A 40-year-old woman with a medical history significant for obstructive hypertrophic cardiomyopathy is scheduled for elective hysterectomy under general anesthesia due to large, symptomatic uterine fibroids and blood loss anemia. At baseline, the patient develops mild dyspnea with moderate exercise. She takes metoprolol. Blood pressure is 120/80 mm Hg and pulse is 65/min. Examination shows clear lungs and a midsystolic murmur. There is no jugular venous distension or peripheral edema. During anesthesia, which of the following is recommended to prevent perioperative complications in this patient?

Question

A 40-year-old woman with a medical history significant for obstructive hypertrophic cardiomyopathy is scheduled for elective hysterectomy under general anesthesia due to large, symptomatic uterine fibroids and blood loss anemia.  At baseline, the patient develops mild dyspnea with moderate exercise.  She takes metoprolol.  Blood pressure is 120/80 mm Hg and pulse is 65/min.  Examination shows clear lungs and a midsystolic murmur.  There is no jugular venous distension or peripheral edema.  During anesthesia, which of the following is recommended to prevent perioperative complications in this patient?

Quizplus · Accepted Answer

Explanation: Many patients with hypertrophic cardiomyopathy (HCM) have dynamic left ventricular outflow tract (LVOT) obstruction that, when severe, can drastically limit cardiac output. The degree of LVOT obstruction is worsened by low LV blood volume; therefore, hemodynamics should be optimized to encourage high LV blood volume throughout the cardiac cycle (ie, both end-diastolic and end-systolic): degree of LVOT obstruction High LV end-diastolic volume (ie, high preload) is encouraged by adequate hydration and avoidance of venous dilators (eg, nitroglycerin). Maintaining a relatively low heart rate is also beneficial as it lengthens diastolic filling time to increase end-diastolic volume. High LV end-systolic volume is encouraged by a relatively low stroke volume (SV). A relatively low SV, whether from low contractility or high afterload (pressure that the left ventricle must contract against), leads to blood being ejected (during systole) at a higher LV blood volume. This higher LV blood volume minimizes LVOT obstruction, allowing for more effective cardiac output. In contrast, if end-systolic volume gets too low, there is a precipitous drop in SV, leading to severe LVOT obstruction. Beta blockers (eg, metoprolol) are highly useful in treating HCM because they decrease heart rate to lengthen diastolic filling time and increase LV end-diastolic volume; and they decrease LV contractility to increase LV end-systolic volume. These effects help minimize LVOT obstruction (Choice C). (Choice A) Dobutamine primarily stimulates beta-1 receptors. The increased heart rate and contractility caused by beta-1 stimulation decrease LV end-diastolic and LV end-systolic volume, respectively, and can worsen LVOT obstruction in HCM. (Choice B) Norepinephrine stimulates alpha-1 and beta-1 receptors. The peripheral vasoconstriction and resulting increased LV afterload (induced by alpha-1 stimulation) are beneficial for LVOT obstruction in HCM, but the increased heart rate and contractility (induced by beta-1 stimulation) worsen the obstruction and outweigh the positive effect. (Choice E) High peak airway pressures increase intrathoracic pressure and reduce venous return to heart; the decrease in LV end-diastolic volume can worsen LVOT obstruction in HCM. Educational objective: The degree of left ventricular (LV) outflow tract obstruction in hypertrophic cardiomyopathy is minimized by relatively high LV blood volume. High LV end-diastolic blood volume (ie, preload) is encouraged by adequate hydration and low heart rate. High LV end-systolic volume is encouraged by relatively low stroke volume, which is facilitated by high LV afterload and low LV contractility.

A 40-Year-Old Woman with a Medical History Significant for Obstructive