45. Mitral Stenosis- Clinical Scenarios

Marek Polomsky, MD, and Robert A. Guyton, MD

Concept

• Indications for mitral valve replacement (MVR) in setting of mitral stenosis (MS)
• Preoperative conditions
• Valve choices
• Critical steps of MVR
• Pitfalls and alternative solutions

Chief complaint

“A 53 yrar-old immigrant man presents with a diagnosis of mitral stenosis. His primary care physician heard a diastolic apical heart murmur, and subsequent echocardiogram revealed severe mitral stenosis.”

Differential

The diagnosis of mitral stenosis is established. Differential causes of mitral stenosis include rheumatic heart disease (majority), congenital malformation, infective endocarditis (IE), mitral annular calcification, rheumatologic disorders, endomyocardial fibrosis, conditions that obstruct the mitral valve (left atrial myxoma, cor triatriatum), and prosthetic valve complications (thrombosis, calcification).

History and physical

A focused history is performed to elicit symptoms of dyspnea and hemoptysis, as well as chest pain and hoarseness, which occur less frequently. Symptoms are brought on by any situation that increase the transmitral pressure gradient (exertion, stress, exercise, tachycardia, fever, infection, atrial fibrillation (AF), pregnancy). Many patients deny symptoms because progression of disease is very slow, thus there is a gradual decrease in activity and exercise tolerance. MS can present with complications such as AF, pulmonary edema, embolic events, IE, and right heart failure. One should ascertain whether there is a prior history of rheumatic heart disease (if treated and which kind of antibiotics) and if the patient is an immigrant from another country. A complete physical should be performed focusing on the cardiovascular exam with presence of murmur (low-pitched diastolic rumble most prominent at the apex), opening snap of the mitral valve heard at the apex, and signs of right heart failure indicative of advanced disease. Pinkish blue patches on cheeks (“mitral facies”) may be present from vasoconstriction due to low cardiac output.             

Tests

• EKG. An EKG is performed to assess for any arrhythmias (particularly AF). In addition, a broad p-wave that is notched with increased amplitude (“p-mitrale”) from left atrial (LA) hypertrophy or enlargement may be present.
• Echo (M-mode, two-dimensional and color Doppler flow mapping). Echocardiography is used to assess morphology of the valve apparatus and subvalvular structures (chordae and papillary muscles), measurement of valve orifice, Doppler transvalvular gradient and valve area (calculated from diastolic velocity curve), coexisting mitral regurgitation, pulmonary pressures, systolic function, exclusion of LA thrombus, and size of LA, left ventricle, and right ventricle. Transesophageal echo (TEE) is generally preferred over transthoracic echo (TTE).
• Cardiac catheterization. Cardiac catheterization is performed in order to assess the coronaries, mitral valve gradient, and pulmonary artery pressures.
• CXR. LA enlargement, a calcified mitral annulus, and pulmonary vasculature congestion or cephalization may be visible on a CXR. If aorta appears calcified check CT.
• Stress echo (exercise or dobutamine stress echo). A stress echocardiogram is used to objectively evaluate exercise activity, which is important for provocation of symptoms in inactive patients, and to assess pulmonary artery pressures with exertion.

Index scenario (additional information)

“The patient had history of rheumatic heart disease as child, and after diagnostic work-up was found to have very calcified severe MS (valve area 0.8 cm²) with severe pulmonary hypertension (70 mmHg). He is mildly symptomatic.”

Treatment/management

This patient meets criteria for mitral valve replacement. Surgery (MVR) is indicated (2006 ACC/AHA guidelines) in patients who are found to have moderate-severe MS (MV area < 1.5 cm²), NYHA class III or IV symptoms, and the valve is not amenable to either percutaneous mitral balloon valvuloplasty (PMBV). In addition, mildly symptomatic patients (NYHA II) with severe MS and pulmonary hypertension (PAP > 50 mmHg at rest, > 60 with exercise) who are not candidates for valvulotomy are considered for surgery. Severe PHTN, however, raises a red flag. It is hard to tell whether this will be readily reversible or not. It is worth a chance, but care must be taken in the postoperative setting. PMBV is not appropriate if there is presence of LA thrombus that persists despite anticoagulation, mitral valve is nonpliable or severely calcified, or if there is moderate-severe mitral regurgitation (MR). Wilkins score > 8 predicts failure with valvuloplasty (leaflet mobility, thickening, calcs, subvalvular apparatus). Mechanical prosthesis is recommended in this patient, and in patients that present young (< 65 yo) especially with long standing AF. A bioprosthetic valve would be indicated in patients who are elderly, who cannot have warfarin, or who are not compliant.

Operative steps

Mitral valve replacement

Goals – relieve obstruction, replace the valve, protect the heart/coronaries, prevent further clot formation and embolization.

• Place central line with Swan-Ganz catheter, arterial line, general endotracheal anesthesia (GETA), foley.
• Assess mitral valve via TEE.
• Perform median sternotomy. Palpate for aortic calcifications +/- epiaortic US.
• Systemic heparin, aortic cannulation, 3-stage venous or bicaval cannulation, retrograde cardioplegia cannula.
• Initiate cardiopulmonary bypass (CPB) once ACT level appropriate (400-600), +/- cooling (28-32° C).
• Cross-clamp, run cold blood antegrade cardioplegia, followed by retrograde.
• Vertical left atriotomy incision in Sondergaard’s groove anterior to the right pulmonary veins (or use exposure of choice).
• Place sump vent into LA in dependent position near left superior pulmonary vein.
• Inspect the mitral valve.
• Note: perform any necessary afib procedures such as left atrial appendage excision/ligation/ MAZE at this time to avoid manipulating the heart too much after the prosthesis is in place.
• Excise calcified leaflets leaving 1-2 mm of leaflet tissue along the annular circumference, dividing chordae along tips of papillary muscles (preserve subvalvular apparatus and papillary muscle-chordal-leaflet attachments whenever possible, but not at the expense of outflow tract obstruction in a small ventricle). Usually the posterior leaflet can be salvaged to maintain continuity while the anterior is resected.
• Size the valve, place horizontal mattress sutures 8-10 mm apart (usually with pledgets) around the annulus, everting (atrium –ventricle) for mechanical valve, and non-everting for bioprosthetic valve (ventricle-atrium) or calcified annulus.
• Pass sutures through sewing ring and seat the valve. Mechanical valve should be in anti-anatomic position, bioprosthetic valve with largest leaflet facing the left ventricular outflow tract (LVOT) avoiding outflow obstruction. Use a dental mirror to double check.
• Tie down sutures and start rewarming if cool.
• Close left atriotomy with 3-0 or 4-0 prolene, leaving LV vent.
• Give hot shot cardioplegia before releasing the cross-clamp, deair, wean from bypass, and assess valve by TEE, leave pacing wires.

Potential questions/alternative scenarios

“Patient is a pregnant female.”

In previously asymptomatic female, elevations in heart rate and cardiac output during pregnancy can increase the transmitral gradient which can lead to symptoms. Medical management should be the first line of therapy, and if fails then anatomically suitable valves can undergo PMBV. Mitral valve surgery during pregnancy is associated with an increased maternal and fetal risk. Females with MS planning to become pregnant should have their MS treated prior to conception.       

“Patient has a non-calcified and pliable mitral valve.”

The patient is candidate for PMBV or open commissurotomy and valve repair. Patients who have pliable and non calcified valves, with little or no subvalvular fusion and no calcification in commissures, absence of 3+ or 4+ MR (moderate – severe MR), and no LA thrombus are candidates for PMBV or open commissurotomy and valve repair. If there are not any contraindications, PMBV should be performed first. Extent of valve pathology dictates PMBV vs. open commissurotomy and repair (“soft” rheumatic changes without extensive subvalvular pathology are amenable to PMBV). In addition, patients who are at high surgical risk from comorbidities to undergo MVR should be considered for PMBV.

“In what order would you proceed with concomitant AVR, TVR, or CABG.”

Distal coronary anastomoses are performed first, which avoids lifting of the heart after mitral prosthesis is placed and allows using the bypass grafts for cardioplegia. Aortic valve leaflets are excised, and then perform MVR. Then perform AVR. TVR is performed after MVR, and it can be performed after removing the cross-clamp.

“A 64-year-old female with ESRD has severe mitral annular calcification (MAC).”

Patients with ESRD are at increased risk for MAC. The degree of MAC influences the surgical approach. Mild amounts can be handled by placing the sutures in an inverted manner (ventricle → atria) around or even through the calcium (if soft enough). Moderate amounts can be debrided until you have a smooth symmetrical surface for the prosthesis to attach. You can then take the inverted sutures along the posterior half of the annulus and pass them through a pericardial patch or felt strip before going through the sewing ring for additional reinforcement. Greater degrees of MAC may require radical debridement of the calcified annulus down to epicardial fat followed by reconstruction with a pericardial patch (autologous pericardium or glutaraldehyde-fixed bovine pericardium) that saddles/sandwiches the annulus. The patch is attached to LV endocardium on the LV side and atrial tissue on the LA side. Valve sutures would then pass through the patch going from the LV to LA and then the sewing ring. Other alternatives include seating the mitral prosthesis at the intra-atrial level with the aid of a Dacron collar. Be sure you are familiar with these approaches before describing or performing them.

“You discover AV groove rupture.”

Atrioventricular groove rupture can occur if the sutures are placed too deep, if there is excessive retraction, if the heart is massaged too vigorously at time of deairing, or if there is overly aggressive debridement or decalcification of the posterior leaflet and annulus. If an AV groove rupture is discovered rearrest the heart if not already cross-clamped and close the full extent of the tear with a pericardial patch. The patch should be secured by sutures into healthy myocardium for a tension-free repair, with careful placement of sutures near coronary vessels.

“After coming off bypass EKG changes are noted in the lateral leads with lateral wall motion abnormalities and depressed ventricular function.”

A circumflex artery injury is suspected which can happen if sutures are placed too deep along the posterior annulus. In order to fix this problem, a RSVG to the circumflex artery distribution will be needed.

“After removing cross-clamp you see increased LV distention.”

An aortic valve injury may happen when sutures are placed too deep across the anterior annulus, thus injuring the non-coronary or left aortic valve cusps. It is recognized once one removes the cross-clamp and sees the LV distend due to aortic insufficiency, which can be visualized on TEE as well. Re-arrest the heart, open the aorta and left atrium, and after inspection remove the offending suture or possibly the whole mitral prosthesis. The aortic cusp will need to be repaired or replaced.

“Conduction block post-op.”

A conduction block can happen if one takes sutures too deep near the posterior commissure and right trigone where the AV node and Bundle of His can be injured. Often with radical debridement there is no other room to place sutures. If the conduction disturbance does not improve after several days post-op, a permanent pacemaker will be needed.

“When coming off bypass you note increased gradients across the left ventricular outflow tract (LVOT).”    
LVOT obstruction can occur from the prosthesis if it is a high-profile mechanical valve, large stented biologic valve posts, or even from low-profile valves that are not properly seated. Typically, one will need to replace the valve with a lower profile valve. In addition, if one leaves the mitral anterior leaflet unresected with chordal sparing techniques, systolic anterior motion (SAM) can occur due to retained anterior leaflet and chordae, especially if there is septal hypertrophy. In general SAM usually improves if one stops inotropes, volume loads, adds beta-blockers, and adds vasopressors (increasing afterload). Occasionally one may need to perform an aortotomy with transaortic excision of the offending subaortic mitral tissue, and myectomy.

“Perivalvular leak on the postoperative echo.”

Most small leaks will stop after protamine administration. If there is a significant leak, then you will have to go back on bypass and fix or re-implant the valve.

“How would you manage patients postoperatively after MVR.”

Close attention should be paid to patient’s respiratory status and pulmonary pressures. If a patient develops or has elevated pulmonary artery pressures signifying severe pulmonary hypertension, more aggressive diuresis than usual will be needed. Right ventricular function may be compromised necessitating ionotropic and pulmonary vasodilatory therapy. Be very careful with volume overload on these patients. Run them high (inotropes) and dry (diuretics). Anticoagulation (AC) therapy will need to be initiated for mechanical valves (goal INR 2.5-3.5).

Pearls/pitfalls

• Mitral valve replacement is indicated for moderate-severe MS (MV area < 1.5 cm²), NYHA class III or IV symptoms, and the valve is not amenable to either percutaneous mitral balloon valvuloplasty (PMBV) or open commissurotomy.
• Mildly symptomatic patients (NYHA II) with severe MS and pulmonary hypertension (PAP > 50 mmHg at rest, > 60 with exercise) who are not candidates for valvulotomy are considered for surgery. Patients with severe MS and new onset afib are also considered for PMBV or replacement.
• Tissue valve in patients > 65 yo, sinus rhythm, and who cannot take or are non-compliant with warfarin.
• Order of concomitant procedures: distal coronary anastomosis → debride aortic valve → MVR → AVR → TVR (can be done w ccx removed).
• Overly aggressive debridement or retraction/lifting of the heart can lead to AV groove rupture.
• Deep valve sutures can cause injury to the circumflex artery, aortic cusps, and conduction system.

Suggested readings

• Yun KL and Miller DC. Acquired valvular heart disease: mitral valve replacement. Mastery of Cardiothoracic Surgery 2007. 378-390.
• Gallegos RP, Gudbjartsson T, and Aranki S. Mitral valve replacement. Cardiac Surgery in the Adult 2012.
• Bonow RO et al. 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). JACC 2006. 48:e1.