Introducing EP Calipers

epcalipersicon-180x180Ever since the 1990s, when computer-based electrophysiology (EP) systems were introduced, HV intervals and ventricular tachycardia cycle lengths have been measured in the EP lab by electronic calipers — simple but accurate measurements accomplished on-screen using a track ball or a mouse. Despite this, physicians still often carry a physical pair of calipers, perhaps preserved from the pre-Sunshine Act days when they were provided for free by drug companies. They use these calipers to measure heart rates and QT intervals on printed electrocardiograms (ECGs). But more and more, ECGs are viewed electronically. All physicians now use smart phones and frequently send and receive photos of ECGs or rhythm strips for analysis. For example, when I was on-call there would often be a patient who went into atrial fibrillation in the middle of the night, or a patient who would be due a dose of dofetilide (a potentially dangerous QT interval prolonging drug). The nurse would have a rhythm strip or ECG that needed analyzing and the easiest way to do that in the post-fax machine era was for them to take a photo with a smart phone and text or email it to me for analysis. Measuring heart rates or corrected QT intervals requires the use of calipers, but physical calipers don’t work well with smart phones — maybe even scratching the glass screen! Electronic calipers akin to those used in the EP lab would be useful to make accurate measurements on ECG and rhythm strip images.

I did not realize that there weren’t any apps (as far as I can tell) providing electronic calipers until this was pointed out to me by one of my Twitter buddies, Dr. Michael Katz. So I wrote an app, EP Calipers, that provides these calipers.

Making EP measurements on an iPad
Making EP measurements on an iPad
Measuring RR interval, iPhone 6 Plus
Measuring RR interval, iPhone 6 Plus
Amplitude measurement
Amplitude measurement
QT measurement with QTc calculation
QT measurement with QTc calculation
Multiple calipers, showing heart rate
Multiple calipers, showing heart rate

As the screen shots show, these calipers look just like those provided by EP recording systems, such as the GE (formerly Prucka) Cardiolab system. Multiple calipers can be used at the same time. Both time and amplitude calipers are available.  Unlike real calipers, it is possible to zoom images and make much more accurate measurements. Also unlike real calipers, it is easy to measure mean heart rates and calculate QTc intervals automatically.  The app makes the necessary calculations.

I am hoping these electronic calipers will be easy to use and helpful to anyone who has to deal with ECG recordings. This is the first iteration of the app and I am open to suggestions to improve it. Right now the app is available for Apple iOS (version 8.1 or higher required), but the Android version will be available Real Soon Now. Have fun measuring intervals electronically to your heart’s content!

About mannd

I am a retired cardiac electrophysiologist who has worked both in private practice in Louisville, Kentucky and as a Professor of Medicine at the University of Colorado in Denver. I am interested not only in medicine, but also in computer programming, music, science fiction, fantasy, 30s pulp literature, and a whole lot more.

11 thoughts on “Introducing EP Calipers

  1. I teach nurses cardiac rhythms. I am interested in have ecalipers for each strip to show PRI, QRS and rates. Currently the teching document is in word but could be changed to power point very easily. Would this product work for that. We review about 60 – 70 strips in the class. Could I have ecalipers enbeded with strip. Thank you

    1. Sorry for the late reply. Your comment went under the radar. The Mac and Windows versions of the app have a transparent window option so you can overlay the calipers over another window on the screen (e.g. Word document or PowerPoint).

  2. On windows for opening PDFs it says you must install ghostscript library and to look in help for more information. I didn’t see anything mentioned in help about it. I also tried to install the library and still can’t open PDFs.

    1. Sorry it isn’t working. The instructions are in the Images section of Help. But here they are: The download site is https://www.ghostscript.com/download/gsdnld.html
      Install either the 32 bit or 64 bit version of the Ghostscript AGPL Release depending on your computer. Right click on This PC in a file explore window and then properties to check if you have 32 bit or 64 bit windows installed to make sure you install the right version. Double click the exe file that is downloaded to install it. Restart EP Calipers. You should be able to open a PDF. If this isn’t working, please email me at mannd@epstudiossoftware.com. Let me know what version of Windows you have and what happens when you try to open a PDF.

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