Which of the following disorders is LEAST likely to cause high output failure?
**Core Concept**
High output heart failure is characterized by an increase in cardiac output, often resulting from conditions that lead to a decrease in peripheral resistance or an increase in venous return. This contrasts with low output heart failure, which is typically associated with a decrease in cardiac output.
**Why the Correct Answer is Right**
Option B: Constrictive pericarditis is a condition where the pericardium becomes thickened and fibrotic, leading to impaired diastolic filling of the heart. This results in a decrease in cardiac output, making it a classic cause of low output heart failure rather than high output failure. The pathophysiology involves impaired diastolic relaxation and reduced ventricular filling, which would not lead to the increased cardiac output characteristic of high output heart failure.
**Why Each Wrong Option is Incorrect**
**Option A:** Heart failure due to dilated cardiomyopathy often results in a decrease in cardiac contractility, leading to low output heart failure. However, some forms of dilated cardiomyopathy can lead to high output failure, particularly if there is significant mitral regurgitation or aortic regurgitation.
**Option C:** Anaphylaxis is a severe, life-threatening allergic reaction that can cause a significant increase in cardiac output due to the release of histamine and other mediators. This leads to vasodilation, increased venous return, and a high output state.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that high output heart failure is often associated with conditions that lead to an increase in cardiac output, such as anaphylaxis, beriberi, or hyperthyroidism. In contrast, low output heart failure is typically seen in conditions that decrease cardiac output, like constrictive pericarditis or dilated cardiomyopathy.
**Correct Answer:** C. Anaphylaxis is LEAST likely to cause high output failure.