I have two ideas for you.
The first one is:
<hyperlinkbutton content="{Binding ECG}" navigateuri="/ECG.xaml" background="Aqua" />
Another idea is this:
<hyperlinkbutton navigateuri="/ECG.xaml" background="Aqua">
<hyperlinkbutton.content>
<datatemplate>
<textblock text="{Binding ECG}" />
</datatemplate>
</hyperlinkbutton.content>
</hyperlinkbutton>
Hope it helps.