P wave and atrial depolarization — MCQs

A 23-year-old man comes to the emergency department because of palpitations, dizziness, and substernal chest pain for three hours. The day prior, he was at a friend’s wedding, where he consumed seven glasses of wine. The patient appears diaphoretic. His pulse is 220/min and blood pressure is 120/84 mm Hg. Based on the patient's findings on electrocardiography, the physician diagnoses atrial fibrillation with rapid ventricular response and administers verapamil for rate control. Ten minutes later, the patient is unresponsive and loses consciousness. Despite resuscitative efforts, the patient dies. Histopathologic examination of the heart at autopsy shows an accessory atrioventricular conduction pathway. Electrocardiography prior to the onset of this patient's symptoms would most likely have shown which of the following findings?

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 42-year-old woman comes to the physician because of 2 episodes of loss of consciousness over the past week. She recovered immediately and was not confused following the episodes. During the past 5 months, she has also had increased shortness of breath and palpitations. She has been unable to carry out her daily activities. She also reports some chest tightness that resolves with rest. She has no history of serious illness and takes no medications. She immigrated with her family from India 10 years ago. Her temperature is 37.3°C (99.1°F), pulse is 115/min and irregular, and blood pressure is 108/70 mm Hg. Examination shows jugular venous distention and pitting edema below the knees. Bilateral crackles are heard at the lung bases. Cardiac examination shows an accentuated and split S2. There is an opening snap followed by a low-pitched diastolic murmur in the fifth left intercostal space at the midclavicular line. An ECG shows atrial fibrillation and right axis deviation. Which of the following is the most likely underlying mechanism of these findings?

A 42-year-old woman comes to the physician because of a 12 month history of progressive fatigue and shortness of breath with exertion. Five years ago, she emigrated from Eastern Europe. She has smoked one pack of cigarettes daily for 20 years. She has a history of using methamphetamines and cocaine but quit 5 years ago. Vital signs are within normal limits. Physical examination shows jugular venous pulsations 9 cm above the sternal angle. The lungs are clear to auscultation. There is a normal S1 and a loud, split S2. An impulse can be felt with the fingers left of the sternum. The abdomen is soft and nontender. The fingertips are enlarged and the nails are curved. There is pitting edema around the ankles bilaterally. An x-ray of the chest shows pronounced central pulmonary arteries and a prominent right heart border. Which of the following is most likely to confirm the diagnosis?

A 65-year-old woman comes to the physician because of a 3-month history of intermittent palpitations and shortness of breath. Cardiopulmonary examination shows no other abnormalities. An ECG shows an absence of P waves, an oscillating baseline, and irregular RR intervals at a rate of approximately 95 beats per minute. The difference between atrial and ventricular rates in this patient is most likely due to which of the following?

A 41-year-old woman presents to the emergency room with chest pain. She has had progressive substernal chest pain accompanied by weakness and mild shortness of breath for the past 2 hours. Her past medical history is notable for poorly controlled systemic lupus erythematosus (SLE), Sjogren syndrome, and interstitial lung disease. She was hospitalized last year with pericarditis presumed to be from SLE. Her temperature is 98.6°F (37°C), blood pressure is 106/56 mmHg, pulse is 132/min, and respirations are 26/min. On exam, the skin overlying the internal jugular vein fills at 9 cm above the sternal angle and distant heart sounds are appreciated. There is no friction rub. She is given 1000cc of intravenous fluids with no appreciable change in her blood pressure. An electrocardiogram in this patient would most likely reveal which of the following findings?

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 cardiologist is studying how a new virus that infects the heart affects the electrical conduction system of the cardiac myocytes. He decides to obtain electrocardiograms on patients with this disease in order to see how the wave patterns and durations change over time. While studying these records, he asks a medical student who is working with him to interpret the traces. Specifically, he asks her to identify the part that represents initial ventricular depolarization. Which of the following characteristics is most consistent with this feature of the electrocardiogram?

A 44-year-old man comes to the emergency department because of persistent palpitations for the past 2 hours. The day before, he was at a wedding, where he drank several glasses of wine and 9–10 vodka cocktails. He has never had similar symptoms before. He is a manager at a software company and has recently had a lot of work-related stress. He is otherwise healthy and takes no medications. His temperature is 36.5°C (97.7°F), pulse is 90/min and irregularly irregular, respirations are 13/min, and his blood pressure is 128/60 mm Hg. Physical examination shows no other abnormalities. An ECG is performed; no P-waves can be identified. Echocardiography shows no valvular abnormalities and normal ventricular function. One hour later, a repeat ECG shows normal P waves followed by narrow QRS complexes. He is still experiencing occasional palpitations. Which of the following is the most appropriate next step in management?

A 17-year-old girl suddenly grabs her chest and collapses to the ground while playing volleyball at school. The teacher rushes to evaluate the situation and finds that the girl has no pulse and is not breathing. He starts chest compressions. An automated external defibrillator (AED) is brought to the scene within 3 minutes and a shock is delivered. The girl regains consciousness and regular sinus rhythm. She is rushed to the emergency department. The vital signs include: blood pressure 122/77 mm Hg and pulse 65/min. The pulse is regular. An electrocardiogram (ECG) shows a shortened PR interval, a wide QRS complex, a delta wave, and an inverted T wave. Which of the following is the most likely pathology in the conduction system of this patient’s heart?