The validity of your old medical will not have changed as I recall. I.e. it will be for 5 years, but not past your 42nd birthday if that comes earlier.
You will then renew to JAR class 2, with the addition of ECG. This will be valid then for 2 years.
More details on <A HREF="http://www.jaa.nl/jar/jar.html" TARGET="_blank">www.jaa.nl/jar/jar.html</A>