Regurgitant lesions of cardiac valves are often tricky for the heart . Myocardium shows “love- hate” relationship with these leaky valves. Some of them are “sort of” stress relievers for LV . A mild MR will make the LV comfortable in terms of wall stress. When the wall stress is reduced the contractility increases and LV EF may raise a little.Hence EF is never going to help us to assess true LV function in MR .
LV end diastolic dimension(LVEDD) is a preload dependent parameter .A patient with 6.5cm LV EDD may still have good contractility and he may reach even a 40mm LV ESD, implying an intact LV function.
LV function should be best assessed in systole .(After all , systole is the prime function of heart) .Further , it should be assessed when the LV is free from influence of the all loading conditions of heart . (Note : The initial part of systole depends on after load. As the systole progresses the influence of after-load lessens .In the pressure volume loop* , the point at which loading conditions are least operative is end systole.)
* Please realise , heart is a dynamic organ there is no true load independent point in cardiac cycle as pressure and volume are eternally coupled.
What happens in AR ?
The same rule applies for Aortic regurgitation, but the parameters worsen little later than that of MR. For same degree of regurgitant fraction MR will require early surgery than AR.The reason for better tolerablity of AR is due to largely intact LA function and compliance till very late stages of AR.(In AR- it’s single chamber volume overload , while in MR it’s two chambers !)
LVEDD is not used in assessing MR as it is a pre-load dependent parameter that will not reflect true myocardial function /dysfunction. LV ESD is fairly accurate measure of LV systolic function minus all loading factors .
Watch out for next topic
Vasodilator therapy in MR and AR : How is it different ?