“This is a group of extremely experienced investigators who know the literature well. They’re typically quite savvy with patient selection, and they’re vested in getting the right patients into these trials. Unfortunately, there’s not a registry of all eligible patients, so we can’t tell exactly how those patients were selected. It would have been helpful,” Dr. Estes said.
It’s clear from the randomized trials that the ideal patient for CRT is a woman under age 65 with nonischemic cardiomyopathy with a left bundle branch block, normal sinus rhythm, and a QRS duration of 150 milliseconds or more. That’s who’s most likely to obtain clinical benefit from the therapy. The flip side of that is that an older male patient with ischemia, atrial fibrillation, a QRS of 120-150 milliseconds, and non–left bundle branch block is less likely to respond.
“We’ve figured this out. I think we’ve gotten pretty good at giving patients an honest estimate of their probability of responding independent of our ability to get a lead into a good spot in the coronary sinus,” Dr. Estes said. “More than 95% of patients can be adequately resynchronized currently with the tools we have, so it’s not the barrier that it once represented. We have many different techniques available.”
Despite intensive efforts by investigators using sophisticated nuclear studies, echocardiography, and MRI, however, nothing to date has been able to predict who’s going to respond to CRT as well as a simple electrical parameter: the QRS duration.
“It remains really the gold standard. It’s an electrical marker for what is a mechanical event,” Dr. Estes said.
He reported serving as a consultant to Medtronic, St. Jude Medical, and Boston Scientific and receiving research support from Boston Scientific and St. Jude Medical.