FORT LAUDERDALE, FLA. — Less-invasive mitral valve surgery was linked with several advantages and one major disadvantage, compared with standard sternotomy mitral valve surgery, in a review of the Society of Thoracic Surgeons database records for more than 28,000 patients treated during 2004-2008.
The major increased adverse outcome with less-invasive mitral valve surgery was a significant, nearly twofold rise in the risk of permanent stroke, Dr. James S. Gammie said at the annual meeting of the Society of Thoracic Surgeons. Benefits significantly linked with less-invasive approaches in a multivariate analysis included a 21% drop in the rate of postoperative atrial fibrillation, a 14% decreased need for perioperative red blood cell transfusions, and a reduction in the median length of hospital stay, from 6.0 days with standard sternotomy to 5.0 days with less-invasive approaches, said Dr. Gammie, a cardiothoracic surgeon at the University of Maryland, Baltimore.
“I think we can do better with the stroke rate,” Dr. Gammie said in an interview. “Our challenge is to reduce the stroke rate while maintaining the advantages” of less-invasive mitral valve surgery. One possible remedy for reducing strokes may be to decrease bypass time during less-invasive surgery, he said.
The data also showed a marked increase in the rate of less-invasive mitral valve operations, which steadily rose from 11% of all mitral valve procedures in 2004 to 20% in 2008. Despite this sharp rise, a minority of centers performed mitral valve surgery using less-invasive procedures in 2008, and of the 709 U.S. centers performing mitral valve surgery and entering patients into the STS database, 186 (26%) performed at least one less-invasive operation. The median number of less-invasive operations done at each of the 186 centers was three, with only about a dozen centers doing 20 or more less-invasive mitral valve operations in 2008.
“A lot of surgeons are doing this operation at low volume, early in their learning curve,” Dr. Gammie said. “I don't know if less-invasive mitral valve surgery is good for the occasional surgery. The volume and outcome issue is important. There are opportunities for improvement” of patient outcomes.
The review identified 23,821 patients who underwent conventional sternotomy mitral valve surgery and 4,322 who had a less-invasive mitral valve procedure. Patients undergoing the less-invasive procedure were significantly younger, with a median age of 59 years, compared with 62 years in the sternotomy group. They also were significantly more likely to be women, to have comorbidities such as diabetes or chronic lung disease and to have prolonged surgery, with a median time on cardiopulmonary bypass of 135 minutes, vs. a median of 108 minutes in patients having a sternotomy—a statistically significant difference.
The benefits from less-invasive surgery of a reduced rate of postoperative atrial fibrillation and less need for perioperative transfusions appeared in a multivariate analysis that controlled for baseline demographic and clinical characteristics. This analysis also showed a significantly increased risk for permanent stroke.
Dr. Gammie and his associates performed a propensity analysis that matched each of the 4,322 patients undergoing less-invasive surgery with a very similar patient in the sternotomy group. In this analysis, the rate of postoperative stroke was again doubled with less-invasive surgery, a 1.87% rate, compared with a 0.93% in the sternotomy patients.
The propensity analysis also showed a significantly increased risk for reoperations because of bleeding in the less-invasive surgery patients, a 3.7% rate, compared with a 2.7% rate in the sternotomy patients.
Further analysis showed one factor that significantly linked with the increased stroke risk: not using aortic occlusion, which tripled the stroke risk, compared with patients managed with cross clamping. However, in a subanalysis that excluded patients without aortic occlusion, less-invasive surgery still was linked with a significant 50% increased risk for peri- and postoperative stroke compared with the sternotomy patients.
Despite the observation that the absence of cross clamping did not fully explain the increased risk for stroke, Dr. Gammie concluded that less-invasive mitral valve surgery might avoid having to operate on patients who have a beating or fibrillating heart.
Dr. Gammie said that he had no disclosures relevant to this topic.
Gaps in Data
Minimally invasive mitral valve surgery began in 1996, but few studies have compared the outcomes of this approach with those of traditional sternotomy. The analysis presented by Dr. Gammie is the most comprehensive scientific study to date. It is a high-water mark in determining the value of minimally invasive operations and represents a nationwide spectrum of surgery that includes groups with different methods, different patient volumes, and different levels of expertise. It is the best real-world picture we have so far. But the data set has glaring omissions, including no information on long-term durability and no assessment of repair quality using transesophageal echo. We need longer-term follow-up to assess durability. However, the data show that minimally invasive mitral valve surgery is becoming a standard of care that can be safe and effective, at least in the short term.