technical cardiac question on HR

Daytonite, BSN, RN · Oct 18, 2007

I think this has to do with cardiovascular conditioning. It is well known that many atheletes have low heart rates. However, heart rates below 60 are not normal as I can tell you. I had a pacemaker inserted recently for sick sinus syndrome and heart rates that were down in the high 30's and 40's at rest. I always had a low heart rate in the 60s and often 50s.

danh3190 · Oct 18, 2007

The way the atrial repolarization was explained to us is that the wave would be buried in the QRS.

Also I suspect that it would be pretty small so not very visible anyhow (the height of the T wave is less than the QRS generally, and look how small the P wave is). When I've seen P waves alone (ventricular standstill after 3rd degree block) I haven't seen any repolarization waves, but the noise of the baseline would have hidden them.

Conrad283, BSN, RN · Oct 22, 2007

If you think about the A&P of how we (humans) function. Blood is circulated to organs and muscles to distribute o2 and carry wastes and whatnot. What are runners doing? Stressing their muscles. When muscles are tested they require more o2, so in preparation the body build more RBC's, and more hemoglobin. The more hemoglobin in the body, the more concentrated the blood is with o2. Inside the heart are baroreceptors that detect changes, and something called atrial naturetic peptide. They both detect changes in the body and can adjust the HR at any time. So the body builds up all of this hemoglobin to transport the o2 when the body is stressed, so when the body is at rest there is still an excess of these products so that the heart doesn't have to work as hard during rest.

Hope that makes sense.

queenjean · Oct 23, 2007

Your question about heart rate and the SA node is really interesting.

My husband used to be an a semi-pro athlete, and his heart rate was in the 40s and 50s. He had fellow athletes who had resting heart rates in the 30s. Now that he is just a normal Joe in terms of physical fitness, his resting heart rate is more in the 60s.

I never thought about it in terms of the SA node. Great question.

So Conrad, you are saying that the baroreceptors will override the SA node and cause it to fire less often than it's regularly programmed 60-100/minute? Did I understand your explanation correctly?

sharona97, BSN, RN · Oct 23, 2007

The U wave or the delta wave is seen in abnormal conduction at the Bundle of His as seen in WPW.(Wolf Parkinson White Syndrome)

EricJRN, MSN, RN · Oct 23, 2007

The delta wave is the curving (or "slurring") at the beginning of the QRS in WPW syndrome.

The U wave is something different - and it's a little bit of a mystery. It follows the T wave in some people, many of them completely normal people. Certain endocrine, neuro, electrolyte, and drug issues are associated with a U wave. You're more likely to see the U wave if a patient's heart rate is slow.

Here's a link:

http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson12/index.html

EricJRN, MSN, RN · Oct 23, 2007

And F waves are the sawtooth-shaped waves characteristic of atrial flutter.

sharona97, BSN, RN · Oct 23, 2007

I stand corrected! Thanks. I had never heard of an F wave before, but had known of the sawtooth pattern.

Conrad283, BSN, RN · Oct 25, 2007

So Conrad, you are saying that the baroreceptors will override the SA node and cause it to fire less often than it's regularly programmed 60-100/minute? Did I understand your explanation correctly?

Can't say for sure. If I run into the cardiac fellow at the hospital, I'll ask him.