Although the LV is small and underfilled in Mitral Stenosis,the myocardium is not normal
• Predominant difficulty in MS is not only the mechanical block but also myocardial insufficiency.
• Myocardial mechanical performance is responsible for LV dysfunction in MS.
• Filling is limited at higher heart rates as it prohibits adequate diastolic filling and limit cardiac output and stroke work.Thisfailure to increase stroke work in MS is due to abnormal LV function.
• Impairment may be localised to posterior ventricular wall,selective atrophy of posterior wall of LV due to fibrosis downward from PML involving chordae and immobilised adjacent muscle can occur.
• Adherence of scarred,shortened ALPM to contagious ventricular wall can cause poor contraction in anterior wall.
• Subtle changes in LV contraction have been reported in MS.Distortion, immobility and rigidity ofposterobasal area of LV is seen more so because of fibrosis in papillary muscle.
• Abnormalities in contractility of LV myocardium are responsible for the impaired myocardial function in patients with MS
• Intrinsic Myocardial Function may be impaired due to –
Papillary muscle ischaemia and fibrosis extending into myocardium
Severe pulmonary hypertension and pulmonary artery dilatation compresses left main artery causing ischaemia
Atrial fibrillation causing coronary embolism leading to myocardial ischaemia
LV dysfunction secondary to RV dysfunction
• Reduced systolic performance appears to be a result of increased afterload without adequate FrankStarling compensation.
• Indices of LV performance like cardiac output, strokeoutput, EF, mean rate of circumferential fibre shortening (Vcf) ,Vpw are all reduced in MS.