A friend told me about the following question at her exam:
Why is there collapse of the right atrium and ventricle during diastole in pericardial tamponade?
She could not come up with an answer, just marked smth, she does not remember the choices - very vague, but formulated more like a Step 1 question. However, I thought we should discuss this here.
good question- and thank you in advance for posting- you should continue to post questions for discussion sake
so here is answer to your question
first think of what goes wrong in tamponade- there is pericardial fluid present which increases the pressure in the pericardial cavity; this basically compresses the heart as a whole and restricts it from filling ( so this is main defect/initial insult)- so heart does not get blood; now as the pressure rises on the outside; its compressing the heart more and more impairing it from filling; (thats why emergency- on CCS as soon as you see this you dont even go for CXR or ECHO- you go straight to pericardiocentesis to remove the fluid)
so back to question- as pressure is increasing on the outside and compressing the heart, there is right atrial and ventricular collapse during diastole; why? so the heart on the right side is affected more because it has least pressure as compared to the left; remember the left ventricle has highest pressure; its wall can sustain itself to a point; and also diastole is the vulnerable phase again because it is the point in where pressure is the least, remember it is the filling phase/relaxation; so during diastole if the wall cant relax and fill, and on top of that you have increase pressure from the outside (versus inside);therefore wall collapses; so long story cut short, it collapses because A) not filling and B) you have increased pressure from the outside so its like pushing down on the heart; and if they ask why right is affected more or first than left, its because the right is more vulnerable because it has the least pressure as compared to the left side.
I hope this was helpful; yes sometimes stupid usmle exam their answer choices are vague but in this question I would have looked in answer choice that at least implied that there is a filling defect and increase pressure in in pericardium that exceeds the cardiac chamber pressure leading to collapse
didnt mean to write essay lol but wanted to explain as this is a good question and they can ask many variations in this concept