Can anyone help me where I can find out more information about this condition and whether being a still fit and running runner should affect the approach to treatment?

After seeing my GP about suffering from occasional dizziness, I was sent off for a 24 hour ECG tape. This showed a number of short AV blocks (Grade 3) during the night, the longest of which (I think) was about 8 secs. I have seen a consultant, whose inclination was to fit a pacemaker but felt that it was not urgent as the blocks were asymptomatic and nocturnal. He did talk about the fact that athletes with low pulse rates (my resting rate is 46) sometimes have more pronounced irregularities at night but said (without explaining why) that he felt that these abnormalities could not really be explained by that alone. He sent me off for an exercise test, which was fine (whew!). The dizzy spells are unconnected, he thinks.

I am in my late 40s. I have trained regularly and enjoyed my running for 20 years. I am still running though rarely racing now. All this has been a bit of a shock. I feel that I need to make a big decision without really knowing enough. Should I really be having a pacemaker fitted to a heart because of irregularities which (the consultant implies) may not be a problem at all? Really, I suppose I want to find out more about the sorts of irregularities that might be normal (or, at least, harmless) for my sort of heart.

Any help would be most welcome. Thanks.