LONDON (Reuters) - Papworth Hospital can resume heart transplant operations after a review failed to find one single reason for a sharp rise in recent deaths, the health watchdog said on Monday.

Operations were suspended at the Cambridge hospital earlier this month after it discovered seven of the 20 transplant patients had died within 30 days, a rate of 35 percent, between January and September this year.

An eighth died following a transplant in October.

Papworth's average rate is seven percent, with the average across all transplant centres 10 percent.

It notified the Healthcare Commission, which following a two-week review, said there were no common factors to explain the increase.

The independent watchdog did find that the time the transplanted heart was without blood supply was longer for those patients who died.

But the times, on average, were lower than in previous years and generally in line with the national average.

The review team, which included leading heart surgeons, found the patient selection procedure was extremely rigorous, and there was no evidence of inadequate care or that the deaths could have been prevented.

Nigel Ellis, head of investigations at the Healthcare Commission, said: "Heart transplantation is extremely high-risk surgery carried out on very ill patients. In so many ways, the Papworth Hospital Transplantation Service represents best practice and its good reputation is well deserved."

It added: "But the number of deaths since January has clearly been high. This is why we are asking the trust to put in place a number of important checks and safeguards."

The NHS trust agreed to implement the commission's recommendations, including ensuring hearts are stored in transit in a similar way to other UK trusts, and a review of the ways hearts are kept cool during surgery.

It also agreed to look at post-operative care arrangements, and to inform patients of recent events before they undergo a heart transplant.

On a national level, the commission recommended mortality rates should be monitored and a threshold established.

Steven Tsui, clinical director, transplant services at Papworth Hospital, said: "We believe the process we have gone through in this review has been rigorous and proper and will help us continue to provide the best possible outcomes for our patients."