China has returned 272 heart pacemakers imported from the United States after they failed quality inspections, China's top quality control agency announced on Monday.

The General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) said the heart pacemakers, valued at about US$240,000 in total, were detained by Shanghai Entry-Exit Inspection and Quarantine Bureau at the end of April.

The administration said the pulse strength of the devices, made by St Jude Medical Inc, was not in line with its indicated properties.

The difference between the testing parameters and the default ones exceeded the two-percent limit set by the Chinese technical authorities, AQSIQ said.

The pacemakers pose potential threats to patients' lives as they could cause misdiagnoses, the statement said.

In 2001, China's State Food and Drug Administration launched an urgent investigation into four types of pacemakers produced by St Jude Medical Inc because of reliability issues, resulting in imports of the pacemakers being banned.

According to the quality control agency, it would ask the producers to solve the problems and improve the quality of their products. Imports will be resumed once the problems are solved, said AQSIQ.

Generally speaking, a ban can be rescinded within six months to one year, an official from AQSIQ said.