4.12

Novacode 4: borderline QT prolongation (QTc ≥ 450 ms men / ≥ 460 ms women, < 500 ms) — causes and medication safety.

Code 4.12 (Novacode NC-4) — moderate (borderline) prolongation of ventricular repolarisation. The heart-rate-corrected QT interval (QTc) is above the upper limit of normal, 450 ms in men or 460 ms in women, but below the 500 ms level that is considered marked prolongation. The risk of arrhythmia is lower than with marked prolongation, but the finding is a reason to look for a cause and to take care with medicines that prolong the QT interval.

Novacode 4QT intervalDrug safety

MenQTc ≥ 450 and < 500 ms

WomenQTc ≥ 460 and < 500 ms

Higher classcode 4.11 (≥ 500 ms)

Checkdrugs, K⁺, Mg²⁺, repeat ECG

Why the boundaries are fuzzy

QT values in healthy people and in people with congenital long QT syndrome overlap. QTc also varies with heart rate, the correction formula, time of day, meals and the measuring method (manual or automated). A single borderline value is therefore interpreted together with the clinical situation and, if necessary, confirmed with repeat ECGs. Novacode uses its own rate-adjusted QT index; this article gives the AHA/ACCF/HRS QTc thresholds.

Figure 1. At the same heart rate: normal QT (left) and moderately prolonged QT of about 470 ms (right) — above the upper limit of normal but below 500 ms.

Common causes

Medicines: antiarrhythmics, some antibiotics (macrolides, fluoroquinolones), antipsychotics, antidepressants, antiemetics, methadone
Low potassium, magnesium or calcium — for example due to diuretics, vomiting or diarrhoea
Slow heart rate, left ventricular hypertrophy, ischaemia, heart failure
Hypothyroidism, liver disease, eating disorders
Mild forms of congenital long QT syndrome

What to do

Usually sufficient

Review medications, check blood potassium and magnesium, repeat the ECG, avoid combining QT-prolonging drugs.

Needs specialist assessment

Fainting, seizures, palpitations, family history of sudden death or long QT, QTc rising on repeat ECGs.

Tell every doctor and pharmacist

If you have a prolonged QT interval, mention it whenever a new medicine is prescribed. Do not stop prescribed medicines on your own. Seek urgent care in case of fainting or palpitations.

References

Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241–e250. doi:10.1161/CIRCULATIONAHA.108.191096
Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation. 2010;121(8):1047–1060. doi:10.1161/CIRCULATIONAHA.109.192704
Vandenberk B, Vandael E, Robyns T, et al. Which QT correction formulae to use for QT monitoring? J Am Heart Assoc. 2016;5(6):e003264. doi:10.1161/JAHA.116.003264

This article is for general information and does not replace a consultation with a doctor. ECG findings must be interpreted by a physician together with symptoms and other tests.

Published on 14 May 2019

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