Hello Connor,
You may be aware already about these but I checked
Polar faq site where they mention something about arrhytmia:
"Polar products are not designed to detect arrhythmia or irregular rhythms and will interpret them as noise or interference. The computer in the wrist unit will make error corrections, so that arrhythmia beats are not included in the averaged beats per minute. The blinking heart symbol in the face of the unit, however, will continue to show all heart beats received. In most cases the Polar products will work fine for persons with arrhythmia. "
About that peak-to-peak meters. Most of them are little more expensive but they measure and saves every beat from the heart (Suunto T6 for example is that kind but it would not work underwater until it is under the suit close the belt).
At the Polar site they also mention that:
"Depending on the Polar product model and accessories used, the samples of your heart rate, speed, cycling cadence, power and altitude are stored in 1, 5, 15 or 60 second intervals. A longer interval gives you more recording time, while a shorter interval allows you to record more detailed data. A shorter recording rate uses the memory of the running and cycling computer up more rapidly. The remaining recording time is shown at the start of the workout or on the bottom row of the product display when setting the recording rate. The samples recorded during your workout are transferred to the software where they can be used to further analyse your training."
I also found these threads which may contain interesting information.
[ame=http://forum.polar.fi/showthread.php?t=603]Which Polar model would be good for regular swimming training? - Polar Forum[/ame]
[ame=http://forum.polar.fi/showthread.php?t=765]Heart rate of 217 while swimming??? - Polar Forum[/ame]
As I´m not anykind of specialist in this kind of technical stuff I may also be wrong
Hopefully this helps,
- kimmo