AMBOSS Flashcards
A 46-year-old woman is brought to the emergency department by her wife 1 hour after the onset of chest palpitations. Her symptoms began suddenly while she was drinking coffee and have persisted since then. She has not had shortness of breath, chest pain, dizziness, or loss of consciousness. She has experienced these palpitations before, but they typically resolve spontaneously within a few minutes. She has no history of serious illness and takes no medications. Her temperature is 36.8°C (98.2°F), pulse is 155/min, respirations are 18/min, and blood pressure is 130/82 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 97%. Physical examination shows no abnormalities other than tachycardia. An ECG is shown. Repeated, forceful exhalation against a closed glottis while supine fails to relieve her symptoms. Which of the following is the most appropriate next step in management?
Administer adenosine intravenously
If vagal maneuvers are ineffective in terminating AVNRT, intravenous administration of adenosine is the next step in management. It successfully terminates AVNRT in over 80% of cases, and has a rapid onset of action. Patients should be supine and have continuous blood pressure and electrocardiographic monitoring. Adverse effects include facial flushing and shortness of breath, hypotension, and bradycardia. Patients with asthma and reactive airway disease should not receive adenosine because of the risk of inducing bronchospasm.
A 40-year-old woman comes to the physician for a 6-month history of recurrent episodes of chest pain, racing pulse, dizziness, and difficulty breathing. The episodes last up to several minutes. She also reports urinary urgency and two episodes of loss of consciousness followed by spontaneous recovery. There is no personal or family history of serious illness. She does not smoke or drink alcohol. Vitals signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Holter monitoring is performed. ECG recordings during episodes of tachycardia show a QRS duration of 100 ms, regular RR-interval, and absent P waves. Which of the following is the most likely underlying cause of this patient’s condition?
AV node with slow and fast pathway
Two alternative electrical conduction pathways, one fast and one slow, within the atrioventricular (AV) node is the underlying mechanism for AVNRT. The presence of an extra, fast accessory pathway occasionally leads to a nonextinguishable circulating electrical impulse, or reentrant circuit, within the AV node that activates the atria and ventricles simultaneously and at a rapid rate. This produces episodic symptoms of palpitations, dyspnea, chest pain, dizziness and/or syncope.
A 62-year-old man is brought to the emergency department because of syncope. He reports sudden onset of palpitations followed by loss of consciousness while carrying his groceries to his car. He is unable to recall any further details and does not have any chest pain or dizziness. He has a history of hypertension, type 2 diabetes mellitus, gastroparesis, and osteoarthritis of the knees. Medications include lisinopril, metformin, and ondansetron as needed for nausea. He also takes methadone daily for chronic pain. Apart from an abrasion on his forehead, he appears well. His temperature is 37.2 °C (98.9 F), heart rate is 104/min and regular, and blood pressure is 135/70 mm Hg. While he is in the emergency department, he loses consciousness again. Telemetry shows polymorphic ventricular tachycardia with cyclic alteration of the QRS axis that spontaneously resolves after 30 seconds. Results of a complete blood count, serum electrolyte concentrations, and serum thyroid studies show no abnormalities. Cardiac enzymes are within normal limits. Which of the following is the most likely underlying cause of this patient’s syncope?
Prolonged QT interval
A prolonged QT interval may be congenital or acquired, and typically remains asymptomatic until patients present with syncope or life-threatening arrhythmias such as torsade de pointes, as seen in this patient. Acquired prolongation of the QT interval can be caused by certain medications (e.g., amiodarone, methadone, ondansetron) or electrolyte imbalances (e.g., hypokalemia, hypomagnesemia, and hypocalcemia). This patient’s history of ondansetron and methadone therapy makes drug-induced QT prolongation that progressed to torsade de pointes the most likely cause of his syncope.
