Exercise induced (relative) bradycardia, heart rate drops during exercise

[darmaggi]

I've had a continuous issue with my heart rate dropping radically during exercise since April 2013, I am now 60 years old. I'm overall in good to excellent physical condition (5'11"/160 lbs.) as I exercise regularly, including weight training, cycling, and swimming. I first noticed an unexpected weakness in my legs during a spin class, and rapidly traced the issue to my heart rate. I now wear a heart rate monitor when exercising. The threshold heart rate that precipitates the event has varied over time, but generally I'll be exercising normally with a heart rate of anywhere between say 100 to 150 bpm when within one complete heart cycle my rate will drop to approximately half the preceding rate.  So if I was at 140 it drops to around 70, with an instantaneous resulting weakness felt in my legs. The triggering threshold heart rate has varied from being in the 140's, 130's, 120's, 110's, and even been as low as 100's, and seems to have gotten progressively lower over time. If I continue to exercise at the previous rate my heart rate will stay suppressed with some limited increase if I increase my effort but seems to top out at around 80bpm, if I back off the exercise rate substantially my heart rate will shortly return to the higher rate(usually anywhere from few seconds to half a minute). The triggering rate, the suppressed rate, and the recovery time all fluctuate on any given day.  Luckily, I've never passed out during these events. I've seen 3 cardiologists with the last one being an electrophysiologist, and they've all been baffled by what's going on.  My ekg shows a RBBB, right bundle branch blockage, and I have a history of rheumatic fever. I've worn a holter monitor, had an echo, and an echo stress test.  During my stress echo the usual event was triggered at 146 bpm and dropped to 76 then climbed to 84 where it stayed while the treadmill was at a 16% grade and 4.2mph until the recovery phase of the test. I've been an avid cyclist all my life, and average 20 miles a day and 30-40 on the weekend, so my resting heart rate is usually in the low 50's.  I believe the issue is (relative)reflex bradycardia in response to my baroreceptor reflex, although when it drops it's usually in the 60's or 70's, I've seen it drop below 40bpm.  My cardiac electrophysiologist is thinking my vagal tone is too high or hyper sensitive. He suggested trying an experiment with the anticholinergic scopolamine, which also would seem to be effective if in fact the issue is my baroreceptor reflex since it's acetylcholine that brings the heart rate down to control blood pressure. My blood pressure during the echo stress test went from a resting 122/83 to a max of 166/83.  Could all this have been precipitated by excessive blood pressure and aging? I've cut back on most anything I could identify that might increase my blood pressure overall, like coffee, salt, my medication of methylphenidate, but the problems persists. I have yet to start the trial with scopolamine, which the electrophysiologist believes, if effective would point to the diagnosis of excessive vagal tone/ baroreceptor reflex activity. The most baffling part for me is that this issue seemed to come out of nowhere, it didn't seem like a gradual reduction, also the variability of the triggering threshold rate has me concerned since it seems to have been going down over time....I'd be happy if the triggering rate these days was in the mid 140's, which would be 90% of my predicted maximum since I'm 60 years old. Anyone have any ideas as to the possible cause, other than the ones I've mentioned, or alternate therapeutic ideas?  Thanks,

[Ftuttle]

I am having very similar effects only when I road bike. I wear a HR monitor which indicates that my HR drops. It wasn't until I purchased an Alivecor KardiaMobile device and took readings immediately upon seeing my HR drop via my monitor. In actuality my HR starts beating erratically at a slower rate. I have many other symptoms including muscle weakness, loss in endurance, tiredness. I have seen 3 cardiologists of which the last diagnosed a condition that resulted in my getting a pacemaker. It has done nothing for my condition. I regret it every day. I was also on HCTZ for almost 2 years which I know caused my condition. Once I got off it, many other symptoms went away included really bad tacycardia. When i ride and see my HR drop via my monitor, I will stop riding and eait until my HR restores to normal which can take from 30 seconds to 15 minutes. It is vital to stop and let it recover by lying flat, standing , ie changing postures until restored. Potassium seems to help but not too much. I am now focusing on iron anemia to eliminate it as a cause. It all goes back to the HCTZ which flushed my system for too long, especially since i eould ride up to 80 miles at a time. I am interested in following others success here. Hope my small input helps.

[Tiffsterty]

Me too! I just started having this problem 10/2017. Had the heart monitor for 2 wks. Showed PVC’s but the dang company didn’t open up what was going on when I was exercising. I’m having the exact same thing you guys. During exercise, heart rate drop about half for about 90 secs and then back up. I too want answers. I miss working out. I have a stress test coming up soon.

[2210485]

Not good, stress test needed. 50% drop in heart rate at any point while exercising is not good at all. Stress tests get stopped and patients get refferred for immediate treatment for something like this.

Most likely explanation:

Rate dependent heart block.

Most likely fix:

Pacemaker.

[Tiffsterty]

Really? Not what I wanted to hear. I have an EPS in a week with possible Ablation. Doctor thinks it’s SVT atrial tachycardia. I really hope that’s the fix. But like the others have said, it’s getting worse and worse. Happened in the shower today while washing my hair and then drying off. Felt the fast HR and then drop. Thanks for answering.

[MRosenberg]

Darmaggi etal.,
I just came across this thread, and I am so glad. I have identical symptoms, not similar, but identical.  It started May 2017. Initially it was intermittent, but then became every day. Each week my trigger point was lower than the last, and once I hit that point my HR would abruptly drop. My HR would then settle in at a lower rate, no matter how fast I walked or when I go uphill. When I exercised my HR would go up to 135-145, with an average of 119.  My set point is currently 112-114, the new maximal rate is 103-104, and average HR for the exercise period is 90-94.  I should say my routine is a brisk walk/jog for 6-7 miles.  Now I am doing well if I can go for 6 miles.

I have been wearing a FitBit for 16 months so I have data to verify my experience.  Before the issue cropped up the plot of HR was smooth, with even transitions. Now it looks like a saw blade, the rates go up and down - it never holds steady. If I jog or go uphill there is a delay in my HR going up, but it does not go up beyond 104. Same going upstairs, my HR does not go up until I reach the top of the stairs.  

I have no orthostatic hypotension; in fact my BP has gone up, and it was well controled with HCTZ and Losinopril beforehand. I have been a well controlled type 1 diabetic for 53 years (now 64 years old).

Cardio stress test - perfusion studies showed no blockage, exercise 12 lead stress test was normal (except at the time it was done I reached a max of 132 bpm which was low for me, but felt the effort to reach that was more than what it should have been) cardiac echo showed some aortic stenosis, I have an obvious murmur, and RBBB.

Thyroid, adrenal-corticol, and other blood tests are all normal. My resting HR is 40-42.
While there is some overlap of symptoms to Cardia Autonomic Neuropathy, there are distinct differences. So it could still be some type of autonomic dysfunction. My potassium levels are normal. It could be an infectious disease, but none are known affecting only the heart.
My cardiologists seemed not to be convinced there is anything wrong, but then they are used to dealing with very sick cardiac patients.

So I hope you are still monitoring this thread and have some more insight into this disease. Maybe we could contact each other directly.

Regards,
Mike

[Tiffsterty]

I’m having the same issue but I’m in the beginning stages of trying to figure it out. Do you have better answers yet?

[Anglia0730]

Same here...I'm having problems with simple dance exercise as of this week. The dizzy, nausea sets in and legs become weak...hard to breath properly.  
When I spoke to the doctor in December 2015 about the type of exercise I was doing he never advised against it since I had been doing the same exercise since June 2015.  Now another report something is not working properly or more test.  

[Davemar]

I have the same issue. I am a 53-year-old male 6 foot 210 pounds I am an avid biker and I do spinning class 3 to 4 times a week.  When my heart rate gets to 160 it immediately drops to 70 to 80 I always thought it was my heart rate monitor. Last week I went to mayo clinic in Jacksonville and had a stress test and sure enough there was nothing wrong with my heart rate monitor.  I am presently wearing an event monitor. I would like to stay in touch with you and find out if you have any more information, and I will let you know what I hear from Mayo in 3 weeks when I meet with the cardiologist. You can reach me at ***@****

[darmaggi]

The trial experiment with scopolamine did nothing to normalize my heart rate, so the initial conclusion is that it wasn't a baroreceptor reflex to high blood pressure. I've also seen a second cardiac electrophysiologist who had no answers, and they always fall back on treating the symptoms with the suggestion of a pacemaker. As the years have progressed my usual threshold HR trigger has lowered from an initial 140-150 to now at times I can't go above 100-110 and then it drops into the 50-60 range instead of the 70's. Another fact that may or may not be important is it seems when the event is initially triggered the rate is normal until the drop, but the recovery, which usually takes longer now, is arrhythmic as it's recovering and until it normalizes at whatever the higher rate is depending on my level of exertion. The element I find most puzzling is the very definite nature of the threshold triggering rate on any given day whether it's 102 or 105, it's very exact and doesn't fluctuate from  where my system has decided that's where it's going to drop. I don't even have to be exercising per se any more, I could just be walking up stair or shampooing  my hair and it will happen. At this point it almost seems as though something has crossed the wires in my nervous system and my heart (rate) is doing the opposite of what it should be doing. I'm wondering if it could be hormonal because of the very definite nature of rates. I don't know if it was strictly electrical (RBBB or SSS) in nature that it would be so distinct and definite. I'm also guessing my general health and heart health (structurally) from regular exercise has a mitigating or masking effect, which is why when my HR drops into the low 40's and below while exercising I've never felt dizzy or passed out. The dysautonomia diagnosis could make sense, but again would the triggering and suppressed rates be so definite in that case as opposed to hormonal malfunction. I've got to look more into the idea of pre Parkinson's, and I've also found out that hypothyroidism runs in my family.

[darmaggi]

First couple of cardiologists I saw said they didn't think I was a candidate for beta blockers or a pacemaker....which I guess I was glad to hear, but I also was hoping for a little more intellectual curiousness as to the etiology. I guess the idea of too much exercise never really computed with me.  I suppose I could try laying off all exercise for a while to see if it can detune my cardiac system and the parasympathetic nervous system and my vagal tone. I'm grabbing at straws here, but my mom had hypertension and she wasn't obese, and she also had Parkinson's disease which is known for a dopamine & acetylcholine imbalance, so I was wondering if I could have early symptoms of PD without the tremors because I get so much physical activity, which they say is a natural antidote to the physical manifestations of the disease.

[itdood]

p.s., unexplained brady seems to increase with age, and the only way I know to deal with it is a pacemaker.  meds can't help.

[itdood]

Salt has been shown not to affect BP in caucasian males.

Low resting pulse is not necessarily an indicator of heart efficiency or health, I'm not athletic at all, my resting will be high 40s, low 50s.  

I can also induce a rapid rate change, like yours, with a  Valsalva maneuver.  I've done it.  

As more and more studies are being published about this, Hyper trained athletes are hurting themselves.  There can be too much exercise.  

It sounds to me like some sort of dysautonomia.  Dysautonomia is a crappy diagnosis though, because it doesn't define the root cause or address it.  It's like calling something a "syndrome".  We know the ANS is screwing up but we don't know why and we don't know how to fix it.

Sorry I couldn't offer better advice than the docs involved.  As I read it I'm thinking your ANS is sending your heart a sudden metric - ton of parasympathetic tone for some reason.  ..... dysautonomia.