The electrocardiograms of these 3 patients (clear female predominance for this valve disease) are characteristic of a post-rheumatic mitral stenosis (the most frequent etiology). Mitral stenosis is nowadays a relatively rare valve disease with the exception of rheumatic endemic areas. The stenosis produces a diastolic obstruction impeding the flow of blood from the left atrium to the left ventricle and causes hypertension upstream of the mitral orifice. Left atrial hypertension leads, on the long term, to a distension of the atrial cavity followed by, depending on the degree of stenosis, pre-capillary pulmonary arterial hypertension and systolic overload of the right ventricle without left ventricular overload.
Mitral stenoses virtually always have a rheumatic etiology contributing to their remarkable anatomical unity, with electrocardiographic manifestations easily deducible from pathophysiology and varying according to the degree of stenosis. The electrocardiogram may be initially normal and subsequently show signs of left atrial enlargement (or atrial fibrillation) as a function of the course of the disease, followed by signs of right ventricular hypertrophy secondary to pulmonary hypertension.
- left atrial enlargement is related to the dilatation of the left atrium but has no predictive value with regard to the degree of stenosis; the most characteristic aspect is that of "mitral" P wave with various signs which are not all necessarily observed: prolongation of the duration beyond 110 ms, notching or significant bifidity of the P wave, in particular in limb leads and left precordial leads, significant and prolonged terminal negativity in V1, left axis deviation of the P wave;
- a pattern of isolated right atrial enlargement or associated with left atrial enlargement can be observed and is an indicator of significant pulmonary arterial hypertension;
- atrial rhythm disorders are common with evidence of atrial extrasystoles or atrial fibrillation, often coarse (f wave amplitude greater than 1 mm in V1);
- changes in QRS pattern are rarer, occur later and are a good indicator of disease progression; all degrees of signs of right ventricular hypertrophy can be observed; the QRS axis may be sharply deviated to the right when stenosis is severe; a right bundle branch block, most often incomplete, an R/S ratio > 1 in V1, an R wave in V1 greater than 5 mm, repolarization disorders in right precordial leads may indicate the repercussions of pulmonary hypertension;
- in conventional mitral stenosis, there are no signs of left ventricular hypertrophy;
- after cardiac surgery, it is typical to observe a regression of the electrical signs (rapid regression of the atrial signs, slower for the signs of right ventricular hypertrophy).