SNOWMASS, COLO. – Primary mitral regurgitation and secondary mitral regurgitation may sound a lot alike, but they are in fact starkly different diseases, Blase A. Carabello, MD, said at the Annual Cardiovascular Conference at Snowmass.
“They are almost entirely different in their etiologies, in their pathophysiologies, and in their therapies,” according to Dr. Carabello, professor of medicine and chief of cardiology at East Carolina University in Greenville, N.C.
Dr. Blase Carabello
“On the other hand, if you fix the valve, you fix the disease,” he said.
In contrast, in secondary MR, the dysfunctional valve is a result of the ventricular problem, not its cause.
“In secondary MR, it’s the ventricle that made the valve sick. It’s the regional wall motion abnormalities, the displacement of the papillary muscles, and the dilation of the mitral annulus that pulls the mitral valve apart and prevents it from coapting,” he explained.
Dr. Carabello, who was on the writing committee for the current American College of Cardiology/American Heart Association guidelines on management of valvular heart disease (Circulation. 2014 Jun 10;129[23]:e521-643), highlighted other key distinctions between the two diseases.
Primary MR
“Primary MR, unlike aortic regurgitation, is not well tolerated. Early repair is key,” the cardiologist stressed.
The ACC/AHA guidelines emphasize the importance of early referral for surgery for primary MR because of surgery’s proven survival benefit. The triggers for surgery, as described in the guidelines, are easy to remember, namely, “symptoms/60/50/40.” That is, it’s time to move on to surgery when any of the following occurs: The patient becomes even mildly symptomatic, the left ventricular ejection fraction (LVEF) drops to 60%, the pulmonary artery pressure climbs to 50 mm Hg, or the LV end-systolic dimension reaches 40 mm.
Dr. Carabello said he believes those surgical thresholds are conservative, and it’s best to make the surgical referral when a patient approaches one or more of those triggers, but before actually reaching them.
“That’s the way I practice: Don’t wait for any of those things. Just get it done. One advantage to early repair is the patient can’t get lost to follow-up. They’re repaired, and they can’t take it out,” he said.
It’s possible that the next iteration of the guidelines will utilize stricter thresholds for surgery. French investigators have shown that surgery for primary MR achieves a significantly higher rate of normal LV function if the operation occurs when patients have an LVEF of 64% or more and an LV end-systolic dimension of less than 37 mm (Eur J Echocardiogr. 2011 Sep;12[9]:702-10). So far, though, there hasn’t been a confirmatory study.
“I think the normal EF in primary MR is about 70%. By the time the EF in a patient with primary MR gets down into the 50s, you’re looking at an extraordinarily sick ventricle,” according to Dr. Carabello.
The impetus for including the “symptoms/60/50/40” surgical triggers in the guidelines is to encourage physicians to make the surgical referral earlier than has often been the case. Too frequently, the surgical referral is delayed until damage to the ventricle is irreversible, with a resultant worsened prognosis.
“The natural history is such that, from the time a patient with severe primary MR enters your office to the annual mortality risk reaching 50% is only about 5 years. So if you’re going to do watchful waiting, fine, but remember: You don’t have all that long to watch and wait before something bad happens to these folks,” the cardiologist cautioned.
He added that it’s possible that, in the future, cardiac biomarkers will be utilized to help predict the long-term mortality risk of patients under medical management of their primary MR. In a recent study of 1,331 patients with primary MR, the investigators showed that the ratio of B-type natriuretic peptide (BNP) to the upper limit of normal BNP, adjusted for age and sex, was a powerful independent predictor of this risk (J Am Coll Cardiol. 2016 Sep 20;68[12]:1297-307).
The guidelines state that mitral valve repair is preferable to replacement as long as the heart team determines there’s at least a 95% chance of a durable repair. That’s because the operative mortality associated with replacement is significantly higher than with repair.
Secondary MR
Unlike in primary MR, it’s unclear whether surgery prolongs life for patients with secondary MR, or if mitral repair is superior to replacement. Thus, the current guidelines recommend surgery only for patients who are still severely symptomatic despite maximal guideline-directed medical therapy for heart failure as well as cardiac resynchronization therapy, provided they have a conduction system abnormality and qualify for the device therapy.
“If you’ve done all that and they’re still sick, I think that surgery or the MitraClip may benefit them very much,” Dr. Carabello said.
In the United States, the MitraClip transcatheter device is approved only for the treatment of primary MR in inoperable patients. But in the rest of the world, roughly three-quarters of these devices are used for treatment of secondary MR. That potential indication is currently under study in the United States in the phase III COAPT trial (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation).
“In the acute setting, the changes in hemodynamic variables and left ventricular performance that occur with the MitraClip are quite dramatic, with a marked decrease in wedge pressure and a markedly increased stroke volume, which is what it’s supposed to do. So I’m encouraged. We’ll wait for the results of the COAPT trial, which I believe is likely to demonstrate a reduction in hospitalizations and certainly an improvement in patient symptoms. But I doubt very much that we’ll ever see a change in lifespan because the ventricle is still sick, and we in 2017 have not found a way yet to revive a sick ventricle. It’s unlikely that fixing the MR will do so,” according to Dr. Carabello.
He reported serving on a data safety monitoring board for Edwards Lifesciences.