A judge who watched dramatic CCTV footage of Mark Rutter smashing his way though a security screen and lashing out with a pair of scissors said: “It is clear to me you must have terrified the two employees.”
One man was stabbed in the neck and another was punched as angry punter Rutter, 40, demanded his money back.
Defence QC Jim Keegan QC claimed that super-fast gaming machines - featured in a BBC Panorama programme - can rake in ten pounds a minute and had sparked violence throughout Britain.
The lawyer told the High Court in Edinburgh that many of the incidents went unreported because the operators did not want to jeopardise their profits.
Mr Keegan admitted: “I don’t say that excuses the level of violence which was used after the accused went across the counter and attacked the two men. But the machine was the catalyst.”
Judge Lord Uist noted that Liverpudlian Rutter had a record dating back to 1985 which included prison terms for burglary, serious assault and attempted rape.
Background reports - including an assessment prepared for Rutter’s defence team - branded him a high risk.
Lord Uist said it was clear that the conclusions opened the way for him to impose a life sentence - known as an order for lifelong restriction. The judge also ordered Rutter to serve at least two years and eight months before he can ask to be released.
Lord Uist warned him: “You must not assume that you will automatically be released at the end of that period.
“You will be released only when the Parole Board of Scotland is satisfied you are no longer considered to be a danger to the public.”
Footage from security cameras in a William Hill’s shop in Dalkeith, Midlothian, showed Rutter toppling the roulette-type machine which he had been playing.
It smashed into a gantry of TV screens showing horse races and other sports events.
Furious Rutter then smashed a security screen with his hands and pulled himself into the staff area behind the counter.
Advocate depute Richard Goddard, prosecuting, said Rutter was yelling: “I want my money back. Give me my £200 back.”
Rutter tried to open the tills then punched cashier Ryan Drummond on the head.
He then approached deputy manager Daniel Hardwick, armed with a pair of scissors.
Mr Goddard continued: “Mr Hardwick, fearing for his life, began pleading with the accused and shouted: ‘Don’t do it, don’t do it mate.”
But Rutter struck Mr Hardwick twice on the neck with the scissors, in spite of his attempts to ward off the blows.
Doctors later found one wound was superficial but the other was two centimetres deep and medics said it was potentially life threatening because it was so close to major blood vessels.
Another customer told Rutter the police were on their way and he fled with about £180 in notes and another £20 in coins.
Police answering the 999 call to the shop in Dalkeith’s High Street brought in a dog to help search nearby woods after reports of a man seen there, counting money.
Rutter was found sitting on a river bank and detained. He claimed he had been fishing. A thorough search of the area uncovered the bloodstained scissors - with DNA on the handle matching that of Rutter.
In court he pleaded guilty to a charge of robbery last August 23, which included assaulting Mr Hardwick to the danger of his life and assaulting Mr Drummond.
Lord Uist heard that Rutter, whose address was given as Castleview House, Craigour Place, Edinburgh, was in Scotland visiting a girlfriend.