An 80-year-old woman is brought to the emergency department due to an episode of near-syncope. The patient feels excessively tired and breathless on moderate exertion and has had occasional palpitations over the past 6 months. She has had several brief episodes of lightheadedness during the last 2 weeks, and while walking in a mall today, she felt extremely weak and dizzy. The patient was helped by her family and did not fall or lose consciousness. She has had no chest pain, cough, or pedal edema. The patient has hypertension, hyperlipidemia, and coronary artery disease treated with bypass graft surgery 15 years ago. She takes aspirin, atorvastatin, and metoprolol. Blood pressure is 136/80 mm Hg and pulse is 52/min without significant orthostatic changes. No jugular venous distension is present. Cardiac auscultation reveals regular S1 and S2 with an additional S4. Breath sounds are normal with no crackles. There is no extremity edema. ECG shows sinus bradycardia. During her hospital stay, cardiac telemonitoring reveals episodes of 3-6 seconds with no sinus nodal activity, during which the patient experiences dizziness. Which of the following is the most likely cause of this patient's cardiac arrhythmia?

Question

An 80-year-old woman is brought to the emergency department due to an episode of near-syncope.  The patient feels excessively tired and breathless on moderate exertion and has had occasional palpitations over the past 6 months.  She has had several brief episodes of lightheadedness during the last 2 weeks, and while walking in a mall today, she felt extremely weak and dizzy.  The patient was helped by her family and did not fall or lose consciousness.  She has had no chest pain, cough, or pedal edema.  The patient has hypertension, hyperlipidemia, and coronary artery disease treated with bypass graft surgery 15 years ago.  She takes aspirin, atorvastatin, and metoprolol.  Blood pressure is 136/80 mm Hg and pulse is 52/min without significant orthostatic changes.  No jugular venous distension is present.  Cardiac auscultation reveals regular S1 and S2 with an additional S4.  Breath sounds are normal with no crackles.  There is no extremity edema.  ECG shows sinus bradycardia.  During her hospital stay, cardiac telemonitoring reveals episodes of 3-6 seconds with no sinus nodal activity, during which the patient experiences dizziness.  Which of the following is the most likely cause of this patient's cardiac arrhythmia?

Quizplus · Accepted Answer

11ec25c8_d369_1a48_bc81_255d7772ad81_MD0003_00 This elderly patient most likely has sick sinus syndrome (SSS), which is characterized by inability of the sinoatrial node to generate an adequate heart rate. Age-related degeneration of the cardiac conduction system with fibrosis of the sinus node is the most common cause. Ischemia and infiltrative cardiac disease (eg, sarcoidosis, amyloidosis) are other potential causes. SSS typically presents with bradycardia, leading to fatigue, dyspnea on exertion, lightheadedness, confusion, and syncope or presyncope. Fibrosis may also affect the atria, leading to paroxysmal atrial arrhythmias such as atrial fibrillation (likely cause of palpitations in this patient) or bradycardia-tachycardia syndrome (bradycardia alternating with supraventricular tachycardia). ECG typically shows sinus bradycardia, sinus pauses (delayed P waves), and sinoatrial nodal exit block (dropped P waves), and exercise testing demonstrates chronotropic incompetence (inadequate heart rate response to exercise). Definitive management for SSS requires placement of a pacemaker. Once a pacemaker is placed, rate-control medications (eg, beta blockers) can be administered in patients with persistent paroxysmal tachyarrhythmias. (Choice A) An aberrant or accessory conduction pathway between the atria and the ventricles is the cause of Wolff-Parkinson-White syndrome. Patients have paroxysmal tachyarrhythmias, but bradycardia is not typical. Preexcitation of the ventricles produces a characteristic triad of ECG changes, including short PR interval, widened QRS interval, and slurred upstroke of the QRS complex (delta wave). conduction pathway ECG changes (Choice B) Abnormal automaticity of cardiac myocytes located around the pulmonary veins is the most common cause of atrial fibrillation. However, bradycardia and sinus pauses are not typical. (Choice D) Vagal tone normally varies with respiration, which can result in sinus arrhythmia; the heart rate decreases with expiration and increases with inspiration. Significant symptoms (eg, fatigue, dyspnea, lightheadedness) do not typically occur. (Choice E) In most patients, the right coronary artery supplies blood to the sinoatrial node, atrioventricular node, and bundle of His; occlusion can lead to varying degrees of sinus node dysfunction and atrioventricular conduction block. However, sudden-onset chest discomfort with ST-segment elevation in the inferior ECG leads would be expected. Educational objective: Degeneration of the sinus node and replacement with fibrous tissue is the most common cause of sick sinus syndrome. Elderly patients are typically affected and have bradycardia, leading to fatigue, dyspnea on exertion, lightheadedness, confusion, and syncope or presyncope. ECG demonstrates sinus bradycardia with delayed or dropped P waves. References: Sick sinus syndrome and atrial fibrillation in older persons - a view from the sinoatrial nodal myocyte. (http://www.ncbi.nlm.nih.gov/pubmed/25668431)

An 80-Year-Old Woman Is Brought to the Emergency Department Due