Rollercoaster

George Newton, the man who contributed  much of the material regarding the interpreting heart rate recording during atrial fibrillation (AF) on the afibbers website [1], had left an interesting comment on my previous post on 27th June questioning whether my Polar RS800cx was a boon or curse.  As illustrated in my post on 28th February, some of my chaotic recordings had raised the spectre of AF, but due to various inconsistencies in the data, I was left in a quandary.  George’s initial conclusion was ‘Your data clearly looks like afib’. 

AF is widely regarded as enigmatic and unpredictable, but in his own experience, George had found that systematic monitoring  using various different methods ranging for simple manual recording of the pulse to recording the full ECG, can provide a large measure of control over the condition  He has virtually eliminated his own AF by adjusting intake of electrolytes and other supplements according to the frequency of premature contractions, which at least in his case, are a fairly reliable indicator of imminent AF.  

Although he has acquired experience of many different recording devices, he largely uses a Polar S810 (similar to my RS800cx) to record the rhythm abnormalities.  By comparison with full ECG recordings, he has established the R-R tachogram signatures of the various relevant abnormalities, including premature atrial contractions (PACs), premature ventricular contractions (PVCs) and AF itself. He has also assembled a body of useful information about the artifacts that can arise from poor electrode contact or movement

I myself have had several reasons for continuing to doubt whether or not I truly had AF. The most important piece of evidence had emerged during a recent relaxed run in delightful countryside in Leicestershire with my friend Marie (who had run in the London marathon with her husband a few weeks after she had been diagnosed with cancer, and has subsequently recovered well from surgery).  During our run through the Leicestershire country-side I was feeling quite relaxed, but when I glanced at my Polar monitor I noted that it was displaying a heart rate around 125 whereas I would have expected a rate of around 110 at that pace.  I immediately stopped to palpate my pulse.  It was regular apart from the decreasing  rate expected on cessation of running.  There was certainly so evidence of AF, so we continued on our way. 

When I got home I was dismayed when I examined the beat-by-beat record of my hear rate (the R-R tachogram).  It indicated a horrible chaotic rhythm throughout much of the run – though frustratingly, it had failed to record the data for about half of the duration of the run,  including the time when I had stopped to examine my pulse manually.  The only absolutely certain conclusion was that my Polar RS800Cx was not storing data properly.  It was impossible to determine if my heart was also malfunctioning.  Nonetheless, the normal manual assessment during a run in which the recorded segments of the tachogram showed a chaotic rhythm raised serious doubts in my mind about the reliability of the evidence for AF.

I had also been puzzled by two other features of my chaotic tachograms.  In the recording I had posted in February, careful inspection reveals that interspersed with the chaos are many brief periods (typically 5-15 seconds in duration) of what appears to be fairly normal sinus rhythm (figure 1).  In fact the heart rate is a little higher than expected for the pace.  Within the periods of apparently normal sinus rhythm, the average rate was 122 bpm compared with an expected rate around 115, but in the icy conditions on that December day, I would not have been surprised if my average heart rate was a little higher than usual as I struggled to remain upright.  However, the heart rate variability is also somewhat greater than usual. At this pace, I would normally expect a value of RMSSD (root mean square of successive R-R intervals, a measure of high frequency variability) of around 5 ms, but RMMSD is in the range 10-20 ms during the periods of apparent sinus rhythm.  I would usually compute RMSSD over a longer period than 10 sec, so this value should be interpreted with caution.  Nonetheless, it suggests excessive parasympathetic activity.    Thus my provisional (and very speculative) interpretation of the rhythm during this period is of a series of premature atrial contractions occurring against a background of sinus rhythm with excessive parasympathetic activity. 

R-R tachogram showing apparent premature atrial contractions interspersed within sinus rhythm

Secondly, on several of the occasions when I had recorded apparent AF, the average pulse was as low, or lower, than that expected for the pace.  It is hard to imagine that a chaotic rhythm could pump enough blood to allow me to continue to run comfortably without any increase in overall rate to compensate for the inefficient ventricular filling.

With these uncertainties in mind I sent two of my tachograms to George – the one showing interspersed periods of apparently near normal sinus rhythm, and one showing a net decrease in rate.  He was kind enough to search through his own records and produced a similar record which included periods of normal sinus rhythm interspersed within chaos.  On account of the fact that his AF episodes are symptomatic, he was quite confident that this was not AF.  He was also able to reassure me that overall rate would certainly increase rather than decease during true AF.  Meanwhile Henry Szwinto, who had commented on my post of 5^th June, had also sent me some traces of his experiences with AF while racing – confirming the dramatic increase in HR during AF.  As an aside, Henry achieved 2:41:11 in the London marathon this year and was 3^rd placed in the 50 year old veteran group.

So in this roller-coaster experience in which the evidence has swung to and fro, the pendulum is now swinging away from a diagnosis of AF, though I think that the evidence does suggest that I am prone to premature atrial contractions.   There are still a few puzzles.  Why did the early evidence indicate a strong association with use of the salbutamol inhaler which I use to control my asthma?  As the evidence of chaotic rhythms has continued to accumulate, it has become clear that salbutamol was only associated with chaotic rhythm in winter. On some occasions when I had used salbutamol, I had noted in my log that the paths were icy, as in the run depicted in figure 1.  Perhaps freezing temperatures increase the risk of both wheeziness and poor electrode contact; or perhaps salbutamol increases the risk of premature atrial contractions.   

At this stage I am fairly optimistic that I do not have AF.  I am still on the waiting list for a 3 weeks continuous ECG recording and I will await the outcome of that before attempting to reach a definitive conclusion.  If the picture is still ambiguous after that, I will happily accept that some uncertainties in life are inevitable, and it would be foolish to limit ones activities for fear of vague uncertainty.  The simple fact that elderly men have a substantial risk of AF already places me in a high risk group, and ambiguous evidence from a heart rate monitor scarcely adds to the level of risk.

With regard to the question of whether or not my HRM is a boon or a curse, I am fairly sure the answer is that  a trustworthy HRM with the capability of recording R-R tachograms is a boon – although my unreliable RS800cx has been something of a nuisance.  I did not send it back to Polar last week because I was eager to acquire as much information about both the behavior of the monitor itself and the behavior of my heart before relinquishing it, but I will send it back this week.

The important issue that this episode of chaos has brought home to me is the fact that for an elderly runner, the risk of AF is appreciable, and the consequences potentially serious.   Furthermore, the experiences of George Newton, and others who have learned how to monitor their heart rhythm in an intelligent manner, is that paroxysmal AF is not necessarily an enigmatic mystery, but might be amenable to control. 

And finally, while the association between endurance training and increased risk of AF remains a subject of debate, it seems to me very plausible that the sustained autonomic imbalance associated with over-training is likely to play a large role in determining whether AF becomes an intractable problem or resolves relatively harmlessly.  I will return to a more detailed discussion of this issue in further posts, but meanwhile, I am more impressed than ever by the importance of avoiding over-training.  So far, the evidence suggests that systematic monitoring of autonomic function by recording both HR and HRV is a useful way to minimize the risk.

So the answer to the question posed in my last post is that my particular Polar RS800cx was indeed something of a nuisance, but despite this, it taught me a lot, and I have little doubt that a reliable HRM with R-R recording capability is a worthwhile investment for any ‘serious’ elderly athlete*.  

* For monitoring autonomic funtion via measurement of HRV to minimise risk of over-training; not for diagnosing AF, which requires  a clinical-quality ECG recording interpreted by a qualified person.

 References

[1] http://www.afibbers.org/conference/session52.pdf