Quick Navigation

QTc Intervals

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

Our evidence-based analysis on qtc intervals features 5 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
Last Updated:

Summary of QTc Intervals

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.

Easily stay on top of the latest nutrition research

Become an Examine Member to get access to the latest research. Get 150+ studies summarized for you across 25 different categories every month.

Members also have access to the Examine Study Database of 400+ supplements and their effects on 600+ health outcomes, as well as in-depth research analyses. Understand the whole body of nutrition and supplement evidence at a glance.

Get instant access — start your free 14-day trial

Already a Member? Click here to log in.


Human Effect Matrix

Unlocked for Examine Members

Easily stay on top of the latest nutrition research

Become an Examine Member to get access to the latest research. Get 150+ studies summarized for you across 25 different categories every month.

Members also have access to the Examine Study Database of 400+ supplements and their effects on 600+ health outcomes, as well as in-depth research analyses. Understand the whole body of nutrition and supplement evidence at a glance.

Get instant access — start your free 14-day trial

Already a Member? Click here to log in.


The Human Effect Matrix looks at human studies to tell you what supplements affect QTc Intervals.

Unlock the full Study Database with an Examine Membership. Get a 14-day free trial.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Supplement Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-c Minor - See study
One study in diabetic persons found shortened QTc intervals, suggestive of a cardioprotective effect.

Stay on top of the latest research

To unlock the full archives of our Study Database and research analyses, become an Examine Member today.

Start your 14-day free trial

Study Deep Dives

Things to Note

Also Known As

corrected QT interval

Click here to see all 5 references.