Does sinus tachycardia while running mean I should take it easier?

Cross-posting for cardiology and running bc it's right at the nexus of the two:

Currently wearing the Zywie nano cardia event monitor for 14 days (on day 10). Two weeks ago I mentioned recent lightheadedness unrelated to activity to my GP, they did an in-office EKG and thought they saw an arrhythmia; Cardio was able to see me right away and their EKG did not show arrhythmia.
I mentioned I am currently training for a half marathon and would be ramping up my miles in next few weeks, so Cardio suggest I wear the Zywie for 14 days and keep training, log any symptoms, and then we'll discuss any findings. We are not able to meet for 2 more weeks and I will only be 2 weeks out from my half by then (so, most of the running is happening NOW).

I've worn the Zywie for 6 runs of various lengths (3 miles to 8 miles; one with very high winds; some with hills, some flats); twice, it has flagged my runs for prolonged sinus tachycardia for all or almost all of a run (the device report says "bpm >170). Considering we're looking for arrhythmia, I don't feel particularly worried to see this - but I also do usually have a low heart rate (in the 50s - when my athletic ability is not "elite") so to see this getting flagged over 170 bpm caught my eye.

So this is partly a running question and partly a cardio question: if I am often winding up in prolonged tachycardia while running, should I scale back on the effort? Does it mean I am pushing too hard, and should keep my HR elevated but not THIS elevated? Or, is this just a part of getting my heart stronger? When it does flag the runs, it's the WHOLE run (not just the portions with hills for example).

Will discuss with doctor when I see him in 2 weeks, and his office hasn't reached out, so I assume that because he knows I am running, they are seeing these results as not a big deal - but I want to be sure I am training smart, both for my heart and for my upcoming run.