A 22-year-old male is admitted to the intensive care unit (ICU) after sustaining a cardiac arrest while playing soccer in a rural area. Cardiopulmonary resuscitation was performed, but no automatic external defibrillator was available; he was intubated in the field because of poor mental status. He is transferred to your tertiary care ICU. Examination reveals an ejection systolic murmur, and he followed commands when sedation was lightened. Transthoracic echocardiography reveals discrete upper septal hypertrophy measuring 18 mm and an elevated left ventricular outflow velocity. He successfully passes a spontaneous awakening trial and spontaneous breathing trial. Unfortunately, at that time, he develops atrial fibrillation, became hypotensive to blood pressures of 94/52, and FiO2 was increased from 0.4 to 0.6 in response to desaturations to the low 80s.
The best treatment for this patient’s atrial fibrillation is:
A. SotalolCorrect Answer: D
Hypertrophic cardiomyopathy (HCM) is defined as left ventricular wall thickness >15 mm not explained by loading conditions including hypertension or aortic valve stenosis. Patients with HCM are at risk for lethal ventricular arrhythmias, and cardiac arrest may be the initial presentation, whereas other patients may experience dyspnea, palpitations, chest pain, or syncope as presenting symptoms. However, the most common arrhythmia experienced by patients with HCM is atrial fibrillation that occurs in approximately 20% to 25%.
HCM may cause obstruction to left ventricular outflow, caused by systolic anterior motion of the anterior mitral valve leaflet. Conditions that worsen the obstruction include hypotension and tachycardia. Atrial fibrillation can cause both of these. Also, patients with HCM are markedly dependent on the “atrial kick” for adequate ventricular filling. These conditions can worsen left ventricular outflow tract obstruction resulting in flash pulmonary edema and hemodynamic collapse.
As such, any patient with hypertrophic obstructive cardiomyopathy experiencing hemodynamic stressors with acute changes to preload or afterload, such as intubation or extubation, should have close monitoring and titration of hemodynamics. Avoiding hypotension by maintaining preload and afterload, preventing a hyperdynamic state, and maintenance of sinus rhythm are essential to optimize hemodynamics.
Digoxin and norepinephrine should be avoided in this patient population as it can increase contractility and thereby worsen left ventricular outflow tract obstruction. In patients with HCM who develop atrial fibrillation, AHA/ACC guidelines recommend amiodarone or disopyramide combined with beta blocker or nondihydropyridine calcium channel blocker as first line medications. Although beta blocker can help reduce left ventricular outflow tract obstruction, these could possibly exacerbate hypotension and thus not the best initial choice. In the setting of moderate hypotension, amiodarone bolus and load is the best initial choice for medical management. Should the hypotension be profound, immediate cardioversion would be the best step in management.
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