Mitral valve stenosis

What mitral stenosis is

The mitral valve is the left atrioventricular valve: it lies between the left atrium, which receives oxygenated blood from the pulmonary veins, and the left ventricle, which distributes it to the systemic circulation. It consists of two leaflets (anterior and posterior), the valve annulus and the subvalvular apparatus (the chordae tendineae and papillary muscles). During diastole the leaflets open and blood passes from the atrium into the ventricle; during systole they close and prevent blood from returning toward the lungs. The normal opening area (MVA, mitral valve area) is 4–6 cm².

Mitral stenosis is a narrowing of this opening that obstructs emptying of the left atrium during diastole. In the rheumatic form, the most common, the pathological process involves fibrotic thickening of the leaflets, fusion of the commissures (the edges where the leaflets meet) and shortening of the chordae, so the opening takes the form of a narrow slit, often with later calcification. Severity is defined by MVA: above 1.5 cm² is mild stenosis; 1.5 cm² or less is clinically significant (moderate to severe) stenosis, and below 1.0 cm² is considered very severe. Full assessment also takes into account the transmitral gradient, pulmonary pressure and symptoms.

Pathophysiology: from valve narrowing to symptoms and complications

The symptoms and complications of the disease follow from a chain of events that is useful to understand, because it also explains the logic of treatment:

1. Rise in left atrial pressure. To pass the same volume of blood through a smaller opening, a greater pressure gradient is needed between atrium and ventricle. Left atrial pressure rises, while diastolic pressure in the ventricle remains normal or low.
2. Pulmonary venous hypertension and pulmonary congestion. Because there is no valve between the left atrium and the pulmonary veins, the raised pressure is transmitted retrogradely to the pulmonary veins and capillaries. When pulmonary capillary pressure exceeds the plasma oncotic pressure (about 25–30 mmHg), fluid leaves the capillaries into the interstitium and the alveoli, causing congestion and, in acute cases, pulmonary edema. The clinical consequences are dyspnea, orthopnea, cough and hemoptysis (coughing up blood from rupture of dilated bronchial veins).
3. Pulmonary hypertension. Sustained elevation of venous pressure first leads to a passive rise of pressure in the pulmonary artery (post-capillary pulmonary hypertension). Over the years, vasoconstriction and remodeling of the pulmonary arterioles also develop, further raising pulmonary vascular resistance. This is pulmonary hypertension and should not be confused with ordinary arterial hypertension (blood pressure in the arm).
4. Right ventricular failure. The right ventricle works against raised resistance and over time dilates and weakens; functional tricuspid regurgitation often appears. The result is right-sided heart failure: systemic venous congestion, peripheral edema (swelling of the legs), hepatomegaly and ascites.
5. Left atrial dilatation and fibrosis. Chronic pressure overload leads to atrial dilatation and fibrosis, which disturb electrical conduction. This is the basis of atrial fibrillation, which occurs in a large proportion of patients with significant mitral stenosis.
6. Stasis, thrombosis and thromboembolism. In atrial fibrillation the atrium no longer contracts in a coordinated way; blood in it (especially in the left atrial appendage, a small sac-like pouch) stagnates and coagulation is activated. The dilated atrium, stasis and the inflammatory state present in rheumatic disease markedly raise the risk of thrombus formation. If a fragment breaks off it causes an embolic stroke or embolism to other arteries. This risk is high even when the stenosis has not yet produced marked symptoms.

The left ventricle usually has preserved systolic function and fills less than normal. Mitral stenosis is therefore a disease of filling and not of contractility, which distinguishes it from most other heart diseases.

The role of heart rate

Blood passes through the mitral valve only in diastole. When heart rate rises, the duration of diastole shortens proportionally more than that of systole: at 60 beats per minute diastole lasts roughly 0.6–0.65 seconds, whereas at 120 beats only about 0.25 seconds. With a normal valve this has no consequence, but in stenosis the transmitral gradient rises sharply, the atrium cannot empty and pulmonary capillary pressure climbs quickly. Any condition that speeds the heart (physical exertion, fever, anemia, hyperthyroidism, strong emotion, pregnancy, atrial fibrillation with a fast rate) can therefore cause rapid worsening of symptoms, even pulmonary edema, in a patient who previously felt well. This is why heart rate control is one of the pillars of treatment.

Causes

The most common cause worldwide is rheumatic heart disease, a long-term complication of acute rheumatic fever. Rheumatic fever is an autoimmune inflammatory disease that appears 2–4 weeks after pharyngitis caused by group A beta-hemolytic streptococcus (Streptococcus pyogenes) when it has not been treated with an antibiotic, and mainly affects ages 5–15. The mechanism is molecular mimicry: antibodies and T lymphocytes generated against bacterial proteins (especially the M protein) cross-react with antigens in the body’s own tissues, above all the heart, joints, skin and central nervous system. The acute picture includes fever, migratory polyarthritis, carditis, Sydenham chorea, erythema marginatum and subcutaneous nodules, and is diagnosed using the Jones criteria.

When the process involves the heart (rheumatic carditis), the mitral valve is the one most often damaged, because it carries the greatest hemodynamic load. Acute inflammation leaves fibrosis behind; over the years, turbulent blood flow through the damaged leaflets continues the process of thickening, commissural fusion and calcification. Stenosis therefore usually appears 10–30 years after the initial fever, that is, in adulthood, and women are affected more often than men. A considerable proportion of patients recall no obvious episode of rheumatic fever, because it may have passed with mild signs. In countries where streptococcal pharyngitis is treated in time this disease has become rare, but it remains common in patients who had the infection when treatment was not possible.

Other causes are much rarer:

• degenerative calcification of the mitral annulus in older people: calcium deposition in the annulus and at the base of the leaflets can narrow the opening. It is associated with chronic kidney disease, long-standing hypertension, diabetes and atherosclerotic disease;
• congenital mitral stenosis, when the valve has structural anomalies from birth;
• systemic inflammatory diseases (e.g. systemic lupus erythematosus) and chest radiation given for a neoplasm, which years later can cause valvular fibrosis and calcification.

Symptoms

The disease has a long asymptomatic phase that can last years, because the narrowing advances slowly and the body compensates. Symptoms usually appear when MVA falls below 2 cm² and especially below 1.5 cm², often precipitated by a condition that raises heart rate or blood flow: exertion, fever, infection, anemia, pregnancy or the onset of atrial fibrillation. The most common are:

• dyspnea (shortness of breath), at first on exertion (stairs, hills), later during light activity and at rest. As it progresses, orthopnea (the need to sleep with the head raised) and paroxysmal nocturnal dyspnea (waking at night short of breath) appear. It is caused by pulmonary congestion;
• fatigue and reduced exercise tolerance, a result of inadequate filling of the left ventricle and reduced output;
• palpitations, usually in atrial fibrillation;
• dry cough, especially on exertion or at night, and hemoptysis (coughing up blood);
• edema (swelling) of the ankles, abdominal heaviness and bloating, in advanced stages with right heart involvement;
• stroke or peripheral embolism, sometimes as the first presentation of the disease.

It is important to know that symptoms can worsen suddenly when a condition with tachycardia appears, even though the situation had been stable. Some patients adapt without realizing by reducing their activity, so any change in tolerance of walking, climbing stairs or sleeping lying flat should be reported to the doctor.

How it is diagnosed

Clinical suspicion arises from the physical examination. On auscultation the cardiologist hears a low-pitched diastolic murmur at the apex, resulting from turbulent flow through the narrowed valve and often preceded by an opening snap, which occurs when the stiffened leaflets reach the limit of their movement. Confirmation and grading are done with echocardiography.

Transthoracic echocardiography is the essential examination and often the only one needed. It assesses:

• valve morphology: leaflet thickening, calcification, restricted motion and the “doming” of the anterior leaflet in diastole;
• the mitral valve area (MVA), measured by direct planimetry or calculated from the pressure half-time;
• the mean transmitral gradient. It depends on heart rate and flow, so it is always interpreted together with the pulse;
• systolic pulmonary artery pressure, left atrial size, right ventricular function and the tricuspid valve;
• accompanying mitral regurgitation and, if present, a thrombus in the atrium;
• suitability for balloon valvuloplasty, using the Wilkins score: four elements (leaflet mobility, valve thickening, calcification, subvalvular changes) are each graded 1–4; a total of 8 or less suggests suitable anatomy.

The ECG may show left atrial enlargement (a prolonged, notched P wave, “P mitrale”), atrial fibrillation and signs of right heart strain. When the arrhythmia is intermittent, a 24–48-hour Holter ECG documents it. When transthoracic echocardiography does not give a complete answer, for example before an intervention or to exclude thrombus in the left atrial appendage, transesophageal echocardiography is needed; it is not performed at the polyclinic and is recommended at a specialized center. When symptoms do not match the resting ultrasound findings, the cardiologist may suggest additional tests at a specialized center.

Follow-up and treatment

Treatment has two components: medical therapy, which relieves symptoms and prevents complications, and intervention on the valve, which restores its opening. No drug widens the narrowed valve; medicines act on the hemodynamic consequences.

Medical therapy

• Heart rate control with beta-blockers, non-dihydropyridine calcium channel blockers (verapamil, diltiazem) or digoxin. Lengthening diastole lowers the transmitral gradient and atrial pressure, which eases dyspnea; in atrial fibrillation these drugs also control the ventricular rate.
• Diuretics reduce volume overload (pulmonary congestion and edema) and are accompanied by salt restriction in the diet.
• Oral anticoagulation is indicated in atrial fibrillation (paroxysmal, persistent or permanent), after a thromboembolic episode and when thrombus is documented in the atrium. The drugs of choice are vitamin K antagonists (warfarin) with INR monitoring, usually targeting 2–3. The newer oral anticoagulants (DOACs) are not recommended in moderate-to-severe mitral stenosis, because in the INVICTUS trial (2022) rivaroxaban was less effective than a vitamin K antagonist in patients with atrial fibrillation and rheumatic valve disease. Patients should not change their anticoagulant on their own.
• Secondary prophylaxis with penicillin in patients with a history of rheumatic fever: intramuscular benzathine penicillin every 3–4 weeks, or daily oral penicillin. It prevents new attacks that would worsen valve damage. The duration is many years, usually until about age 40 or at least 10 years after the last attack, as appropriate, and is determined by the doctor.

Patients with valve disease should maintain careful oral hygiene and treat infections promptly, because bacteremia originating from the oral cavity is a possible source of infective endocarditis.

When the valve needs to be opened

Intervention on the valve is recommended when stenosis is significant (MVA ≤ 1.5 cm²) and causes symptoms. In selected cases it may also be recommended without symptoms, when there are risk markers such as raised systolic pulmonary pressure at rest (about 50 mmHg or more) or newly appeared atrial fibrillation. There are two approaches:

• Percutaneous balloon mitral commissurotomy (balloon valvuloplasty) is the first-choice intervention when anatomy is suitable (Wilkins score ≤ 8, no thrombus in the atrium, no more than mild mitral regurgitation). A catheter is introduced through the femoral vein, passes into the left atrium across the interatrial septum, and an inflated balloon separates the fused commissures. It needs no thoracotomy and results are durable for many years, although restenosis is possible.
• Valve surgery (replacement, rarely repair) is indicated when a balloon is not suitable: heavy calcification, unfavorable anatomy, significant accompanying regurgitation or thrombus that does not resolve with anticoagulation. Mechanical prostheses are durable for life but require lifelong warfarin with a higher INR (usually around 3); biological prostheses do not require this permanent anticoagulation but degenerate after 10–15 years and may need replacing.

The decision is made by the heart team (cardiologist, cardiac surgeon and imaging specialist) according to valve anatomy, symptoms, age, comorbidities and patient preference. These procedures are not performed at Tirana Polyclinic; the cardiologist directs you to the appropriate center and follows you before and after the intervention.

Check-ups

Mitral stenosis is followed with a cardiology visit, ECG and echocardiography, usually every 6 months to a year, or sooner when the doctor considers it reasonable: with new symptoms, with newly appeared atrial fibrillation, during fever or severe infection, and before and during pregnancy. The aim is to identify the right time for intervention before irreversible damage to the pulmonary circulation and the right heart.

Activity, pregnancy and daily life

Physical activity. Exertion raises heart rate and transmitral flow, so the permitted level depends on the severity of the stenosis. In mild stenosis most activities are allowed; in significant stenosis maximal exertion and intense sports are avoided. Regular walking at moderate intensity is advisable. The cardiologist should be consulted before demanding sports, high altitude or long journeys.

Diet and habits. Salt restriction helps control fluid retention. Alcohol and caffeine in large amounts can trigger arrhythmia. Patients taking warfarin should keep their intake of vitamin K-rich foods (spinach, broccoli, cabbage) steady, because fluctuations affect the INR.

Pregnancy. During pregnancy circulating blood volume rises by 40–50% and heart rate by 10–20 beats per minute, while diastole shortens; the transmitral gradient therefore rises markedly. A stenosis that had caused no complaints can lead to pulmonary edema or atrial fibrillation, with risk to the mother and the fetus. Every woman with mitral stenosis who plans a pregnancy should be assessed by a cardiologist before conception; when the stenosis is significant, treating the valve before pregnancy is recommended. During pregnancy therapy, including anticoagulation, is adjusted by trimester, because some drugs, such as warfarin, are not suitable in every period. With close monitoring many women have pregnancies and deliveries without complications.

Preventing rheumatic fever. Every pharyngitis with fever, especially in children, should be assessed by a doctor and, when streptococcal, treated with an antibiotic for the full prescribed course. This is the most effective measure to prevent rheumatic fever and its consequences for the heart.

When to see your doctor

Contact your doctor without waiting for the next check-up when dyspnea or fatigue increases, when you wake at night short of breath or cannot sleep lying flat, when palpitations or leg swelling appear, or when you have a fever after a sore throat. Call 127 for the signs listed in the emergency box above. This information is educational and does not replace a medical visit.