If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 57-year-old female with a history of hypertension comes to the physician because of shortness of breath. She says that she has been experiencing progressively worsening dyspnea while climbing the stairs in her house. She denies both chest pain and dyspnea at rest. She appears comfortable at rest. She is on aspirin and metoprolol. Physical examination shows a regular heart rate and rhythm with absence of murmurs or rubs but does have an S4. Blood pressure is 150/80 mm Hg and pulse 55/min. Pulmonary exam reveals rales at the bases. She has lower extremity edema. Echocardiogram shows increased LV filling pressures with a normal ejection fraction. Which of the following is the next best step?
C. Reduce the dose of metoprolol
E. Transesophageal echocardiography
The correct answer is A.
Kaplan Medical explains why
This patient has been diagnosed with diastolic left ventricular dysfunction as a result of long-standing hypertension. The chronic effects of advanced hypertrophy in response to long-standing hypertension are the most likely cause of diastolic left ventricular dysfunction. Essentially, the concentric hypertrophy leads to a heart that cannot relax during diastole, which manifests clinically as dyspnea on exertion.
The left ventricle, thus, is not filling properly because:
- The concentric hypertrophy prevents the heart from relaxing during diastole.
- The relative time spent in diastole is shortened during a tachycardia.
The end diastolic left ventricular volume is reduced, and the end diastole pressure is increased because the LV is stiff and noncompliant, leading to pulmonary congestion as excess preload backs up into the lungs, thus resulting in exertional dyspnea. The best way to counteract the symptoms of diastolic left ventricular dysfunction is to administer a negative inotropic agent in an attempt to relax the heart during diastole, thus improving filling pressures. The goal heart rate is 55–60. If you push the heart rate down, the heart spends more time in diastole and has more time for diastolic filling. Therefore, you would not want to decrease the dose of metoprolol (Choice C). You may also use cardiac calcium channel blockers, such as verapamil or diltiazem (Choice D), but you would not want to push the HR <55.
In addition to decreasing the heart rate, reducing the afterload with ACE inhibitors or ARBs is also a target for therapy. Candesartan (Choice A) has been shown to improve exercise tolerance but not mortality in patients with diastolic dysfunction.
Digoxin (Choice B) has not shown benefit in isolated diastolic heart failure and should not be used unless required for the treatment of coexisting atrial arrhythmias.
Transesophageal echocardiography (Choice E) is not indicated for diastolic left ventricular dysfunction because a transthoracic echo is sufficient to make the diagnosis, which involves documentation of normal or only minimally reduced left ventricular systolic function and evidence of abnormalities of left ventricular relaxation. One of the indications for transesophageal echo is to determine the presence of a thoracic aortic aneurysm.
One key tip to remember
The most common etiology of diastolic heart failure is chronic hypertension leading to left ventricular concentric hypertrophy. Treatment should be aimed at decreasing heart rate through the use of beta-blockers or calcium-channel blockers. A decreased heart rate increases the amount of time for the ventricle to fill. Other medications used in the treatment of heart failure include ACE inhibitors or ARBs (prevent remodeling and act to regress hypertrophy) and aldosterone antagonists (prevents and regresses hypertrophy and fibrosis).
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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