First of all when do you calculate an ventricular rate vs. an atrial rate? How do you know which one you want to calculate? (I know the SA node is in the right atrium and is the main pacemaker)
We are learning about ECG/EKG interpretation in class. One of the class of the class objectives is to calculate the rate for regular and irregular rhythms. I got the regular part down fine (count the # of QRS complexes in 6 seconds and X10, my teacher said this can not be used for irregular rhythms but "ECG made incredibly easy says it can be used for both...just not very accurate right?); its the irregular rhythms that confuse me. It just seems like unless it is a regularly irregular rate there is no way to determine an irregular rate unless you count for an entire min of strip; yet this is what one books says to count the # large boxes and divide into 300 or count the number of small boxes and divide into 1500; give a rate range (slowest and fastest rate)...so a range is sufficient when the teacher asks to calculate the rate of an irregular rhythm and only gives a 6 second strip?
Feb 28, '09
You've got it right, take the number of QRSs in 6 seconds and multiply by 10. Because the rate is irregular you're not going to get an exact rate. That is unless you print a minute of strip and count, which is a little silly. The better way for calculating an irregular rate is the 300, 150...method. Counting each big box you get 300, 150, 100, 75, 60, 50. Counting from the first complex count the big boxes to get your rate range.
This link gives a visual for this: http://medinfo.ufl.edu/~ekg/Rate%20and%20Rhythm.html
Technically you shouldn't use the x10 method, but it gives you a quick idea of how fast the rate is going. Hopefully your instructor will take a range, because it is near impossible in a 6-second strip to get an exact rate.
Feb 28, '09
thanks; and the website really help!
one more question. I am looking at a a-fib strip in the book, it says, "one of the first things you notice is that the ventricle rhythm is irregular"....ummm not I don't; I mean I see that it is irregular, but how do I know that it is a ventricular rhythm rather than an atrial rhythm when looking at a strip??
Feb 28, '09
not all the atrial beats showing up on the ekg may be getting through the av node. if atrial cells are excited and firing off pulses from different sites too fast only one pulse can go through the av node at a time (think of the av node as a turnstile that accommodates customers single file). if two pulses from two different sites of the atrium arrive at the av node at the same time, they both might show up on the ekg monitor, but only one gets through the av node to complete its cycle and go on to become a qrs wave. remember there is also a recovery time before ventricular cells can respond to the next electrical impulse. some p waves die waiting.
a ventricular rhythm will have no p waves before it that initiate it. a ventricular rhythm is when the ventricle of the heart is beating on its own--it's getting no p wave stimulus coming through the av node to stimulate it so an ectopic pulse in a cell in the ventricle will fire off creating its own electrical stimulus wave. this is a compensatory mechanism. isn't the heart a wonderful organ? ventricular stimulated beats will be much slower than atrial stimulated ones. if the atrium is sending out pulses but they are not getting through the av node there will be av dissociation and you can literally get a rate for the p waves and a rate for the qrs waves. the qrs waves will be palpated as pulsations at the patient's pulse points on their body.
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