According to the American College of Cardiology website, an ICD is a small device which is inserted into the chest or abdomen and uses electrical pulses or shocks to help control life-threatening, irregular heartbeats, especially those that could lead the heart to suddenly stop beating.
Rugby Southland spokesman Mark Wilson said it had been a tumultuous week for MacDonald and his family and they were taking time to "regroup and reflect".
"He can walk around and all the tests that have come back so far have been negative for any damage, so I guess ... he's doing as well as he could be considering what's happened.
MacDonald's fiancee Michelle Notman this week posted a photo on Facebook of the couple at the Trevi Fountain in Rome, where people toss in coins for good luck.
"A bit of Trevi luck never goes astray!!! Bring it!!" she wrote. The couple have two sons.