PACs and autonomic tone

[arthur]

I have PACs which occur at about a 1-5/min frequency on average and these have been established as due to PV foci (several). Given a normal heart rate (athletic) of about 40-45 bpm, the PACs can be troublesome at times...however, my question has to do with a factor which appears to control their presentation.

There are two situations which appear to block their production: (1) for hours after exercising (with the heart rate at a normal 45 bpm) they do not occur; but do resume subsequently.
(2) while lying prone they are significantly blocked, only to resume within minutes of sitting up or standing.

So, I'm wondering what's controlling the signalling between these PV foci and the heart's pacemaker...is it a physical phenomenon, ie, pushing tissues together or apart?
...or is it a function of the autonomic system, which I understand is altered for a while after exercising and while lying down?

I am aware of the increased likelihood of PACs surfacing while the heart rate is slower...but I don't think the above observations support that explanation...since after exercising. my heart rate's down while refractory to PAC production for hours.

Thanks for any insight you can provide.  Don't be afraid to be technical!

[arthur]

Premature atrial contractions (PACs) or atrial premature depolarizations (APDs) are the result of an extraneous electronic signal reaching the normal internal pacemaker circuitry causing the heart to go through its normal beat a bit early.  The result is that the early contraction doesn't have a normal volume of blood and is either not felt at all or felt very weakly.  It's followed by a normal beat, wherein an extra volume of blood is pumped (the result of the pause needed to get to the next normal beat)...this beat may be felt more strongly...thus the thudding effect.  The causation is the extraneous signal, and this signal can have a variety of sources;  the most popular source is a focus, ie, a bundle of electrically active cardiac cells typically located at the pulmonary vein connections behind the heart.  Foci can be found in other locations as well.  Foci are stimulated into stronger action directly or indirectly by a variety of chemicals, which include adrenaline and caffeine.  In addition, the general tone of the nervous system can influence how well the foci disrupt the normal beat.  And there is the effect of posture, which presumably reflects an alteration of sympathetic tone and changes the internal microenvironment surrounding the foci.  

So, in a nutshell, all sorts of things that stimulate or affect your nervous system will probably have some effect on foci and the sensitivity of the heart's pacemaker system.  Of course, this narrative is limited to a very brief synopsis of PACs/APDs caused by foci...there are a bunch of other ways one can get a heart to skip a beat, including the pressure of a tumor near the atria, valve problems, ischemia, etc etc...all conditions suggesting an underlying physical problem beyond the scope of a benign skip.  As I am certainly not a medical doctor and my narrative is based on personal research, please consider my comments as intellectual stimulation designed to catalyze further research on your part.

Thus, for the typical case of atrially-induced skipped beats, the  condition is one wherein an active focus or two is present, which will engender skips at varying frequencies.  Then there are the precipitating factors, which are ennumerated throughout these archives, and include the adrenaline rush, the caffeine (coffee or chocolate), sugar, alcohol, and lots of other things.  Most folks not interested in using drugs to control how sensitive the heart is to external noise, or in the ablation of these troublesome foci, will opt to control their diets...with varying success.  For most of us, there are good days and bad days, since these buggers go off for so many reasons, that no amount of controlled dieting or behavior can guarantee avoiding them completely.

[shirleyc]

I have been diagnosed as having PAC's these first started when I was pregnant and continued throughout my pregnancy and recovery from a c section they then seemed to disappear. Now after 6 months have started up again.  Is it normal for these to come and go with months in between occurances? Has anyone else had the same experience.  Also I can't seem tp pinpoint what makes them occur for me?  I am just trying to get more educated on what these PAC's are all about and how if possible to control them.  I also get short of breath and very tired after having a few in a row.

[madaboutyou]

Hello - sorry to intrude on someone else's question, but I've been trying to post my own since March and it wont allow me to.  I guess that means I can't have a doctor's opinion, but any of the other member's thoughts would be greatly appreciated.

I've been having odd feelings in my heart since March.  The occur at night, usually right before I fall asleep.  I went to the doctor, who listned to my heart for a bit and said it was either a PVC or PAC.  He did an EKG and found "one extra beat" (I guess that means per minute?).  As I'm in between insurance until school starts up again, he said to wait until I have my insurance back and then he'll do a Holter monitor.  He made it sound like it's no big deal at all.  After a month of this, the symptoms subsided and I figured I was fine to wait.  Now the feelings are back.  They wake me in the middle of the night.  Sometimes it hurts, but mostly it's just REALLY uncomfortable.  Unlike some of the other posters, mine last for hours.  Is there anything I can do?  Is there any cause for worry?  I find it strange that doctors can say, "It's nothing to worry about," when I'm so uncomfortable for so long.  I'd really appreciate anyone's thoughts.  Thank you!

[BillyboyAA]

I also have a slow resing rate about 45-50.  I just did a Holter Test and it came out about the same as it did 2 years ago. I always get so worried about it being so slow.  It used to always be 60-70 years ago before I got a gym membership and started about 5 years ago with 30-45 min of cardio workouts about 4-5 times a week. My average on the 2 yr. old Holter was 51 and the new one is 45.  I had a checkup with my cardiologist yesterday and his nurse practitioner came in before he did.  I guess this is something new.  She was nice but was looking at my chart and file and said I should go and get an EPS.  Because my heart rate during sleep was 31.  I thought this was ok for someone who is healthy and fit.  Needless to say, I was worked up when my doctor came in and stressed out.  He said she was mistaken and he would send me for an EPS if I were alot older and my heart rate was that low.  Also if my heart did not increase with excercise.  While I had the holter on my heart rate during a workout was 110.  I am not an Olympic athlete but I think I am pretty damn fit for a 33 year old.  I am 5'9" 155#.  I do however get lightheaded and a headache every now and then.  But he seems to think that is all anxiety and that I am too focused on my heart beat.  Anyone who has any advice or anything, please Email me at ***@**** and take care....

[jan]

HI Alex,
Thanks for your comments.  I guess I am a mule. LOL  
Wow, you certainly are athletic!!!  Of course I am just about twice your age. :oP  
I have been exercising for 3 yrs now.  I don't know what my heart rate is during exercise, I can't find it standing still most the time.  Even my drs. have difficulty finding my pulse, sometimes they just use the stethoscope.  I bet I don't reach the heart rate I should because I am on the atenolol and verapamil, after all it is to slow my heart rate down.  I was just made curious by this post and was wondering why the meds in combo with the exercise didn't bring my rate down that much.  My EP told my hubby at a recent visit that he had wanted to bring it down to the 50's, but he gave up on that.
I guess I am doing ok with the exercising anyway and at this age I am content to be a mule. LOL

[alexawesome1]

Hey Jan, just reading your comments.  If you're resting rate is 85 then 170BPM on a treadmill would surpass your 85% max goal.  There's nothing wrong with keeping a rate of 155-165 while jogging (this is average unless your really trained) or on a heavy incline on the treadmill. As for lowering your resting heart rate, everyone is different as Arthur has mentioned. You can train an mule all you want but you'll never get a race horse out of it! That's just a silly example (non directional off course).  I do the tread mill thing 4-5X per week at 40 minutes in additon to 40 minutes of weight training in addition to boxing, swimming, walking and constantly being active.  I've been doing this since the age of 10 (now 28), that would be considered athletic.  If you've just recently began your exercise regimen then lowering your resting heart rate will take some time, anywhere from 6 months to a few years, it depends on the individual and again the amount will vary.  If you feel well while your training then your doing it correctly.  Professional athletes are 10X more likely to experience arrythmia's or sudden cardiac death... It's like the stock market, you invest long term for long term benefits, if you survey 100 athletic people and a similar crowd of 100 "couch-potatoes", stats will show that the athletic bunch will have less occurances of heart and other diseases. Hope that helps... ***@****

[jan]

Thank you.  But if I went 2x's my normal bpm I would be beyond my max heart rate.  I am fit, I guess, but I could never play soccer. LOL  I don't know how fit is defined.  I am a 45 yr old f, 5'5" and 125lbs. Like I said I exercise on the treadmill. The formula I know is 220 - your age = max bpm and then 85% of that for your bpm during exercise.  If that isn't it, it is close. LOL  It is on this forum somewhere.
What I was wondering is, if doing that much on the treadmill, (which I thought was good, just not great) should've lowered my resting heart rate as it does to others as yourself. Esp given that I am on atenolol and verapamil.  I was just curious.

[arthur]

Athletes come in all sorts of sizes, shapes and abilities. Some, like me, are not professional, so they just exercise regularly, others only show up on weekends.  My understanding of "keeping in shape" and "being athletic" suggests that the heart needs to get to 2X your normal bpm for at least 20 min for at least 2-3 times per week in order to sustain your current fitness.  Anything more, and you should be able to increase that level.  In my case, for that one hour of running my head off, every other day, it appears that my fitness is sustained...and with added soccer games at a clip of one per week (during season) that fitness appears to increase.  You should check with your doc about the 20 min of 2X your normal bpm, but I believe it's considered pretty much a standard.

-Arthur

[jan]

At the risk of really sounding stupid, is that all you do and you are considered athletic? I assume you must do more than that.  The reason I am asking is because I know I am not athletic, but I do 45 mins on the treadmill, which includes 5 mins for warm up and 5 mins for cool down.  I do 2 miles and I do it every other day.  I can't seem to get above my current speed (which is laughable) or the time which is very frustrating, but I can live with it, too.  Ok, here's the gist of all of that, I am on a low dose of atenolol and verapamil for inappropriate sinus tachycardia (and ncs) and my resting heart rate is all over the place, but nowhere near low.  My last EKG it was 85 bpm.  I know you aren't a dr., but I know you are very informed, so I am wondering what do you think of that?

[arthur]

My exercise regimen consists of one hour of sprints/jogging (3-4 mi) on a soccer field every two days, skipping a session in the event of a game.  My heart rate drops to normal in a couple of hours (normal being around 45 bpm).  The PACs stay inhibited for several more hours. I should say that I get a slight increase in PACs during the first 10-15 min of exercising, in particular, when there are adrenaline surges due to sudden sprinting.

-Arthur

[alexawesome1]

Hello Arthur, I hope I'm not intruding but a I have a few questions relating to your post.  You mention that your athletic, hence the low resting HR. I too participate in routine sports and was wondering what kind of exercise program you follow? I find that after a work, it takes a few hours for my HR to return to resting, around 50-54 BPM.
***@****

Thanks, Alex.

[CCF-M.D.-RCJ]

Arthur,
I would agree that PACs likely are less present after exercise and while lying down due to a change in the autonomic tone (activity) of the nervous system.

My best theory is that after exercise and while supine, your sympathetic tone is withdrawn. The withdrawal of the sympathetic tone then leads to a lessening frequency of the PACs. One way to test this hypothesis would be to increase your sympathetic tone while supine, such as by drinking a caffeinated beverage or doing something stressful or frightening, such as watching a frightening movie.

Hope that helps.