Around 670 patients' records have been checked as part of an ongoing review by the Belfast Health Trust into the work of a cardiologist who fitted specialist heart devices between 2007 and 2023.
In May, BBC News NI reported that more than 160 patients with advanced heart conditions may have undergone unnecessary procedures.
It said patients treated by cardiologist Dr Ernest Lau do not need to take immediate action. Its medical director apologised for any distress caused and said those impacted would receive a letter.
The patients were fitted with a Cardiac Resynchronization Therapy (CRT) device - a small implant that treats heart rhythm and pumping issues.
A complaint by a patient in 2023 prompted the Belfast Health Trust to notify the Royal College of Physicians (RCP), which asked for a review of the cases.
The patients have now been recalled and, according to the trust, their records are being checked by specialists.
In a statement, the Belfast Health Trust said it is in the process of assessing a total of 135 living patients to determine whether their CRT device was "clinically indicated".
While it confirmed 29 patients have had their look back review appointment it said the process would take several months to complete.
A look back review appointment is a process by which historical patient data is reviewed to identify potential past errors or missed opportunities for care.
In May the trust's Medical Director Dr Chris Hagan said it would never bring back patients for review unless it thought it was necessary.
"We need to work out if anything more needs to be done with that device, but I want to reassure them that they don't need to worry about it at the minute."
Hagan confirmed that Lau remained a paid employee but was not seeing patients and has not done so since 2023.
When asked in July by BBC News NI to explain why Lau, if not engaged in clinical work or seeing patients, continued to be on a full salary, the trust said internal HR processes are ongoing and it would not be appropriate to comment further at this time.