Hensley's Practical Approach to Cardiothoracic Anesthesia

16. Anesthetic Considerations for Surgical Myectomy in Patients With Hypertrophic Cardiomyopathy 345

to the mid-ventricle (Figures 16.1C, 16.2B, C). Hypertrophy of the free wall of the LV is variable. There may be isolated obstruction in the mid-ventricle where hypertrophy of the septum leads to contact with the papillary muscles, producing obstruction to the ejection of blood; in other patients, there may be an apical distribution of hypertrophy (Figure 16.1D). The HCM phenotype and severity of hypertrophy do not correlate with the genotype. In deed, multiple ventricular morphologic appearances may be found in the same family. In obstructive HCM, as blood is ejected through a narrow LVOT with high velocity, turbulent flow results in a drag force effect on the mitral valve, resulting in systolic anterior mitral apparatus movement into LVOT, further narrowing the LVOT (Figure 16.3A). Dis placement of the valve leaflets in systole, described as SAM, may lead to variable degrees of MR (Figure 16.3A, B). The MR jet is typically, but not always, directed posteriorly. 4 It is important to recognize that LVOT obstruction is often dynamic, and provocative maneu vers, such as Valsalva, repetitive squat-to-stand exercise, and adrenergic stimulation, may be necessary to elicit SAM, MR, and LVOT obstruction. 6 3. Histopathology Myocyte hypertrophy, myocardial disarray, and interstitial fibrosis are histopathologic findings that are characteristic of, but not specific to, HCM. Myocardial disarray may be present in any condition with ventricular pressure overload. 7 Interstitial fibrosis of variable degrees is another important histologic feature of the myocardium of patients with HCM 8 that contributes to diastolic dysfunction. Late gadolinium enhancement on cardiac mag netic resonance imaging (MRI) provides assessment of myocardial fibrosis burden, associ ated with an increased risk of sudden death. 9 4. Genetics The disorder of the cardiac muscle in HCM is caused by autosomal dominant mutations in one of several genes encoding both the thin and thick myofilaments of the sarcomere as well as nonsarcomeric proteins. The most common mutation involves the gene encod ing cardiac myosin–binding protein C; however, there is considerable genetic heteroge neity, and at least 15 other genes have been identified with > 1,000 distinct mutations. 10 FIGURE 16.2 Transthoracic echocardiography demonstrates different variants of myocardial hypertrophy distribu tion. (A) Massive basal interventricular septal hypertrophy. (B) Arrow points to near obliteration of left ventricular cavity in patient with midventricular HCM in systole. (C) Arrow points to near obliteration of left ventricular cavity in patient with midventricular HCM in diastole. HCM, hypertrophic cardiomyopathy.

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