New formula for evaluation of the QT interval in patients with left bundle branch block

Harilaos Bogossian, Gerrit Frommeyer, Ilias Ninios, Fuad Hasan, Quy Suu Nguyen, Zana Karosiene, Dejan Mijic, Axel Kloppe, Hawal Suleiman, Dirk Bandorski, Melchior Seyfarth, Bernd Lemke, Lars Eckardt, Markus Zarse

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

Background Left bundle branch block (LBBB) and QT prolongation both are associated with a worse prognosis. LBBB lengthens the QT interval. To date it is not known whether QT prolongation during LBBB differs in repolarization from QT prolongation during narrow QRS.

Methods Sixty consecutive patients with sinus rhythm (SR) and narrow QRS underwent electrophysiologic study for ablation. In all patients, the intrinsic QRS,QT, and JT times were measured during SR, and ventricular pacing from both the right ventricular apex (RVA) and the right ventricular outflow tract (RVOT) caused LBBB. We determined prolongation of the QT during as compared to SR (ΔQT). ΔQT was then divided by the QRS length during pacing QRS (QRSb). This describes the percentage of the QRS duration at LBBB, which must be subtracted from the measured QT (QTb) to determine the modified QT interval (QTm).

Results The ratio of ΔQT to paced QRS was calculated as 48.3% (RVA) and 48.8% (RVOT) (mean 48.5%). The ratio intrinsic of JTi to paced JT was 1.0055 (RVA) and 1.0087 (RVOT). There was no significant difference in intrinsic JT vs paced JT (P =.2).

Conclusion Right ventricular pacing causes prolongation of the QT due to a paced LBBB without prolongation of the JT time. In our study, we showed that QT prolongation caused by LBBB constitutes 48.5% of the QRS width. This is the value that must be subtracted from the measured QT in LBBB in order to estimate the modified QT. Thus, the resulting formula for "modified QT" estimation in LBBB is QTm = QTb - 48.5%∗ (QRSb).

Original languageEnglish
Pages (from-to)2273-2277
Number of pages5
JournalHeart Rhythm
Volume11
Issue number12
DOIs
StatePublished - 1 Dec 2014
Externally publishedYes

Keywords

  • JT interval
  • Left bundle branch block
  • Long QT
  • QT formula
  • QT interval
  • QT prolongation

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