If an issue is pending, it means it is not yet concluded or resolved. It is waiting for a decision or confirmation.
The results of the experiment are pending.
We have a few pending issues on which we need the CEO's input.
The cause of death is pending investigation.
There are two pending transactions in the bank account. or the transactions have been initiated, but have not yet finished
An impending event is one that will happen very soon. Impending often has a negative connotation (though not always):
The weather forecasters are advising people to stay home due to the impending storm.
The soldiers prepared themselves for the impending battle.
She faced her impending death with peace and tranquility.
My father is wrapping up his projects at work, in preparation for his impending retirement. (not a negative connotation; simply means that he will retire very soon)
For more positive events that will happen soon, we can use the word upcoming -"I'm looking forward to my upcoming trip!"