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Difficulty: Very hardCardiovascular System

A 62-year-old man presents to the emergency department with a 3-day history of progressive exertional dyspnea, chest tightness, and a near-syncopal episode while climbing stairs. He has a 40-pack-year smoking history and does not take any daily medications. His temperature is 37.1°C (98.8°F), blood pressure is 112/68 mmHg, pulse is 88/min, and respirations are 20/min. Pulse oximetry shows 95% on room air. Pulmonary auscultation reveals mild, bilateral end-expiratory wheezing. Cardiac examination demonstrates a prominent apical impulse and a grade 3/6 harsh systolic crescendo-decrescendo murmur heard best at the left lower sternal border. An electrocardiogram shows left ventricular hypertrophy and deep, narrow Q waves in leads I, aVL, V5, and V6. Suspecting an acute exacerbation of chronic obstructive pulmonary disease and possible cardiac ischemia, the physician administers nebulized albuterol and sublingual nitroglycerin. Twenty minutes later, the patient becomes lightheaded and lethargic. His blood pressure drops to 76/42 mmHg, and his heart rate increases to 128/min. Cardiac auscultation now reveals a significantly louder and longer systolic murmur. Which of the following is the most appropriate next step in the management of this patient's acute deterioration?

  1. Intravenous 0.9% sodium chloride bolusAnswer
  2. B
    Intravenous furosemide
  3. C
    Non-invasive positive pressure ventilation
  4. D
    Intravenous dobutamine infusion
  5. E
    Synchronized electrical cardioversion

Answer

Intravenous 0.9% sodium chloride bolus
The correct answer is to administer an intravenous normal saline bolus. This patient's clinical presentation—featuring a harsh crescendo-decrescendo systolic murmur at the lower left sternal border and deep septal Q waves on ECG—is characteristic of Hypertrophic Obstructive Cardiomyopathy (HOCM). The patient was mistakenly treated for a COPD exacerbation and ischemic chest pain with albuterol and nitroglycerin. Albuterol stimulates beta-receptors, increasing heart rate and myocardial contractility. Nitroglycerin causes venodilation, significantly reducing venous return and left ventricular preload. In HOCM, dynamic left ventricular outflow tract (LVOT) obstruction is highly dependent on LV cavity volume. Both increased contractility and decreased preload reduce the end-systolic dimensions of the LV, exacerbating systolic anterior motion (SAM) of the mitral valve. This results in acute hemodynamic collapse (hypotension, reflex tachycardia) and a louder murmur due to the increased pressure gradient. The most immediate and effective step to reverse this physiology is to administer intravenous fluids to expand the LV volume, separate the mitral valve from the septum, and relieve the obstruction. Intravenous negative inotropes (like short-acting beta-blockers) or alpha-agonists (like phenylephrine) can also be used if fluid resuscitation is insufficient.

Step-by-Step Solution

1
Analyze the initial clinical presentation and diagnostic findings.
The patient has a harsh systolic murmur at the lower left sternal border, a prominent apical impulse, and deep, narrow 'septal' Q waves on ECG.
These findings are classic for Hypertrophic Obstructive Cardiomyopathy (HOCM), despite the older age and smoking history which often mislead clinicians toward COPD or ischemic heart disease.
2
Evaluate the physiologic effect of the administered medications.
Albuterol (a beta-agonist) increases heart rate and contractility. Nitroglycerin (a venodilator) decreases preload.
Understanding the pharmacodynamics of these drugs is essential to identifying the iatrogenic cause of the patient's deterioration.
3
Determine the mechanism of the patient's hemodynamic collapse.
Decreased preload (nitroglycerin) and increased contractility (albuterol) led to severe exacerbation of dynamic left ventricular outflow tract (LVOT) obstruction.
In HOCM, a smaller left ventricular cavity (from low preload) and a more forceful contraction pull the anterior leaflet of the mitral valve against the hypertrophied septum (systolic anterior motion), obstructing blood flow and causing hypotension.
4
Select the appropriate intervention to reverse the underlying pathophysiology.
Administer an intravenous fluid bolus.
Increasing preload with IV fluids expands the left ventricular cavity, separating the mitral valve from the septum, thereby reducing the outflow gradient and restoring cardiac output.

Key Concept

Hypertrophic obstructive cardiomyopathy (HOCM) hemodynamics and iatrogenic exacerbation
Estimated Time:1m 30s
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Topics

Cardiovascular System

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