[ Scientific Activities - Actividades Científicas ]Usefulness of Eco-stress in mitral valvulopathy
Dr. Oscar Francisco Sanchez Osella
Doppler echocardiography during stress (stress echo), using pharmacological or physical stress (exercise) is very useful in studying this pathology. Its application to insufficiency and mitral stenosis will be analyzed separately.
Mitral Regurgitation (MR). It is necessary to differentiate MR of rheumatic origin and in mitral valve prolapse (primary MR) from MR secondary to other pathologies as dilated cardiomyophaty, ischemic cardiomyophaty and obstructive hypertrophic cardiomyophaty.
The pharmacological stress with Dobutamine is useful in secondary MR, and in studies of myocardial viability. In the latter case, diminution of the intensity of regurgitation is a strong indication of viability.
In primary MR, physical stress offers advantages over the pharmacological stress, by allowing the analysis of a larger number of variables, as will be analyzed later. Physical stress with isotonic exercise is indicated in MR of rheumatic origin, in mitral valve prolapse, and in secondary MR. Isometric exercise may be used in mitral valve prolapse, and as coadjutant in Dobutamine induced stress.
MR of rheumatic origin usually does not significantly modify the regurgitation intensity during stress, but in mitral valve prolapse and in secondary MR, the differences could be marked, and they go from the disappearance of regurgitation, to the increase to severe levels. The ventricular function could be modified, showing a diminution on the myocardial functional reserve. Other factors, as pre- and post-load, cardiac output and cardiac rate, modify the intensity of regurgitation as well. All this information permits a better understanding of the hemodynamic overload of MR, directing with precision the therapeutic conduct.
Mitral Stenosis (MS). Diagnosis and therapeutic conduct do not offer difficulties in the case of patients with important or light stenosis. Difficulties arise in stenosis with areas between 1.0 and 2.0 cm2, because in these patients the clinical profile varies, as well as the hemodynamic significance and the degree of impairment of lung circulation. It is precisely those patients, who benefit from an evaluation with Stress-Eco, because it is a dynamic analysis in variable hemodynamic conditions. Either the pharmacological or physical stress could be used.
In the experience of Hecker et al., pharmacological stress using Dobutamine, while compared to exercise in MS, showed similar hemodynamic response. In spite of that, exercise offers advantages over Dobutamine in MS, because it lets us know the effective adaptation of the patient to the effort. There is no consensus as to the protocol to be used, some authors use treadmill exercise, doing the examination immediately after effort, others do it in an ergometric bike, in supine position. At our institution, we use exercising in supine position, in an ergometric stress bed, beginning without load, with progressive increases of 25 W at every 3 minutes, at a constant pedal speed of approximately 60 rotations per minute.
The evaluation with Echo-Doppler was continuously done during exercise and in the recovery phase.
Besides the traditional criteria to interrupt the exercise, in MS we used the following:
a) Maximum load of 100 W, considering enough effort level for this pathology, and
b) Mean gradient equal or greater than 26 mmHg, because this is the physiological limit after which a net gain of liquid in the extravascular space start being produced, putting the patient in the imminence of an acute pulmonary edema.
The recovery phase goes until the return of gradients to their initial values, independently of the time to reach them.
In our institution, we evaluated a group of 41 female patients with a discrete to moderate degree of MS with and without previous surgery with stress echo and the methodology just described. Of this group, 22 with pure stenosis were selected, that did not present other abnormalities. They were divided in two groups of 11 each, one without previous surgery (StenosisGr), (Age 37.8 +- 12.4 years), the other with previous valvuloplasty (ValvuloplastyGr), (Age 39.2 +- 12.8 years). The results were compared with a group of 10 normal individuals (NormalGr) (30 +- 10.9 years). The summary of this experience is being presented to this Congress.
Numerous observations arise from this experience; the main ones are presented as follows:
Sub-group 1, with gradient less than or equal to 17 mmHg;
Sub-group 2, with gradient greater than 17 mmHg, and time of exercising greater than 9 min.;
Sub-group 3, with gradient greater than 17 mmHg and exercising time less than 9 min
The basal valve area did not present significant differences between sub-groups, indicating that it is not a parameter that permits the forecast of the hemodynamic response in these patients.
The analysis of the valve area with maximum effort showed that patients, who increased the area on a mean of 15.9%, had a more benign hemodynamic response, and those are in Sub-group 1. Those who increased the area the mean of 2.2% could do the physical exercise for more than 9 min, even if they showed steep gradient increase, and are found in Sub-group 2. Patients whose areas increase, in mean, 0.3 %, which indicates a minimal degree of valve elasticity, showed more severe hemodynamic response, with fast gradient increase, interrupting exercise in less than 9 min, and thus are in Sub-group3.
It is important to emphasize that in Sub-group 3, (with more important hemodynamic response), there was no patient of ValvuloplastyGr, indicating that post-surgery patients showed a greater degree of elasticity in the valve, and a greater degree of increase in the area during effort, even if differences were not statistically significant. Even if the recovery time did not show such statistically significant differences, the means are representative of the degree of hemodynamic significance. In Sub-group 1, the recovery time mean was 6.6 minutes, in Sub-group 2 it was 10 minutes, and in Sub-group 3 it was 9 minutes.
1 - Increase in the valve area.
2 - The degree of increase in the cardiac output.
Those two variables are independent. No anatomical characteristics were identified that permit the forecast of which valves will increase their area during effort, neither the degree in which this will happen. Neither is it possible to predict the degree to which the cardiac output will increase. These aspects make the hemodynamic response unforeseeable during exercise.
Conclusions: The hemodynamic significance of mitral stenosis responds to multiple independent variables, such as: basal valve area, increase in this area during effort, variations in the cardiac rate, cardiac output, degree of lung adaptation, pre-load and afterload, and ventricular function. Therefore, hemodynamic significance during effort could not be predicted by the aforementioned parameters during rest, in patients with MS of intensity equivalent to the group studied. Doppler echocardiography during exercise could make those influences clear, allowing us to follow the evolution, and to direct the therapeutic conduct with precision.