The concept of patient–prosthesis mismatch (PPM) has been recognized since the 1970s, and the adverse effects of this mismatch have been well documented in numerous publications over the past two decades. In essence, PPM occurs when the implanted prosthesis is too small for the patient. This issue arises in approximately 5-10% of valve replacements, although large registries and studies indicate that aortic root enlargement techniques are employed in only 1-4% of patients. Severe PPM is defined as an indexed effective orifice area (iEOA) less than 0.65 cm²/m². It is known that this condition is associated with increased morbidity and mortality, symptom persistence, and early degeneration of bioprostheses.
Today’s article builds upon previous publications by Dr. Yang on his novel technique for aortic root enlargement, aimed at demonstrating its efficacy and safety. Data were collected from the first 50 consecutive cases operated within a year and a half since its description (August 2020 – February 2022). Both isolated root enlargement and concomitant surgeries were included.
The median age was 65 years, with 70% of the cohort being female and one-third undergoing reoperation. In two-thirds of cases, the surgery was performed in isolation. The preoperative mean aortic transvalvular gradient was 40 mm Hg, and the average native aortic annulus diameter was 21 mm. Following root enlargement, the median prosthesis size implanted was 27 mm, with half of the patients receiving a size 29 mm or the largest size permitted by the manufacturer. The median annulus increment was 3 sizes. Nearly 90% of patients required no blood transfusion during surgery or hospitalization. There were no major postoperative complications, including mortality, permanent dialysis-dependent renal failure, mediastinitis, or reoperation due to bleeding. One case of stroke occurred in a patient with a previous history of cerebrovascular accident. Follow-up computed tomography (CT) aortograms at 3 months showed an increase in root diameter from 27 mm to 40 mm, with no cases of pseudoaneurysm. The postoperative mean gradient was 7 mm Hg, and the mean valve area was 1.9 cm² at both 3 and 12 months. Additionally, improvements were observed in mitral and tricuspid valve function related to reduced afterload. At 18-month follow-up, 100% of the cohort was alive.
Dr. Bo Yang and his team consider the Y-incision aortic root enlargement procedure a safe and effective technique for increasing the aortic annulus by 3-4 sizes.
A more detailed description of the technique is available in a previous blog post.
COMMENTARY:
There are many types of valve prostheses available on the market: mechanical, biological, bovine, porcine, etc. These come in boxes decorated with various references such as serial numbers, expiration dates, and lot numbers, yet they lack the one metric that should matter most to us as surgeons—the inner diameter of the valve, i.e., the effective orifice through which all the blood of our patients must flow. This information is conspicuously absent, and the closest approximation we have is the so-called valve size, which bears no relationship to the true orifice of the prosthesis. Depending on the brand, there may be a discrepancy of more than two valve sizes (over 4 mm) between the valve label and its true inner diameter. Furthermore, valve sizes from one manufacturer do not necessarily correspond to those from another, necessitating the use of brand-specific sizers. This would be like measuring the distance between two points based on the feet of Michael Jordan or Michael Jackson. Everyone would see the absurdity in this, yet such comparisons are permissible in the field of cardiac valve prostheses.
Why do we have so much discrepancy between different brands and measurements of the true effective orifice? All this confusion and complication began about 20 years ago with ISO standards, where the concept of tissue annulus diameter was introduced, referring to the diameter of the valve annulus after leaflet excision. Manufacturers were allowed to label prostheses based on the tissue diameter for which they were intended. Here is where considerable variability arises, particularly with supravalvular prostheses, where dimensions can be oversized. However, the relationship between tissue diameter and internal valve diameter is not always consistent. This is because we do not have standardized descriptions or definitions for the various components of valve prostheses: stent diameter, stent height, external suture ring—some parameters with lax definitions. Defining the internal diameter of a valve is more complex than we might imagine; should we measure it with a Hegar dilator? At what height do we consider the true internal diameter? Some prostheses have a diameter reduction at the cranial end. Do we measure it according to pressure drop at a known flow rate? Or is an optical measurement better? Even assessing the hemodynamics of prostheses is complex. In vitro studies are conducted with Newtonian fluids, while the viscosity of blood varies depending on its components and the applied force. Consequently, laboratory results diverge significantly from real life. If we examine various studies to determine PPM for different commercial brands, we would be surprised by the limited sample sizes on which they are based. We would realize that for certain prosthetic sizes, it is even nonexistent.
When operating on an aortic valve, we must know the true internal diameter of the prosthesis we plan to use. We must know this before bringing the patient into the operating room, despite all the confusion factors previously mentioned. This decision becomes critical when dealing with small annuli, as we risk causing PPM. We must be prudent in enlarging the aortic root and understand the hemodynamic needs of our patient, comorbidities, life expectancy, clinical situation, surgical complexity, and finally, the unique characteristics of the prosthesis we intend to choose.
Yang’s procedure is an intriguing option for enlarging the aortic root and avoiding moderate or severe PPM. However, we should be aware that the results of this series are limited by the typical restrictions of a single-center, retrospective study with a small sample size, short follow-up, and, most importantly, the outcomes reflect those of a single surgeon. The results are surprisingly favorable as no reoperation for bleeding was reported, despite the aggressive nature of the root enlargement.
In conclusion, we must offer our patients the surgery they need, not the one we would prefer to perform. Aortic root enlargement makes sense to avoid moderate or severe PPM. It remains to be demonstrated whether the aggressive oversizing of prostheses provides any long-term benefit, especially if aimed primarily at obtaining larger prostheses for future valve-in-valve percutaneous approaches. As a surgical community, we need to standardize the definitions of the different components of prostheses and conduct studies based on these new universal definitions. In other words, we should measure distances in metric units and not based on the feet of Michael Jordan or Michael Jackson.
REFERENCE:
Yang B, Ghita C, Makkinejad A, Green C, Wu X. Early outcomes of the Y-incision technique to enlarge the aortic annulus 3 to 4 valve sizes. J Thorac Cardiovasc Surg. 2024 Apr;167(4):1196-1205.e2. doi: 10.1016/j.jtcvs.2022.07.006.
