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Phone conversation with an EP nurse yesterday: Me: Lately, on the treadmill, I've noticed the max heart rate I can achieve (@ 3mph) is 115 - 120. In the not too distant past, I could get my HR up to 145. Do I need my PM adjusted to permit a higher HR? Nurse's answer: "No, since you are taking Metoprolol, that's what is keeping your pulse from climbing any higher." (BTW, I've been taking 50mg 2X daily Metoprolol, aka Lopressor, for 2 years now).
I'm suspicious of her answer-----I'm under the impression my pacemaker is what controls heart rate (I am pacing 100% since an A-V node ablation 2.5 years ago.)

Any thoughts?
--Dave--

4 Comments

She's right

by Theknotguy - 2014-12-13 02:12:30

The Metoprolol is slowing your heart. While I was in cardiac rehab I could only get my heart rate up to about 115. Just couldn't get it to go any higher and I was on Metoprolol too.

Depending upon the time I took my meds, my heart rate would fluctuate on the treadmill. Some days I could get it higher, other days not.

Also had chronotropic incompetence because of the Metoprolol. It wouldn't let my heart beat accelerate as quickly as needed to match my exercise.

The PM will keep your heart going at the minimum - mine is set to 60 BPM. The computer algorithms in your PM will determine if you need a faster rate. If you go over the maximum setting - mine is 120 BPM - it will just sit there and observe.

For most of your activities the Metoprolol will limit your maximum heart rate. One exception being afib with RVR. Then your heart rate can go up above 120 BPM in spite of the Metoprolol.

Hope your cardiac rehab goes well.

Upper rate

by golden_snitch - 2014-12-14 02:12:54

All pacemaker's have an upper rate limit programmed, it can be sensor-driven or not. If you have the rate response sensor switched on, that's the max. rate that the sensor will do. If you do not have the rate response on, the upper rate limit is rather an upper "tracking" rate limit: the ventricular pacemaker lead tracks the sinus node rhythm up to this rate. The sinus node might go faster, but - provided that you have a complete, permanent heart block - the ventricles won't.

So, the fact that you used to be able to reach the upper rate limit does not necessarily mean that your pacemaker's rate response sensor is activated. As long as your sinus node works, it responds to activity. As I said before, normally a heart block patient like you does not have the rate response sensor switched on. So, when your heart rate increases during exercise, it's not the pacemaker that's responding to activity, but your sinus node, and all the pacemaker does is that it makes the ventricles beat at the same pace that your sinus node is running at.

Inga

Upper rate

by golden_snitch - 2014-12-14 03:12:36

Hi Dave,

the pacemaker only controls your heart rate when you exercise, when the rate response sensor is switched on. If it's not switched on, it keeps your heart rate from dropping below a programmed lower rate limit and it tracks the rhythm of the sinus node and makes your ventricles beat at the same pace.

Are you in permanent Afib or why did you have the AV-node ablation?

Usually, the rate response is not switched on in heart block patients; it's a feature that's mostly used for patients with a sick/slow sinus node.
So, if it's not switched on and you are on a betablocker (Metoprolol) this can cause the chronotopic incompetence that Theknotguy has already mentioned. If that's the case, it might help to switch the rate response sensor on. If it is already switched on, you could increase the upper rate limit and some other settings to allow your heart rate to go higher than 115-120.

Inga

Upper Limit II

by Dave H - 2014-12-14 12:12:23

Hi, Inga:
Months ago, while I was still on 50mg Metoprolol 2X daily, the EP I was seeing at the time had increased the upper limit to around 140 - a number I could easily reach while "treadmilling." Lately, it seems I cannot get much higher than 115 -120 max. As long as I don't dial in an "incline" I don't really get short of breath. -- PM does respond to the activity -- at rest I'm typically 82, within 5 minutes of excercise, I'll arrive at the 115 number. Only real change to my health lately was the hyponatremia (low sodium) issue of Oct & Nov - which my primary and ENT docs missed. (I'll be reviewing them on healthgrades shortly).

--Dave--

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