Hensley's Practical Approach to Cardiothoracic Anesthesia

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III. Cardiac Anesthesia

CLINICAL PEARL The development of dynamic LVOT obstruction, MR, and/or diastolic dysfunction frequently precipitates fatigue, dyspnea, and syncope in HCM. D. Natural History In contemporary series of HCM, survival is similar to individuals without disease with an an nual mortality rate of ∼ 1%. However, certain subgroups have an increased risk of cardiac death. The greatest risk factor for sudden death is a personal history of prior cardiac arrest or sus tained ventricular tachycardia. Other major risk factors include a family history of sudden death due to HCM, massive ventricular hypertrophy (wall thickness > 30 mm), unexplained syncope, LV systolic dysfunction (ejection fraction < 50%), and apical aneurysm. Both non sustained ventricular tachycardia on ambulatory monitoring and extensive late gadolinium enhancement on cardiac MRI may also portend arrhythmogenic risk. 16 An implantable cardioverter-defibrillator (ICD) is strongly recommended for secondary prevention of sudden cardiac death in patients with prior cardiac arrest or sustained ventricu lar tachycardia. Although primary prevention risk stratification can be complex, an ICD should be considered in patients with a major risk factor. E. Surgical Treatment Septal myectomy is indicated for patients with limiting symptoms despite medical treatment. Surgical treatment of HCM was introduced at Mayo Clinic in 1958 by J. Kirklin, who described a simple myotomy without actual muscle resection. Surgical management further evolved and has been replaced by the more predictable and complete transaortic extended myectomy. 17 Operation is performed through a median sternotomy utilizing normothermic cardiopulmo nary bypass established with a single, two-stage venous cannula. After aortic cross-clamping, cold blood cardioplegia (1,000-1,200 mL) is infused through the aortic needle vent to arrest the heart. An oblique aortotomy is made slightly closer to the sinotubular ridge than is usual for aortic valve replacement, and the incision is carried through the midpoint of the noncoronary aortic sinus of Valsalva to a level ∼ 1 cm above the valve annulus. Exposure of the distal septum can be improved by depressing the right ventricle to rotate the septum posteriorly. The inci sion in the septum begins just to the right of the nadir of the right aortic sinus and continues upward and to the left to a point near the attachment of the anterior leaflet of the mitral valve. Scissors are used to complete the excision of this initial portion of the myocardium. The area of septal excision is then deepened and lengthened toward the apex to remove hypertrophied septum beyond the endocardial scar. A typical septal myectomy usually yields 3-12 g of muscle. In some patients with apical HCM, the small volume of LV cavity impairs ventricular filling, causing progressive diastolic heart failure. Such patients respond poorly to medical therapy. For most, cardiac transplantation has been the only surgical option. However, apical myectomy can enlarge the LV cavity and improve stroke volume (Figure 16.4). At operation with car dioplegic arrest, the apex of the heart is delivered anteriorly, and a left ventriculotomy is made lateral and parallel to the left anterior descending coronary artery. Hypertrophied muscle from the septum is excised with special care to avoid injury to the papillary muscles, and, if greatly hypertrophied, the papillary muscles may be shaved to further increase LV volume. The myec tomy is extended proximally, beyond the midventricular level. If an apical aneurysm is present, the outpouching is resected completely. The ventriculotomy is closed using a two-layer ap proximation over strips of Teflon felt. Survival of patients following apical myectomy is similar to those who received heart transplants for apical HCM and better than those on the waiting list for transplant. In addition to improved survival, 76% of patients had significant improve ments in functional capacity. 18 Both operative mortality and complications, such as complete heart block, iatrogenic ventricular septal defect, injury to aortic and mitral valves, and incomplete relief of ob struction, are related to the surgical team’s experience. In a nationwide survey, over all perioperative mortality following septal myectomy was 2.6%, but only 0.9% in centers

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