Q. How to Investigate mitral stenosis by Electrocardiogram?

Electrocardiographic changes are not specific for mitral stenosis and are never diagnostic for any valvular heart disease. They essentially reflect pathophysiological changes. Left atrial enlargement seen in more than 90 per cent of patients is reflected as increase in p-wave duration (>120 m sec.) in lead II or P mitrale. The p-wave axis is between + 45 to - 30 degrees. QRS axis correlates well with the severity of the mitral stenosis and degree of pulmonary hypertension. In pure or predominant mitral stenosis, QRS axis less than 60 degrees suggests a valve area more than 1.3 sq. cm., while a an axis more than that would indicate a valve area less than 1.3 sq. cm., right axis deviation also correlates with the degree of pulmonary hypertension. Absence of right axis deviation in the presence of features of pulmonary hypertension should suggest other associated valvular lesions causing left ventricular hypertrophy. Evidence of right ventricular hypertrophy in the form of R/S ratio more than 1 in lead V1 and poor progression of R-wave height in precordial leads also correlate well with the degree of right ventricular systolic pressure. Atrial fibrillation is common rhythm in patients with mitral stenosis and indicates a large left atrium.