A 34-year-old woman comes to the office due to intermittent palpitations for 2 weeks. The patient has no chest pain or shortness of breath. She was diagnosed with hypertrophic cardiomyopathy 10 years ago and hypothyroidism 5 years ago. The patient takes metoprolol and levothyroxine. Temperature is 37.1 C (98.8 F), blood pressure is 120/80 mm Hg, pulse is 65/min and regular, and respirations are 15/min. BMI is 27 kg/m². Oxygen saturation is 98% on room air. Mucous membranes are moist. Jugular venous pressure is normal. The thyroid gland is symmetrically enlarged and nontender. The lungs are clear to auscultation. A grade 2/6 systolic murmur is heard best at the left sternal border. Complete blood count and serum chemistries are normal. Serum TSH concentration is 1.4 μU/mL. ECG shows normal sinus rhythm with T-wave inversions in the anterior leads, unchanged from 6 months ago. Which of the following is the most appropriate next step in management of this patient?

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Explanation: 11ec2b69_be32_e651_8f63_ebc6af82fd2b_MD0005_00 Patients with hypertrophic cardiomyopathy (HCM) are at increased risk for cardiac arrhythmia, namely the following: Atrial fibrillation: The increased risk in HCM likely results from left ventricular diastolic dysfunction leading to left atrial enlargement, creating a substrate for atrial fibrillation. Thromboembolic stroke related to atrial fibrillation is an important cause of morbidity and mortality in patients with HCM. Ventricular tachycardia: The increased risk in HCM is related to myocardial disarray and fibrosis, as well as chronic myocardial ischemia resulting from myocardial oxygen supply-demand mismatch. Sustained ventricular tachycardia is the typical cause of sudden cardiac arrest, the most common cause of mortality in HCM. Periodic ambulatory ECG monitoring (eg, 24-hr Holter monitoring) is indicated in patients with HCM so that arrhythmic complications can be promptly recognized. This monitoring is especially important in those with symptoms suggestive of paroxysmal arrhythmia, as in this patient with palpitations. Evidence of atrial fibrillation on ECG monitoring warrants the initiation of chronic anticoagulation, and evidence of ventricular tachycardia (eg, bursts of nonsustained ventricular tachycardia) may warrant placement of an implantable cardioverter defibrillator. (Choice A) Adding verapamil to metoprolol for additional negative chronotropy and inotropy can be appropriate in HCM patients with persistent exertional symptoms (eg, dyspnea, chest pain) thought to be due to left ventricular outflow tract obstruction. However, palpitations are more suggestive of cardiac arrhythmia that needs to be investigated. (Choice C) Coronary angiography is of minimal use in relatively young patients with HCM as most have normal epicardial coronary arteries. The coronary microvascular dysfunction that is common with HCM and contributes to myocardial ischemia is not detectable (or treatable) via coronary angiography. (Choice D) CT pulmonary angiography is used to diagnose acute pulmonary embolism, which is unlikely in this patient with no shortness of breath and normal oxygen saturation. (Choice E) Serum free thyroxine (T4) concentration can help assess the degree of hyperthyroidism or hypothyroidism when the TSH level is abnormal. However, because a normal TSH level is accurately representative of normal T4 levels, free T4 concentration is of little use when the TSH level is normal, as in this patient. Educational objective: Patients with hypertrophic cardiomyopathy are at increased risk for atrial fibrillation and ventricular tachycardia. Periodic ambulatory ECG monitoring is indicated to facilitate prompt recognition and management of these arrhythmias, especially in patients with suggestive symptoms (eg, palpitations). References: Atrial fibrillation in hypertrophic cardiomyopathy: a turning point towards increased morbidity and mortality. (http://www.ncbi.nlm.nih.gov/pubmed/28219794)

A 34-Year-Old Woman Comes to the Office Due to Intermittent