QRS complex analysis — MCQs

A previously healthy 19-year-old man is brought to the emergency department by his girlfriend after briefly losing consciousness. He passed out while moving furniture into her apartment. She said that he was unresponsive for a minute but regained consciousness and was not confused. The patient did not have any chest pain, palpitations, or difficulty breathing before or after the episode. He has had episodes of dizziness when exercising at the gym. His blood pressure is 125/75 mm Hg while supine and 120/70 mm Hg while standing. Pulse is 70/min while supine and 75/min while standing. On examination, there is a grade 3/6 systolic murmur at the left lower sternal border and a systolic murmur at the apex, both of which disappear with passive leg elevation. Which of the following is the most likely cause?

A researcher measures action potential propagation velocity in various regions of the heart in a 42-year-old Caucasian female. Which of the following set of measurements corresponds to the velocities found in the atrial muscle, AV Node, Purkinje system, and ventricular muscle, respectively?

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 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?

In a patient with acute myocardial ischemia, which of the following cardiovascular structures is at greatest risk of damage?

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 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?

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?

An investigator develops a new drug that decreases the number of voltage-gated potassium channels in cardiac muscle cell membranes. Which of the following is the most likely effect of this drug on the myocardial action potential?