Yes, memory loss surrounding the hours/days of the treatment is the major side effect.
Care to share the meta-analysis? How does 1/39 compare to the base rate of those with severe depression who did not receive ECT?
The stats are from the Wikipedia page for ECT--I'm not sure about the base rate/risk ratio.
https://pubmed.ncbi.nlm.nih.gov/30557212/
About 1 in 50 patients may experience a major cardiac event (or death) during the course of ECT