Sunshine Heart Inc., an Eden Prairie company that is testing a device to treat severe heart failure, has halted enrollment in its pivotal study after four patients died.

The company said the deaths don't appear related to use of its C-Pulse device. But it notified the Food and Drug Administration of a "pause" in the research anyway, because study rules required a stop if more than three of the first 20 patients died from any cause.

Sunshine Heart had high hopes for the randomized, 40-hospital study, called Counter HF. The company recently announced that the FDA had approved an early analysis of study data, with the goal of ending it early if results were good enough. Company stock rose 11 percent on that news.

Now company officials are working to submit a plan to the FDA on how to restart their trial as soon as possible. That plan is expected to be submitted on Monday, one day before the company presents its fourth-quarter financial results. Sunshine's stock has dropped 33 percent since the study pause was announced on March 6, closing at $4.03 on Tuesday.

"We are confident this matter will be resolved in a very short time frame," Sunshine Heart President and CEO Dave Rosa said in a written statement. "We remain excited by the increasing number of patients who are being ­presented for study review and are pleased that the screening process for enrollment will continue while we resolve this matter."

A company news release said two of the four deaths have been analyzed by an independent clinical-events committee and found to be not related to the device. The two most recent deaths do not appear to have been caused by the device, according to initial documentation provided by the hospitals to the company.

The C-Pulse is a device that includes an implantable pressure cuff that encircles the heart's descending aorta, and an external "driver" worn around the shoulder outside the body. The two parts, connected via a lead, work together to detect irregular heart beats and adjust the pressure in the aortic cuff to allow the heart to pump more blood with less effort.

The device is being tested on 388 patients in a national pivotal trial to see how well it treats the symptoms of heart-failure, a progressive condition that happens when narrowed blood vessels make it difficult for a heart to beat normally. The device has investigational approval in the U.S. for Class III and Class IV heart-failure patients, who have limited to no mobility because of their heart failure.

An early feasibility study found that the device may sustain a patient's condition or improve it, reducing the need for future interventions like artificial or transplanted hearts. Some patients may see enough improvement to stop using the device, the company has said.

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