The primary goal in patients with chronic MR is maintaining forward systemic flow.3 The heart rate should be maintained in the high-normal range, i.e., 80 to 100 beats/minute. Tachycardia decreases the regurgitant volume by shortening systole. Bradycardia has dual detrimental effects on MR: it increases the systolic period duration, thus prolonging regurgitation, and it increases the diastolic filling interval, which can lead to LV distention. A sinus rhythm is preferred, but there is
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IARS 2010 REVIEW COURSE LECTURES
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less dependency on the atrial kick than in stenotic valvular heart disease.
As with most compensated forms of valvular heart disease, patients with hemodynamically significant MR are sensitive to ventricular loading conditions. It must be remembered that anesthetic effects on afterload and preload can drastically alter the severity of MR from its baseline level as seen in preoperative echocardiographic or catheterization assessments. In general, afterload reduction in combination with mild preload augmentation will enhance forward cardiac output and blood pressure. Adequate anesthetic depth, systemic vasodilators, or inodilators may be clinical options, depending on the situation. However, higher systolic driving pressures, as in hypertension, can increase the regurgitant volume, while fluid overload with ventricular distension can lead to expansion of an already dilated mitral annulus and thus worsen MR.
In early compensated MR, left ventricular contractility may be preserved. However, in patients with moderate to severe MR, ejection fraction indices are poorly correlated with left ventricular systolic function so that underlying systolic dysfunction may be underestimated. Hypotension in patients with significant MR can often be managed by manipulating heart rate and volume, but persistent hemodynamic instability may be best treated with inotropic support. Direct-acting α1-agonists increase SVR and blood pressure, lower heart rate, and may worsen MR. Temporary use of small doses of ephedrine may be a better choice. Dobutamine, low-dose epinephrine, and milrinone are all acceptable inotropic choices for continuous infusion.
Pulmonary artery pressures and pulmonary vascular resistance may be elevated in patients with MR. Factors that may increase pulmonary vascular resistance and unfavorably load an already dysfunctional right ventricle, such as hypoxia, hypercarbia, and acidosis, should be avoided.