Critical Care Medicine

Mitral incompetence; mitral regurgitation

Mitral incompetence

Synonym

Mitral regurgitation (MR)

1. Description of the problem

After aortic stenosis, mitral incompetence is the second most frequent valvular disease in hospitalized patients.

Options for medical treatment of chronic MR remain limited. Valve repair, in the hands of an experienced surgeon, is preferred over valve replacement when the time comes for surgery.

Clinical features

Chronic MR

Characterized by a holosystolic murmur, heard loudest at the apex and radiating to the axilla. The murmur is loudest in expiration.

There may be evidence of cardiac decompensation, with an S3, bibasal rales on auscultation of the lungs, a raised JVP, hepatomegaly and lower limb edema. Lateral displacement of the apex beat occurs in LV dilatation. There may be signs of pulmonary hypertension, such as a loud P2. Atrial fibrillation is not uncommon as the left atrium becomes dilated and scarred in chronic MR

Acute MR

In acute MR, patients can present in cardiogenic shock and pulmonary edema. The murmur tends to be more early systolic and softer in intensity. In anterior chordal rupture the murmur may radiate to the base of the heart and the back, rather than the axilla. The left atrial 'v' wave is markedly elevated.

Key management points

Acute MR should be dealt with as an emergency (see below). For chronic MR the cause of the valvular dysfunction should be clarified. LV dysfunction and dilatation is a common cause of MR, and use of ACE inhibitors and beta-blockers in this setting can reduce the severity of the MR. Bi-ventricular pacing has also been shown to improve functional MR secondary to LV dysfunction. Diuretics and nitrates are used for symptoms of pulmonary congestion. Close outpatient clinical and echocardiographic monitoring is required to assess progression of valve dysfunction, particularly with respect to timing for surgical intervention.

2. Emergency Management

Acute severe MR leads to reduced forward output and pulmonary congestion. This state is usually poorly sustained and therefore urgent surgical referral is warranted. In normotensive patients nitroprusside is used to increase forward output and reduces pulmonary congestion.

Dobutamine or other intotropes can be used along with nitroprusside if the patient is hypotensive. Insertion of an intra-aortic balloon pump (IABP) improves mean arterial pressure and decreases MR and can be used as a bridge to definitive surgical intervention.

In cases where bacterial endocarditis is suspected, multiple (4-6) blood culture samples should be reserved. Following consultation with local microbiology services, antibiotic therapy should be initiated as early as possible.

3. Diagnosis

Most commonly diagnosed following auscultation of the characteristic holosystolic murmur on clinical examination.

Following clinical examination, transthoracic echocardiography (TTE) is used to confirm the diagnosis and quantify the severity of the MR. The severity of the MR can be assessed using a number of different techniques, including visualization of the color flow jet, measurement of the narrowest portion of the proximal regurgitant jet (vena contracta), the proximal isovelocity surface area (PISA) and the regurgitant orifice area (ROA). With severe MR flow reversal in the pulmonary veins will be seen. TTE will also enable clarification of LV dimensions and systolic function, as well as estimations of pulmonary pressures. The TTE should also provide the anatomic cause for the MR. If that is not feasible, due to poor images, etc., you should proceed to transesphogeal echocardiography (TEE).

Differential Diagnosis for Holosystolic Murmur of MR

Aortic Stenosis - The classic early-systolic murmur in AS can extend later into systole in severe AS. It may also be loudest at the apex (the Gallavardin phenomenon).

Tricuspid Regurgitation - TR is also pansystolic, but is loudest at the lower left sternal edge. It also increases in inspiration.

Ventricular Septal Defects - The holosystolic VSD murmur is also loudest at the lower left sternal edge.

A ruptured sinus of Valsalva aneurysm or patent ductus arteriosus - These rarities can be confused with MR, but their murmurs tend to be continuous and extend into diastole.

In any situation where there is doubt as to the cause of the auscultated murmur, TTE will clarify the diagnosis.

Confirmatory tests

TEE, either in 2D or 3D, is used to further evaluate the etiology of MR. For example. it can clearly define to the cardiac surgeon which scallop may be prolapsing and whether the valve is repairable versus the necessity for valve replacement. Right heart and pulmonary pressures can be measured with a Swan-Ganz cathether inserted via the right internal jugular. This allows us to assess pulmonary hypertension secondary to the MR. Prior to any planned surgery for the valve, a diagnostic coronary angiogram is done to ensure that there is no concomitant coronary artery disease that may need grafting at the time of surgery.

4. Specific Treatment

When patients fulfill the criteria for surgical treatment, the next key decision is whether to repair or replace the valve.

In centers with surgeons experienced in valve repair, it is the preferred strategy over valve replacement whenever possible.

Figure 1 shows a pathway for treatment of chronic MR.

Figure 1.

Treatment pathway for chronic mitral regurgitation

Drugs and dosages

Niroprusside is diluted in 5% glucose and administered at a dose of 0.5 - 8.0 micrograms per kilogram per minute, titrating to blood pressure. Nitroprusside solution should be wrapped in a foil container to protect it from sunlight.

Dobutamine is infused via a central line or long peripheral line at a dosage usually of 2.5 - 10 micrograms per kilogram per minute. It can be given at a dose of up to 40 micrograms per kilogram per minute.

ACE inhibitors and beta-blockers are given as per their standard doses.

Surgery

Mitral valve replacement has been traditional "gold-standard" surgical correction, but MV repair now advocated because it offers

  • improved long- and short-term mortality vs. traditional replacement

  • less post-operative LV dysfunction

  • less risk of thromboembolism as compared with metal MVR

MV repair is particularly used in cases of

  • younger patients

  • prolapsing leaflet

  • chordal rupture

  • perforation of a leaflet secondary to endocarditis

Repair should be accompanied by insertion of a annuloplasty ring to decrease functional MR secondary to a annular dilatation in ischemic and idiopathic LV dilatation. Should be directed by intra-operative TEE to ensure a good post-operative result with minimal residual MR. Surgery can be accompanied by a Maze procedure if the patient has atrial fibrillation.

Percutaneous options

Percutaneous clip is available for MR; it is inserted under TEE guidance via an atrial trans-septal puncture. The clip grasps the leaflets, forcing coaptation. Initial trials have shown that it is not as successful as conventional surgery in reducing MR, though it was associated with less periprocedural adverse events. This represents a field of ongoing development within interventional cardiology.

5. Disease monitoring, follow-up and disposition

Follow-up is required to reassess symptoms and functional capacity. TTE is used to assess changes in severity of regurgitation, LV size and function and increased pulmonary pressures.

Severe MR

Patients with severe MR should be seen every 6 to 12 months for a history, physical examination and echocardiogram.

Moderate MR

Patients require the above assessment annually or more frequently depending on symptoms.

Mild MR

Patients can be followed annually, but echocardiography is not needed unless there is a change in symptoms.

After Surgery

Early follow-up is required to assess post-operative LV function and detect surgical failure.

Pathophysiology

Mitral incompetence is due to dysfunction of any one of the mitral annulus, mitral leaflets, chordae tendinae, or papillary muscles (see below).

Chronic MR

LV dilates with eccentric hypertrophy. Preload is elevated through Frank-Starling mechanisms. Much of the increased LV volume is regurgitated into the left atrium, so the afterload is normal. Because of the increase in preload and normal afterload, stroke volume increases. The left atrium dilates secondary to increased left atrial pressure in systole. Pulmonary arterial hypertension develops as the tone of pulmonary arteries increases to protect the pulmonary capillaries from the increased pressure. Patients with MR, even severe MR, may remain asymptomatic or minimally symptomatic for years until finally decompensation occurs through loss of myocardial contractility. At this stage, with only a moderate reduction in ejection fraction, contractility can be severely and irreversibly impaired. At this stage, LV dysfunction and enlargement evokes a cycle of worsening MR and LV dysfunction.

Acute MR

In acute MR the compensatory mechanisms of chronic MR do not have sufficient time to develop. A marked increase in left atrial pressure feeds through to give a dramatic rise in pulmonary capillary pressure, and pulmonary edema ensues. Total stroke volume is increased, but because of the regurgitant stroke volume the overall forward stroke volume is diminished, leading to forward failure.

Causes of MR

Chronic MR

Mitral valve prolapse

Papillary muscle dysfunction - LV failure or ischaemia

Mitral annular dilatation secondary to LV dysfunction

Connective tissue disease - Marfan's syndrome, rheumatoid arthritis

Congenital heart disease - Atrioventricular canal defect

Acute MR

Myocardial Infarction (usually inferior) - rupture or dysfunction of papillary muscle

Infective endocarditis

Spontaneous rupture of a myxomatous chord

Epidemiology

After aortic stenosis, MR is the second most common valvular abnormality in the US. Most common cause is mitral valve prolapse, which is estimated to affect 4% of the population. In developing countries rheumatic heart disease remains the most common cause of MR. It is also worth remembering that up to 20% of middle-aged or older people have evidence of at least mild MR with Doppler echocardiography studies.

Prognosis

MR is progressive and, with severe MR secondary to flail leaflets at 10 years, 90 percent have died or undergone surgery. The annual mortality rate in this group is up to 6.3%, highest if there is LV dysfunction. Post-operative mortality is approximately 6% for replacement and 2% for repair. Mortality increases if associated with CABG, in presence of LV dysfunction, or severe symptoms.

Special considerations for nursing and allied health professionals.

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What's the evidence?

Bonow, RO. "ACC/AHA 2006 Guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/ American Heart Association Task force on Practice Guidelines (writing committee to revise the 1998 Guidelines for the Management of Patients with Valvular Heart Disease): Developed with the collaboration with the Society of Cardiovascular Anesthesiologists; endorsed by the Society for Cardiovascular Angiography and Interventions and the Society for Thoracic Surgeons". Circulation. vol. 114. 2006. pp. e84-231.

The definitive guidelines from the ACC/AHA for the treatment of all valvular diseases.

Enriquez-Serrano, M. "Valve repair improves the outcome for surgery for Mitral Regurgitation: a multivariate analysis". Circulation. vol. 91. 1995. pp. 1002-1028.

195 patients with MV repair were compared to 214 with MV replacement and were shown to have significantly better 10-year survival (68% vs 58%). The authors advocate MV repair, where feasible, as the operation of choice for MR.

Enriquez-Serrano, M. "Echocardiographic prediction of survival after surgical correction of organic mitral regurgitation". Circulation. vol. 90. 1994. pp. 830-837.

Pre-operative LV dysfunction in patients with MR is a marker of poorer post-operative outcome. This eveidence suggested that patients should be operated on earlier, even if asymptomatic.

Feldman, T. "Percutaneous repair or surgery for mitral regurgitation". N Engl J Med. vol. 364. 2011. pp. 1395-1406.

Initial experiences with novel percutaneous treatments for MR, comparing outcomes to those of patients undergoing conventional surgical treatment.

Nishimura, RA. "ACC/AHA guideline update on Valvular Heart Disease: Focused update on Infective Endocarditis: A Report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines Endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Intervention, and Society of Thoracic Surgeons". Circulation. vol. 118. 2008. pp. e523-e661.

An update on the 2006 guidelines, with reference to endocarditis

Ling, LH. "Clinical outcomes of mitral regurgitation due to flail leaflet". N Engl J Med. vol. 335. 1996. pp. 1417-1423.

An observational study following outcomes in 229 patients with severe MR due to flail leaflet, revealing the high mortality in patients with this condition, even if asymptomatic.
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