themselves.
Is Romano-Ward syndrome dangerous?
Yes, it increases the risk of polymorphic ventricular tachycardia of the torsades de pointes type and sudden cardiac death, especially during physical or emotional exertion, depending on the genotype.
Can a diagnosis be made from a single ECG?
A single borderline ECG is insufficient: acquired causes of QT prolongation must be excluded, family history and symptoms evaluated, repeat recordings performed, and the Schwartz score calculated. Genetic testing is recommended when LQTS is suspected, but its absence or negative result does not rule out the diagnosis.
Why is T-wave morphology important in LQTS?
The morphology and timing of the T wave appearance are roughly associated with a specific genotype (LQT1, LQT2, LQT3), but this relationship is inconsistent and overlaps between subtypes; therefore, morphology only helps to hypothesize the mechanism prior to genetic confirmation rather than replacing it.
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Related terms
More in the «Channelopathies and Cardiomyopathies» section
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
- Goldberger A. Clinical Electrocardiography: A Simplified Approach
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, 2009
- Orlov V.N. Guide to Electrocardiography
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.