QTc Intervals

Last Updated: March 16, 2022

The corrected QT interval (QTc) is derived from an electrocardiogram (ECG). Prolonged QTc intervals are a risk factor for potentially serious heartbeat problems.

examine-databaseExamine Database

The QTc interval, which is shorthand for “corrected QT” interval is part of an electrocardiogram (ECG), which allows clinicians to observe the electrical activity of the heart.

A normal ECG is shown in Figure 1. Notice that each part of the wave is labeled with the letters P, Q, R, S, and T. This clarifies what a QT interval is: it’s the distance between Q and T, and represents[1] the electrical depolarization and repolarization of the heart’s ventricles that makes for a heartbeat. These electrical currents are caused by ion channels opening and closing, letting charged ions into and out of heart cells. If these channels malfunction, this process can take longer than normal, which makes the QT interval longer. The thing is, everyone’s QT interval varies a little, so the QT is often corrected in a few ways, the most simple of which is the Bazett method, which divides the QT interval by the square root of the RR distance (also shown in Figure 1), which is a measure of heart rate. A QTc interval corrected with the Bazett method is considered prolonged[2] if it is greater than 450 milliseconds for men and 470 milliseconds for women.

Figure 1: The ABCs of QTc


A prolonged QTc interval is bad news, as it can lead to a serious heartbeat problem known as “Torsade de Pointes,” which is French for “turning of the points,” because the peaks in the ECG looks like they’re twisting around. Risk factors[3] for a prolonged QTc interval include age, electrolyte imbalance, and some drugs. A long QTc[4] interval as well as a short QTc[5] interval can be dangerous, as these indicate disruptions in the normal heartbeat rhythm and could lead to something as (relatively) harmless as dizziness, or as fatal as cardiac arrest.

Examine Database: QTc Intervals
What works and what doesn't?

Unlock the full potential of Examine

Get started

Don't miss out on the latest research

  1. ^Al-Khatib SM, LaPointe NM, Kramer JM, Califf RMWhat clinicians should know about the QT intervalJAMA.(2003 Apr 23-30)
  2. ^Goldenberg I, Moss AJ, Zareba WQT interval: how to measure it and what is "normal"J Cardiovasc Electrophysiol.(2006 Mar)
  3. ^Heemskerk CPM, Pereboom M, van Stralen K, Berger FA, van den Bemt PMLA, Kuijper AFM, van der Hoeven RTM, Mantel-Teeuwisse AK, Becker MLRisk factors for QTc interval prolongationEur J Clin Pharmacol.(2018 Feb)
  4. ^Long QT Syndrome
  5. ^Short QT syndrome
Examine Database References
  1. Chromium - Vrtovec M, Vrtovec B, Briski A, Kocijancic A, Anderson RA, Radovancevic BChromium supplementation shortens QTc interval duration in patients with type 2 diabetes mellitusAm Heart J.(2005 Apr)
  2. Bitter orange - Shara M, Stohs SJ, Smadi MMSafety evaluation of p-synephrine following 15 days of oral administration to healthy subjects: A clinical study.Phytother Res.(2018-Jan)
  3. Bitter orange - Min B, Cios D, Kluger J, White CMAbsence of QTc-interval-prolonging or hemodynamic effects of a single dose of bitter-orange extract in healthy subjectsPharmacotherapy.(2005 Dec)
  4. Bitter orange - Shara M, Stohs SJ, Mukattash TLCardiovascular Safety of Oral p-Synephrine (Bitter Orange) in Healthy Subjects: A Randomized Placebo-Controlled Cross-over Clinical Trial.Phytother Res.(2016-May)
  5. Energy Drinks - Gualberto PIB, Benvindo VV, Waclawovsky G, Deresz LFAcute effects of energy drink consumption on cardiovascular parameters in healthy adults: a systematic review and meta-analysis of randomized clinical trials.Nutr Rev.(2023-Sep-11)
  6. Energy Drinks - Lasheras I, Seral P, Alonso-Ventura V, Santabárbara JThe impact of acute energy drink consumption on electrical heart disease: A systematic review and meta-analysis.J Electrocardiol.(2021)