Patient-Prosthesis Mismatch May Diminish Transcatheter Valve Benefit
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In patients who have undergone transcatheter aortic valve replacement (TAVR), the presence of an imbalance between prosthesis functioning and body size can lessen the positive hemodynamic impact of the procedure, according to a retrospective study published online October 5, 2011, ahead of print in the Journal of the American College of Cardiology. Moreover, the phenomenon, known as prosthesis-patient mismatch, reduces the chances of clinical improvement.
Researchers led by Nina Ajmone Marsan, MD, of Leiden University Medical Center (Leiden, The Netherlands), analyzed data from 165 patients with severe symptomatic aortic stenosis who underwent TAVR at 2 medical centers. All had contraindications to conventional aortic valve surgery or were considered at high operative risk.
The Edwards Sapien bioprosthesis (Edwards Lifesciences, Irvine, CA) was used in all patients; a 23-mm device was implanted when the aortic annulus was 18 to 22 mm, while a 26-mm model was used when the annulus measured 18 mm to 22 mm.
The incidence of patient-prosthesis mismatch, defined as an effective orifice area indexed to body surface area of 0.85 cm2/m2 or less and assessed by transthoracic echocardiography before hospital discharge, was 18.2%.
Adverse Impact on Hemodynamics
Because patients with mismatch after TAVR were characterized by a smaller effective orifice area, both at discharge and 6 months (0.79 ± 0.08 cm2 vs. 1.24 ± 0.28 cm2 for no mismatch; P < 0.05), they showed a slower and smaller reduction in mean transaortic gradient, resulting in a higher gradient at 6 months (16 ± 8 mm Hg vs. 10 ± 4 mm Hg for no mismatch; P < 0.001). LV mass regression was smaller at 6 months in patients with vs. without mismatch (-7.2 ± 4.6% vs. -21.1 ± 10.6%; P < 0.001), as were reductions in LV filling pressure (-4.6 ± 21% vs. -29.7 ± 7.0%; P < 0.001). However, there was no difference in LVEF (56 ±14% for mismatch and 59 ±10% for no mismatch; P = NS).
The proportion of patients with aortic regurgitation grade 2 or greater was similar for patients with or without mismatch, both before hospital discharge (P = 0.33) and at 6 months (P = 0.11). In addition, during 6-month follow-up, the presence of patient-prosthesis mismatch did not have an effect on aortic regurgitation after valve replacement. Similar proportions of patients in the 2 groups showed improvement (33.3% for mismatch and 29.6% for no mismatch) as well as no improvement (66.7% and 70.4%; P = 0.83).
At 6 months, the vast majority of patients (92.1%) reported an improvement in New York Heart Association (NYHA) functional class. However, 36.7% of mismatch patients failed to show such improvement compared with only 1.5% of those without mismatch. On the other hand, over a mean follow-up of 17.6 months, no difference was seen between the groups in rates of the combined endpoint of major adverse valve-related and cardiovascular events (log-rank P = 0.82).
Multiple Factors Affect Hemodynamic Results
In an accompanying editorial, E. Murat Tuzcu, MD, and colleagues from the Cleveland Clinic (Cleveland, OH) note that 2 key factors make assessment and prevention of patient-prosthesis mismatch challenging:
- Variability in the positioning of prosthetic valves relative to the annulus
- The necessity of using the same-size device (only 2 sizes were available during the study) for a wide range of annular sizes
The fact that procedural variables other than patient-prosthesis mismatch may have influenced hemodynamic outcomes also complicates analysis, the editorial notes. For example, use of smaller prostheses and the transfemoral approach were more common among mismatch patients. Variable medical management of hypertension after valve replacement also may have contributed to differences in hemodynamic outcomes, Dr. Tuzcu and colleagues add.
The clinical significance of patient-prosthesis mismatch is unclear, they observe. The prognosis is clouded by the fact that TAVR patients are typically high-risk and elderly. Thus, it “remains to be seen whether [patient-prosthesis mismatch] equivalent to moderate nonprogressive aortic stenosis leads to any adverse outcomes in this patient population,” the editorial says.
In the long term, outcomes likely will be determined primarily by valve durability and patient comorbidities, Dr. Tuzcu and colleagues write, yet “less than optimal improvement in symptom relief associated with [patient-prosthesis mismatch] is a concern and should be further investigated.
“Optimizing the size of the aortic annulus and the availability of more valve sizes will help in the prevention of [patient-prosthesis mismatch],” they conclude.
Transcatheter Data Add to Surgical Experience
One strength of the paper is that it assesses the effects of prosthesis-patient mismatch in a larger series of TAVR patients than previous reports, Josep Rodés-Cabau, MD, of Laval University (Quebec City, Canada), told TCTMD in a telephone interview, and the new data largely recapitulate what is known from the surgical literature.
“However, if severe prosthesis-patient mismatch does occur, many surgical studies clearly show that it can be associated with higher mortality,” Dr. Rodés-Cabau said. The fact that this study includes mild and moderate mismatch may be one reason it fails to show a strong correlation with major clinical endpoints, he noted.
Nonetheless, it is telling that more than one-third of patients with prosthesis-patient mismatch in the study did not respond to valve replacement with functional improvement, Dr. Rodés-Cabau said.
Optimal Valve Size Makes a Difference
One surprising finding is that larger annuli—not smaller, as highlighted in the surgical literature--were associated with more prosthesis-patient mismatch, Dr. Rodés-Cabau observed. An explanation may lie in the fact that although prostheses impart better results when somewhat oversized, the largest Edwards valve available at the time was 26 mm, which was recommended for use in annuli measuring from 21 mm to 25 mm. But a 26-mm prosthesis implanted in a valve at the larger end of this range might still be undersized, he suggested.
“Nowadays we have a larger, 29-mm Edwards valve, and that can make a difference [in terms of minimizing mismatch],” said Dr. Rodés-Cabau. In fact, Edwards valves now range from 20 to 29 mm, while the CoreValve System (Medtronic, Minneapolis, MN) comes in 26-mm, 29-mm, and 31-mm sizes, he added.
Recent data from his group show that aortic annulus size, measured appropriately, is the main predictor of final valve area following TAVR and thus a potential predictor of prosthesis-patient mismatch, Dr. Rodés-Cabau concluded.
At baseline, patients with patient-prosthesis mismatch had a larger body surface area (P = 0.003) and greater severity of aortic stenosis (P = 0.005) than those without mismatch. However, the aortic annulus diameter, on which prosthesis sizing was based, did not differ between the 2 groups (P = 0.15).
1. Ewe SH, Muratori M, Delgado V, et al. Hemodynamic and clinical impact of prosthesis-patient mismatch after transcatheter aortic valve implantation. J Am Coll Cardiol. 2011;Epub ahead of print.
2. Tuzcu EM, Özkan A, Kapadia SR. Patient-prosthesis mismatch in the transcatheter aortic valve replacement era. J Am Coll Cardiol. 2011;Epub ahead of print.
Patient-Prosthesis Mismatch May Diminish Transcatheter Valve Benefit
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- Drs. Marsan and Tuzcu report no relevant conflicts of interest.
- Dr. Rodés-Cabau reports serving as a consultant for Edwards Lifesciences and St. Jude Medical.