US presidential candidate Senator Bernie Sanders was treated for a blocked artery after experiencing chest discomfort and has cancelled campaign events until further notice, an adviser said yesterday.

Sanders (above), 78, was in Las Vegas to campaign when he was taken to a hospital on Tuesday night for evaluation.

"He was found to have a blockage in one artery, and two stents were successfully inserted," Sanders senior adviser Jeff Weaver said in a statement.

"Senator Sanders is conversing and in good spirits. He will be resting over the next few days. We are cancelling his events and appearances until further notice, and we will continue to provide appropriate updates," Weaver said.

Sanders, the oldest of 19 contenders for the Democratic presidential nomination, had visited a community healing garden in Las Vegas on Tuesday night and had been scheduled to hold a town hall and appear at a gun safety forum yesterday.

Aides did not offer any guidance on how long Sanders might be off the campaign trail. The first nominating contest is not until Feb 3 in Iowa, but Sanders is one of 12 candidates scheduled to participate in the fourth Democratic debate in Ohio on Oct 15.

Sanders thanked supporters for offering well wishes and said on Twitter that he was "feeling good." He then shifted to a plug for his signature “Medicare for All” healthcare insurance plan.

"I'm fortunate to have good health care and great doctors and nurses helping me to recover," Sanders said. "None of us know when a medical emergency might affect us. And no one should fear going bankrupt if it occurs. Medicare for All!"

A democratic socialist, Sanders galvanised progressives during a 2016 run for president when he lost the nomination to Hillary Clinton, pushing the party to the left and popularising ideas such as “Medicare for All”, a proposal for a government-run healthcare plan based on the system for Americans over the age of 65.

The US senator from Vermont has been among the top contenders in the crowded field seeking the 2020 nomination to challenge Republican President Donald Trump.

His campaign cancelled at least US$136,000 in cable and US$600,000 in broadcast television spending following the news, according to Medium Buying, a company that tracks political ad spending.

The incident could renew questions about Sanders' age in a Democratic race featuring a generational divide between older candidates such as Sanders and front-runner Joe Biden, 76, and younger contenders such as Pete Buttigieg, 37, the mayor of South Bend, Indiana.

Common procedure

In a letter made public during the 2016 campaign, Sanders' doctor said he was in "overall good health" and had no history of cardiovascular disease.

The insertion of stents to open blocked heart arteries is a relatively common procedure, with as many as one million Americans a year undergoing it. After a balloon-tipped catheter is used to clear the blockage, stents - tiny, wire-mesh tubes - are used to prop open the artery.

Former Presidents Bill Clinton and George W Bush (photo) both underwent the stent procedure after they left the White House.

In general, recovery takes a few days, but how quickly Sanders will bounce back depends on his symptoms before he got the stents, said Dr Steven Nissen, a cardiologist at the Cleveland Clinic.

"People recover quickly, and assuming no complications, there is no reason why he could not get back on the campaign trail in a timely fashion," Nissen said.

Sanders had been running in second place in the Democratic race behind Biden, the former vice president, until last month, when a surge by fellow progressive and US Senator Elizabeth Warren of Massachusetts moved her ahead of Sanders in many opinion polls.

The campaign halt comes the day after Sanders reported a big US$25.3 million fundraising haul for the third quarter, putting him in the early lead in the closely watched campaign money race.

Sanders' Democratic rivals in the presidential race rushed to send him wishes for a speedy recovery.

"I hope to see my friend back on the campaign trail very soon," Warren wrote on Twitter.

A former mayor of Burlington, Vermont, Sanders won a US House of Representatives seat in 1990, making him the first independent elected to the House in 40 years. In 2006, he won a US Senate seat and in 2018 was voted in for a third six-year term. He remains an independent but caucuses with Democrats in the Senate.

- Reuters