Your understanding about the mechanism by which the K+ ions leak out of the cardiac cell during ischaemia is correct.
But, regarding the latter part, lets discuss what is the situation of K+ ions in a normal cardiac cell.
In a normal cardiac cell, the concentration of K+ ions is more inside compared to the outside of the cell (150mM inside as compared to 4mM ...
The answer is hypertrophy, but if the injury is disabling, then it will lead to muscle atrophy due to disuse. Note that body builders lift weight until causing minor injury.