QT/RR ratio from a paper rhythm strip
Photograph or import an ECG rhythm strip, place four markers, and compare the ratio with sex-specific reference cut-points. A measurement aid for clinicians.
Coming soon to the App Store
How it works
Capture.
Take a photo with the iPhone camera or choose one from Photos.
Place.
Drag four markers to the previous R wave, QRS onset, R wave, and T-wave end. Pinch to zoom for precise placement.
Calculate.
Choose sex and tap Calculate.
Compare.
See where the ratio falls against the reference cut-points, with a reminder of when to obtain a formal 12-lead QTc.
Why a ratio
QT and RR are measured on the same image, so paper speed, zoom, and camera distance cancel out. There is no calibration step, no grid counting, and no ruler.
QT/RR ratio = (T-wave end − QRS onset) ÷ (R − previous R)
Reference cut-points
At 60 bpm the QT/RR ratio equals the Bazett QTc in seconds, so published adult QTc limits can be restated as ratios at that rate.
| Sex | Within reference range | Borderline | Above cut-point | Above 0.50 |
|---|---|---|---|---|
| Men | ≤ 0.43 | 0.43–0.45 | 0.45–0.50 | > 0.50 |
| Women | ≤ 0.45 | 0.45–0.47 | 0.47–0.50 | > 0.50 |
References: Goldenberg I, Moss AJ, Zareba W. QT interval: how to measure it and what is "normal". J Cardiovasc Electrophysiol. 2006;17:333–336. Drew BJ, et al. Prevention of torsade de pointes in hospital settings. Circulation. 2010;121:1047–1060. Rautaharju PM, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, Part IV. Circulation. 2009;119:e241–e250. The ratio cut-points have not been independently validated.
Know the limits
The QT/RR ratio equals the QTc only at 60 bpm. Above 60 bpm it reads high and may flag a normal QTc; below 60 bpm it reads low and can miss a prolonged QTc. Use it in regular rhythm only, and obtain a formal QTc if the rate is below 60 or above 100 bpm or the result is not within range. Atrial fibrillation and other irregular rhythms, prominent U waves, bundle branch block, paced rhythms, and poor photos (glare, curvature, tilt) make the markers harder to place.
Practice strips
Four built-in synthetic strips with known values let you learn the workflow and compare your marker placement with the reference values, without a patient ECG.
Private by design
QTvision collects no data. Strip images are shown on your iPhone while you measure and are never saved. Only the numeric results you choose to save are stored, on your device only. No account, no tracking, no analytics. Read the privacy policy →
Intended use
QTvision is a measurement aid for qualified healthcare professionals. It calculates the QT/RR ratio from marker positions the clinician places and confirms on an ECG rhythm strip image, and displays sex-specific reference cut-points derived from published QTc limits. It is intended to help the clinician check a manual QT measurement they are already performing. It does not acquire or interpret ECGs, does not replace formal 12-lead QTc measurement or clinical judgment, and is not a medical device cleared or approved by FDA.
Made by a clinician
QTvision was developed by Craig Napolitano, MD, FACC, a board-certified cardiologist, and is made by ClinicianBuilt.