Pathophysiology
During systole, a portion of the ejection fraction regurgitates into the left atrium. The portion is known as the regurgitant volume. This can also be expressed as the regurgitant fraction which is the regurgitant volume/ejection volume. Moderate MR is said to be present when the regurgitant fraction is in the range of 30-50%; severe MR is defined as a regurgitant fraction >50%.
In acute MR, there is sudden volume and pressure overloading of the LA and pulmonary veins leading to acute pulmonary congestion. The LV stroke volume increases to maintain cardiac output but in acute myocardial infarction the ventricle may fail leading to cardiogenic shock.
Chronic mitral regurgitation
With progressive leaking of the mitral valve the left side of the heart has time to adapt. Both the LA and LV will enlarge to cope with the increase in blood volume and the LV will hypertrophy to deliver the increase in stroke volume needed to maintain cardiac output. Dilatation of the LA may result in AF and marked symptoms.
Acute mitral regurgitation
The patient will be acutely unwell with signs and symptoms of acute pulmonary oedema as well as signs of the underlying cause such as acute myocardial infarction or infective endocarditis. An echocardiogram should be obtained urgently to rule out VSD, diagnose MR and assess LV function.
The clinical features, ECG, CXR and ECHO findings associated with MR are shown in Table 1.
Table 1
|
| ||
| Acute MR | Chronic MR | |
| Pulse | Tachycardia | Tachycardia/AF common (Prominent ‘a’ wave in JVP in SR) |
| Cardiac impulse | Hyperdynamic | Diffuse and displaced laterally. Systolic thrill at apex |
| Auscultation | Pansystolic murmur radiating to the axilla and back third heart sound. May be difficult to hear in the acutely breathless and tachycardic patient | Pansystolic murmur radiating to the axilla and back third heart sound. |
| ECG | No changes or acute MI | LA and LV hypertrophy AF common |
| CXR | Pulmonary oedema with a normal sized heart or minimally enlarged LA | Increased LA and LV size Pulmonary venous congestion. |
| ECHO | Urgent – to rule out ventricular septal defect, diagnose MR and assess LV function. | |