stupid EKG question! how to calculate exact HR??

[nope80]

Stupid question, I know but how do you calculate the exact HR using calipers?

I know the 300 rule and the count the number of QRS's in six seconds, but those methods don't give an exact rate. I was wondering what the method is to calculate the exact rate, presumably using calipers?

Sorry for the stupid question, I have an exam coming up and am apparently having a brain fart.

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[amine2086]

Stupid question, I know but how do you calculate the exact HR using calipers?

I know the 300 rule and the count the number of QRS's in six seconds, but those methods don't give an exact rate. I was wondering what the method is to calculate the exact rate, presumably using calipers?

Sorry for the stupid question, I have an exam coming up and am apparently having a brain fart.

I am not a medical student yet, so take it for what it is worth:

Atrial rate can be determined by measuring the time intervals between P waves (P-P intervals). Ventricular rate can be determined by measuring the time intervals between the QRS complexes, which is done by looking at the R-R intervals.

There are different short-cut methods that can be used to calculate rate, all of which assume a recording speed of 25 mm/sec. One method is to divide 1500 by the number of small squares between two R waves. For example, if there are 22 small squares between two R wave, HR is 1500/22, which equals 68 beats/min. Alternatively, one can divide 300 by the number of large squares (red boxes in most diagrams). If there are 4 large square between the two R waves, the HR would be 300/4 (75 beats/min). Another method, which gives a rough approximation, is the "count off" method. Simply count the number of large squares between R waves with the following rates: 300 - 150 - 100 - 75 - 60. For example, if there are three large boxes between R waves, then the rate is 100 beats/min. One must extrapolate, however, between boxes. Atrial rate can be determined like the ventricular rate, but using the P waves. Remember, if the heart in in sinus rhythm and there is a one-to-one correspondence between P waves and QRS completes, then the atrial rate will be the same as ventricular rate.

 

[Rendar5]

Stupid question, I know but how do you calculate the exact HR using calipers?

I know the 300 rule and the count the number of QRS's in six seconds, but those methods don't give an exact rate. I was wondering what the method is to calculate the exact rate, presumably using calipers?

Sorry for the stupid question, I have an exam coming up and am apparently having a brain fart.

Honestly, those methods give such a close approximation of the actual rate that you don't need to know anything more specifically, like ever. Especiallyconsidering that there will be beat-to-beat irregularity in even the most regular rhythms provided that someone is not being paced electronically (which would show up as pacer spikes on the EKG).

Not to mentionat that the 300 rule can actually be broken down by small boxes to give a more exact rate. For widely irregular rhythms, you can also count the number of QRS's in 10 seconds and multiply by 6 for something slightly more accurate.

If you have an extremely anal professor who expects you to calculate the rate within 1bpm because he likes to make students squirm despite this having absolutely no real world value, just find the average number of small boxes between beats, and add up the number of milliseconds per beat (each small box is 40). Then divide 60,000 (number of milliseconds per minute) by that number. There ya go. All done.

 

[csmmedic]

My fave is the 300 method. I know you think it is inaccurate but I have found this not to be the case. You can also print a 6 second strip if your using a monitor and count complexes, multiply by 10. In my experience, this method is not as accurate as the 300 method, however it is preferred if you have a AV block or irregular rhythm. Also, why is this even an issue? There probably does not exist a machine capable of printing out an EKG these days that does not calculate rate for you.

 

[J-Rad]

Yeah, I use the 300 divided by # of large boxes with each small box valued at 0.2. But seriously, what Rendar said. In addition to what Rendar said, the EKG machine generally gives a reasonably accurate HR on most rhythms. I just look at the machine read and save myself the effort most of the time. There are more important things to look at on an EKG than the rate most of the time, despite what those in love with mental masturbation might tell you.

 

[Bluesaurus]

The 300, 150, 100, 75 , 60, 50 method is great.

I think the multiplying by 6 thing is meant to get more accurate data on high heart rates and irregular rhythms.