Mitral regurgitation is expected to occur only in systole during left ventricular contraction. In rare pathological states , if LV pressure exceeds the mean LA pressure at any point in diastole , small puffs of regurgitation into LA can occur.The genesis of this MR and its hemodynamic significance has generated much interest .
- Aortic regurgitation -Severe . (Occurs mainly in acute AR or chronic AR with decompensated LV )
- AV blocks (especially complete AV block )
- Any cardiomyopathy with severely elevated LV diastolic pressures
No single mechanism is responsible.
- Common hemodynamic denominator is transient cross over of LV pressure over and above LA pressure curve .
- This tends to happen often soon after the atria contracts specifically so , if the atrial contraction is not followed by a QRS complex as in heart block .
- The fact that its reported even in the presence of atrial fibrillation (As in some cardiomyopathy ) atrial mechanism is not exclusive.
- In Aortic regurgitation the mechanism is different (More of volume dependent , Read below )
It occurs in later part of diastole as it takes a time lapse for raising LV diastolic pressure to cross the LAP and generate a reversed ventricular gradient.
Will there be a clinical evidence for this MR ?
Its silent in most cases .Some patients with complete heart block may generate mid diastolic murmur . (Rytand AHJ 1946) .Retrospectively this could be due to diastolic MR
Is there a link between Austin flint murmur and diastolic MR ?
Many researchers believe the generation of diastolic murmur in severe AR is attributable to premature closure of mitral valve and the poorly compliant LV is not able to accommodate the leaking blood and it tends to regurgitate into LA through partially closed mitral valve in diastole (Ochaya S, Am Heart J. 74 1967:161-169)
- Doppler flow signal in mitral inflow is diagnostic
- Color M-mode is ideal to map diastolic MR.
Wong has demonstrated this phenomenon by direct hemodynamic recording in 4 patients
While the field of diastology is growing , still we are not clear how significant this MR in clinical diastolic dysfunction and acute LV failure that results in flash edema.