1- Treatment strategy
When managing a patient with valvular mitral regurgitation the following considerations need to be taken into account :
- The natural history of the disease
- Preoperative determinants of postoperative outcome
- The morphology of the mitral valve itself and the likelihood of achieving a successful mitral valve repair (versus replacement)
- Operative Risk for the individual patient in a specific center
- The overall outcome with regard to survival and morbidity of the chosen treatment strategy
Valve morphology may influence management decisions but it is also important to consider the hemodynamic consequences of the volume overload on the left ventricle with regard to its size and function so as to optimise outcome.
Mitral regurgitation leads to a volume overload on the left ventricle. The adaptive consequence is left ventricular dilatation. At advanced stages of the disease, excessive left ventricular enlargement and deterioration of left ventricular function may occur.
During follow-up, regular echocardiographic exams are therefore warranted since they may identify criteria potentially indicating mitral valve surgery.
Left ventricular hypertrophy on the other hand is not a consequence of mitral regurgitation, and does not affect decisions with regard to the timing of surgery. However some patients may have concomittant left ventricular hypertrophy due to the presence of arterial hypertension.
2- Preoperative determinants of post-operative outcome
Surgical criteria in mitral regurgitation have been defined by studies that have looked at different preoperative predictors of long-term postoperative outcome in patients with mitral regurgitation (see Table).
- Impaired preoperative ejection fraction predicts lower post-operative long-term survival
Long-term outcome after mitral valve surgery is significantly impaired if the preoperative ejection fraction is below 60%(1). The 10-year survival after surgery was 73%, 53% and 32% for the groups with an ejection fraction ≥60%, 50 to 60% and <50% respectively.
- Severe symptoms predict an unfavorable outcome
The outcome after surgery is significantly better when patients are operated on before they develop severe symptoms (NYHA classes III and IV)(2).
- Excessive left-ventricular dilation predicts a lower postoperative ejection fraction
Furthermore significant left-ventricular dilation is negatively correlated with postoperative ejection fraction(3).
- Development of pulmonary hypertension and of atrial fibrillation are unfavorable prognostic indicators.
In addition, the above mentioned criteria also affect the operative risk itself.
3- Debate over to how to approach asymptomatic patients
A recent study based on quantification of MR by effective regurgitant orifice area (EROA) measurement reported a five-year cardiac mortality of almost 40% and a cardiac event-rate of more than 60% for asymptomatic severe MR and suggested that EROA predicts the outcome in these patients and that these patients should be promptly considered for surgery(4).
However, it has been shown that asymptomatic patients can be managed safely until they reach classical criteria for surgery(5). Such an approach requires careful clinical follow-up including serial echocardiographic examinations in experienced hands. The ESC guidelines therefore consider surgery in asymptomatic pts with preserved left ventricular function as a class IIb indication(6). The ACC/AHA would consider surgery in these pts as a class IIa indication, but only provided that the chances of successful valve repair are above 90% (see Table)(7).
Table : Indications for mitral valve surgery in patients with organic mitral regurgitation (adapted from the guidelines on the management of valve disease from the ESC(6) and ACC/AHA(7))
Class I : Symptomatic patients
Asymptomatic patients with:
Class I : LV-enlargement (LVESD ≥ 40mm [ACC/AHA] / ≥ 45mm [ESC])
Class I : LV-dysfunction (EF < 60%)
Class IIa IIa : Pulmonary hypertension (sPAP at rest > 50 mmHg)
Class IIa : Atrial fibrillation [ESC] / New onset atrial fibrillation [ACC/AHA]
Class IIaAsympt pts when likelihood of repair without residual MR >90% [ACC/AHA]
Class IIb : Asympt pts with preserved LV function, high likelihood of durable repair and low risk for surgery [ESC]
4- Improved patient care can be achieved by standardising the quality of follow-up and surgery
From the ongoing debate it becomes evident that key issues affecting the outcome of patients with mitral regurgitation is the quality of follow-up and surgery.
When giving recommendations, the overall picture needs to be considered. On one hand, the conditions at a specific center have to be incorporated in the decision-making process for an individual patient. On the other hand, generalisation and extrapolation of a specific experience might be problematic. Attempts should be undertaken to standardise the quality of care(8).
4a- Issues involving the cardiological follow-up
Particular care needs to be paid to the quality of follow-up while patients are still asymptomatic. Event free-survival of such patients is 92%, 78% and 55% after 2, 4, and 8 years respectively(5): indications for surgery are thus reached continuously.
About two thirds of the patients who require surgery are determined as such based on the development of symptoms, one third on left ventricular criteria and to a minor degree on pulmonary hypertension or atrial fibrillation alone.
It is therefore important to follow asymptomatic patients with severe mitral regurgitation at regular intervals (6-monthly exams are recommendable) in an appropriate setting. Also, the patients need to be instructed to recognise and promptly report the onset of symptoms.
An analysis of the EuroHeart Survey has shown, that 49% of 396 symptomatic patients with MR, were not referred to surgery(9). Non-operated patients were older and more frequently had an impaired left ventricular function. However, even patients without concomitant comborbidities were denied surgery. Another aspect that needs to be considered is that many patients are first diagnosed at the stage of advanced symptoms.
4b- Centers with the highest volume of valve repair have the highest success rates
Excellent surgical centers provide excellent results and high rates of successful mitral valve repair with a low perioperative mortality. On a general level both United States (STS database)(10) and European data (EuroHeart survey)(11) demonstrate that currently, only about half of the patients undergo successful mitral valve repair, whereas the other half receives valve replacement, which is associated with a markedly higher operative mortality and prosthetic valve related long-term mortality and morbidity.
A more detailed analysis of the STS data(12) has recently pointed out, that the results of mitral valve surgery are directly related to the hospital volume. Centers with the highest volumes (more than 140 procedures per year), not only had the highest rates for successful repair (77.4%) but also lower unadjusted mortality rates (1.11%) and morbidity. In contrast, centers with lowest volumes (1 to 35 cases per year) had repair rates of only 47.7% and an unadjusted mortality of 3.08%. It is striking that about one quarter (n=3479) of the patients underwent surgery in 27 of the highest volume centers and about one quarter (n=3519) of patients were operated in one of 361 of lowest volume centers. Furthermore 19.4% of the patients operated in the lowest volume centers were asymptomatic.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
To conclude, the quality of mitral regurgitation management may be improved Follow-up examinations should be performed at regular intervals in standardized conditions. The disease should be recognised at an early symptomatic stage in the community and delayed referral should be avoided. Finally, mitral valve surgery should be performed in dedicated centers and in the hands of a dedicated team of heart surgeons.