Recognizing Zebras in Cardiology Board Exam Clinical Vignettes

Every multiple-choice exam question is presented to you on the cardiology board exam only after being vetted to be clinically relevant and fair. (Note that there are a certain percentage – maybe 10-15% – of MCQs included in exams that are under assessment and not counted in results until they pass muster. This does lead exam candidates to sometimes scratch their heads when reading poorly written questions. These questions will likely be revised or retired.)

Simply put, the boards are not trying to trick you with confusing or overly clever questions. The majority of the questions describe a patient with a common variant of the disease, as these are the clinical cases that most of us physicians assess and treat on a regular basis. However, we should also be able to recognize rare diseases or conditions. So, the question that arises is: how to differentiate whether the question is about a “horse” or a “zebra?”

If the question is about a “zebra”, it will provide some information about the demography of the patient that is unusual for that particular disease state, such as patient’s age, gender, race or ethnicity. For example, on the family medicine boards, the question describes an adolescent patient with a classic presentation of acute cholelithiasis who has never been pregnant. The age of the patient should prompt you to think about etiologies that are common in children and adolescents and not common in adults, like hemolytic disease, which can lead to the formation of black pigment stones. Or, if on the cardiovascular board, the question describes a young patient presenting with heart failure; the age of the patient should make you think about congenital or infectious etiologies as compared to causes of heart failure in adults, which usually include coronary artery disease or hypertension. Or, if the clinical vignette describes a young woman from East-Asia presenting in the ER in an unconscious state, you should think about why the race or ethnicity of the patient is mentioned in the question. Let’s suppose the vignette further describes that the family members of the patient state that the patient is an immigrant from a rural province of China and has been severely depressed ever since she has moved to the US.

Maybe the question is about a “zebra” because the clinical presentation of the patient is clearly out of place. For example, the clinical vignette describes a patient with nocturnal panic attacks taking some unnamed medication prescribed by his primary care physician for anxiety. The initial impression from the question may be that the current treatment is not working. Although this may be the case, another explanation is that the patient has been taking a short-acting drug whose effects wear off before the next dose. A common drug that causes nocturnal anxiety or panic is immediate release alprazolam. However, the FDA has approved this drug for the treatment of a panic disorder; it has a very short half-life and commonly causes drug-withdrawal anxiety when the plasma levels of the drug decline. The mention of nocturnal attacks, along with information about a patient taking “some drug” in the clinical vignette may be enough to prompt you to think beyond the initial impression.

Another clue about a “zebra” question relates to the nature of the disease or disorder. Maybe the clinical vignette mentions recent international travel to a tropical country or unusual activity or hobbies like high-altitude mountain climbing, or the patient’s occupation, in which case attention should be paid to the information related to the workplace (factory/agriculture). For example, individuals working and living in farming or rural community are more commonly exposed to organophosphates, as many herbicides contain organophosphate compounds that are readily available. Organophosphates are cholinesterase inhibitors and can case muscarinic and nicotinic overactivity in case of poisoning, leading to death from diaphragmatic failure. In rural China, intentional poisoning is the most common way of suicide in young women. However, accidental poisoning is also common. As mentioned earlier, the young immigrant woman from rural China may know the harmful actions of these readily available chemicals. Another vital clue in the question mentioned was her depressed state of mind.

The principle of board exams is, “there is no accident when it comes to the information placed in the vignette”. Every fact or information mentioned in the question is there to guide toward one or another diagnostic or treatment path. The available information present leads you to make diagnostic and treatment distinctions.

Example Exam Question from Cardiology

A 65-year-old man presents to the emergency room with chest pain radiating to the back, associated with diaphoresis, that started an hour ago. The patient has hypertension but is non-compliant with the medication he is prescribed. There is no other significant past medical or surgical history. On examination, the patient is lethargic with a blood pressure of 71/42 mmHg. Chest x-ray shows mediastinal widening with a prominent aortic knob and right pleural effusion. Echocardiography of the heart shows a dilated aortic root with mild aortic regurgitation and pericardial effusion. What is the most likely diagnosis?

1. Acute coronary syndrome (ACS)
2. Aortic dissection
3. Esophageal rupture
4. Peptic ulceration
5. Pericarditis

Explanation:

The patient is presenting with acute onset chest pain with hypotension along with mediastinal widening, a prominent aortic knob on chest radiograph, aortic regurgitation, and pericardial effusion on imaging, which are all consistent with the diagnosis of aortic dissection. Esophageal rupture may present with chest pain, but most of the imaging findings are not consistent with its diagnosis. Peptic ulceration may present with epigastric pain, but there is no history of risk factors or previous symptoms related to a peptic ulcer, and also the imaging findings suggest a diagnosis of aortic dissection rather than a peptic ulcer. Pericarditis is unlikely, as patients usually do not present with chest pain and almost always present with elevated jugular venous pressures. The acute coronary syndrome can be mostly differentiated by imaging findings, as the clinical presentation can be similar in patients with aortic dissection. Echocardiography of the heart in ACS mostly shows regional, wall-motion abnormalities.

References

Zipes DP, Libby P, Bonow RO, Mann DL, Tomaselli GF, Braunwald E. Braunwald’s Heart Disease A Textbook of Cardiovascular Medicine. 11th ed. Philadelphia: Elsevier; 2018.

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