Published in UAB Insight, Summer 2008
Valvuloplasty and Less Invasive Mitral Valve Repair
The prevalence of moderate or severe valvular heart disease in Westernized populations is 1.8%, a number that will increase as the population ages, swelling demand for less invasive approaches to valve repair and replacement. Advances in imaging, catheter-based techniques, and valvular devices provide options for patients who are not candidates for open heart surgery.
The two most common forms of valvular heart disease in patients with these issues are aortic stenosis and mitral regurgitation (MR). UAB's interventional valve program includes percutaneous balloon valvuloplasty for aortic, mitral, pulmonic, and rare cases of tricuspid valve stenosis. Interventional cardiologists Vijay K. Misra, MD, FACC, and Gilbert Zoghbi, MD, FACC, are evaluating a percutaneous mitral clip implant based on the edge-to-edge repair pioneered by Ottavio R. Alfieri, MD, of Milan and currently in use for MR.
Valvular Stenosis
In most cases severe aortic stenosis requires open heart surgical valve replacement. The procedure has good clinical outcomes and a low operative mortality rate of 4%. However patients aged ≥80 years, who have mortality rates as high as 15%, and those with significant comorbidities are not surgical candidates and often undergo percutaneous balloon valvuloplasty as a palliative measure.
"Valvuloplasty for calcific aortic stenosis is not a permanent solution," Misra says, "but we can dilate the aortic valve and increase its area by as much as 50%, a result that usually lasts for about 6 months, providing symptomatic relief and improving quality of life. In those with depressed heart function, the ejection fraction tends to increase after aortic valvuloplasty. A 50% restenosis rate within 6 months limits the procedure to critically ill patients and those with
contraindications to surgery or as a bridge to aortic valve replacement," he says.
Rheumatic fever is the predominant cause of mitral stenosis. Symptomatic mitral stenosis may progress rapidly to heart failure and death if the obstruction is not relieved mechanically. Percutaneous mitral balloon valvuloplasty is indicated in such patients with favorable valve morphology. The procedure is less effective in those with restenosis after surgical commissurotomy or with stenotic porcine bioprosthetic valves. "Balloon valvuloplasty for mitral stenosis has very durable results," Zoghbi says. "In carefully selected patients this treatment is as effective as closed surgical commissurotomy."
Misra and Zoghbi perform the procedure using the Inoue balloon. Intracardiac echocardiography combined with fluoroscopic imaging allows for a safe transseptal puncture, continuous imaging of balloon placement across the mitral valve, and evaluation of valvotomy results after balloon dilatation.
Balloon valvuloplasty also is appropriate for tricuspid and pulmonic stenosis. Almost always rheumatic in origin, tricuspid stenosis occurs in <1% of the US population. Most often congenital, pulmonic stenosis typically is seen in pediatric patients, who usually undergo surgery or a balloon procedure at an early age. These patients now are surviving into adulthood and require ongoing assessment. "When stenosis returns, we treat it with valvuloplasty to palliate symptoms and defer surgical treatment," Zoghbi says.
Mitral Regurgitation: EVEREST Trial
Mitral regurgitation is a common valvular abnormality that increases in prevalence and worsens with age. It affects an estimated 4 million Americans with an annual incidence of 250,000 newly diagnosed patients. Most people tolerate mild to moderate leakage, but chronic severe regurgitation can lead to congestive heart failure, cardiac arrhythmias, and increased mortality.
Surgical mitral valve repair or replacement is standard treatment for moderate to severe MR with suitable mitral valve anatomy. However, not all patients with MR are candidates for open heart surgery. High-risk surgery patients are those with severe left ventricle dysfunction (ejection fraction ≤30%), significantly enlarged end-systolic dimension, severe pulmonary hypertension prior to open heart surgery, or multiple comorbidities.
In a recent scientific statement in Circulation from the American Heart Association (AHA) Council on Cardiovascular Surgery and Anesthesia, the authors point out that only half of patients undergoing surgery for MR receive valve repair. The remaining patients have mitral valve replacement, which carries higher mortality and morbidity (2008;117:1750-1767).
"Taking such current practices into consideration, there is a need for a less invasive option," Zoghbi says. The percutaneous procedure will provide alternative therapeutic options to the overall patient population with MR and particularly to those patients who are denied surgery because of their high-risk status.
A percutaneous approach that replicates the surgical edge-to-edge technique decreases MR severity and may stimulate left ventricular reverse remodeling. Interventional cardiologists conduct the procedure in the cardiac catheterization laboratory with patients under general anesthesia. After transseptal access to the left atrium, the cardiologist positions a clip delivery system above the mitral valve and advances into the left ventricle a clip device that approximates the central mitral leaflet scallops. When retracted the clip grasps the leaflets and closes to create an edge-to-edge repair. Deployment is timed to systolic coaptation of the leaflets and facilitated by fluoroscopic and transesophageal echocardiographic imaging that provides optimal visualization and allows cardiologists to assess the extent of remaining regurgitation in real time. After checking for residual regurgitation, cardiologists can reposition the clip or add a second. An additional advantage of the percutaneous procedure is that standard surgery can still be done if necessary.
Patients are on anticoagulation during the procedure to prevent clotting. Risk of access site hematoma - the most frequent complication with percutaneous coronary intervention - is 1% to 3%. "There also is a possibility of trauma to the aorta or cardiac perforation, but additional imaging with echocardiography has lessened that risk," Misra says.
The implant, called MitraClip and developed by Evalve Inc in Menlo Park, California, is being evaluated under a Food and Drug Administration Investigational Device Exemption. The first Endovascular Valve Edge-to-Edge Repair Study (EVEREST I) enrolled 55 participants with American Society of Echocardiography grade 3+ (moderate to severe) or 4+ (severe) MR. Investigators for the pivotal clinical study EVEREST II are currently enrolling patients and more than 225 participants have been randomized thus far. UAB interventional cardiologists are participating in the ongoing arm of EVEREST II, comparing the MitraClip system with surgical repair or replacement in a 2:1 ratio.
Reported results for the studies show that at 36-month follow-up, patients demonstrated 82% Kaplan-Meier freedom from surgery after successful MitraClip repair; 76% experienced a reduction to ≤grade 2+ MR; and statistically significant reverse left ventricular remodeling occurred 12 months after repair. Researchers assessed reverse remodeling based on four echocardiographic measures, including left ventricular end-systolic dimension. In addition, 94% of patients showed improved or stable New York Heart Association class 12 months after the MitralClip procedure.
Forty medical centers across the country will enroll a total of 280 patients. Candidates must have AHA grade 3+ or 4+ MR with symptoms, or if asymptomatic, must have left ventricular dysfunction (but with left ventricular ejection fraction ≥25%). The regurgitant jet should originate from the A2-P2 scallops of the mitral valve, and the patient should be a candidate for mitral valve surgery with cardiopulmonary bypass.
Misra notes the process requires considerable technical skill and cooperation among the echocardiographers, surgeons, anesthesiologists, and interventional cardiologists who are collaborating on the study. "The MitraClip could prove to be one of the most important advances in interventional percutaneous management of valvular heart disease," Misra says.
An area Misra has targeted for future research is percutaneous aortic valve implantation (PAVI). Still in early developmental stages, percutaneous aortic valve replacements have not yet demonstrated durability and lack long-term outcome results. "PAVI shows promise as an alternative for treatment of symptomatic patients with aortic stenosis who are not suitable candidates for standard aortic valve replacement," Misra says.
"Advanced imaging and new catheter-based techniques are reshaping interventional cardiology, providing less invasive treatment options for patients with a wider variety of structural heart disease," Misra says. "Although still investigational, heart valve devices that enable percutaneous repair or replacement will refashion current practices in surgical and interventional cardiology."
FOR MORE INFORMATION:
Dr. Vijay Misra
Dr. Gilbert Zoghbi
1.800.UAB.MIST
mist@uabmc.edu