A 77-year-old woman is brought to the emergency department with severe lightheadedness and near-syncope that began earlier in the day. Over the past several months, she has experienced occasional episodes of lightheadedness and feeling unsteady, which she attributed to "old age." The patient has not had chest pain, shortness of breath, or lower extremity swelling. She was diagnosed with hypertension 10 years ago and has been taking losartan. The patient does not take any other medications. She lives alone and is independent in her daily activities. An ECG obtained in the emergency department is shown in the exhibit. Cell degeneration in which of the following locations is most likely responsible for this patient's current condition?

Question

A 77-year-old woman is brought to the emergency department with severe lightheadedness and near-syncope that began earlier in the day.  Over the past several months, she has experienced occasional episodes of lightheadedness and feeling unsteady, which she attributed to "old age."  The patient has not had chest pain, shortness of breath, or lower extremity swelling.  She was diagnosed with hypertension 10 years ago and has been taking losartan.  The patient does not take any other medications.  She lives alone and is independent in her daily activities.  An ECG obtained in the emergency department is shown in the exhibit.  Cell degeneration in which of the following locations is most likely responsible for this patient's current condition?

Quizplus · Accepted Answer

11ec160b_3a9e_f59d_9249_cdcaa58b6bcc_MD0001_00 This elderly patient with recent lightheadedness and near-syncope has an ECG showing bradycardia with dropped P waves; these findings are consistent with sick sinus syndrome. Sick sinus syndrome most commonly results from age-related degeneration of the sinoatrial node, which is located on the right atrial wall and is responsible for initiating normal cardiac conduction. Impaired signaling from the sinoatrial node can markedly slow the rate of ventricular contraction, leading to reduced cardiac output and symptoms of dyspnea, fatigue, lightheadedness, presyncope, and syncope. Typical ECG findings include bradycardia, sinus pauses (delayed P waves), and sinus arrest (prolonged delay of a P wave such that the P wave is dropped). Because the atrioventricular node triggers conduction based on its own pacemaker if it does not receive a timely signal from the sinoatrial node, sinus arrest will lead to a junctional escape beat (narrow QRS complex preceded by a long pause and no P wave). Sick sinus syndrome can also cause brief periods of atrial tachycardia (eg, atrial fibrillation) alternating with bradycardia. (Choice A) The inferior portion of the interatrial septum contains the His bundle. Conduction abnormalities in this region can manifest as varying degrees of atrioventricular block with prolongation of the PR interval (first degree), dropped QRS complexes (second degree), or dissociation of P waves and QRS complexes (third degree). (Choice B) Conduction through the interventricular septum mostly involves the left and right bundle branches. Conduction abnormalities in this region can lead to bundle branch blocks; the QRS complex is widened in bundle branch block due to impaired synchronization of ventricular depolarization. (Choice C) After initiation in the sinoatrial node, conduction propagates through the cardiomyocytes of the left atrial wall to stimulate left atrial contraction. Abnormal electrical foci can develop in the nearby pulmonary veins, which is a common trigger for atrial fibrillation. (Choice D) Conduction abnormalities may originate in ischemic areas of the left ventricular free wall, leading to ventricular tachycardia. Educational objective: Sick sinus syndrome results from degeneration (usually age-related) of the sinoatrial node, leading to impaired conduction and reduced cardiac output with symptoms of dyspnea, fatigue, lightheadedness, presyncope, and syncope. ECG typically demonstrates bradycardia with sinus pauses (delayed P waves), sinus arrest (dropped P waves), and junctional escape beats.

A 77-Year-Old Woman Is Brought to the Emergency Department with Severe