Mitral regurgitation

ECG 1: Sinus rhythm; left atrial enlargement (large P wave duration > 120 ms, biphasic in leads I, II, V3-V6, negative widened component in V1); possible left ventricular hypertrophy (increase in R wave amplitude in V3, V4) of the diastolic type (positive T waves in the left precordium);

Comments: This patient has a typical electrocardiogram of chronic mitral regurgitation. Mitral regurgitation is characterized by the systolic reflux of part of the blood from the left ventricle to the left atrium due to incomplete valve closure. Chronic mitral regurgitation causes a prolonged volumetric overload of the left atrium and left ventricle, which can generate, on the long term and in the absence of intervention, dilatation and hypertrophy of these two cavities. Ventricular volumetric overload mainly occurs during diastole in relation to the increase in ventricular volume, with the left ventricle being dynamically discharged during systole, part of the blood volume flowing into the left atrium, a low-pressure cavity. Pulmonary capillary pressure only increases at a later stage in the course of the disease and less frequently than in mitral stenosis. Mitral regurgitation comprises a group of highly heterogeneous conditions with variable etiologies (acute rheumatic fever, mitral valve prolapse, endocarditis, pillar malfunction or cord rupture, annular dilatation, etc.) and modes of presentation (acute or chronic). Electrocardiographic expression therefore varies according to the patients, the etiology, the mode of presentation, the degree of regurgitation and the presence of an associated valve disease (mitral disease encompassing stenosis and mitral leakage). In chronic mitral regurgitation we may observe:

• A strictly normal electrocardiogram; indeed, electrical modifications are sporadic especially in minor and moderate forms; the QRS complexes remain normal in at least 50% of cases with a possible verticalization of the axis as the only sign;
• Left atrial enlargement with a prolongation of the duration of the P wave (> 110 ms) which becomes bifid in leads I, II, V5, V6 and biphasic in V1 with a wide and concave upward negative deflection; this enlargement is frequent with a generally less marked pattern than in the mitral stenosis; it is related to atrial dilatation induced by volumetric overload;
• Left ventricular hypertrophy generally of the diastolic type: presence of large amplitude R waves in the left precordial leads and followed by positive T waves (which can be preceded by relatively deep Q waves); the Sokolow index may be positive or the pattern more modest (simple increase in voltages, discrete delayed intrinsicoïd deflection, flattening or inversion of T waves);
• Pulmonary arterial hypertension is rare, signs of right ventricular hypertrophy are mostly absent; ventricular hypertrophy may sometimes be associated with right ventricular hypertrophy, although left ventricular hypertrophy remains overwhelmingly predominant; an isolated right ventricular hypertrophy (right axis deviation, predominant positive deflection of QRS complexes in right precordial leads) is exceptional and reflects a major increase in pulmonary arterial pressure;
• Rhythm remains mostly sinus, with atrial fibrillation appearing only at a late stage in the course of the disease (later than for mitral stenosis) when the atrium is dilated;

Take-home message: During chronic mitral regurgitation, the volumetric overload of the left atrium and left ventricle explains the electrical signs of left atrial enlargement and diastolic left ventricular hypertrophy.