NEW ORLEANS — A new-generation heart pump was at least as effective as prior models and was also substantially safer, causing fewer deaths and complications in a study with 133 patients. The new unit is also one-seventh the size of the existing model, and is silent.
These results, in a study that assessed the HeartMate II assist device as a bridge to heart transplant, “give us an encouraging look to the future of the primary indication for this treatment,” as destination therapy for patients who are not eligible for a heart transplant, Dr. Leslie W. Miller said at the annual meeting of the American College of Cardiology. A study of the device as destination therapy that's designed to include 200 patients had enrolled 151 patients by late January 2007.
Despite the limitations of the current results based on the indication studied, “the data are a benchmark and branch point in the field of mechanical support. This represents an amazing accomplishment. It is a device for the future,” said Dr. Miller in a conference call following his report at the meeting. The new results “will significantly impact the use of this technology.”
With the new device, “there's a great future for our patients with severe heart failure,” said Dr. Christopher M. O'Connor, director of the heart failure and transplant program at Duke University, Durham, N.C., at the meeting.
The HeartMate II is made by Thoratec Corp., which markets the HeartMate XVE, the current, standard left ventricular assist device. Dr. Miller is a consultant to and has received honoraria and research support from Thoratec.
HeartMate II produces continuous blood flow, unlike the pulsatile pumps of prior-generation devices. In addition to being substantially smaller, the new pump is about 75% lighter than the XVE model, with a 40% smaller percutaneous lead and just one moving part, which is expected to result in much greater durability. The device should last 5–10 years in most patients, said Dr. Miller, chief of the integrated divisions of cardiology at Georgetown University, Washington.
The device was tested at 26 sites in the United States during March 2005-March 2006. The study was not randomized, and instead compared the new unit to an objective performance criterion based on the historic performance of three prior assist devices. The derived criterion stipulated that at least 75% of patients who received the new device had to survive either to heart transplant or for at least 180 days while remaining transplant eligible.
The enrolled patients were 18–69 years old, and were all listed as status 1A or 1B for a heart transplant. Their average left ventricular ejection fraction was 16%. Because of the device's smaller size, the entry criteria were expanded to include smaller patients; 21% of the patients were women, including seven women with a body surface area of less than 1.5 m2, a size that was previously unable to accommodate an implanted assist device.
During follow-up, 100 patients (75%) either went on to receive a heart transplant (68 patients), survived for more than 180 days while awaiting a transplant (29), or recovered substantially and had the device explanted (3), which meant that the results met the study's primary end point. The overall average duration of device support was 168 days. Among the 29 patients who went longer than 180 days without a transplant, the average time on the device was 360 days, with one patient maintained for 600 days. Among the remaining patients, 25 died within 180 days.
Actuarial 6-month survival for all 133 patients was 75%, and 68% survived for 1 year. Most of the deaths occurred prior to hospital discharge, with only three patients dying during the period 4.5–12 months after their devices were placed. The most common causes of death were sepsis, stroke, and multiorgan failure. The most common adverse events were bleeding (41 patients), infections (37), ventricular arrhythmias (32), and renal failure (18). Five patients had to have their devices replaced, with one death linked to explantation.
While on the device, patients showed dramatic improvements in their heart failure status, their 6-minute walk distance, and their quality of life.
“What's most impressive was the survival rate after 4.5 months,” when only three patients died, said Dr. Miller. In contrast, in the landmark, pivotal trial of the XVE model, the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial, 52% of patients survived for 1 year and 25% survived for 2 years. When deaths immediately after surgery in the new trial are discounted, survival with the HeartMate II model looks to be about 20% better, in absolute terms, compared with the XVE model.