Many articles referring to PPM have been published. PPM is classified according to EOAI as mild-to-moderate (>0.65 to ≤0.85 cm2
) or severe (<0.65 cm2
). Some studies found that PPM had adverse effects on clinical outcomes, [9
] and others did not [13
]. Adverse effects include elevated N-terminal pro B-type natriuretic peptide levels, [9
] early stenotic dysfunction of bioprosthetic valves, [10
] and delayed left ventricular mass (LVM) regression [11
]. Tomoeda et al. [12
] found that EOAI should be greater than 0.77 cm2
for adequate LVM regression, but an increasing number of studies have found that LVM regression was not related to EOAI [13
]. Some investigators reported that postoperative survival was not significantly different between patients with and without PPM [17
]. Jamieson et al. [19
] analyzed 3,343 cases of AVR and found that the predictors of overall mortality were age, age category, New York Heart Association functional class III/IV, concomitant coronary artery bypass graft surgery, prosthesis type, preoperative congestive heart failure, diabetes mellitus, renal failure, and chronic obstructive pulmonary disease. Furthermore, they conclude that EOAI category was not predictive of overall mortality, early mortality, or late mortality.
Aortic root enlargement is sometimes performed to avoid the PPM, but clinical results including increased surgical risks are controversial [21
]. Newly developed prosthetic valves with smaller sewing rings and supra-annular implantation techniques contribute to avoiding the PPM. Not surprisingly, the incidence of mismatch also increases with diminishing prosthesis size, and it is widely recognized that patients with a valve size ≤21 mm tend to have much higher gradients. Nonetheless, it must be emphasized that severe mismatch can also occur in patients receiving a prosthesis size >21 mm and that, ultimately, it is always the relation between prosthesis size and body size, rather than each factor taken separately, that determines the final hemodynamic outcome [5
PPM was observed in 8.5 % patients who underwent isolated AVR during 2008 and 2009 in Japan. Dumesni and PiBarot [11
] reported that the rates of PPM were between 20 and 70 %. The low rate of PPM in this series might be due to the physical differences between Japanese people and other people. PPM may be very rare in patients undergoing AVR; therefore, its clinical significance may be less in Japan than previously hypothesized in the Western countries. Thus, aggressive over-sizing or root enlargement strategies may be unwarranted in Japan.
The fact that mismatch occurs more frequently in patients with stenotic native valves and in older patients is also consistent with this concept because patients with stenotic native valves generally have smaller valvular annuli than those with regurgitant valves, and calcific aortic stenosis is by far the most prevalent lesion in older patients undergoing aortic valve replacement. Elderly patients had a higher rate of PPM. PPM could be justified in some elderly patients with lower metabolic requirements and limited physical activity.
Preoperative risk factors for PPM are related to lifestyle-related diseases. The Japan Society for the Study of Obesity defines obesity as BMI ≥25 kg/m2. Our study shows that weight control is mandatory in obese patients to reduce the potential adverse effects of PPM. The prevalence of atherosclerotic aortic valve stenosis has increased over recent years. The risk factors for PPM in this study are consistent with the causes of aortic valve disease. Annular stiffness due to calcification and post-inflammatory changes in patients with aortic valve stenosis might cause an inappropriate valve choice followed by PPM.
The rate of PPM was significantly reduced in Japan during the 2 years studied. New generation prosthetic valves such as the Carpentier-Edwards Magna and the SJM Regent valves might have contributed to this reduction. As the JACVSD records do not include valve implantation techniques (supra-annular or intra-annular position), we cannot determine whether such technical differences contributed to the reduction in the rate of PPM.
There was no difference in early postoperative mortality rates between the two groups, but mechanical ventilation longer than 24 h, renal failure requiring dialysis, and intensive care unit stay longer than 7 days were significantly higher in the PPM group. Postoperative complications including early mortality and major morbidity were significantly more frequent in the PPM group than the non-PPM group, resulting in PPM patients requiring more health resources than non-PPM patients. The high morbidity rates may be caused by postoperative low cardiac output syndrome. As the JACVSD records do not include the treatment details such as catecholamine doses, we cannot determine the causes of the high morbidity rate in the PPM group.
This is a retrospective study, limited to the evaluation of early clinical outcomes. We have used in vitro manufactures’ EOA, which may overestimate in vivo echocardiographic EOA, and we have no data on postoperative transvalvular gradients. The impact of PPM on the functional outcome following AVR is difficult to evaluate because of the confounding effects of concomitant cardiovascular and non-cardiovascular disease. Perioperative cardiac function may be the most important factor for the outcome. We have neither follow-up data on patient functional status nor follow-up echocardiographic data on EOA or left ventricular mass regression. Further studies should be indicated specifically to examine the effect of mismatch on symptomatic improvement and exercise tolerance after aortic valve replacement.