The increase in stroke volume is explained by the Frank–Starling mechanism, in which increased ventricular pre-load stretches the myocardium such that contractions are more forceful.The regurgitant volume causes a volume overload and a pressure overload of the left atrium and the left ventricle. The increased pressures in the left side of the heart may inhibit drainage of blood from the lungs via the pulmonary veins and lead to pulmonary congestion. Chronic phase
Compensated
If the MR develops slowly over months to years or if the acute phase cannot be managed with medical therapy, the individual will enter the chronic compensated phase of the disease. In this phase, the left ventricle develops eccentric hypertrophy in order to better manage the larger than normal stroke volume. The eccentric hypertrophy and the increased diastolic volume combine to increase the stroke volume (to levels well above normal) so that the forward stroke volume (forward cardiac output) approaches the normal levels.In the left atrium, the volume overload causes enlargement of the left atrium, allowing the filling pressure in the left atrium to decrease. This improves the drainage from the pulmonary veins, and signs and symptoms of pulmonary congestion will decrease.These changes in the left ventricle and left atrium improve the low forward cardiac output state and the pulmonary congestion that occur in the acute phase of the disease. Individuals in the chronic compensated phase may be asymptomatic and have normal exercise tolerances.
Diagnosis
There are many diagnostic tests that have abnormal results in the presence of MR. These tests suggest the diagnosis of MR and may indicate to the physician that further testing is warranted. For instance, the electrocardiogram (ECG) in long-standing MR may show evidence of left atrial enlargement and left ventricular dilatation. Atrial fibrillation may also be noted on the ECG in individuals with chronic mitral regurgitation. The ECG may not show any of these findings in the setting of acute MR. The quantification of MR usually employs imaging studies such as echocardiography or magnetic resonance angiography of the heart. Chest X-ray
The chest X-ray in individuals with chronic MR is characterized by enlargement of the left atrium and the left ventricle, and then maybe calcification of the mitral valve. Echocardiogram
An echocardiogram is commonly used to confirm the diagnosis of MR. Color doppler flow on the transthoracic echocardiogram (TTE) will reveal a jet of blood flowing from the left ventricle into the left atrium during ventricular systole. Also, it may detect a dilated left atrium and ventricle and decreased left ventricular function. A transesophageal echocardiogram can give clearer images if needed as the back of the heart can also be viewed. Electrocardiography
P mitrale is a broad, bifid notched P wave in several or many leads with a prominent late negative component to the P wave in lead V1, and may be seen in MR, but also in mitral stenosis, and, potentially, any cause of overload of the left atrium.