The lead of A♠ required declarer to ruff. Declarer has three remaining losing spades to deal with, as a dummy reversal does not look too promising after dummy's trumps have already been shortened. One of them can go on the K♣, but it is likely two further ruffs will be required. This looks a dodgy line as keeping control of the trump situation may prove to be impossible. A better line is to try and see if a friendly situation exists in the club suit. So declarer cashed the A and K♣, and was pleased to see the Q♣ come down. Now only one further spade ruff should be required in dummy. But some trumps need to be drawn first. Declarer cannot really cash A♦ and then another diamond,  as the holder of the K♦ may have a further trump to lead so killing the final spade ruff required. Declarer therefore led a low diamond, which not only retains ruffing ability in dummy, but also keeps control of the situation if a 4-1 diamond break is present. East won with the K♦ and made life a bit easier for declarer by exiting with a club, another diamond would have been better.West was forced to ruff and declarer over ruffed, trumped a spade and then cashed the A♦, gratefully seeing all of the diamonds had now been removed from the defenders hands. Now the J♣ could be cashed so declarer could get rid of the final spade. Declarer was left with four hearts and the final diamond and needed a singleton Q♥ to drop or a 3/2 heart break plus successfully picking up the Q♥. East had already shown up with 5 clubs, and two diamonds and was bound to have some length in spades.The odds were on shorter hearts in East's hand. The A♥ was cashed and the Q♥ successfully finessed  to land the only slam bid and made on the deal.