HR not responding for Cyclist

I'm 1yr out from Bos Sci L131 Implant for Bradycardia & an avid cyclist with 150+ rides since using HR monitor and Power Meter on bike

Riding on same trail, using same power/speed, Sometimes my HR does not respond. 

Ex: Yesterday my HR hit a high of 113 and averaged 101 (yes i felt crappy and may have had some fatigue in legs),,,while on same trail/power my HR will hang out at my Upper Rate of 140.

Thoughts? Does a pacemakered heart respond differently when fatigued? I know pre pace, i would have a hard time getting HR up if i was fatigued.

1 Comments

Lack of appropriate RR from Boston Sci MV

by crustyg - 2024-08-23 18:42:24

To answer your question, the PM will drive your heart to the same rate (for any given sensor inputs and settings) as any other time - it doesn't 'know' that you are feeling tired.

There are a number of reasons why you may not get the HR that you expect when cycling (with RR mostly/exclusively driven by MV):

1 the MV feed into RR is the difference between short-term MV and the long-term MV: long term MV is locked while your HR is >90BPM (unless your device Fitness level is set to Endurance in which case it's 110BPM).  If you have any time with HR below 90BPM that long-term baseline slowly creeps up - the difference between the two gets smaller and smaller until it's too small to drive RR to any useful level.  A real problem for long rides with plenty of downhill sections, or in a decent peloton.  Fix: get MV sensitivity set to at least 12-14 and use the Vent Threshold set to 120 or 130BPM and Vent Threshold Response to 70%.

2 Interference with MV signal.  This is very sensitive to external magnetic fields (power transformers on roadside poles, magnetic braking on static bikes or local electrical noise.  Usually recovers when you move away.

3 Factors that affect *your* heart: I get atrial-derived tachyarrhythmias when cyling hard uphill and become too dehydrated - PM stops providing pacing outputs and cardiac output crashes. I stop immediately and drink whatever water / liquid I have on my bike.

4 MV vector change.  If you have MV SAM enabled (and you should), it can *sometimes* happen that this will trigger a vector change *and* an automatic MV calibration which can take up to 6hrs, during which time you will have *no* MV feed into RR => no fun on the bike.

5 Wenckebach HB: some people develop tachycardia induced HB (not always present) so that atrial pacing no longer produces 1 vent activation for each atrial activation.  Many/most of us with a PM have an underlying condition that is commonly progressive (not the CCHB folk), so while you may not have had this happen before it's now crept up on you. If this drop in HR becomes a common problem you need a Holter for 2-3days or perhaps a Linq Reveal to identify exactly what's happening.

There may be other factors personal to you that can cause lack of response to pacing.

Hope that helps.

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