I implemented via custom amp template. More info on that here.
Add to your head:
<script async custom-element="amp-analytics" src="https://cdn.ampproject.org/v0/amp-analytics-0.1.js"></script>
And right after your opening body tag:
<amp-analytics type="googleanalytics">
<script type="application/json">
{
"vars": {
"account": "YOUR_TRACKING_ID"
},
"triggers": {
"trackPageview": {
"on": "visible",
"request": "pageview"
}
}
}
</script>
</amp-analytics>