二尖瓣反流示意图

Mitral regurgitation/insufficiency

Basics:

Mitral regurgitation/insufficiency (MR/MI) results from a dilated mitral annulus, diseased leaflets, or abnormal leaflet coaptation (including a leaflet cleft). Severe MR can lead to left atrial enlargement, atrial fibrillation and heart failure since the heart must pump more to maintain adequate systemic flow. Left ventricular hypertrophy and impaired myocardial perfusion can result. Surgical correction is aimed at repairing the physical valve or replacing it with a tissue valve or mechanical valve. Mitral valve repair in pediatric patients is favored over mechanical replacement since it allows for growth and may preclude the need for lifelong anticoagulation, especially in active young patients. Repair of the valve may include placing an annuloplasty ring that helps control the annulus size and provide for improved leaflet coaptation. Mechanical replacement is more common as one progresses through the adult years.

Bypass notes:

• Maximum anticipated flow for equipment selection: 3.0 L/min/m2.

• Cardioplegia is required. Consideration must be given to higher cardioplegia delivery pressures/flows if significant ventricular hypertrophy exists. This will help ensure proper myocardial distribution of cardioplegia.• Bicaval cannulation is required.

• Left ventricular vent is common.

• Target temperature is 28–32 °C.

• Minimum dilutional hematocrit is 25–30%. An increased hematocrit before coming off bypass must be considered for sick myocardium.

• Valve irrigation solution is ideally scavenged with cell saver or wall suction.

• Valve testing solution may be scavenged with pump suckers or the cell saver suction.

• Excessive valve testing solution returned to the pump will require sodium bicarbonate for buffering. The patient’s sodium may rise if bicarbonate administration is regular.

• Consideration should be given to informing the surgeon of the sodium load when the patient’s sodium level rises above 150 mmol/L.

• Aggressive conventional ultrafiltration may be helpful in maintaining the hematocrit.

• DUF or ZBUF may be helpful in adjusting the sodium level when relatively large volumes of test solution are returned to the pump.• Severe and/or long-standing MR may negatively impact the pulmonary vasculature. Inhaled nitric oxide is com-monly made available when there is concern for pulmonary hypertension after bypass.

• It is not uncommon to see reoperative mitral valve repairs (See section “Reoperations” in Chapter 5)

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Figure 6.32 Mitral regurgitation. Adapted from Mullins and Mayer [1]. Reproduced with permission of John Wiley & Sons.