Basic electrophysiology — MCQs

A molecular biologist is studying the roles of different types of ion channels regulating cardiac excitation. He identifies a voltage-gated calcium channel in the sinoatrial node, which is also present throughout the myocardium. The channel is activated at ~ -40 mV of membrane potential, undergoes voltage-dependent inactivation, and is highly sensitive to nifedipine. Which of the following phases of the action potential in the sinoatrial node is primarily mediated by ion currents through the channel that the molecular biologist is studying?

An ECG from an 8-year-old male with neurosensory deafness and a family history of sudden cardiac arrest demonstrates QT-interval prolongation. Which of the following is this patient most at risk of developing?

An 8-year-old girl is brought to the physician by her parents for the evaluation of an episode of unconsciousness while at the playground that morning. She was unconscious for about 15 seconds and did not shake, bite her tongue, or lose bowel or bladder control. Her grandfather died suddenly at the age of 29 of an unknown heart condition; her parents are both healthy. An ECG shows sinus rhythm and a QT interval corrected for heart rate (QTc) of 470 milliseconds. Laboratory studies are within normal limits. Which of the following is the most likely additional finding in this patient?

A researcher is studying how electrical activity propagates across the heart. In order to do this, he decides to measure the rate at which an action potential moves within various groups of cardiac muscle tissue. In particular, he isolates fibers from areas of the heart with the following characteristics: A) Dysfunction leads to fixed PR intervals prior to a dropped beat B) Dysfunction leads to increasing PR intervals prior to a dropped beat C) Dysfunction leads to tachycardia with a dramatically widened QRS complex D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation.

A 27-year-old man presents to the clinic for his annual physical examination. He was diagnosed with a rare arrhythmia a couple of years ago following an episode of dizziness. A mutation in the gene encoding for the L-type calcium channel protein was identified by genetic testing. He feels fine today. His vitals include: blood pressure 122/89 mm Hg, pulse 90/min, respiratory rate 14/min, and temperature 36.7°C (98.0°F). The cardiac examination is unremarkable. The patient has been conducting some internet research on how the heart works and specifically asks you about his own “ventricular action potential”. Which of the following would you expect to see in this patient?

A group of investigators is studying a drug to treat refractory angina pectoris. This drug works by selectively inhibiting the late influx of sodium ions into cardiac myocytes. At high doses, the drug also partially inhibits the degradation of fatty acids. Which of the following is the most likely effect of this drug?

While explaining the effects of hypokalemia and hyperkalemia on the cardiac rhythm, a cardiologist explains that the electrophysiology of cardiac tissue is unique. He mentions that potassium ions play an important role in the electrophysiology of the heart, and the resting membrane potential of the cardiac myocytes is close to the equilibrium potential of K+ ions. This is because of the high resting potassium conductance of the ventricular myocytes, which is regulated by specific potassium channels. These are open at rest and are closed when there is depolarization. Which of the following potassium channels is the cardiologist talking about?

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?

A 29-year-old man comes to the physician for a routine health maintenance examination. He has no history of serious illness. His mother has hypertension and his father died of testicular cancer at the age of 51 years. He does not smoke or drink. He is sexually active and uses condoms consistently. He takes no medications. His immunization records are unavailable. He works as a financial consultant and will go on a business trip to Mexico City in 2 weeks. His temperature is 36.7°C (98.7° F), pulse is 78/min, and blood pressure is 122/78 mm Hg. Cardiopulmonary examination shows no abnormalities. Laboratory studies show: Hemoglobin 13.4 g/dL Leukocyte count 9800/mm3 Platelet count 168,000/mm3 Serum Glucose 113 mg/dL Creatinine 1.1 mg/dL Which of the following recommendations is most appropriate at this time?

A patient with a history of hypertension presents with atrial fibrillation, shortness of breath, and bilateral basal crackles on auscultation. Which of the following would be the least important in the management of this patient?