Mitral valves: how to assess them.

 

Remember the very basic fact: mitral closes in systole and opens in diastole. Blood flows through it during diastole. If there is a narrowing of the valve the sound made, a murmur will be heard in diastole. So if you hear a diastolic murmur (it comes after not with the carotid pulse) listen carefully and note whether its onset is as soon as you hear the second heart sound, in which case it is called an early diastolic murmur and is originating from the aortic valve which is leaking as its leaflets (remember there are three of them) are failing to meet together to prevent the leak of the blood back into the left ventricle). If there is a gap between the murmur and the second heart sound then it is a mid-diastolic murmur and is coming from a tight mitral valve. It may be preceded by a clicking sound the opening snap.

What does an opening snap indicate? It indicates that the mitral valve leaflets are still mobile and sclerosis and calcification are not significance. This is usually interpreted that  a valvolvotomy or simply nicking the commissures will allow the valve area to enlarge and the patient can carry on with improvements in his/her symptoms for several years. This is useful where medical facilities are not available for a valve replacement and the follow up that is required after putting in a new valve. This is very important. In rural populations like in Pakistan when the patient is anticoagulated, they will comply with the medication but will not be able to come to a hospital regularly to have their INR or bleeding time monitored. Death or a life threatening situation may arise if the patient is using manually operated machinery for example for cutting fodder for their animals. Here is where your information about what chores they will be doing at home will come in handy. Remember to ask about this in the biosocial history.

The mid diastolic murmur may become louder just before it ends. As the murmur is followed by the first heart sound which may not be well heard at the mitral area and the systole begins soon after, this is called presystolic accentuation.

What does the presystolic accentuation imply? It means that the left atrium is still capable of contracting effectively and pushing 25% of the cardiac output into the left ventricle. this happens when there is sinus rhythm and no atrial fibrillation, AF prevents the left atrium from contracting effectively hence no pre-systolic accentuation,

What is likely to happen when you cardiovert an AF to sinus rhythm? As the atrium has been contracting inadequately blood accumulates and tends to coagulate to form a thrombus. When the atrium contracts effectively in sinus rhythm the effective “push” moves a thrombus into the left ventricle from where it moves into the aorta and bits of it may enter and lodge in the coronary arteries, cerebral arteries or elsewhere in the systemic circulation.

Why do you need to administer heparin  before restoring sinus rhythm? To prevent systemic embolisation and resultant disability.

What will you hear if the mitral valve is leaky (regurgitant)? The mitral valve closes during systole and prevents blood from going back into the left atrium as the left atrium contracts and pumps blood into the aorta to ensure a systemic circulation. The sound of a mitral regurgitation or leak is heard during systole over the designated mitral area but is loud enough to be heard elsewhere. It starts as soon as the left ventricle starts contracting so usually drowns out the first heart sound  which is caused by closure of the mitral valve and tricuspid valves. The murmur continues until the second heart sound signals the onset of diastole. As pulmonary hypertension is a very late feature of MR a loud P2 is unexpected. If you do hear it be prepared to say that mitral stenosis coexists. 

What is an echocardiogram? Echocardiography uses standard two-dimensional, three-dimensional, and Doppler ultrasound to create images of the heart.

What do we see on on an M-mode echocardiogram? We see movements of the mitral valves as blood flows into the left atrium through the valve. There is a gush of blood as the valve opens. As the left ventricle is almost but not quite empty and the pressure gradient between it and the atrium is high. As the pressure gradient reduces the blood from the pulmonary arteries continues to trickle into the left ventricle, the atrium acting as a conduit and then the left atrium contracts and another gush of blood flows into the left atrium.

Here is what you see on an M-mode echocardiogram — The M-mode examination is performed from the precordium and guided from the 2D long and short axis views. Normally, the anterior mitral leaflet exhibits a motion pattern that reflects the phasic nature of ventricular filling and produces a familiar M-shaped pattern. The posterior leaflet moves in a nearly mirror image “W” pattern with a smaller excursion.

  • The initial large opening diastolic movement of the valve, which culminates in the E-point, is the result of rapid left ventricular (LV) filling.
  • The valve assumes a nearly closed position during the middle of diastole (F point), reflecting the deceleration of inflow as the pressure gradient between atrium and ventricle is reduced. On the M-mode echocardiogram, this early diastolic closure is measured as the E-F slope, which is usually >60 mm/sec.
  • During this mid-diastolic phase, in spite of the appearance of closure, there continues to be flow of blood from pulmonary veins to the LV. This period of filling is known as the conduit phase because the atrium briefly functions as a passive channel rather than a reservoir.
  • Following atrial contraction, the valve opens for a second time (A point), completing the second peak of the letter M.
  • Final closure is probably the combined effect of deceleration of atrial inflow and isometric LV contraction.

Two-dimensional echocardiogram — The 2D appearance of the normal mitral valve on TTE depends somewhat upon the imaging plane from which it is viewed. In the parasternal short axis plane, the valve presents itself as an ovoid (fish mouth) orifice, while in parasternal long axis and apical views, it resembles clapping hands, with the anterior hand longer and more mobile than the posterior. In general, the normal mitral valve should appear as a mobile, two leaflet structure that moves freely enough to respond to the normal flux of diastolic filling but forms a stable coaptation plane in systole without breaking the plane defined by the mitral annulus and entering the body of the left atrium.

Anatomically, the mitral valve leaflets are thin and translucent; the rough attachment points of its chordae to their free margins are thicker than their smooth bellies. The chordae from each leaflet connect to both papillary muscles. On M-mode, each leaflet is represented by no more than two linear echoes. On 2D imaging, the valve appears homogeneous and thin, <4 mm in thickness. However, the perception of leaflet thickness also depends upon the transducer frequency.

Doppler echocardiogram — Doppler examination of the normal mitral valve reveals that the velocity pattern of blood entering the LV during diastole closely resembles the M-shaped pattern of the M-mode of that structure; blood flow is most rapid during the early (E) phases of filling, falls to very low levels during the mid-diastolic conduit phase, and accelerates again during atrial (A) contraction.The normal peak flow velocity across the mitral valve is usually just under 1 m/sec and the normal mitral valve area is 4 to 6 cm2.

Three-dimensional echocardiogram . Three-dimensional TTE (transthoracic echocardiogram) image acquisition is performed from the parasternal and apical views, using zoomed or full-volume feature. Changing the display enables visualization of the mitral valve from either the LV or the left atrium (“surgical”) perspective and allows for precise lesion localization.

How can you measure the size of the left ventricle precisely?

This can be done either with a 3D  TTE or a TEE. Echocardiography allows for accurate LV measurements as it avoids LV foreshortening. Subvalvular apparatus can be seen from the LV perspective. Three-dimensional TEE has superior resolution compared with 3D TTE and is a critical aid in percutaneous mitral valve repair.

Role of cardiac magnetic resonance in mitral regurgitation — Cardiac magnetic resonance (CMR) can be clinically useful in the assessment of mitral regurgitation, including identifying the mechanism of mitral regurgitation, quantifying its severity, and determining its cardiac consequences including LV and left atrial volumes.  However, CMR and echocardiographic findings can be discordant, and an integrated approach should be used with caution. In instances where CMR and echocardiographic findings are discrepant, careful history and auscultation may be helpful.

Almost all cases of MS seen in adults are rheumatic in origin. After a bout or several bouts of rheumatic fever the ongoing inflammation in the myocardium, which can be detected as Aschoff’s nodules on atrial biopsy, results in scarring and contraction of the valves, mitral in particular. Initially there is thickening of the valve cusps, followed by the deposition of fibrin and the formation of nodules on the edges of the cusps which then become confluent, the commissures (junction of the valve leaflets) start closing in, resulting in the loss of the surface area of the valve opening. Clinical MS can be manifest by as early as 11/2 years after a severe bout of rheumatic fever and most patients have evidence of MS in 10 years. Cases of rheumatic fever followed up for 45 years show damage to the mitral valve in 75% of patients even if they were not diagnosed initially as MS.

Remember rheumatic fever itself is an autoimmune disease caused by immunity to epitopes on streptococcus beta hemolyticus. These antibodies then attack the connective tissue in joints which are not permanently damaged and the heart which is damaged, and the brain where rheumatic chorea develops but leaves no lasting damage.

Are there other causes of MS?

  • Congenital MS in the form of a parachute valve is seen in infants and children. Please do not diagnose it in an adult or adolescence.
  • Mitral annular calcification (MAC) develops from progressive calcium deposition along and beneath the mitral valve annulus. MAC generally follows the C-shape of the mitral annulus, so the base of the anterior mitral leaflet is generally (but not always) spared. Although data on the pathophysiology of MAC are very limited, an atherosclerotic process similar to that observed for calcific aortic valve disease has been proposed since atherosclerosis and MAC are strongly associated. Data are relatively sparse on the natural history of MS caused by MAC (also known as senile calcific MS since the prevalence of MAC increases with age).
  • Progressive calcification of the mitral valve annulus can develop after radiation therapy for Hodgkin’s disease.
  • Diseases like Fabry’s disease.
  • Symptoms and signs similar to mitral stenosis occur in left atrial myxoma, a benign tumour found in the left atrium.

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shaheenmoin

I am a Professor of Medicine and a Nephrologist. Having served in the Army Medical College, Pakistan Army for 27 years I eventually became the Dean and Principal of the Bahria University Medical and Dental College Karachi from where I retired in 2016. My passion is teaching and mentoring young doctors. I am associated with the College of Physicians and Surgeons Pakistan as a Fellow and an examiner. I find that many young doctors make mistakes because they do not understand how they should answer questions; basically they do not understand why a question is being asked. My aim is to help them process the information they acquire as part of their education to answer questions, pass examinations and to best take care of patients without supervision of a consultant. Read my blog, interact and ask questions so that I can help you more.

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