Heart Failure & Valvular Diseases Q 37

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Acute pulmonary edema caused by heart failure is usually a result of damage to which of the following areas of the heart?

  

     A. Left atrium

     B. Right atrium

     C. Left ventricle

     D. Right ventricle

    

    

Correct Answer: C. Left ventricle

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The left ventricle is responsible for the majority of force for the cardiac output. If the left ventricle is damaged, the output decreases and fluid accumulates in the interstitial and alveolar spaces, causing pulmonary edema. The resultant pathology of increased extravascular fluid content in the lung remains common to all forms of pulmonary edema. However, the underlying mechanism leading to the edema arises from the disruption of various complex physiologic processes, maintaining a delicate balance of filtration of fluid and solute across the pulmonary capillary membrane.

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Option A: Damage to the left atrium would contribute to heart failure but wouldn’t affect cardiac output or, therefore, the onset of pulmonary edema. The relationship between hydrostatic and oncotic forces in relation to net fluid filtration is best explained by Ernest Starling’s equation. The rate of fluid filtration is determined by the differences in the hydrostatic and oncotic pressures between the pulmonary capillaries and interstitial space.

Option B: Because the RV is substantially thinner than the LV with lower elastance, the RV is much more susceptible to increases in afterload. A modest change in PVR may result in a marked decrease in RV stroke volume. Like the LV, contraction of the RV is preload dependent at normal physiologic filling pressures, and excessive RV filling can result in a shift of the septum towards the LV and ventricular interdependence causing impaired LV function.

Option D: If the right atrium and right ventricle were damaged, right-sided heart failure would result. Because of lower right-sided pressures and wall stress, the oxygen requirement of the RV is lower than that of the LV. Coronary blood flow to the RV is lower, as is oxygen extraction. For this reason, the RV is less susceptible to ischemic insults, and increases in oxygen demand are met via increases in coronary flow as is the case in PAH or increased oxygen extraction which occurs with exercise.

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