Valvular heart disease: MV and AV diseases for the trainee Part 1

Valvular heart disease: MV and AV diseases for the trainee Part 1


Aortic valve is opened by high pressure, and also should endure the high pressure during diastole when the valve is closed. Therefore, number of the leaflets must be minimized. The reason why leaflets of the AV is reduced to 3, not to 2, is that…. If there are only 2 leaflets, valve is accompanied by the intrinsic stenosis. To avoid intrinsic stenosis, in case of 2 leaflets, length of the leaflet margin must be greater than the diameter. Because of this reason, majority of the bicuspid AV show cuspal inequality – difference in the size of two cusps. This principle also applies in the mitral valve, which has two leaflets. To maximize the length of the leaflet margin, leaflet margin runs along the circumference. In the mitral valve, in contrast to the aortic valve, valve is opened by low pressure. Therefore, metaphorically, if the aortic valve is like a window, the mitral valve should be like a curtain. Contrary to these requirements during diastole, the mitral valve must withstand high pressure during systole. Therefore, not only the number of leaflets must be reduced to 2, there are supporting structures as chordae and papillary muscle, to endure the high pressure. Therefore, mitral valve is attached on the mitral annulus and supported by the chordae and papillary muscle. We collectively call these 4 components as mitral apparatus. Among the mitral apparatus, mitral annulus looks like a functionally inactive structure. However, area of the mitral valve decreases during systole, implying its sphincter action during systole. In the mitral annulus calcification, when this sphincter action is impaired, abnormal function of the MV could follow. In the aortic valve, not only the leaflet margins are faced to each other to endure the high diastolic pressure, there is a structure called ‘sinus of Valsalva’. Because of this sinus structure, vortex flow
is formed during diastole, which lead to local pressure drop because of the increase in flow velocity, and facilitate valve opening in the next systole. Moreover, this structure allows a space between the coronary orifice and the leaflet during systole, and helps coronary perfusion during systole. Maintaining this sinus structure is important for the normal function of the AV. If the diagosis of ‘obesity’ is made by the weight alone, tall, normal-weighted person may be diagnosed as ‘obesity’ Therefore, both weight and height should be considered in the evaluation of ‘obesity’ Likewise in the evaluation of stenosis and regurgitation, both pressure gradient and orifice area in the evaluation of stenosis, and both regurgitant volume and regurgitant orifice area in the evaluation of regurgitation must be evaluated. Pressure gradient and regurgitant volume represent the actual burden to the heart, but these values may change according to the hemodynamic status at the time of measurement. In contrast, orifice area and regurgitant orifice area are not affected by the hemodynamic status, but do not represent actual burden to the heart. There are 4 situations in MV and AV. MS, MR, AS and AR We will talk about the etiology, pathophysiology, symptoms/signs, diagnosis, severity and treatment. To begin with, in mitral and aortic valves, etiologies of the stenotic lesions are relatively simple, etiologies of the regurgitant lesions are diverse. In MS, etiology was nearly always rheumatic in the past, however, degenerative lesions are increasing recently. Although absolute number of rheumatic MS decreased quite a lot, still in the MS, rheumatic etiology is the major etiology. AS has 3 etiologies. rheumatic, degenerative-calcific and congenital. Among these etiologies, unlike in the past, degenerative-calcific etiology is the major etiology. In MR, abnormality even in one component of the mitral valve apparatus can cause MR. Abnormality in the mitral annulus as mitral annular calcification, abnormality in the leaflet, abnormality in the chordae, and abnormality in the papillary muscle. When the LV size is increased and the LV function is depressed, annulus becomes dilated, tethering effect of the papillary muscle leading to incomplete coaptation of the valve leaflet, eventually results in MR. This MR is called ‘functional MR’. In AR, not only the abnormality in the leaflet, diverse root diseases can cause AR. There are many diseases which can be categorized as root diseases. In the pathophysiology of MS, increased LA pressure due to MS leads to increased pulmonary venous pressure, and increased pulmonary capillary pressure, which ultimately results in pulmonary edema. Because of pulmonary edema, patient complains dyspnea. As the LV filling is impaired due to MS, patient may complain symptoms associated with low cardiac output. Increased LA pressure also lead to increased pulmonary vascular resistance, to decrease flow to the left-sided heart as a compensatory mechanism. Resultant pulmonary arterial hypertension poses RV pressure overload. These are the symptoms associated with MS. One important hemodynamics in MS, which we should keep in mind is that… In normal subject, when heart rate is increased, diastolic period is predominantly reduced, while systolic period is not much affected, even with the reduced diastolic period, normal subject can increase the transmitral flow rate, therefore, can maintain LA emptying. In patient with MS, when diastolic period is decreased with the increase in heart rate, as the transmitral flow cannot be increased, LA emptying is reduced, and increased LA volume causes increase in LA pressure. Therefore, in patient with MS, when the heart rate is increased, increase in heart rate is accompanied by the marked aggravation of dyspnea. Increased heart rate associated with exercise would be subsided by resting, therefore does not cause serious clinical problem, however increased heart rate in atrial fibrillation with rapid ventricular response, or during pregnancy is a clinically challenging problem. As the atrial contraction contributes a lot in LA emptying, loss of atrial kick as in atrial fibrillation is associated with sudden aggravation of symptom, even in the absence of rapid ventricular response. In the pathophysiology of AS, LV hypertrophy due to LV pressure overload can cause dyspnea due to diastolic dysfunction, and can cause myocardial ischemia due to increased myocardial oxygen demand. Moreover, AS is associated with the decrease in coronary flow reserve, associated with the medial hypertrophy of the vessel, which can also affect the oxygen supply of the myocardium. And the myocardial fibrosis might be associated with the advance in the disease process. Most important aspect in the pathophysiology of the regurgitant lesions is….. Having an idea of the difference between the ‘acute’ and ‘chronic’ regurgitations. In chronic regurgitation, volume overload of the receiving chambers, LA in MR and LV in AR, is the main pathophysiologic mechanism for the increase in the receiving chamber pressures. In acute regurgitation, receiving chambers, LA and LV, are ‘non-compliant’, as the receiving chambers are not dilated sufficient enough. In the non-compliant receiving chamber, LA or LV, regurgitation has the effect of transmitting the pressure of the LV or aorta. Therefore, in acute regurgitation, diuresis to correct volume overload is usually ineffective, therefore, in the treatment, we should resort to the vasodilator therapy to reduce regurgiation. To repeat what we have just talked about,… In chronic regurgitation, volume increase in the receiving chamber is the main pathophysiology. In acute regurgitation, non-compliant receiving chamber is an important factor in the pathophysiology. Therefore, main direction of treating pulmonary is, diuresis in chronic regurgitation and vasodilator therapy in acute regurgitation. As a morphologic feature, chamber size is usually enlarged in chronic regurgitation, whereas normal in acute regurgitation. In determining Op timing of MR, systolic function is usually considered. Systolic function is usually represented by the EF. EF represents LV performance, does not represent myocardial contractility. I’ll show you one animation for your understanding. There are two ladies and lady on the right can bend her knees more deeply and quickly. If you compare the function of bending the knee to the systolic function, lady on the right has higher EF than the lady on the left. Then, can we safely say that leg muscle power of the lady on the right is stronger than that of the lady on the left ? No. Loading condition should be taken into consideration. In mitral regurgitation, as the regurgitation occur to the LA, which is the low pressure system, regurgitation is occurring in the afterload reduced state. If we evaluate the LV systolic function by EF, depressed myocardial contractility may be masked. This one example, when the MR was present before operation, LVEF was normal, postoperatively when the MR was corrected, depressed myocardial contractility became manifest. Unfortunately, so far, there is no loading condition independent parameter that can represent myocardial contractility. In MR, we just apply higher value of 60% for EF representing preserved myocardial contractility instead of conventional normal EF of 55%. I will not talk in detail about the symptoms/signs of each valvular diseases. Symptoms in MS have been already mentioned in pathophysiology section. As the auscultatory findings, MS is characterized by the increased S1, opening snap and diastolic rumble murmur. In case of MR, there is no unique symptom for MR. As the auscultatory and physical findings, MR is characterized by the pansystolic murmur at the apex, displaced apex beat when LV is enlarged, and S3 sound in case of LV failure. Typical auscultatory finding in AS is the ejection type mid-systolic murmur. In AR, rapid upstroke in the carotid pulse is seen because of the increase in pulse pressure. Under the same mechanism, peripheral signs such as de Musset’s sign, Muller’s sign and Quincke’s capillary pulse can be seen. Characteristic auscultatory findings are blowing type early diastolic murmur at the left sternal border, and in certain patient, when the functional MS is caused by the AR, diastolic rumble murmur called ‘Austin-Flint’ murmur can be heard. Diagnosis of each valvular heart disease is made based on the morphologic and hemodynamic features. In the stenotic lesion, as the morphologic feature, limitation in the valve opening can be seen, and increase in pressure gradient can be seen as the hemodynamic feature. In case of regurgitation, in the majority of cases, it is difficult to diagnose morphologically. In the past, angiography had been used. But, nowadays, diagnosis can be made by the color flow finding in echocardiography. In this video, MV is thickened and shows limitation in opening. Therefore, the diagnosis is MS. Also note the LA enlargement, here. In this patient, we can see AV thickening and limitation in opening. Therefore, diagnosis is AS. Here, we can see MR in the color flow. More severe MR compared to the previous case. We can easily notice the presence of AR in this echocardiography. Thank you for your attention. To be continued in Part 2.