AV Block

[SJCzar]

After reading through the thread asking about Max Heart rates I noticed a bit of a sub topic on low heart rates.

I was wondering if any of you with the low rates, or SOs with low rates, also have an AV Block?

Since it's supposed to occur more often in athletic people I'm thinking that I must have some company here.

[Zen]

a blocked AV node?
I don't think many people have that. Low resting HR is due to the heart adapting as any other muscle does to exercise. It becomes stronger and pumps more blood volume in a single pulse. Not as many BPM are required to maintain the same blood volume.

How does your heart function with a blocked AV node?

[Jolt]

There are several different types of AV block:
-First degree, where the signal takes a little longer than normal to get from the atria to the ventricles but always does get through
-Mobitz 1/Wenckebach, where the signal gets delayed progressively longer until finally it doesn't get through (causing a skipped beat), and then this cycle repeats
-Mobitz 2, where the signal is delayed the same amount on every beat and then every few beats it doesn't get through
-2:1 etc. where for every 2 (or other number) signals from the atria only 1 (or other number smaller than the number of atrial signals) gets through to the ventricles
-Complete, where none of the signals from the atria get to the ventricles so the ventricles beat at their own slow backup rate that bears no relationship to that of the atria

As far as I know, the first two (first degree and Wenckebach, which are also generally not a big problem) are more common in athletes but I'm not so sure about the others. Which type are you asking about?

[Zen]

If the AV node is blocked, does the impulse continue down to the perkinje fibers? Wouldn't that cause the heart to not slow down?

And why would this be found in athletes?
It's somehow caused by exercise? Something like that sounds like it would almost be congenital.

The way I understand it, it would cause a faster HR (atria don't fully contract so they don't deliver what they should to the ventricles), not a slower one.

[Jolt]

If the AV node is blocked, does the impulse continue down to the perkinje fibers? Wouldn't that cause the heart to not slow down?

And why would this be found in athletes?
It's somehow caused by exercise? Something like that sounds like it would almost be congenital.

The way I understand it, it would cause a faster HR (atria don't fully contract so they don't deliver what they should to the ventricles), not a slower one.

If conduction is blocked in the AV node, the impulse does not continue down to the Purkinje fibers. The reason AV block causes a slower heart rate is because the impulse from the SA node in the right atrium (and this is the set of cells that discharges the fastest and therefore determines the heart rate, assuming normal conduction) is what normally stimulates the ventricles to contract. If this impulse can't get to the ventricles because of a conduction problem with the AV node (we're talking about complete AV block here, to keep it straightforward), the ventricles will not be stimulated by the SA node impulse but will still contract at the intrinsic rate set by their electrical cells which is much slower than that of the SA node. This is a sort of backup system that allows some blood to still be pumped to the body but it really doesn't work very well in comparison. The atria will still contract normally at the rate of the SA node.

As far as AV block being more common in athletes, I think it's just the first-degree and Wenckebach which as I said before are the milder types. The reason for the increased incidence in athletes has to do with increased action of the parasympathetic nervous system (via the vagus nerve) on the AV node, slowing its conduction. The other types of heart block have different causes that as far as I know are not affected by athletic conditioning, and there is such a thing as congenital complete AV block.

[SJCzar]

I guess I could have clarified my question more. Yes, first degree was the type that I was told was more common among athletes (but not caused by the exercise itself). So I figured if that statistic was accurate, and with the number of athletic women on these boards, there would be at least a few that had it.

I had not had any adverse effects from mine until recently when I had an incident where my rate dropped so low that I passed out. After a few days in the hospital and a repeat battery of tests I'm back to my normal routine. I learned to take the warning signs a bit more seriously next time .... before I get to the pass out stage.

Luckily I always feel my healthiest when I'm riding my bike so I don't have to stop doing that. Now I just need to convince my DH that I should probably quit my job and spend all day on my bike.

[Jolt]

I guess I could have clarified my question more. Yes, first degree was the type that I was told was more common among athletes (but not caused by the exercise itself). So I figured if that statistic was accurate, and with the number of athletic women on these boards, there would be at least a few that had it.

I had not had any adverse effects from mine until recently when I had an incident where my rate dropped so low that I passed out. After a few days in the hospital and a repeat battery of tests I'm back to my normal routine. I learned to take the warning signs a bit more seriously next time .... before I get to the pass out stage.

Luckily I always feel my healthiest when I'm riding my bike so I don't have to stop doing that. Now I just need to convince my DH that I should probably quit my job and spend all day on my bike.

Ugh, passing out is not cool! I almost did that a few weeks ago in clinical while watching a procedure (paracentesis, where they stick a big needle into someone's abdomen to drain fluid that has accumulated usually due to liver disease)--was fine until I started thinking about how painful it looked, next thing I knew I was really lightheaded, quickly checked my pulse and found it was really slow (like probably in the 30s!) and sat down before getting to the point of losing consciousness. Very embarrassing. Gotta love those vagal reactions--sometimes they happen in situations like that, and I know other people in my class who have done it as well. With your incident, what were you doing at the time and how did you know it was from a drop in heart rate? Did you get any sort of diagnosis? Here's hoping you don't have that happen again!

[Zen]

Jolt- thanks for the education we didn't go so far into conduction as the parasympathetic NS, just the SA-AV-Perkinje.

my mneumonic for that was to think of an advertisement for a grocery. It would say "SAAV a BUNDLE at Perkinje"

[SJCzar]

I fainted at the most convenient place ... on my doctor's exam table. I had went in because of a problem with my ear. She felt that overstimulation of the nerves when she was flushing out my ear helped bring on the fainting. My pulse and blood pressure would not come up enough, and after a few doses of anti-nausea meds I could still hardly stand to keep my eyes open. I had no strength to even try to sit up, so off to the hospital.

I had already been previously diagnosed with the AV block but they decided that they needed to monitor me further to be sure that I wouldn't randomly drop down to the fainting rate again. Besides all the usual blood tests, numerous EKGs, and ultrasound, they also ran another stress test to see if I'm still able to handle exercise well. Just like the last time I aced that test. My lungs always give out before my heart. I don't think they were able to get my heartrate above 152.